MICRO-PACE Ref 4575 Instruction Manual

TABLE OF CONTENTS Key to Panel Controls and Display

iii

Description of Control Pad Keys

iv

Summary of 4570 Series Parameters and Values

1

General Description

2

Key to Status Indicators

3

Indications, Contraindications and Warnings

4

Indications Contraindications Warnings

4 4 4

Programmable Modes and Parameters

5

Single-Chamber Modes Dual-Chamber Modes Basic Rate Pulse Amplitude Pulse Width Sensitivity Refractory Periods AV Delay Maximum Tracking Rate Blanking Period / Crosstalk

5 5 7 7 7 7 8 9 9 10

Additional Features/Options

11

Ventricular Safety Pacing Inhibit Output PV Delay PMT Termination Algorithm PVC Response Resume Operation Pacemaker Operations

11 11 11 12 12 12 13

Power On/Off/Lock Lead Connection Standard Pacing Emergency Pacing

13 14 14 14

Programming

15

Mode Parameters Automatic Programming of Parameters for High Rate Dual Chamber Pacing I

15 16 17

TABLE OF CONTENTS, CONT'D. Special Parameters Rapid Atrial Stimulation

18 19

Memory

20

Safety Features

20

Determination of Capture Thresholds

21

Determination of Sensing Thresholds

21

Sensing Circuits and the Effects of EMI, Defibrillation and Electrocautery

22

Extension Cables

23

Normal Maintenance

24

Low Battery Indicator and Battery Replacement

24

Potential System Complications

25

Storage

25

Service

25

Warranty

26

Bibliography

27

International Classifications and Certifications

28

Recommended Conditions for Operation, and Storage and Transport

28

ii

Key to Panel Controls and Display

Atrial Terminals

Ventricular Terminals

Ventricular Output Amplitude (V) Atrial Sensitivity Setting (mV)

ATRIAL

Atrial Output Amplitude (V)

Basic Rate (ppm)

AV Delay (ms)

VENTRICULAR

Output V

Sense mV

Output V

Sense mV

5.0 60

1.0 150

5.0 DDD

2.0 AV L

ppm RATE

mS AVD

MODE

PACE/ STATUS SENSE

ATRIAL OUTPUT

ATRIAL SENSE

VENT OUTPUT

VENT SENSE

RATE

A-V DELAY

MODE

SPECIAL PARAMS

STAT PACE

STD VALUES

Ventricular Sensitivity Setting (mV)

Sealed LCD Display

Status Indicator

Pacing (A-V) and Sensing (P-R) Indicators Pacing Mode

Causes DDI pacing if pressed in any mode (Refer to Manual)

Access to Other Programmable Functions

MICRO-PACE

Causes pacing in the programmed mode at standard values

-

+

TM

SELECT

PACE Medical, Inc. Sealed Keypad

Figure 1

iii

DESCRIPTION OF CONTROL PAD KEYS Press to activate atrial output amplitude. Change value using + and - arrows. Confirmation is not required.

Press to activate atrial sensitivity. Change value using + and arrows. Confirmation is not required.

Press to activate ventricular output. Change value using + and - arrows. Confirmation is not required.

Press to activate ventricular sensitivity. Change value using + and - arrows. Confirmation is not required.

Press to activate rate. Change value using + and - arrows. Confirmation is not required.

Press to activate atrioventricular delay. Change value using + and - arrows. Confirmation is not required.

Press to activate mode select. Change mode using + and arrows. Following selection, press again to confirm.

Press repeatedly to scroll through the less frequently used parameters. Change using + and - arrows. Confirmation is not required.

Press to activate high output pacing in the DDI mode. Confirmation is not required

Press to change all settings of the programmed mode to nominal its values. Confirmation is not required

Scroll up through the optional values of parameters or settings for mode to make new selection.

Scroll down through the optional values of parameters or settings for mode to make new selection.

iv

TABLE 1 - MICRO-PACE 4570 SERIES SUMMARY OF PARAMETERS AND VALUES Parameter

Values

Std/STAT

Steps/Units

DDD, DDI, DVI, DOO VDD, VVI, VVT, VOO AAI, AAT, AOO

---- / DDI

N/A

Basic Rates1

30 - 180

72(60) / 60

1 ppm

Rapid Stimulation1

100 - 800

100 / ----

10 ppm

Pulse Amplitude2(A&V)

0.1 - 2.5 2.5 - 5.0 5.0 - 10.0

5.0 / 10.0

0.1 V 0.5 V 1.0 V

Pulse Width3 (A&V)

0.05 - 2.0

1.0 / 1.5

0.05 ms

Sensitivity4 (Atrial)

