BCIT - Test 2 - Pacemakers - CARD 4203

The purpose of rate-adaptive pacing is to:

meet the metabolic demand of the patient during exercise and stress.

theoretically used only in patients who are incapable of attaining rate response to exercise on their own (chronotropically incompetent) it is often used for patients who have a viable sinus response but can sometimes use extra cardiac output due to other factors (atrial fibrillation, Vasovagal syncope.etc.).

Chronic incompetence

Chronotropic Incompetence = the inability of the sinus node to adequately respond to exercise by increasing the heart rate.

Failure to achieve peak heart rate

Slow rise to peak heart rate

Erratic rate response to exercise

Objectives of Rate-Adaptive Pacing

Increases cardiac output in response to metabolic needs:

during exercise

during normal activity

during disease states

during emotional reactions

enhances patient's quality of life and sense of well-being.

Benefit of Rate-Adaptive Pacing

Cardiac Output = Stroke Volume x Heart RateStroke Volume can increase cardiac output > 50%Heart Rate can increase cardiac output 500%

There are three steps involved in rate-modulated pacing:

detection of change in the activity.

processing of the raw data by internal algorithms.

tailoring of rate modulation by adjustment of programmable parameters.

Sensors

Metabolic Parameters

Venous blood temperature

Venous oxygen saturation

Minute ventilation

Cardiac Indices

QT interval

Ventricular depolarization gradient

Pre-ejection interval

Stroke volume

Pressure (dP/dt)

Body Activity

Vibration

Accelerometer

Position and motion

Activity/Vibration rate modulated pacemaker

A layer of piezoelectric material, a pressure sensitive ceramic with electrical properties, is bonded to the inside of the pacemaker case. Vibration generated by movement is transmitted through the body and is detected as pressure waves against the pulse generator case. Voltages are then generated as the ceramic is deformed. These voltages are first processed by the rate modulation algorithms and then tailored to meet individual needs by the programmable sensor settings.

The sensor response is rapid and begins as soon the patient begins to walk. The sensor detects vibrations generated as the heel of the foot hits the floor and the responses are partially determined by footwear and surface.

Since the device is pressure sensitive, tapping the device can increase the pacing rate.

pros/cons Activity/Vibration rate modulated pacemaker

Pro:

Fast reaction to exercise

No special leads required

Easy programming

Self-powered

Con:

Not specific to exercise (coughing, tapping)

Easily influenced by external vibration (helicopter, bumpy road)

Not proportional to workload ( up vs. down stairs)

Difficult to optimize to individual patients

Acceleration rate modulated pacemaker

Most accelerometers use the piezoelectric ceramic material that is used in the vibration sensor but mount the piezoelectric material on the circuit board rather than bonding it to the case of the pulse generator. The piezoelectric material is suspended from the circuit board, by either a diving board type suspension or by a cantilever, in such a way that motion in the forward and backward planes is able to generate the voltages that will be converted changes in pacing rate.

This type of motion is a reflection of workload and also potentially provides a rapid initial response.

Pros/cons Acceleration rate modulated pacemaker

Pro:

Fast reaction to exercise

No special leads

Easy programming

Immune to most external influences

Proportional to workload

Con:

Can be fooled by certain motions ( rocking chair, standing on a bus )

Not sensitive to non-exercise demand (i.e., stress)

Minute Ventilation rate modulated pacemaker

Minute ventilation is a variable that can be monitored by the implanted pacing system and is one that correlates well with normal heart rate variability. What is being monitored is change in transthoracic impedance with both respiratory rate and tidal volume.

A sub-threshold current pulse is delivered every 50 msec between the proximal electrode on the bipolar ventricular lead and the case of the pulse generator. At the same time, the voltage is measured between the distal electrode and the pacemaker case. Using Ohm's Law R=V/I, the known current divides the measured voltage and impedance is calculated. The calculated impedance signal varies with respiratory rate (RR) and tidal volume (TV) and that impedance signal is converted to minute ventilation (RR X TV) from the rate modulation algorithms. The minute ventilation signal is then tailored to give the patient an appropriate rate increase by the programming of the sensor settings.

