Hospital Medicine

Pacemakers

I. Problem/Challenge.

Symptomatic bradyarrhythmias can have important clinical consequences including syncope, heart failure, and sudden death due to inadequate cardiac output. The majority of cases are due to either abnormalities of impulse generation (sinus node dysfunction) or conduction (atrioventricular block). Permanent pacemakers are the mainstay of treatment for clinically significant sinus node dysfunction and atrioventricular block not due to a reversible cause. Over 200,000 new pacemakers are implanted each year in the United States and indications have continued to expand based on the results of recent clinical trials. Given this, clinicians should have a basic understanding of device operation, indications, and common problems encountered with these devices.

II. Identify the Goal Behavior.

It is important to incorporate evidence based care into clinical practice so that patients with sinus node dysfunction and atrioventricular conduction abnormalities who would benefit from permanent pacemaker implantation can be identified. The general practitioner is commonly involved in the evaluation of patients with presyncope and syncope. Clinical history and the 12 lead electrocardiogram are central in the initial evaluation to identify patients with potential cardiac etiologies, including bradyarrhythmias, who are at increased risk of mortality. Clinicians should be familiar with the current guidelines for pacemaker therapy so these patients can be appropriately referred to cardiology. It is also important to understand what elements from the history are important in the evaluation of patients with a pacemaker as well as some of the common issues encountered by patients with these devices in the hospital.

III. Describe a Step-by-Step approach/method to this problem.

Pacemaker types and functioning

The pacemaker consists of a pulse generator, which contains the battery and programming circuitry, and one to three leads, which provide access to the chamber of the heart being paced (right atrium, right ventricle, or coronary sinus for left ventricle pacing). Contemporary pacemakers have numerous programmable features that can be changed to optimize function. The pacing mode selected depends on the underlying rhythm disturbance, associated medical problems, and exercise capacity.

A three to five letter code has been developed to describe a pacemaker's mode of operation. The first letter refers to the chamber being paced (Atrium, Ventricle, Dual), the second letter refers to the chamber being sensed (Atrium, Ventricle, Dual), the third letter refers to the response of the device to the sensed signal (Triggered, Inhibited, Dual), the fourth letter refers to whether the pacemaker modulates the rate independent of cardiac activity, such as with respiration or motion (R), and the fifth letter indicates whether multisite pacing is present. For example, the most common modality is dual chamber rate responsive (DDDR) pacemaker, which is capable of sensing and pacing both the atria and ventricles and has rate modulation that allows for increased heart rate in response to increasing physiologic demand, as occurs during exercise.

Figure 1 shows an example of an EKG with A-V sequential pacing (A-pace V-pace) in a patient with a dual chamber pacemaker (DDD). Atrial and ventricular pacemaker spikes (most easily seen in lead II) occur prior to the P wave and QRS complex, respectively. The ventricular lead is in the right ventricle (RV), typically placed in the RV inferior wall close to the apex, resulting in a QRS complex that is wide with left bundle branch morphology. In DDD pacing mode, atrial pacing occurs at the lower limit unless the native atrial rate is faster than the programmed rate. After the programmed AV delay has timed out then ventricular pacing is triggered unless a native ventricular event is sensed before the end of the AV delay.

Figure 1.

Example of A-V sequential pacing

Indications for permanent pacemaker therapy

Sinus node disease is the most common indication for pacemaker therapy. This includes sinus bradycardia, sinus arrest, sinus pauses, chronotropic incompetence (inability of the sinus node to accelerate), or tachy-brady syndrome, which refers to alternating periods of tachycardia (often atrial fibrillation with rapid ventricular response) and then bradycardia (often prolonged sinus pause after termination of the atrial tachyarrhythmia). Most cases are due to idiopathic degeneration and fibrosis of the sinus node although it can also be due to medication, hypothyroidism, advanced liver disease, hypothermia, amyloidosis, elevated vagal tone, hypoxia, and hypercapnia. Sick sinus syndrome is the combination of symptoms (pre-syncope, syncope, decompensated heart failure) and sinus bradycardia or sinus pauses.

Because sinus bradycardia and pauses are common and in the absence of symptoms have a benign prognosis, it is critical to correlate symptoms with EKG findings of sinus node dysfunction in order to establish the diagnosis. Ambulatory monitoring is often helpful for this. Electrophysiology study is the next step if patients have compatible symptoms but do not have correlating documentation of an arrhythmia after prolonged ambulatory monitoring. Generally, pacemaker therapy is only recommended when symptoms are present if the cause is not reversible or if the patient requires a medication that causes symptomatic bradycardia.