0.3 - 2.0 1.0 - 3.0 2.0 - 12 3.0 - 20

1.0 / 1.0 2.0 / 2.0

0.1 mV 0.1 mV Variable Variable

Atrial Refractory Period1 DDD, DDI, VDD * AAI AAT

196 - 500 196 - 500 300 - 500

250 / 250 400 / ---400 / ----

AutoPgmd AutoPgmd AutoPgmd

1.0 ms 1.0 ms 1.0 ms

Ventricular Refractory Period1 DDD, DDI, VDD DVI, VVI VVT

196 - 500 196 - 500 300 - 500

325 / 325 325 / ---325 / ----

AutoPgmd AutoPgmd AutoPgmd

1.0 ms 1.0 ms 1.0 ms

AV Delay1

50 - 400

150 / 150

AutoPgmd

1.0 ms

Max.Tracking Rate1

90 - 230

120 / ----

AutoPgmd

1 ppm

Vent. Blanking Period

10 - 50

30 / 30

1.0 ms

Vent. Safety Pacing

Enabled

Enabled

N/A

PV Delay1

25 - 375

125 / ----

Modes

(Ventricular) (Atrial) (Ventricular)

PMT Term. Algorithm

10 beats ≥ MTR

AutoPgmd

10 beats ≥ MTR/ --

1.0 ms N/A

PVC Response DVI on PVC DVI on PVC / --N/A ____________________________________________________________________________ __ Specifications @ 20°C ± 2°C with 500 Ohm ± 1% load: 1 = ± 5%

2 = the greater of

3 = ± 10%

±10% or 0.05V * Post-Ventricular Atrial Refractory Period (PVARP)

1

4 = ± 20%

GENERAL DESCRIPTION The Model 4570 MICRO-PACE™ temporary pacemaker is a software programmable, internally-powered stimulator capable of multi-mode, multi-parameter operation. It is capable of operating in all of the commonly accepted pacing modes from ventricular or atrial asynchronous (VOO or AOO) to AV Universal (DDD). Every pacing parameter which may need to be adjusted to suit the needs of a specific patient, can be adjusted, not only over a broad range, but in increments, fine or coarse, which are more physiologically or diagnostically appropriate to that portion of the range of values. Programmable parameters, among others, include: rate, sensitivity, pulse amplitude, pulse width, refractory period(s), AV delay, maximum tracking rate, blanking period, and rapid stimulation. Additional standard pacing parameters are provided as non-programmable features. The Model 4570 MICRO-PACE incorporates several features not commonly found in other temporary pacemakers. These include: 1) a constant voltage output, 2) a memory function to allow the storage and subsequent retrieval of previously programmed mode parameters, 3) the ability to employ the device as a rapid atrial stimulator from any programmed mode, 4) the limited use of parameter interlocks, low value parameter warnings and time-outs, and visual and audible cueing, all of which are intended to limit inadvertent programming errors, 5) a keypad "lock" to thwart tampering, 6) a means to temporarily suspend output to check on underlying rhythm, 7) a dual-chamber, non-competitive STAT PACE from any mode, 8) an enhanced atrial sensitivity adjustable to 0.3 millivolts, and 9) a "resume operation" function which allows prompt recovery of the last programmed mode and parameter settings after the device has been turned off and back on again. The case of the Model 4570 MICRO-PACE is fabricated of durable ABS plastic. The sealed keypad is used to access and perform all functions of the pacemaker. The LCD display provides the means for verifying program settings and changes, and for conveniently monitoring operation while in use. Despite extensive programming capabilities in a Model 4570 MICRO-PACE, it is sufficiently small and light to be worn comfortably by an ambulatory patient. Leg/arm and waist straps made of elastic Velcro® provide for convenient and secure attachment. The MICROPACE along with its straps, batteries, and cables is supplied in a sturdy plastic carrying case. When not in use, it is recommended that the MICRO-PACE always be stored in its carrying case to protect it from accidental damage. If a Model 4570 is dropped onto a hard surface, with or without obvious damage, use should be promptly suspended. Finally, the Model 4570 MICRO-PACE is fully electrically isolated. The circuit is protected against damage due to normal cardioversion and defibrillatory discharges, and the risk of output inhibition caused by detection of environmental EMI is limited by special shielding and signal filtering. Pacemaker "runaway" is prevented by special rate limiting circuitry. WARNING: As with any critical medical device, it is of the utmost importance that a Model 4570 and its extension cables be maintained in excellent operating condition. A Model 4570 which shows evidence of damage, defect or failure to operate in accord with any of its specifications should be promptly removed from service and returned to the company for repair and thorough retesting. Damaged extension cables should be promptly replaced. Serious adverse affects may be associated with the continued operation of an impaired medical device.

2

CAUTION: When handling indwelling leads, the terminal pins or exposed metal conductive elements must not be touched or allowed to come into contact with electrically conductive or wet surfaces. Cardiac pacing leads and heartwires provide a direct electrical pathway to the heart. Strict attention to electrical safety practices must always be observed when performing cardiac pacing in the presence of line-powered monitoring or other support equipment as even minute alternating leakage currents flowing through the heart may induce ventricular fibrillation. When clinically indicated, supplemental monitoring of a patient should be considered during temporary cardiac pacing.

KEY TO STATUS INDICATORS

A = atrial output pulse

V = ventricular output pulse

P = atrial channel sensing event

R = ventricular channel sensing event

L = low battery condition

N = interference detected

W = device is performing Wenckebach in presence of high atrial rate.

B = device is performing 2:1 or greater block in the presence of a high atrial rate (dual-chamber).

S = device is performing ventricular safety pacing.

• = a sense event is occurring in the refractory alert period (see page 8 for discussion).

Figure 2.