Pros/cons Minute Ventilation rate modulated pacemaker

Pro:

Mimics the physiologic response to exercise

Uses standard bipolar lead

Sensitive to workload and non-exercise demand

Immune to most environmental influences

Con:

Cannot use existing unipolar leads (in replacement cases)

Mechanical ventilation and external sources (e.g., cautery)

Contraindicated in patients with asthma & COPD

Closed Loop Stimulation/CLS rate modulated pacemakers

CLS is integrated into the natural, cardiovascular control loop to determine heart rate based on signals sent directly from the Autonomic Nervous System.CLS monitors cardiac contraction dynamics by monitoring a localized intracardiac impedance signalThis impedance signal provides a direct assessment of myocardial wall motion changes around the vicinity of the tip electrode.

Pros/cons Closed Loop Stimulation/CLS rate modulated pacemakers

Pro:

Responds to both exercise and non-exercise demands

Provides appropriate heart rate when needed, an increase during metabolic demand, even when there is less movement (climbing stairs)

Responds to mental (emotional) demands

Con:

Requires a bipolar lead

Cannot be blended with another sensor

Requires cardiac stimulation (paced)

QT Interval sensor rate modulated pacemakers

QT interval shortens as normal heart rate increases and lengthens as heart rate slows. This is based upon autonomic input and levels of circulating catecholamines.

Measurement of the QT interval provides information that allows rate modulation not only with increased activity and exercise but also with emotion and pain. The interval from the output of a pacing stimulus to the point of maximum rate of change on the T wave is measured. When measuring the QT interval, the QRS is blanked for about 200 msec (programmable) and then the system begins to look at the rise time of the T wave.

most frequently used in combination with a second sensor in a dual sensor system.

Non-specific sensor responses include:

ear and anxiety.

pain.

Dual Sensors

Vibration (activity) and minute ventilation

Vibration (activity) and QT interval

Both of these dual sensor systems include the initial speed of response of the vibration sensor with more proportional response to workload of the metabolic sensors at higher levels of activity.

Programming the Rate-Adaptive Pacemaker

A. Sensor on/off.

B. Blended or single.

C. Threshold — the minimum value that the sensor signal must attain to make it possible to affect an increase in the sensor indicated rate.

D. Slope — the slope dictates the amount of rate change above the base rate.

E. Maximum Sensor Rate (MSR) — the highest stimulation rate allowed during sensor-driven pacing.

F. Reaction time — determines the time required to achieve the sensor indicated rate from the onset of exercise or activity.

G. Recovery time — determines the time required to decelerate from the sensor indicated rate to the base rate after cessation of work.

It is beyond the scope of this module to identify all the algorithms and terminology used by the various manufacturers.

Maximum Sensor Rate Considerations

Patient's age

Patient's underlying heart disease

Type of activity the patient wishes to engage in

Sensor Indicated Rate Histograms

Allows the clinician to prospectively titrate the sensor setting to the needs of the patient

Provides the ability to retrospectively evaluate the sensor performance

Offers safety and convenience of being able to test sensor responsiveness to various inputs

A heart rate histogram

takes each paced and sensed event and allocates them into rate bins and may display graphics, percentage of total counts, or raw counts over a range of heart rates.

DDDR pacing with rate-adaptive AV delay allows

higher maximum tracking limits. As the rate increase, the AV delay decreases. This allows a decrease in the total atrial refractory period and a higher upper tracking limit

Rate-adaptive AV delay is designed to mimic the intrinsic response to increasing heart rate. In a normal heart, PR intervals decrease as the heart rate increases.

Future Sensors

More esoteric sensors have also been developed, such as those that measure central venous temperature, mixed venous oxygen saturation and Intracardiac impedances. The usefulness of sensors extends to ICDs where sensors to evaluate hemodynamic deterioration and the timing of shock delivery would be valuable.

