MICRO-PACE Ref 4580 Instruction Manual

TABLE OF CONTENTS Key to Panel Controls and Display

iii

Description of Control Pad Keys

iv

REF 4580 MICRO-PACE - Summary of Modes and Parameters

1

General Description

2

Use of the IV Pole Hanger / Arm Strap

4

Key to Status Indicators

5

Indications, Contraindications and Warnings

6

Indications Contraindications Warnings

6 6 7

Programmable Modes and Parameters

7

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

7 8 11 11 11 12 12 13 14 15

Additional Features/Options

16

Ventricular Safety Pacing Inhibit Output PV Delay PMT Termination Algorithm PVC Response

16 17 18 18 19

Pacemaker Operations

20

DDD On, Resume On, Off, and the Lock Function Lead Connection Nominal (Values) Pacing Emergency Pacing

i

20 22 23 24

TABLE OF CONTENTS, CONTINUED. Programming

25

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

25 27 29

Menu Rapid Atrial Stimulation

29 31

Memory

32

Safety Features

33

Determination of Capture Thresholds

33

Determination of Sensing Thresholds

34

Sensing Circuits and the Effects of EMI, Defibrillation and Electrocautery

34

Normal Maintenance of the REF 4580 MICRO-PACE

35

Care and Use of the Extension Cables

36

Low Battery Indicator and Battery Replacement

37

Potential System Complications

39

Storage

40

Service

40

Warranty

40

Product Disposal

41

International Classifications and Certifications

41

Recommended Conditions for Operation, and Storage and Transport

42

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REF 4580 DUAL-CHAMBER TEMPORARY CARDIAC PACEMAKER

Ventricular Output Connector

Atrial Output Connector

Pacing Annunciator Legends LCD Display

ATRIAL

VENTRICULAR

Output V

Sense mV

Output V

Sense mV

5.0 60

1.0 150

5.0 DDD

2.0 L

ppm RATE

ms AVD

MODE

PACE/ SENSE STATUS

ATR OUTPUT

ATR SENSE

VNT OUTPUT

VNT SENSE

RATE

A-V DELAY

MODE

MENU

STAT PACE

NOMINAL

Keypad

On / Off Control Keys

DDD ON

OFF

RESUME ON

PRESS / HOLD BOTH FOR OFF

MODEL 4580 TM MICRO-PACE

PACE Medical, Inc.

iii

Status Legend

Keypad Lock Switch

Figure 1 KEY TO PANEL CONTROLS AND DISPLAY DESCRIPTION OF CONTROL PAD KEYS ATR OUTPUT

Press to activate atrial output. Change value using + and – arrow keys. Confirmation is not required.

ATR SENSE

Press to activate atrial sensitivity. Change value using + and – arrow keys. Confirmation is not required.

VNT OUTPUT

Press to activate ventricular output. Change value using + and – arrow keys. Confirmation is not required.

VNT SENSE

Press to activate ventricular sensitivity. Change value using + and – arrow keys. Confirmation is not required.

RATE

Press to activate pacing rate. Change value using + and – arrow keys. Confirmation is not required.

A-V DELAY

Press to activate atrioventricular delay. Change value using + and – arrow keys. Confirmation is not required.

MODE

Press to activate mode select. Change value using + and – arrow keys. Following selection, press again to confirm.

MENU

Press repeatedly to scroll through less frequently used parameters. Change values using + and – arrow keys. Confirmation is not required.

STAT PACE

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

NOMINAL

Press to change all parameter settings of the programmed mode to their nominal 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.

DDD ON

Energizes the device in DDD mode pacing nominal values.

OFF

Press and hold the DDD ON and OFF keys simultaneously to turn off the device.

RESUME ON

Energizes the device pacing the previously selected mode and programmed values.