Recommended conditions for: Operation: +10oC (+50°F) to +40oC (+104°F); RH 30% to 70% Transport and Storage: -20oC (-4°F) to +60oC (+140°F); RH less than 85% Exceeding the transport and storage temperature range may result in damage to the liquid crystal display (LCD) and keypad of a Model 4570.

CAUTION: When clinically indicated, supplemental monitoring of a patient should be considered during temporary cardiac pacing.

3

INDICATIONS, CONTRAINDICATIONS AND WARNINGS Indications The Model 4570 MICRO-PACE temporary pacemaker may be used in any clinical situation in which the use of a temporary pacemaker on a patient provides therapeutic or diagnostic value, or serves a prophylactic purpose. Specifically, indications for the use of temporary cardiac pacemakers include, but are not limited to, the following: intermittent or complete heart block associated with asystole or bradycardia, symptomatic sinus bradycardia, surgically-induced heart block, and heart block accompanying an acute myocardial infarction. Additionally, temporary cardiac pacing has been used to overdrive and thereby terminate atrial arrhythmias, including atrial flutter. It has been used in preparation for permanent pacemaker implantation to ascertain the thresholds for sensing and pacing on the acute lead system. Although the intended uses of a Model 4570 MICRO-PACE are primarily therapeutic and prophylactic, the ability to extensively program both the amplitude of the constant voltage output and the pulse width in the MICRO-PACE does make it, when necessary, a satisfactory alternative to a properly functioning Pacing System Analyzer (PSA) for the determination of the thresholds for sensing and stimulation. Contraindications There are no known contraindications to the use of temporary cardiac pacing as a therapeutic or prophylactic modality. Certain relative contraindications can exist, however, if a particular pacing mode or parameter is applied to inappropriate circumstances. For example, in the presence of atrial fibrillation, atrial pacing and/or sensing modes will not be effective in controlling atrial activity and carry the risk of inappropriately responding to detected atrial fibrillatory waves. Therefore, there is a relative contraindication against the application of such modes in patients who demonstrate chronic, persistent atrial fibrillation. Additional noteworthy examples include, but are not limited to: 1) atrial pacing in the presence of certain AV conduction disorders, and 2) the application of any asynchronous mode of pacing such that competition with an intrinsic rhythm results. WARNINGS The Model 4570 MICRO-PACE temporary pacemaker is a sophisticated electronic device capable of complex modes of operation, and having functions and characteristics which may be unfamiliar to medical personnel whose experience with the varied techniques of cardiac pacing may be limited. Although this Instruction Manual provides reasonable explanations of both operations and functions, it should not be relied upon for a comprehensive understanding of the complexities of cardiac pacing therapy. The operating instructions contained in this manual should be well understood prior to using a Model 4570 on a patient. A Model 4570 MICRO-PACE which has been subjected to conditions of transport or storage at temperatures below 10°C (50°F) or above 40°C (104°F), should be allowed to sit at room temperature (about 20°C or 68°F) for an hour before being placed in use on a patient. Before handling an external pulse generator, patient cable(s), or indwelling lead(s), steps should be taken to equalize the electrostatic potential between the user and the patient; e.g. by touching the patient at a site remote to the pacing lead. 4

PROGRAMMABLE MODES AND PARAMETERS Single-Chamber Modes AOO - Atrial asynchronous pacing Atrial pacing is provided at the programmed rate regardless of intrinsic rhythm. AAT - Atrial synchronous pacing* Atrial pacing at the programmed rate is provided in the absence of intrinsic activity. Intrinsic activity occurring in the alert period will reset pacemaker timing and result in an output pulse being issued synchronously with the detected activity. AAI - Atrial inhibited pacing Atrial pacing at the programmed rate is provided in the absence of intrinsic activity. Intrinsic activity occurring in the alert period will reset pacemaker timing to the beginning of the refractory period with inhibition of the output pulse. VOO - Ventricular asynchronous pacing Ventricular pacing is provided at the programmed rate regardless of intrinsic rhythm. VVT - Ventricular synchronous pacing* Ventricular pacing at the programmed rate is provided in the absence of intrinsic activity. Intrinsic activity occurring in the alert period will reset pacemaker timing and result in an output pulse being issued synchronously with the detected activity. VVI - Ventricular inhibited pacing Ventricular pacing at the programmed rate is provided in the absence of intrinsic activity. Intrinsic activity occurring in the alert period will reset pacemaker timing to the beginning of the refractory period with inhibition of the output pulse. * In the Model 4570, the maximum triggering rate is limited to the lesser of 60,000 divided by the programmed refractory period, or 200 ppm. Dual-Chamber Modes DOO - Dual-chamber asynchronous pacing Both chambers will be paced at the programmed rate regardless of the underlying rhythm. DVI - AV sequential pacing The capability for pacing is available in both chambers with sensing only in the ventricle. In the absence of ventricular activity, both chambers will be paced at the programmed rate and AV delay. Ventricular activity occurring during the ventricular alert period and before the atrial output pulse will inhibit both output pulses and reset pacemaker timing to the end of the AV delay. In the absence of ventricular activity during this period, an atrial output pulse will be provided at the end of the atrial escape interval and the timing for the AV delay will be initiated. 5