Rate-responsive pacemakers rely on sensor(s) to detect patient activity

The ideal sensor should be

Physiologic

Quick to respond

Able to increase the rate proportionally to the patient's need

Able to work compatibly with the rest of the pacemaker

Able to work well with minimum energy demands or current drain

Easy to program and adjust

Types of Sensors

Activity sensors

Vibration sensors (piezoelectric sensors)

Accelerometers

Physiologic sensors

Minute ventilation

Temperature

Evoked response

QT interval

Closed loop system (CLS)

Programmability

refers to the ability to non-invasively adjust the functioning parameters of the implanted pacing system.

Programming is possible when a telemetry link has been established between the external programmer and the implanted device.

The programmable parameters that are common to single chamber and dual chamber pacing systems include the following:

mode

rate

hysteresis

output

voltage and pulse width

sensitivity

refractory and blanking periods

SSI

is a manufacturers' designation of a device that can be used as either an atrial or ventricular pacemaker.

An SSI pulse generator has programmable refractory period and sensitivity that can be programmed below 1.0 mV.

Reasons for reprogramming mode: VVI to

1. VOO if the patient is going into a high interference environment or if electrocautery is used in the operating room.

2. VVT to define the exact point of sensing of intrinsic R or P wave during troubleshooting or sensitivity testing. This mode could also potentially be used in a high interference environment because instead of being inhibited, a ventricular response is triggered.

Reasons for reprogramming mode: SSIR to

1. AAIR if to be used as an atrial pacemaker and VVIR if to be used as a ventricular pacemaker.

2. AAI or VVI if the patient is chronotropically competent. AAIR or VVIR are available if there is any decrease in normal chronotropic response.

3. AAT or VVT during follow-up in sensitivity testing in troubleshooting.

4. AAI or VVI if pacemaker syndrome occurs or if pacemaker syndrome is intensified by rate modulated increase in pacing rate. Pacemaker syndrome may occur in AAIR mode if pacing rate increases in the absence of increased sympathetic tone and the pacing stimulus to intrinsic R wave interval lengthens.

Reasons for reprogramming mode: DDD to

1. DDI, when tracking of atrial fibrillation or atrial flutter causes an inappropriate increase in ventricular pacing rate.

2. VDD in chronotropically competent patients.

3. AAI if AV conduction is intact.

4. AAT or VVT for sensitivity testing or troubleshooting.

5. DOO or VOO in a high interference environment and when electrocautery is to be used.

6. VVI in the presence of chronic atrial fibrillation or atrial flutter or when the atrial lead is failing to function appropriately (high capture thresholds).

DDDR reprogramming is the same as

in DDD with or with-out the rate response feature

Base rate (standby rate or minimum rate) is usually programmable

from 30-120

The nominal (manufacturers' setting) rate is usually 60 or 70 ppm.

The longer the AV interval and the post-ventricular atrial refractory (PVARP)

the less time there will be for sensing spontaneous atrial events

FOR EXAMPLE: if there is an AV interval of 200 msec and a PVARP of 300 msec, the total atrial refractory period will be 500 msec and it will not be possible to track P waves or follow the sensor above 120 ppm. Upper rates vary from 100 - 200 ppm.

Reasons to increase the base rate include:

1. prevention of ventricular tachyarrhythmias (overdrive suppression).

2. pediatric applications.

3. low cardiac output.

4. long QT interval and prevention of torsades de pointes.

5. in ambulatory monitoring when assessing for lead failure.

6. in follow-up, for testing of capture threshold and when testing for myopotential inhibition.

Reasons for decreasing the base rate include:

1. patient accustomed to low intrinsic rates.

2. chronotropic competence most of the time.

3. symptoms with pacing and/or pacemaker syndrome.

4. coronary artery disease where low heart rates are desirable.

5. economy of energy expenditure from the pulse generator.

6. during follow-up for determining dependency and assessing sensing threshold.