Atrioventricular (AV) conduction disease is the second most common indication for pacemaker therapy. The causes of AV conduction disease include degenerative disease (Lev's disease, Lenegre disease), medications, myocardial infarction (often inferior MI), infiltrative disease (sarcoid, amyloid), and infection (lyme disease, endocarditis). The clinical significance of conduction disease depends on the site of the conduction abnormality, the probability of progression to complete heart block, and the rate and stability of the escape rhythm. For example, conduction disturbance below the AV node in the His-Purkinje system, as is seen in Mobitz type II second degree block, is considered less stable with a high rate of progression to complete heart block with risk of slow, unstable escape rhythm that may not be sufficient to meet hemodynamic requirements. Generally, pacemaker therapy is recommended in patients with symptoms or with His-Purkinje disease (Mobitz type II block, complete AV block, alternating bundle branch block).

Neurocardiogenic syncope, which includes carotid sinus hypersensitivity and vasovagal syncope, is a less common indication for pacemaker therapy. Syncope is thought to be due to a brief imbalance in autonomic regulation resulting in vasodilation with or without inappropriate bradycardia. Patients where vasodilation is the predominant mechanism of hypotension would not benefit from a pacemaker but the subset where a significant cardioinhibitory response (bradycardia) is produced during tilt table testing may benefit from dual chamber pacing with rate drop response.

SeeTable I for ACC/AHA/HRS indications for permanent Pacemaker.

Table I.

ACC/AHA/HRS Indications for Permanent Pacemaker
Sinus Node Dysfunction Class I -Symptomatic sinus bradycardia (including sinus pauses that cause symptoms) -Symptomatic chronotropic incompetence (inability of the sinus rate to accelerate) -Symptomatic sinus bradycardia due to drug therapy for which there is no acceptable alternative Class II -Symptomatic patients (heart rates <40 beats per minute) without a clear association between symptoms and bradycardia -Syncope of unexplained origin with discovery of sinus node dysfunction -Chronic heart rate <40 beats per minute in minimally symptomatic patients
Atrioventricular Block Class I -Complete heart block and advanced second degree block with any of the following: -symptoms -when associated with arrhythmia or other medical condition where drug therapy that may cause bradycardia is required -escape rate <40 beats per minute or asystole > 3.0 seconds -following atrioventricular node ablation -following cardiac surgery and not expected to resolve -associated with neuromuscular disease -Symptomatic second degree heart block (Mobitz type I or type II) -Complete heart block with escape rate >40 beats per minute with left ventricular dysfunction or cardiomegaly -Second or third degree heart block during exercise in the absence of cardiac ischemia Class II -Complete heart block with escape rate >40 beats per minute without left ventricular dysfunction or cardiomegaly -Second degree AV block at intra or infra His level of electrophysiology study
Neurocardiogenic Syncope Class I -Syncope caused by carotid sinus stimulation (carotid sinus pressure causes ventricular asystole of > 3 seconds) Class II -Syncope without clear provocative events and with a hypersensitive cardioinhibitory response -Recurrent neurocardiogenic syncope associated with bradycardia documented spontaneously or during tilt table testing
Following Myocardial Infarction Class I -Third degree AV block within or below the His-Purkinje system -Second degree AV block in the His-Purkinje system with bilateral bundle branch block -Transient second or third degree infranodal AV block with associated bundle branch block Class II -Persistent second or third degree AV block at the AV node level
Bifascicular and Trifascicular Block Class I -Intermittent third degree AV block -Type II second degree AV block -Alternating bundle branch block Class II -Syncope not demonstrated to be caused by AV block when other likely causes have been excluded
Pacemaker Not Indicated -Sinus node dysfunction in asymptomatic patients -Sinus node dysfunction with symptomatic bradycardia due to nonessential drug therapy -Asymptomatic PR prolongation (first degree block) -Asymptomatic second degree Mobitz type I (Wenckenback) AV block -Reversible AV block (due to electrolyte abnormalities, medication, sleep apnea, enhanced vagal tone, Lyme disease) -Fascicular block with or without first degree AV block -Presyncope or syncope in the absence of hyperactive cardioinhibitory response -Transient AV block in the absence of intraventricular conduction defects post-myocardial infarction -Fascicular block without AV block or symptoms -Torsades de pontes from reversible causes

Cardiac resynchronization therapy

Cardiac resynchronization therapy (CRT) or biventricular pacing (pacing of the right and left ventricle) refers to reestablishing synchronous timing of contraction between the left ventricular free wall and ventricular septum in order to improve diastolic and systolic function. Dyssynchrony between the right and left ventricles, which can be caused by intraventricular conduction delay such as a left bundle branch block, is associated with impaired systolic and diastolic function, worsening mitral regurgitation, and adverse prognosis.