PROGRAMMABLE MODES AND PARAMETERS, CONT'D. Intrinsic ventricular activity during the AV delay will inhibit the ventricular output pulse and reset pacemaker timing to the end of the AV delay. If intrinsic ventricular activity does not occur during the AV delay, a ventricular output pulse will be provided at the end of this interval, and a new atrial escape interval will be initiated. A ventricular blanking period occurs coincident with any atrial output pulse. This blanking period is intended to prevent detection of the atrial output pulse by the ventricular channel. DDI - Improved AV sequential (with intact atrial sensing) pacing The capability for pacing and sensing is present in both chambers. However, sensed atrial activity will inhibit the atrial output pulse at the end of the V-A interval. DDI is a refinement of the DVI mode and will prevent competitive atrial pacing by maintaining atrial sensing. As with the DVI mode, AV sequential pacing at the programmed rate will be provided in the absence of intrinsic activity. Additionally, intrinsic ventricular activity occurring during the atrial escape interval or AV delay will inhibit the pacemaker and reset the timing as previously described. However, unlike the DVI mode, intrinsic atrial activity during the atrial alert period will inhibit the atrial output pulse and prevent competitive atrial pacing. This sensing will not affect pacemaker timing and, in the absence of intrinsic ventricular activity, a ventricular output pulse will be provided at the basic rate. As with the DVI mode, a ventricular blanking period occurs coincident with any atrial output pulse. VDD - Atrial tracking, ventricular inhibited pacing This mode allows for sensing in both chambers, but pacing only in the ventricle. In the absence of intrinsic activity, the ventricle will be paced at the programmed rate. Intrinsic atrial activity during the atrial alert period will terminate the atrial escape interval and begin the AV delay. Ventricular activity during the programmed AV delay will inhibit the ventricular output pulse, reset pacemaker timing to the end of the AV delay and initiate a new atrial sensing interval. Atrial activity may be only be detected and tracked from the end of the PVARP up to the end of the atrial escape interval. Thus, there is no difference between the programmed rate and the minimum tracked rate. DDD - Dual-chamber atrial tracking This mode allows for pacing and sensing in both chambers. In the absence of intrinsic activity, both chambers will be paced at the programmed rate. Intrinsic atrial activity during the atrial alert period will inhibit the atrial output pulse, terminate the atrial escape interval and begin the AV delay. Ventricular activity during the programmed AV delay will inhibit the ventricular output pulse, reset pacemaker timing to the end of the AV delay and initiate a new atrial escape interval. The absence of atrial activity during the atrial alert period will result in an atrial output pulse at the end of the atrial escape interval and AV delay timing will begin. Intrinsic ventricular activity occurring during the ventricular alert period will always recycle both channels, inhibit both output pulses, and reinitiate a new atrial escape interval. As with the DDI mode, a ventricular blanking period occurs coincident with any atrial output pulse.

6

PROGRAMMABLE MODES AND PARAMETERS, CONT'D. Basic Pacing Rate The Model 4570 may be programmed from 30 ppm to 180 ppm in increments of 1 ppm in any single-chamber or dual-chamber pacing mode. All ventricular modes have a standard rate of 72 ppm. All other modes have a standard rate of 60 ppm. Rates below 45 ppm are intended for temporary diagnostic purposes. If the operator attempts to program them, a brief message, "Rate Below Typical Range", interrupts the process, after which the normal status display returns, allowing a further reduction of the rate. The pacing rate is independent of battery voltage, providing a constant pacing rate as the battery voltage gradually declines to and beyond the point at which the voltage drop triggers the low battery indicator, "L", on the status display. Timing functions of a MICRO-PACE are precisely determined by a crystal-controlled oscillator. As a consequence, there will be little difference between the rate of the MICRO-PACE as programmed and displayed and that as determined by independent measurement of the pacing interval. The Model 4570 MICROPACE is rate limited to 240 ppm on the ventricular channel in all modes, except the Rapid Atrial Stimulating mode. Pulse Amplitude The pulse amplitude of the Model 4570 MICRO-PACE is programmable in steps of 0.1V from 0.1 to 2.5V, in steps of 0.5V from 2.5 to 5.0V, and in steps of 1.0V from 5 to 10V. If the operator attempts to program a value for pulse amplitude lower than 2.5V, a confirming message, "For Lower Output / Press [A (or V) OUT] Key", will be displayed. When the key is pressed, the display will change to "Output Below Typical Range", before returning to the normal status display. The pulse amplitude is independent of battery voltage, providing a constant output as the battery voltage gradually declines to and beyond the point at which the voltage drop triggers the low battery indicator, "L", on the status display. Pulse Width Pulse width for the Model 4570 MICRO-PACE is programmable from 0.05 millisecond to 2.0 milliseconds in steps of 0.05 millisecond. Values less than 0.25 millisecond may only be programmed for 60 seconds at a time. A warning display will appear when the operator attempts to reduce pulse width below this level. At the end of 60 seconds, pulse width will revert to the standard value, 1.0 millisecond. The pulse width is independent of battery voltage, providing a constant output as the battery voltage gradually declines to and beyond the point at which the voltage drop triggers the low battery indicator, "L", on the status display. Sensitivity Atrial sensitivity may be programmed from 0.3 to 12 millivolts. From 0.3 to 2.0 millivolts, the steps are 0.1 millivolt. From 2.0 to 4.0 millivolts, the steps are 0.2 millivolt. From 4.0 to 6.0 millivolts, the steps are 0.5 millivolt. Between 6.0 and 8.0 millivolts the increment is 1.0 millivolts. And, from 8.0 to 12 millivolts, the increment is 2.0 millivolts. Ventricular sensitivity may be programmed from 1.0 to 20 millivolts. From 1.0 to 3.0 millivolts, the steps are 0.1 millivolt. From 3.0 to 5.0 millivolts, the steps are 0.2 millivolt. From 5.0 to 8.0 millivolts, the steps are 0.5 millivolt. And, from 8.0 to 20 millivolts, the increment is 4.0 millivolts. The lower the numerical value, the higher the sensitivity. If the operator attempts to program a value greater than 5mV, the brief warning message, "Leaving Typical Sensing Range", will be displayed.