7. when performing a 12 lead ECG to evaluate the native rhythm in ischemia, infarction, hypertrophy and other changes.

hysteresis rate

After a sensed (intrinsic event), a second rate becomes operational and that is called the

Hysteresis allows sensing to occur to a lower rate but once the intrinsic rate drops below the hysteresis rate, pacing occurs at the faster basic pacing rate.

encourages intrinsic conduction.

Natural AV synchrony

Extends the life of the pulse generator

Situations in which hysteresis is not helpful include:

1. atrial fibrillation because of the lack of atrial contribution to cardiac output and because of the inherent irregularity of the ventricular response.

2. with bigeminal rhythms with a paced beat followed by a PVC or frequent PVCs. The short filling time of the PVC followed by the long pause (hysteresis) can result in a very low effective ventricular rate and diminished cardiac output.

DDD Hysteresis with search also called Rate Drop Response

Search hysteresis is useful in patients having systematic episodes due to autonomic syncope, especially in the presence of mixed response (cardioinhibitory and vasodepressor effects).

DDD hysteresis provides a rapid, significant rate boost, with AV synchrony, to counter the effects of the acute rate and pressure drops.

Pulse amplitude is generally programmable from

0.10 volts up to 7.5

Nominal values for amplitude are usually between 3 and 4 volts

Pulse widths are usually programmable from about

0.05 msec to 2.0 msec

nominal pulse width is usually 0.35 to 0.4 msec.

Programmable output parameters include:

1. Amplitude — The need to increase pulse amplitude is usually related to the need to maintain capture and to maintain an appropriate capture safety margin.

Pulse amplitude may be decreased after capture thresholds are performed on the mature pacing lead. In addition, when pectoral muscle stimulation or diaphragmatic stimulation occurs, decreasing the amplitude is more effective in solving the problem than decreasing the pulse width.

2. Pulse Width — Pulse width programming is performed to assure appropriate margins of safety in energy delivery.

Considerations when programming voltage and pulse width include:

1. threshold measurement.

2. setting of appropriate safety margin.

3. maximizing pacemaker longevity.

safety margin

It is generally felt that programming a voltage (amp) that is two times the voltage threshold will provide an adequate safety margin

the pulse width should be programmed at three times the threshold value.

The most efficient pulse duration is where the chronaxie intersects the strength duration curve

It must be remembered that increasing the pulse width beyond 0.7 msec

does not increase the safety margin for capture and would result in energy being expended without safety being increased.

(the increasingly flat part of the strength duration curve)

instead program higher voltage

Manual Capture Threshold Testing

may be done by keeping the pulse width constant and decreasing the voltage in a step-wise fashion or by keeping the voltage constant and decreasing the pulse width in a step-wise fashion.

In a unipolar lead, the capture thresholds are always in unipolar configuration

In a bipolar lead, the configuration for testing should be the same as the programmed pacing polarity.

When a problem with lead integrity is suspected, both unipolar and bipolar thresholds should be evaluated.

In AAI pacing

it is imperative that 1:1 pacing be intact, therefore pacing at the final output at a rate > 120 bpm to ensure 1:1 pacing should be done routinely.

Voltage threshold (VVI or AAI)

the pulse width is maintained at a constant value while the voltage is decreased in a step-wise manner. The last voltage setting at which capture was consistently maintained is called the voltage threshold for capture. A 2:1 safety margin is necessary when programming the voltage component of the output pulse.

Voltage threshold can be tested at multiple pulse widths and a strength duration curve can be plotted. This would allow the choice of the narrowest pulse width at which a 2:1 voltage safety margin can be maintained.

Pulse width threshold (VVI or AAI)

the voltage is maintained at a constant value while pulse width is decreased in a step-wise fashion. The last pulse width setting at which capture was consistently maintained is called the pulse width threshold for capture. A 3:1 safety margin is necessary when programming the pulse width component of the output pulse. If it would be necessary to program the pulse width to 0.75 msec or greater to achieve this safety margin, a higher voltage is generally chosen. Wider pulse widths increase the amount of energy being delivered without increasing the actual safety margin for capture

DDD Testing for atrial capture can be difficult because captured P waves may be difficult to visualize on the surface ECG.