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TABLE 1 - REF 4580 MICRO-PACE SUMMARY OF MODES AND PARAMETERS Values DDD, DDI, DVI, DOO VDD, VVI, VVT, VOO AAI, AAT, AOO

Nominal/STAT ---- / DDI

Basic Rates1

30 – 200

72(60) / 60

1 ppm

Rapid Stimulation1

60 – 800

100 / ----

10 ppm

Pulse Amplitude2(A&V)

0.1 – 3.0 3.0 – 6.0 6.0 – 10 10 – 14

Pulse Width3 (A&V)

0.05 – 2.0

1.0 / 1.5

0.05 ms

Sensitivity4 (Atrial) (Ventricular) (Atr & Vnt) (Atr & Vnt) (Atr & Vnt)

0.2 – 3.0 0.5 – 3.0 3.0 – 6.0 6.0 – 10 10 – 20

1.0 / 1.0 2.0 / 2.0

0.1 mV 0.1 mV 0.2 mV 0.5 mV 1.0 mV

Atrial Refractory Period1 DDD, DDI, VDD* AAI AAT

196 – 500 196 – 500 250 – 500

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

AutoPgmd AutoPgmd AutoPgmd

1.0 ms 1.0 ms 1.0 ms

Ventricular Refractory Period1 DDD, DDI, VDD 196 – 500 DVI, VVI 196 – 500 VVT 250 – 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

AVD - 25ms

125 / ----

Modes/Parameters Modes

PV Delay1 PMT Term. Algorithm PVC Response

Steps/Units N/A

0.1 V 0.2 V 0.5 V 1.0 V

5.0 / 10

AutoPgmd

1.0 ms

10 beats ≥ MTR

10 beats ≥ MTR/ --

N/A

DVI on PVC

DVI on PVC / ---

N/A

____________________________________________________________________________

Specifications @ 20°C ± 2°C with 500 Ohm ± 1% load: 1 = ± 5%

2 = the greater of ±10% or 0.05V

3 = ± 10%

* Post-Ventricular Atrial Refractory Period (PVARP)

1

4 = ± 20%

GENERAL DESCRIPTION The REF 4580 MICRO-PACE™ Dual-Chamber, DDD, Temporary Cardiac Pacemaker is a software programmable, internally-powered pulse generator designed for 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 REF 4580 MICRO-PACE has several important features, including: 1) a basic programmable rate as high as 200 ppm in any mode, 2) constant voltage output, 3) a non-volatile memory function to allow the storage and subsequent retrieval of previously programmed mode parameters, 4) the ability to employ the device as a rapid atrial stimulator from any programmed mode, 5) a maximum output capability of 14 volts on both channels, 6) a keypad "lock" to prevent unintended changes, 7) a means to suspend output to check on underlying rhythm, 8) a dual-chamber, non-competitive, high output STAT PACE from any mode, 9) an enhanced atrial sensitivity adjustable to 0.2 millivolts, 10) a "resume" function which allows prompt recovery of the last programmed mode and parameter settings when the device is turned on using the RESUME ON key, 11) enhanced low battery indicators, and 12) recessed output connectors. The case of the REF 4580 MICRO-PACE is fabricated of a durable plastic case incorporating an integral IV pole hanger, which can be configured to accommodate an arm strap allowing the device to be attached to the patient. See page 4. A sealed keypad is used to turn the device on and off, and to access and perform all functions of the pacemaker. A continuously active liquid crystal display (LCD) provides the means for verifying program settings and changes, and for conveniently monitoring operation while in use. A REF 4580 MICRO-PACE is small and light and may be worn comfortably by an ambulatory patient. The MICRO-PACE along with its batteries, cables and instruction manual is supplied in a padded carrying case. When not in use, it is recommended that the MICRO-PACE always be stored in its carrying case, with batteries removed, to protect it from accidental damage and potential battery leakage. Finally, the REF 4580 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 circuit design. Pacemaker "runaway" is prevented by special rate limiting circuitry.

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WARNING:

As with any critical-care medical device, it is of the utmost importance that a REF 4580 and its extension cables be maintained in excellent condition. A REF 4580 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.