7

PROGRAMMABLE MODES AND PARAMETERS, CONT'D. This broad range of programmable values on both the atrial and ventricular channels serves primarily two purposes: 1) oversensing or undersensing problems require great programming flexibility for successful management, and 2) unusually small incremental steps allow a physician to determine the amplitude of the signal as detected by the pacemaker with reasonable accuracy. Knowing this, sensitivity may be programmed to a value which provides for a reasonable 2 - 4 fold margin of safety. Unless the value so determined is smaller than that available with the standard values, it is recommended that standard values be used. The standard values are generally adequate in the acute setting. It is recommended that physicians avoid making unnecessary changes in the standard settings for sensitivity as they have been carefully selected as a compromise between the dual risks of over-sensing and undersensing. Sensitivity should not be increased without awareness that even modest changes may produce a dramatic increase in the risk of detecting unwanted interference. On the other hand, sensitivity should not be reduced on an acute lead with a modest R (or P) wave, nor in an ischemic patient with PVC's without appreciating that competition-induced arrhythmias may occur in any borderline sensing situation. Refractory Periods Pacemakers which operate in a sensing mode incorporate a feature known as the refractory period. Immediately following a pacemaker output pulse or a sensed event, the pacemaker ceases to be responsive to detectable signals for a pre-determined period. This prevents the pacemaker from detecting the terminal portion of the depolarization signal and, in some circumstances, the repolarization signal which may result in timing errors. NOTE:

Use of short pacing intervals (high pacing rates) with long refractory periods may result in intermittent asynchronous pacing and may be contraindicated in some patients. Additionally, when programmed to high output levels, the standard refractory period on the ventricular channel may be inadequate to prevent detection of "noise" associated with the ventricular output pulse, resulting in a recycling of the noise sampling period. When this is occurring, a dot will be seen alternating with the "V" enunciator. Extending the refractory period just enough to eliminate the dot is recommended.

When the pacemaker is programmed to a dual-chamber sensing mode, there is a refractory period for each sensing channel. The pacemaker's ventricular refractory period is always initiated by a paced or sensed ventricular event. The total atrial refractory period is composed of two segments. Immediately following a paced or sensed atrial event, the atrial sensing amplifier becomes refractory for the AV delay or until a sensed ventricular event. Additionally, immediately following a paced or sensed ventricular event, the atrial sensing amplifier will become refractory for the programmed atrial refractory period. The atrial refractory period displayed is always the post-ventricular atrial refractory period (PVARP). The refractory period is comprised of two parts: the absolute refractory period during which the detection of all signals is blocked, and the relative refractory (noise sampling) period during which signals are evaluated for repetition rate. Signals which occur at a frequency of 10Hz or more cause the pacemaker to revert to asynchronous operation at the programmed rate while continuing to monitor for the presence of noise. 8

PROGRAMMABLE MODES AND PARAMETERS, CONT'D. Signals which occur at a frequency below 10Hz have no effect upon pulse generator timing, unless the signal is detected during the normal sensing (or alert) period following the noise sampling period. Should this occur, pacemaker output will be inhibited or triggered depending on the operating mode. See page 17 for automatic changes with increasing rate in dual-chamber modes. AV Delay The AV delay defines the time interval between an atrial output pulse and a ventricular output pulse. The available range of AV delays makes it possible to significantly shorten the time between atrial and ventricular events, if it is hemodynamically or electrophysiologically advantageous in a particular instance. The time may also be lengthened to allow for inhibition of the ventricular output pulse in those individuals without significant AV conduction defect. At any given rate, the AV delay plays an important role, as the value selected can improve, normalize or adversely influence stroke volume and, therefore, cardiac output. The standard value for AV delay is 150 milliseconds. changes with increasing rate in dual-chamber modes.