1. Choose the monitoring lead that best demonstrates P waves and atrial capture.

2. Increase the paper speed or gain on the ECG tracing.

3. Run a 12 lead ECG and observe for capture.

4. Program a long AV interval. This allows for better definition of P waves and, if intrinsic AV conduction is intact, will allow either intrinsic conduction or fusion in the ventricle.

5. The slower the pacing rate for atrial capture threshold testing, the less likely it will be that there will be the fusion of T waves, atrial spikes and paced P waves on the ECG and the easier it will be to assess capture.

6. Use marker channels with atrial capture, there will usually be AV sequential pacing only. When capture is lost, the native or intrinsic P wave activity will be sensed on the atrial marker channel. In addition, the rhythm often becomes irregular because of ventricular tracking of the native P waves.

7. When absolutely sure that AV conduction is intact, AAI mode may be used for testing atrial capture threshold. Even if P wave activity cannot be clearly identified, capture can be judged by observation of the intrinsically conducted QRS following each atrial-pacing stimulus.

Factors that will affect the ability of the stimulus to capture, include: (DDD)

1. the programmed voltage and pulse with of the output pulse.

2. the integrity of the pacing system.

3. the proximity of the stimulating electrode to cardiac muscle.

4. the viability of the muscle.

5. the threshold of the muscle cells which may be affected by drugs, electrolyte levels, acid-base balance, perfusion and oxygenation.

Capture Issues in Dual Chamber Pacing

It may be difficult to assess atrial capture on the surface ECG. Some strategies, which may be helpful, include:

1. change lead configuration.

2. multiple recording leads.

3. observe 12 lead ECG.

4. increase gain.

5. increase recording speed (50 mm per sec).

6. decrease base rate or minimum rate.

7. increase AV interval may allow better viewing of P waves and/or a change in QRS complex when capture does not occur.

8. look for independently occurring atrial activity as a sign that atrial capture has not occurred.

9. look for 1:1 conduction.

Sensitivity refers to

the programmable parameter that controls the ability to respond to intrinsic cardiac events.

Accurate sensing so that undersensing will not occur - the pacemaker will not miss P or R waves that should have been sensed.

Ensures that oversensing will not occur - the pacemaker will not mistake extra-cardiac activity for intrinsic cardiac events.

Provides for proper timing of the pacing pulse - an appropriately sensed event resets the timing sequence of the pacemaker.

Reasons for Increasing the Sensitivity

1. Undersensing of intrinsic P waves or R waves.

2. Maintenance of appropriate sensitivity safety margin.

Reasons for Decreasing the Sensitivity

Sensitivity may be decreased to prevent or resolve oversensing (inhibition or tracking response).

Causes of oversensing include the detection of myopotentials, electromagnetic interference or cross talk.

Manual sensitivity threshold testing includes: VVI

1. Decrease pacing rate until stable spontaneous rhythm emerges and observe that each spontaneous ventricular event is sensed at the programmed sensitivity setting.

2. Decrease sensitivity setting step-by-step until sensing is lost and asynchronous ventricular pacing occurs.

3. The last programmed value at which consistent sensing was observed is called the sensitivity threshold.

4. The sensitivity is usually set two steps more sensitively or at 50% of the threshold value.

5. Marker channels and VVT mode may aid in testing.

Manual sensitivity threshold testing includes: AAI

Though AAI sensing is done in a manner similar to VVI testing, it is especially important to use marker channels or AAT settings. It is possible that R waves may be sensed and cause inappropriate inhibition of atrial output.