3

IV Pole Hanger / Arm Strap Orientations

IV Pole Hanger Extended

Snapped closed allowing an arm strap to be used

MICRO-PACE PRESS

TM

TEMPORARY DUAL-CHAMBER CARDIAC PACEMAKER

PRESS

REF 4580 Serial No. Caution: Federal (U.S.A.) law restricts this device to sale by or on the order of a physician

USE ONLY 9 VOLT ALKALINE (IEC TYPE 6LR61) OR LITHIUM BATTERIES DO NOT CHANGE BATTERIES WHILE ATTACHED TO A PATIENT DOING SO MAY RESULT IN THE LOSS OF PACING SUPPORT

!

PUSH IN TO RELEASE BATTERY DRAWERS

Pace Medical, Inc. 391 Totten Pond Road Waltham, MA 02451 U.S.A.

USE ONLY 9 VOLT ALKALINE (IEC TYPE 6LR61) OR LITHIUM BATTERIES

0086

DO NOT CHANGE BATTERIES WHILE ATTACHED TO A PATIENT DOING SO MAY RESULT IN THE LOSS OF PACING SUPPORT

!

Side View

4

PUSH IN TO RELEASE BATTERY DRAWERS Pace Medical, Inc. 391 Totten Pond Road Waltham, MA 02451 U.S.A.

0086

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. It is recommended that attending health care professionals discharge any static electricity by touching a large metal or conductive, grounded surface prior to touching the patient or patient cabling. Also neutralize any static electricity from the patient by touching the patient away from the cardiac leads. When clinically indicated, supplemental monitoring of a patient should be considered during temporary cardiac pacing. If a REF 4580 has been subjected to conditions of transport or storage at temperatures below 10°C (50°F) or above 40°C (104°F), it 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.

KEY TO STATUS INDICATORS = atrial output pulse

= ventricular output pulse

P = atrial channel sensing event

R = ventricular channel sensing event

L = low battery condition (flashing)

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 12 for discussion). Figure 2.

5

INDICATIONS, CONTRAINDICATIONS AND WARNINGS Indications The REF 4580 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; sinus bradycardia, symptomatic sinus bradycardia; surgically-induced heart block; sick sinus syndrome; bradycardia with congestive heart failure; atrial and/or ventricular arrhythmias; cardiac arrest; support, management, and evaluation of a patient prior to permanent pacemaker implantation; support during permanent pacemaker replacement; cardiac complications during invasive or surgical procedures; support during cardiac surgery; acute myocardial infarction complicated by heart block; rapid stimulation for the treatment of atrial tachyarrhythmias.

Although the intended uses of a REF 4580 MICRO-PACE are primarily therapeutic and prophylactic, the ability to extensively program the constant voltage output and pulse width allows it to be used to determine capture thresholds of temporary and permanently implanted lead systems. However, Pace Medical recommends the use of a Pace Medical AccuPace™ Pacing Analyzer. 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.

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INDICATIONS, CONTRAINDICATIONS AND WARNINGS, CONTINUED. WARNING: The REF 4580 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. 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. To prevent pacing into the vulnerable period of the T-wave, turn the REF 4580 ON and set the atrial and ventricular output amplitudes down to minimum amplitudes before connecting the REF 4580 to the patients lead system. When using extension cables with the MICRO-PACE, always connect the extension cables to the pulse generator prior to making the connections between the extension cables and the pacing leads heartwires at the patient.

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. * In the REF 4580, the maximum triggering rate is limited to the lesser of 60,000 divided by the programmed refractory period, or 200 ppm. 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.

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PROGRAMMABLE MODES AND PARAMETERS, CONTINUED. 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. * In the REF 4580, the maximum triggering rate is limited to the lesser of 60,000 divided by the programmed refractory period, or 200 ppm. 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. 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. 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.

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PROGRAMMABLE MODES AND PARAMETERS, CONTINUED. DDI - Improved AV sequential pacing (with intact atrial sensing) 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.

