Permanent cardiac pacemaker/implantable cardioverter-defibrillator

Published on 02/04/2015 by admin

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Last modified 22/04/2025

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32 Permanent cardiac pacemaker/implantable cardioverter-defibrillator

Instruction

Examine this patient’s cardiovascular system.

Salient features

History

• Past history of syncope (Stokes–Adams attacks) and heart block

• Dizziness (pacemaker syndrome).

Examination

• Dropped beats caused by occasional ventricular ectopics

• Infraclavicular scar indicating pacemaker insertion

• Palpate the infraclavicular area gently to confirm the presence of a pacemaker.

Remember: electromagnetic interference during MRI or lithotripsy may transiently cause malfunction of pacemakers. Be prepared to discuss the anatomy of cardiac conduction system.

Diagnosis

This patient has a permanent pacemaker (lesion) for previous heart block (aetiology), which is functioning adequately (functional status).

Questions

What are the indications for a permanent pacemaker?

• Symptomatic bradyarrhythmias: heart rate <40 beats/min or documented periods of asystole >30 s when awake. Symptoms include syncope, presyncope, confusion, seizures, or congestive heart failure and they must be clearly related to the bradycardia.

• Asymptomatic Mobitz type II atrioventricular block (N Engl J Med 1998;338:1147–48): you may asked to differentiate between Mobitz type I and II (see Fig. 11.1C,D).

• Complete heart block (see Fig. 11.1A,B).

Advanced-level questions

What do you know about permanent pacemakers?

• They are connected to the heart by one or two electrodes and are powered by long-lasting (5–10 years) solid-state lithium batteries. Most pacemakers are designed to pace and sense the ventricles: called the VVI pacemakers because they pace the ventricle (V), sense the ventricle (V) and are inhibited (I) by the ventricular signal. They are inserted under local anaesthesia and fluoroscopic guidance, subcutaneously under the pectoral muscles.

• In symptomatic sinus tachycardia, an atrial pacemaker may sometimes be implanted (AAI).

• In sick sinus syndrome, a dual chamber pacemaker DDD (because it paces two or dual chambers, senses both (D) and reacts in two (D) ways, i.e. pacing in the same chamber is inhibited by spontaneous atrial and ventricular signals, and ventricular pacing is triggered by spontaneous atrial events) is implanted.

• Rate-responsive pacemakers measure activity, respiration, biochemical and electrical indicators, and change their pacing rate so that it is suitable for that level of exertion.

How soon after pacemaker insertion can a patient drive?

They may not drive until the pacemaker has been shown to be functioning correctly for at least 1 month after implantation. Patients must inform driving licensing authorities and the motor insurers.

Mention some expanded use of cardiac pacing

• Dual chamber pacing has been used to optimize cardiac output and minimize the outflow tract gradient in patients with hypertrophic obstructive cardiomyopathy.

• Dual chamber pacing is currently being utilized in dilated cardiomyopathy with heart failure and intraventricular conduction delay to optimize atrioventricular delay and improve cardiac output: cardiac resynchronization therapy.

• Dual-site atrial pacing to prevent atrial fibrillation is being evaluated.

What are the complications of pacemakers?

• Erosion through the skin caused by mechanical factors

• Infection

• Lead displacement or lead fracture (the most common site of pacing lead fracture is between the first rib and the clavicle)

• Pacemaker malfunction

• Electromagnetic interference

• Pain/ecchymoses at site of insertion

• Pneumothorax.

What are the potential sources of electromagnetic interference?

Electromagnetic interference can occur from heavy electric motors and arc welding. Devices such as airport security devices and ham radios cause single-beat inhibition but they should not cause significant clinical interference. Microwave ovens do not interfere with pacemakers. Cellular phones and anti-theft devices or electronic article surveillance equipment can potentially interfere with pacemakers (N Engl J Med 1997;336:1473–79,1518–19). Analogue phones are less likely to cause interference than phones based on digital technology. Patients should avoid carrying the cellular phones in a pocket directly over the pacemaker.

What is the pacemaker syndrome?

• It is seen in individuals with a single-chamber pacemaker who experience symptoms of low cardiac output (dizziness, etc.) when erect; it is attributed to the lack of atrial kick. Pacemaker syndrome results from haemodynamic changes following inappropriate use of ventricular pacing: it occurs when ventricular pacing is uncoupled from atrial contraction. It is most common when the VVI mode is used in patients with sinus rhythm, but it can occur in any pacing mode when atrioventricular synchrony is lost. Levels of atrial natriuretic factor are high in pacemaker syndrome.

• If pacemaker syndrome occurs in a patient with VVI pacemaker, the only definitive treatment is converting to a DDD. If the patient has occasional use of bradycardia then often symptoms may be ameliorated by programming the pacemaker to a lower limit and programming with hysteresis ‘on’. This allows the patient to stay in normal sinus rhythm for longer periods by minimizing the pacing.

If a patient with an implantable defibrillator requires a pacemaker would you put a separate device or replace it with a ICD with associated pacemaker function?

Placement of a separate pacemaker into a patient who has a defibrillator has the potential to cause serious pacemaker–defibrillator interactions. The most commonly implanted defibrillators have the additional ability to attempt termination of ventricular tachycardia with anti-tachycardia pacing. The obvious advantage of this feature is that an arrhythmia can be terminated painlessly without delivery of a shock. If anti-tachycardia pacing is unsuccessful then the device will administer a shock.

Mention some indications for implantable cardiac defibrillators

• Cardiac arrest as a result of ventricular tachyarrhythmia not the result of a reversible cause or transient cause (remember: patients who have cardiac arrest unrelated to acute myocardial infarction have approximately a 35% chance of recurrent ventricular arrhythmias within the first year)

• Spontaneous sustained ventricular tachycardia

• Syncope of undetermined origin with inducible sustained ventricular tachycardia on electrophysiologic study and when drug therapy is not effective or tolerated

• Non-sustained ventricular tachycardia with coronary artery disease and inducible ventricular tachycardia or electrophysiologic study that is not suppressible by class I antiarrhythmic drug.

What are the contraindications to patients with ICDs?

• MRI

• Lithotripsy is contraindicated if the pulse generator is in the field.

What are the indications for lead removal?

Mandatory:

• Life-threatening condition, leads must be removed

• Indications include septicaemia (endocarditis), migration (causing emboli, arrhythmia, or perforation)

• Device interference (i.e. abandoned ICD lead), and occlusion of all usable vessels.

Necessary:

• Great potential for morbidity or mortality, leads should be removed

• Indications include pocket infection, chronic draining sinus, erosion

• Potential device interference, venous thrombosis, and lead replacement (extract and reimplant via thrombosed vein).

Discretionary:

• Lead removal is optional

• Indications include pain, malignant disease, and replacement of leads abandoned for <3–4 years (not advisable to remove non-infected leads that have been implanted for >8–10 years).

(see Lancet 2004; 364:1701–19.)

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