Manual sensitivity threshold testing includes: DDD or VDD

Assessing R wave sensing:

1. If intrinsic conduction is intact, extend AV delay until R waves are sensed.

2. If there is no intrinsic conduction from atria to ventricles, assess ventricular sensitivity in VVI or VVT mode.

Assessing P wave sensing

1. Shorten AV delay sufficiently that every sensed P wave is followed by paced ventricular event.

2. Use marker channels to document atrial sensing and loss of atrial sensing.

3. If there is a stable and independent ventricular rhythm, P wave sensing may be tested in AAI or AAT mode.

The atrial refractory period should be long enough so the

pacemaker cannot respond to retrograde conduction, but not so long that it limits the pacemaker's ability to respond to physiologic increases in sinus rate.

The blanking period is a time interval in which

the sense amplifier of the pacemaker is incapable of recognizing electrical activity; too long a blanking period may result in nonsensing of premature beats while too short a blanking period may allow for crosstalk.

Retrograde conduction can be measured by

1. pacing in VVI mode at least 10 ppm above spontaneous atrial rate and manually measuring the interval from pacing spike to retrograde P or atrial electrogram.

2. pace in VDD mode 10 ppm faster than spontaneous atrial rate and measure from V pace to sensed retrograde P.

3. automated retrograde test.

Strategies available to prevent endless loop tachycardia

1. programming PVARP longer than retrograde conduction time (usually 50 to 75 msec longer than measured retrograde time).

2. prolongation of PVARP after PVB only. This is a programmable feature in many dual chamber pulse generators. It is called PVARP extension or post-ectopic post-ventricular refractory period.

3. selective programming of sensitivity. Retrograde P waves are often lower voltage than antegrade P waves.

4. ensure an appropriate sensing threshold

5. ensure an appropriate capture safety margin

Crosstalk

Sensing of the atrial output by the ventricular sense amplifier causing inappropriate inhibition of the ventricular output pulse.

Factors affecting Crosstalk:

atrial pulse amplitude and pulse width

ventricular sensitivity

separation of ventricular and atrial electrodes

Causes of Crosstalk:

programming changes

lead problems

Managing Crosstalk:

Increase the post-atrial ventricular blanking period

Reduce atrial output (amplitude and/or pulse width)

Decrease (increase value) ventricular sensitivity

Safety pacing

Program bipolar (if applicable)

Ventricular Blanking Period

Programming changes that affect the blanking period include:

atrial output

ventricular sensitivity

electrode configuration

Also the blanking period can be separately programmed as long as 75 ms.

Safety Pacing/nonphysiologic AV delay (NPAVD)

A period of time that begins at the end of the ventricular blanking period lasting a total of 100-110 ms.

Any signal sensed by the ventricular lead during this period commits the device to pace at the end of 100-110 ms.

Utilized to prevent crosstalk inhibition.

Programming Strategies for Preventing Rapid Tracking of Atrial Tachyarrhythmias

1. Limitation of maximum tracking limit to a rate that the patient will tolerate while in an atrial tachyarrhythmia.

2. Programming the atrial sensitivity so that organized atrial activity is sensed but the lower amplitude atrial fibrillation waves are not sensed and therefore not tracked.

3. Programming of differential maximum tracking rate and maximum sensor rate so the tracking of atrial tachyarrhythmias can be limited to a rate tolerated by the patient but the sensor input can increase the pacing rate appropriately with exercise and activity.

4. Programming to a non-tracking dual chamber mode such as DDIR, DDI, DVIR or DVI. These modes do not allow the tracking of atrial tachyarrhythmias and provide AV synchrony at rest.

5. Automatic mode switching is a frequently used programmable option used to prevent rapid tracking of atrial tachyarrhythmias.

Potential problems with automatic mode switching include:

1. difficulty in consistently sensing atrial fibrillation in order to meet the mode switching rate criteria.

2. difficulty in detecting atrial flutter because of flutter waves falling into atrial blanking periods.

3. When a flutter wave is sensed, an AV interval is initiated. With AV intervals in the normal range of 120 to 200 msec, it is quite possible that the next flutter wave may fall into the atrial‑blanking period, which follows the ventricular paced event. PVAB

Programmability may be defined as:

the ability to change the functioning parameters of the pacing system non-invasively.