See page 17 for automatic

Maximum Tracking Rate The maximum tracking rate (MTR) is a variable parameter only in the dual-chamber tracking modes, DDD and VDD. This parameter has nothing whatsoever to do with the maximum triggering rate which may be achieved in the AAT or VVT modes, nor does it play any role in the rapid atrial stimulation mode. Normal MTR behavior is electronic Wenckebach. However, both the MTR behavior and the maximum tracking rate itself, may be restricted or altered by values selected for the AV delay and the post-ventricular atrial refractory period, which together are called the total atrial refractory period (TARP). For example, if the values selected are, respectively, 175 milliseconds and 300 milliseconds, the upper limit of 1:1 P wave tracking is determined by dividing 60 seconds (60,000 ms) by the sum of the two periods above, (TARP). In this example, the result is a maximum tracking rate of 126 bpm. At faster atrial rates, only every other P wave will be able to be sensed as the alternate P wave will coincide with the TARP. This results in 2:1 pacemaker AV block. From this it will be seen that the TARP is the final determinant of the maximum sensed atrial rate and, thus, whether a desired maximum tracking rate behavior is possible. As an aid to the user, the display associated with the maximum tracking rate (Track Limit) in the Special Parameters loop identifies where 1:1 tracking stops and where Wenckebach begins and ends (and 2:1 block begins) based on the current device settings. In the event the patient develops an atrial rhythm faster than the maximum tracking rate and the total ARP selected does not prevent it, the pacemaker will respond with electronic Wenckebach. Every detectable P wave will be tracked with a progressively lengthening PV interval, while maintaining a stable V to V pacing interval. But, with a frequency which is entirely dependent upon the actual atrial rate being tracked, a P wave will, from time to time, fall in the post-ventricular atrial refractory period and fail detection. The next P wave in the series which is detected will be tracked instead, and the resulting V to V interval will be slightly longer than all the others. 2:1 block will be encountered when the P to P interval is equal to or less than the TARP (PV delay and post-ventricular atrial refractory period).

9

PROGRAMMABLE MODES AND PARAMETERS, CONT'D. Because of the asynchrony that can occur at higher tracking rates and behaviors, the maximum tracking rate should be set to that value which most closely approximates the maximum normally occurring atrial rate in the patient, but which as a ventricular paced rate alone, will not produce angina or discomfort. The operator must always be aware of the impact of the total atrial refractory period upon pacemaker performance at the high end of the normal rate range for the patient. Blanking Period / Crosstalk When a Model 4570 MICRO-PACE temporary pacemaker is employed in the DVI, DDI or DDD mode, a brief period of refractoriness called the "blanking period" will momentarily occur in the ventricular sensing circuit coincident with the atrial output pulse. The length of the blanking period is variable from ten to 50 milliseconds. The standard value is 30 milliseconds. Blanking periods are an inherently undesirable, but necessary parameter in dual unipolar pacing modes which have traditionally employed a common indifferent. However, they also find utility in dual bipolar configurations where complete isolation of the atrial and ventricular channels, particularly over the very broad ranges of output and sensitivity available in some devices, is impractical or impossible. Thus, this brief period of refractoriness is necessary to limit the risk of detection of the atrial output pulse by the ventricular sensing amplifier which, if detected, would result in ventricular output inhibition. This condition is commonly called "crosstalk". Namely, the proper function of one channel causes proper, but inappropriate function in the other. Crosstalk is easily identified in the clinical setting because only the atrial output pulse is present and the atrial pulse interval will measure as the sum of the programmed atrial escape interval (VA interval) plus the amount of the blanking period. In the absence of AV conduction or a native ventricular rhythm, the develop-ment of crosstalk can have catastrophic consequences. To help assure that this will not occur, ventricular safety pacing is always enabled. It is recommended that the blanking period not be programmed longer than that which is necessary to eliminate the occurrence of ventricular safety pacing. The standard value, 30 milliseconds, is typically adequate. Unnecessarily long blanking periods increase the risk that the intrinsic deflection of a native ventricular event, that part of the depolarization signal which is relied upon for appropriate sensing function, will coincide with the blanking period and fail detection. This will result in the delivery of a ventricular output pulse at the end of the programmed AV delay. If the AV delay has been programmed to less than 150 milliseconds or so, such an event occurring on a repetitive basis may not produce deleterious clinical consequences. However, if the AV delay has been programmed long in an attempt to facilitate normal AV conduction, an obligatory ventricular output pulse could then repetitively fall during the vulnerable portion of the cardiac cycle. Such circumstances increase the risk of ventricular arrhythmia in all patients, but that risk is particularly acute in electrically unstable patients.

10

ADDITIONAL FEATURES / OPTIONS Ventricular Safety Pacing Ventricular safety pacing is designed to minimize the risk of inappropriate inhibition of the pacemaker's ventricular output pulse, if crosstalk occurs. This is accomplished by having the pacemaker alert for crosstalk for a short period of time after the blanking period. The duration of the crosstalk detection window is equal to 80 milliseconds minus the blanking period. If any signal is sensed during the crosstalk detection window, the pacemaker is triggered to deliver a ventricular output pulse 120 milliseconds after the atrial output pulse. Normal sensing is maintained after the crosstalk detection window. Therefore, a sensed ventricular event that occurs between 80 and 120 milliseconds after the atrial output pulse will inhibit the pacemaker's ventricular output pulse, unless crosstalk was detected during the crosstalk detection window. In the Model 4570, this function is always enabled. Safety pacing is indicated by the appearance of an "S" occurring coincidentally with the ventricular status enunciator, "V", in the extreme right-hand position on the display, following an initial "A". Inhibit Output To inhibit the output of the Model 4570 MICRO-PACE, ex. to evaluate a patient's underlying rhythm, press the SPECIAL PARAMS key until the inhibit output option is displayed, highlighted by the cursor, then press and hold the ATRIAL OUTPUT and VENT OUTPUT keys simultaneously. To restore pacing, simply release the keys. Release of the keys will result in exit from the Special Parameters display and return of the normal status display. This sequence is shown by Figures 3 and 4, below.