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PROGRAMMABLE MODES AND PARAMETERS, CONTINUED. 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. DDD Timing Scheme ↓ Atrial Escape Interval ↓ Ø | Atrial Channel

Ø

| | | Ventricular Channel

|

× ↑

↑

× Programmed Rate Interval

Blanking Period

× Ø

Pacemaker Output

Pacemaker Refractory

AV Delay

Pacemaker Alert

↑ Limits of ↓ Intervals

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PROGRAMMABLE MODES AND PARAMETERS, CONTINUED. Basic Pacing Rate The REF 4580 MICRO-PACE may be programmed from 30 ppm to 200 ppm in increments of 1 ppm in any single-chamber or dual-chamber pacing mode. Single-chamber modes have a nominal rate of 72 ppm. Dual-chamber modes have a nominal rate of 60 ppm. Rates below 45 ppm are intended for temporary diagnostic purposes. If an attempt is made 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 flashing 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 REF 4580 MICRO-PACE is hardware rate limited to 250 ppm in all modes, except when the rapid atrial stimulation mode is activated. See page 31. Pulse Amplitude The pulse amplitude of the REF 4580 MICRO-PACE is programmable in steps of 0.1V from 0.1 to 3.0V, in steps of 0.2V from 3.0 to 6.0V, in steps of 0.5V from 6 to 10V, and in steps of 1.0V from 10 to 14V. If an attempt is made 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 flashing low battery indicator, "L", on the status display. Pulse Width Pulse width for the REF 4580 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 an attempt is made to reduce pulse width below this level. At the end of 60 seconds, pulse width will revert to the nominal 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 flashing low battery indicator, "L", on the status display.

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PROGRAMMABLE MODES AND PARAMETERS, CONTINUED. Sensitivity Atrial sensitivity may be programmed from 0.2 to 20 millivolts. From 0.2 to 3.0 millivolts, the steps are 0.1 millivolt. From 3.0 to 6.0 millivolts, the steps are 0.2 millivolt. From 6.0 to 10 millivolts, the steps are 0.5 millivolt. And, between 10 and 20 millivolts the increment is 1.0 millivolt. Ventricular sensitivity may be programmed from 0.5 to 20 millivolts. From 0.5 to 3.0 millivolts, the steps are 0.1 millivolt. From 3.0 to 6.0 millivolts, the steps are 0.2 millivolt. From 6.0 to 10 millivolts, the steps are 0.5 millivolt. And, between 10 to 20 millivolts, the increment is 1.0 millivolt. The lower the numerical value, the higher the sensitivity. If an attempt is made to program a value greater than 5mV, the brief warning message, "Leaving Typical Sensing Range", will be displayed. 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 margin of safety. Unless the value so determined is smaller than that available with the nominal values, it is recommended that nominal values be used. The nominal values are generally adequate in the acute setting. It is recommended that unnecessary changes from the nominal settings be avoided 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.

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PROGRAMMABLE MODES AND PARAMETERS, CONTINUED. Refractory Periods, Continued. 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. 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 29 for Automatic Programming of Parameters for High-Rate Dual-Chamber Pacing. AV Delay The AV delay defines the time interval between an atrial output pulse and a ventricular output pulse. The available range of values for AV delay 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 nominal value for AV delay is 150 milliseconds. Parameters for High-Rate Dual-Chamber Pacing.

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See page 29 for Automatic Programming of

PROGRAMMABLE MODES AND PARAMETERS, CONTINUED. 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 Pwave 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 menu 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). 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. Medical personnel should 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.

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PROGRAMMABLE MODES AND PARAMETERS, CONTINUED. Blanking Period / Crosstalk When a REF 4580 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 nominal value is 30 milliseconds. A blanking period 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 occurrence is commonly called "crosstalk". 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 development of crosstalk can have catastrophic consequences. To help assure that this will not occur, ventricular safety pacing is always enabled (See page 16). 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 nominal 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 have 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.

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