Indication for temporary programming to VVT mode may be:

evaluation of sensing.

Reasons for programming from DDD to VVI mode may include:

chronic atrial fibrillation.

Hysteresis in VVI mode is very helpful in patients with:

complete AV block.

2)

atrial fibrillation.

3)

bigeminy.

4)

none of the above.****

Decreasing pulse amplitude may decrease:

1)

pectoral muscle stimulation.

2)

diaphragmatic stimulation.

3)

R wave sensitivity.

4)

A and B.***

Programming the sensitivity from 4 mV to 2 mV may:

solve a problem of undersensing.

Loss of capture may be caused by:

1)

exit block.

2)

lead dislodgement.

3)

electrolyte imbalance.

4)

battery depletion.

5)

all of the above.****

A basic pacing rate of 80 ppm may be found in a patient with:

1)

low cardiac output.

2)

long QT syndrome.

3)

angina pectoris.

4)

A and B***

A patient presents in the ER with no sign of pacemaker activity and an intrinsic rate of 38 bpm. Potential explanations include:

1)

failed pacing system.

2)

basic pacing rate of 35 ppm.

3)

basic pacing rate of 50 ppm with hysteresis to 35 ppm.

4)

all of the above.***

Every time the patient lifts his arm, the output of his pacemaker is inhibited and he feels faint. The ventricular sensitivity is set at 2.5 mV (unipolar). The appropriate direction for reprogramming of sensitivity would be:

less sensitive 3.0, 4.0, etc.

Goals of the Pacemaker Follow-up

Verify appropriate function.

Optimize pacemaker function and longevity.

Recognize, interpret, and correct pacer problems prior to onset of symptoms.

Classification of device recall.

Detect and replace pulse generators approaching elective replacement time (ERT).

Collect and report patient and pacemaker information to appropriate personnel.

Device Recall Management Classifications

Class I

Reasonable probability that the product will cause serious adverse consequences or death. (High Risk)

Class II

Use of product may cause temporary or medically reversible adverse health consequences or the probability of serious adverse health consequences is remote. (Moderate Risk)

Class III

The use of the product is not likely to cause adverse health consequences. (Low Risk)

Notification or Safety Alert - Recall/Advisory

Communication issued by manufacturer to inform of the risk of substantial harm from a medical device.

These situations can be of the same importance as a Class I, Class II, or Class III recall.

Final decision made by Cardiologist or electrophysiologist

Systematic Approach to Pacemaker Follow-up

Patient interview

History and physical exam

Wound site

Non-magnet ECG

Magnet ECG

Inquire/Interrogate

Telemetry

Diagnostics

Underlying rhythm

Stimulation threshold testing

Sensitivity testing

Summarize

Final settings

Inquire/interrogate, print, and document

Safety considerations in pacemaker follow-up include the following:

Familiarity with the programmer to be used.

Identification emergency buttons on the programmer.

Safe electrical environment.

Location of emergency equipment (external defibrillator).

Always carefully checking the programmed settings at the end of follow-up to ensure they have been returned to appropriate values.

The following information is usually obtained: During pacemaker follow up

Name, address, telephone, who to contact

Date of birth

Family physician, follow-up physician, implanting physician

Indication for pacing and pre-implant symptoms

History of devices and leads

Pulse generator: information needed for follow up

date of implant, manufacturer, model, serial number

expected longevity

battery depletion indicators

device recall status

Leads: information needed for follow up

date of implant, manufacturer, model, serial number

routing transvenous, epicardial

implant capture threshold, R and/or P wave measurement, lead impedance

problems encountered at implantation

adaptors, lead repair

lead recall status

History taking inquiry about

changes in cardiovascular conditions

changes in surgeries or trauma since last

changes in symptoms

(dizziness, palpitations, SOB, exercise tolerance, chest pain, return of symptom for which pacemaker was implanted)

changes in problems which patient thinks may be related to pacing system

Inspection of the implantation site observing for the following signs: PA

Hematoma or fluid accumulation

Redness

Tenderness

Poor healing

Erosion

Movement of the generator

Pectoral muscle twitching

Pain at implant site or with arm movement

Pulse generator migration

Blood pressure measurement: PA

Routine surveillance

Assessment for blood pressure drop when going from sinus rhythm to paced rhythm in suspected pacemaker syndrome