Hold Both Output Keys To Inhibit Figure 3.

To Resume Pacing Release Keys Figure 4.

PV Delay The PV delay compensates for the differences, commonly observed in the clinical setting, between the PV interval which exists when P waves are tracked to pace the ventricle and the AV interval which exists when both chambers are paced sequentially. When paced, the mechanical contraction of the atria lags behind the atrial output pulse. To compensate for this difference, the AV delay will automatically shorten by 25 milliseconds when it begins with a sensed P wave, with the goal of having hemodynamically equivalent pacing and sensing intervals. The range of values for the PV delay is 25 - 375 milliseconds; always 25 milliseconds less than the programmed AV delay. This feature may not be independently programmed.

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ADDITIONAL FEATURES/OPTIONS, CONT'D. PMT Termination Algorithm The Model 4570 MICRO-PACE temporary pacemaker is equipped with a special program for dealing with the common problem of endless-loop tachycardias; specifically, pacemakermediated tachycardias (PMTs). A PMT may result when a ventricular sense event occurs without a properly timed, preceding P wave. Such events are usually PVC's. In patients with VA conduction, a PVC may be followed by retrograde conduction to the atria resulting in a P wave which is detected and tracked like any other P wave which occurs during the normal sensing period. Typically, these P waves occur early, resulting in an extended PV interval, producing yet another retrograde P wave. Thus, the cycle tends to repeat itself with marked consistency, unless interrupted. Although a PMT is usually seen at the maximum tracking rate of the pacemaker, there are circumstances involving long VA conduction times in which sustained rates below the MTR are possible. In a Model 4570 programmed to the VDD or DDD mode, the programmed PVC response option is always operative at the MTR. Namely, on the 10th consecutive beat of a sustained series above the MTR which fits the criteria for PMT, the ventricular output pulse will be followed by the PVC response, described below. If the first three beats following the PVC response are normal, the algorithm reverts to the 10 beat threshold. If the PVC response has failed to terminate the PMT, the attempt will be repeated again 127 cycles later. If the attempt is successful, normal DDD or VDD pacing will resume. If not successful, the attempt is repeated every 127 cycles until it is successful. PVC Response In patients with retrograde conduction, detection of retrograde atrial events can result in pacemaker-mediated tachycardias (PMTs). One method of preventing PMTs is to program the post-ventricular atrial refractory period longer than the patient's retrograde conduction time. However, a long PVARP can artificially restrict the normal range of 1:1 AV synchrony. Since the majority of PMTs are initiated by PVCs, MICRO-PACE pacemakers offer a special PVC response intended to prevent PMTs. When a MICRO-PACE is programmed to the VDD or DDD pacing mode, a protective response to the detection of a PVC is always enabled. The pacemaker will determine that a PVC has occurred, if it detects two ventricular events with no intervening paced or sensed atrial event. When this occurs, the pacemaker's atrial channel will be refractory immediately following any detected PVC. It will remain refractory until the delivery of an atrial output pulse. This response is commonly called "DVI on PVC". Resume Operation The Model 4570 is equipped with the ability to be turned off and then on again, promptly recovering the previously operating mode and parameter settings. This is accomplished by moving the OFF/ON/LOCK switch to ON followed immediately by a single press of the SELECT Down [–] key. Although a display will appear briefly to prompt this action, the recovery of the mode and parameters can be speeded by pressing the key any time immediately following switch activation. Also, during this time, the [–] key will function even if the OFF/ON/LOCK switch has been inadvertently moved beyond ON to LOCK. Pressing any other parameter or the mode key will promptly produce the status display and pressing the STAT PACE key will instantly activate emergency pacing. 12

PACEMAKER OPERATIONS Power Off/On/Lock The OFF/ON/LOCK switch is located on the upper left-hand side of the MICRO-PACE. This recessed switch is designed to move smoothly from OFF to ON, and to the LOCK position when it is the operator's intention to render the keypad inoperative. The recessed design of the switch facilitates rapid activation, but substantially limits the risk of inadvertent switch position changes. To turn the unit off, depress the switch guard latch and move the switch to OFF. When first turned ON following battery insertion, the MICRO-PACE will briefly display the phrase, "Model 4570 Diagnostics V*.*", to indicate that an automatic electronic check is being made on the integrity of vital operational components as shown in Figure 5. During any subsequent power on, the display in Figure 5 is replaced by, "Pacing DDD Mode - Std Values", as shown in Figure 6. That is quickly followed by, "[–] Resumes Last Mode (XXX)", where "XXX" is the previously programmed mode, as shown in Figure 7. This allows the user to select the standard power on mode of DDD at standard settings or the previously programmed mode and parameter settings. The display instructs the user to press the SELECT Down [–] key, if immediate return to the previously operating mode is desired. Pressing this key while turning the device on will speed the process. If the battery is low at power on, this display will also include an "L" in the extreme right-hand enunciator position. Finally, the main status display is presented showing the primary pacing parameters and values (Figure 8).