Implantation of a third lead in the lateral branch of the coronary sinus allows for pacing of the left ventricle, which can be coordinated with right ventricular pacing to reestablish synchrony. The ideal candidate is on medical therapy (ACE-inhibitor or ARB, beta blocker, and loop diuretic), has conduction delay and a prolonged QRS duration, systolic heart failure with an ejection fraction less than 35%, echocardiographic evidence of dyssynchrony, and New York Heart Association (NYHA) class II-IV symptoms although indications have expanded as clinical trial data has shown benefit in other populations as well. Of note, the majority of these patients also meet criteria for implantable cardioverter defibrillator (ICD) and these devices are specified as CRT-D (device capable of CRT and defibrillation).

SeeTable II for ACC/AHA/HRS indications for cardiac resynchromisation therapy (CRT)

Table II.

Constellation of clinical features in portal hypertension
Class I -LBBB with QRS duration >150ms, ejection fraction <35%, NYHA class II, III, or ambulatory IV
Class IIA -LBBB with QRS >120ms, ejection fraction < 35%, NYHA class II, III, or ambulatory IV -Non-LBBB pattern w/ QRS >150ms, ejection fraction <35%, NYHA class III or ambulatory IV symptoms -Ejection fraction <35% and undergoing device placement with anticipated requirement >40% ventricular pacing
Class IIB -LBBB with QRS >150ms, ejection fraction <30% with ischemic etiology of heart failure, NYHA class I symptoms -Non-LBBB pattern with QRS >120ms, ejection fraction <35%, NYHA class III or ambulatory IV -Non-LBBB pattern with QRS >150ms, ejection fraction <35%, NYHA class II

Approach to the hospitalized patient with a pacemaker

MRI compatibility: A common question is whether it is possible to perform a magnetic resonance imaging (MRI) study in a patient having permanent pacemaker. MRI is a source of electromagnetic interference (EMI), which is a signal that is within the frequency spectrum detectable by the sensing circuitry of the pacemaker. The risk of exposure to EMI includes sensing abnormalities, rate alteration, and reprogramming. Due to these concerns, the AHA considers MRI use to be a relative contraindication in the general population. At the same time, experts acknowledge that there are studies where MRI has been safely performed in pacemaker dependent patients under certain conditions and in centers with expertise in electrophysiology and MR imaging. For the general practitioner, if you are considering whether the benefit of MRI may outweigh the risk in a patient with a pacemaker then further consultation with cardiology is recommended. Of note, at the time of this writing there are "MRI conditional" pacemakers that have been approved by the Food and Drug Administration for some MRI applications.

Peri-operative management: Another common question is how to manage a permanent pacemaker during an operative procedure. The concern again has to do with electromagnetic interference, from electrocautery. Prior to the procedure, the device should be interrogated. For pacemaker dependent patients the device can be programmed to asynchronous pacing (DOO) or the same effect can be had by placing a magnet over the pacemaker during the operation. In case of emergency, availability of temporary pacing support should be confirmed. Following the procedure, the device should be re-interrogated and re-programmed.

IV. Common Pitfalls.

Distinguishing normal pacemaker operation from device malfunction using the 12 lead electrocardiogram is important but not always straightforward. As the complexity of pacemakers has increased, so has the skill required to identify pacemaker problems and troubleshoot electrocardiographic abnormalities. The adverse effects of pacemaker therapy are usually due to device malfunction due to abnormalities in sensing, failure to deliver an appropriate output stimulus, or lead displacement. Having a systematic approach to interpret paced EKGs is important in order to avoid misinterpretation.

First, clinical history is valuable to identify device related problems. Clinicians should ask about dizziness, syncope, palpitations, or a change in exercise tolerance. When an abnormality in pacemaker function is considered, the evaluation includes physical exam, 12 lead electrocardiogram, and chest radiography to assess for lead position and lead to pin connection, followed by pacemaker interrogation.