Assessment for blood pressure drop from lying to standing in symptoms, which may be related to postural hypotension

Assessment for symptoms of sub-optimal hemodynamics, which may be related to the pacing therapy: PA

Breath sounds

Ankle edema

Weight gain

Heart sounds

Initial review of rhythm strip or 12-lead ECG consists of documentation of:

appropriate capture and sensing.

the presence of arrhythmias and supraventricular or ventricular tachyarrhythmias including new onset atrial fibrillation or flutter.

Systematic Approach to ECG Analysis: Rhythm eval

Identify pacing mode

Identify pacemaker settings

Is there capture?

Check wave morphologies

Is there sensing?

What is the pacing interval?

Are there rate variations and can we account for them?

Is hysteresis present?

Are there examples of fusion or pseudofusion?

Troubleshooting Reminders: ECG analysis: Rhythm eval

Problems with capture

Problems with sensing

Fusion, pseudofusion

Functional non-capture: Rhythm eval

Occurs when a pacing spike is delivered at a time when it could not possibly depolarize the heart (refractory)

Often observed in VOO or AOO (non-sensing modes)

functional non-capture does not necessarily indicate a capture problem (timing problems)

Conclusion: Rhythm eval

Systematic approach to paced ECGs

Look for capture and sensing

Troubleshoot problems

Verify pacing rate (look at pacing interval)

Account for rate variations, if any

Note fusion and pseudofusion (May not require troubleshooting unless too frequent

Magnet Application: considerations

Performed as an early step in follow-up

magnet placed over the pulse generator will disable the sensing (in most devices)

Pacing rate will provide info about battery voltage or impedance

Need to know anticipated behavior when magnet is applied. AOO, VOO, DOO

Need to know if there is an initial "signature" faster rate to overdrive the intrinsic rhythm. After first few pacing will occur at a rate that reflects battery.

is there a threshold margin test. serves as indicator that there is adequate output margin at the output settings.

Does the pacing rate stay at the magnet rate as long as the magnet is applied or does it revert to normal non-magnet function after a certain number of paced events

Potential Problems: Magnet application

Magnet application and asynchronous pacing have been known to initiate atrial or ventricular tachyarrhythmias in vulnerable patients with ischemic or recently infarcted hearts, with a history of VT or VF, with re-entrant paroxysmal supraventricular tachycardias or atrial fibrillation or flutter.

There is also the possibility of initiating an endless loop tachycardia when AV synchrony is lost during magnet application.

There is the possibility of triggering the EOL indicator and change of mode from dual chamber to single chamber pacing.

Device Evaluation: interrogation

Battery status

Lead system parameters\Elective replacement indication

Stored event data with electrograms

Battery Status: Measured Parameters

When evaluating the measured battery parameters, the following information may be useful:

Know the replacement indicators.

Know the exact meaning of the words the manufacturer uses concerning replacement indicators.

Know the expected longevity of the device.

Know if the device is on recall or advisory.

Incorporate clinic's experience with battery longevity in this model.

Know if any factors might be accelerating current drain. Such as....

(very low lead impedance

high output settings (high capture thresholds)high standby rates aggressive sensor rates)

Some battery indicators may be more useful than others

battery voltage

battery impedance

magnet rate

longevity calculation

pulse width

When assessing lead impedance, the following information may be useful: Interrogation

Manufacturer's reports on lead performance.

Clinic experience with this model of lead.

Age of the lead.

Adaptors in the system.

Recall status.

Compare with manufacturer's specifications. high impedance and low impedance lead tolerances for measurement accuracy in that model of lead