Model 4570 Diagnostics V *.* Figure 5.

Pacing DDD Mode Std Values (AV) Figure 6.

[–] Resumes Last Mode (XXX) (AV) Figure 7.

5.0 1.0 5.0 2.0 60 150 DDD (AVL) Figure 8.

Ñ Blinks A or V with each paced beat; blinks P or R on each sensed beat; and shows L with low battery

If ventricular output pulses are being delivered to the terminals of the MICRO-PACE, the Pace / Sense indicator will be flashing "V". Any sensed R wave will be flashed as an "R". If an atrial sensing/pacing mode is selected, the letters "A" and "P" will appear, indicating pacing and sensing, respectively. 13

PACEMAKER OPERATIONS, CONT'D. In dual-chamber modes, combinations of all four may appear as flashing pairs of letters which describe exactly how the pacemaker is acting in each cardiac cycle. Also, it is important to note that crosstalk may be readily identified when it occurs by watching the enunciators. Specifically, the atrial enunciator will flash "A" followed almost instantly by an "V" flashing in the position of the ventricular enunciator and an "S" flashing in the right-hand enunciator position. This means that early AV interval noise is evoking the safety pace response, and that noise is very likely to be attributable to ventricular detection of components of the atrial output pulse (crosstalk). Lead Connection Normal Bipolar Configuration The output terminals of the Model 4570 MICRO-PACE are capable of accepting and holding standard pacing lead pin connectors as well as typical surgical heartwires securely. Each output consists of a pair of terminals; one black and one red. The pair closest to the LCD display of the MICRO-PACE is ventricular and the pair closest to the back is atrial. Each pair is also labeled as to its function and the polarity of the individual terminals. With the MICRO-PACE OFF, connect the pacing leads to the appropriate terminals. Observe polarity. Tighten terminals securely, but not more than finger tight; do not apply a tool of any kind. Changes in the settings or the mode may be made, following the instructions which begin on page 15. Modified Bipolar Configuration This configuration should be used with caution. To adapt an indwelling bipolar lead system which has suffered a single conductor fracture or electrode detachment, connect the positive (+) terminal to a skin electrode or wire placed subcutaneously. Connect the electrode which remains effective to the negative terminal. If both A and V outputs require modification, repeat this procedure for each; DO NOT COMBINE THE LEADS INTO A SINGLE COMMON. An increase in the blanking period may be required, depending upon the resulting lead orientation and the programmed atrial output and ventricular sensitivity settings. Standard Pacing Pressing the STD VALUES key will immediately return all operational parameters of a Model 4570 MICRO-PACE to their nominal or standard values in the mode then programmed. The confirmation message, "NOTE: Values Set To Standard", appears briefly in the display. Emergency Pacing Pressing the STAT PACE key immediately changes the pacing parameters to STAT values (see Table 1) and changes the mode to Improved AV Sequential (DDI), regardless of the mode previously programmed. When [STAT PACE] is pressed, there is a brief message, "WARNING: Enabling Emergency DDI". Return of the status display accompanied by an audible beep confirms completion of the command. This mode is intended as one of the means which might be employed in an attempt to escape rapidly from a situation involving loss of capture with attendant asystole or bradycardia. Since this mode retains sensing, it will not be helpful, if the cause of an asystolic or bradycardic episode is inhibition of pacemaker output due to the presence of interference (environmental EMI) with a low repetition rate. 14

PACEMAKER OPERATIONS, CONT'D. Flashing "P" and/or "R" enunciators on the status display which are not matched by P waves and/or R waves on the patient monitor or ECG are a clear indicator of this latter problem. Selection of an asynchronous pacing mode (pref. VOO or DOO) or adjustment of sensitivity to a higher numerical value should promptly restore pacing and provide an opportunity to identify and remove the source of the interference. CAUTION: The use of high pulse amplitudes and long pulse widths has been associated with the spontaneous development of cross-stimulation related to lead position. PROGRAMMING Mode To program mode, press the MODE key and the display will change to "Current Mode: DDD / [MODE] Re-enters". In this instance, DDD is the presently programmed mode. A fixed cursor beneath "DDD" indicates preparation for a new mode selection. This is accomplished by pressing either the SELECT Up or the SELECT Down arrow. If either is held, rapid scrolling of the options will occur. With the desired mode in the display, press the MODE key again to confirm the selection. This is the meaning of the phrase "[MODE] Confirms". The display now changes to confirm the new program and will briefly show "**CONFIRMED** / Mode is now XXX" before reverting to the normal operational display. This sequence of displays is shown in Figure 9, below, for a change from DDD to VVI mode.

Current Mode: DDD [MODE] Re-enters After 1st press of MODE

Select Mode: VVI [MODE] Confirms After using up [+] and / or [–]

**CONFIRMED** Mode is now VVI Confirming display following 2nd press of [MODE]

OFF OFF 5.0 2.0 60 OFF VVI ( V ) New status display Figure 9

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