Second, the 12 lead electrocardiogram can be approached in the following manner:

1. Is a pacing stimulus present? Failure to deliver an appropriate pacing stimulus can be due to oversensing and then inhibition of output or mechanical failure of the pacemaker. Oversensing refers to inappropriate sensing of cardiac (P wave, T wave, pacing artifact) or non-cardiac (skeletal muscle signals, electromagnetic interference) electrical signals. Application of a magnet, which causes the pacemaker to switch to an asynchronous pacing mode with a programmed atrioventricular delay and fixed magnet rate depending on the manufacturer, can be useful in further evaluation. If magnet application results in pacing and capture then oversensing is likely. If no change occurs then consider battery depletion or mechanical failure.

2. Is capture occurring? Failure to capture (pacing artifact is present but subsequent cardiac depolarization does not occur) can be due to inadequate programmed output, lead malfunction, mechanical failure, or elevated thresholds from medications or metabolic abnormality. Malfunction is unlikely if there is capture and the rate is appropriate. Pacemaker battery depletion can result in either failure to capture due to reduced voltage output or failure to pace due to total battery depletion.

Finally, when reading an EKG with ventricular pacing it is always important to identify the underlying atrial mechanism and consider the possibility of atrial fibrillation or atrial flutter. Most dual chamber pacemakers can detect atrial arrhythmias and will change programming to avoid rapid ventricular pacing. Pacemakers in patients with paroxysmal or permanent atrial fibrillation do not protect against thromboembolism, so if atrial fibrillation is present then the patient should be risk stratified for appropriate thromboembolic prophylaxis.

V. National Standards, Core Indicators and Quality Measures.

No national standards/benchmarks established yet.

What's the Evidence?

Tracy, CM, Epstein, AE, Darbar, D. "2012 ACCF/AHA/HRS Focused Update to the 2008 Guidelines for Device Based Therapy of Cardiac Rhythm Abnormalities.". J Am Coll Cardiol. vol. 60. 2012. pp. 1297.

(The published guidelines providing evidence based recommendations for the appropriate use of cardiac resynchronization therapy.)

Epstein, AE, DiMarco, JP, Ellenbogen, KA. "ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines". Circulation. vol. 21. 2008. pp. e350.

(The published guidelines providing evidence based recommendations for the appropriate use of permanent pacemakers.)

Bristow, MR, Saxon, LA, Boehmer, J. "Comparison of Medical Therapy, Pacing, and Defibrillation in Heart Failure (COMPANION) Investigators: Cardiac-resynchronization with or without an implantable defibrillator in advanced chronic heart failure.". N Engl J Med. vol. 350. 2004.. pp. 2140.

(Landmark randomized trial demonstrating that a pacemaker with cardiac resynchronization capabilities in patients with an ejection fraction of 35% or less, with NYHA class III or IV symptoms, and a QRS duration of greater than 120ms reduced mortality compared to medical therapy.)

Levine, GN, Gomes, AS, Arai, AE. "AHA Scientific statement. Safety of Magnetic Resonance Imaging in patients with cardiovascular devices.". Circulation. vol. 16. 2007. pp. 2878.

(Scientific statement summarizing the safety issues of MRI in patients with cardiac devices with a general recommendation against the routine use of MRI in patients with an permanent pacemaker while recognizing that there may be individual cases where the diagnostic benefit outweighs the risk and what can be done to minimize risk in this situation.)

Libby, Bonow, Mann, Zipes. "Braunwald's Heart Disease". A Textbook of Cardiovascular Medicine. Saunders,. 2008.

(A reference with chapters on bradyarrhythmias and permanent pacemakers, which includes device design, programming, indications, and troubleshooting EKG abnormalities.)

Nathanson, LA, McClennen, S, Safran, C, Goldberger, AL. "ECG Wave-Maven. Self-Assessment Program for Students and Clinicians.". http://ecg.bidmc.harvard.edu.

(An online EKG repository and education tool with numerous examples of bradyarrhythmias and paced rhythms.)

Mond, HG, Proclemer, A.. " The 11th world survey of cardiac pacingimplantable cardioverter-defibrillators: calendar year 2009--a World Society of Arrhythmias project.". Pacing Clin Electrophysiol.. vol. 8. 2001.. pp. 1013.

(Analysis from the National ICD registry highlighting the current use of permanent pacemakers in the general population in the United States.)
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