Pacemaker selection, pacing modes and rate response
THE CONTEXT
Pacemaker chamber selection depends on the underlying rhythm and conduction disorder. Dual-chamber and rate-responsive systems provide additional physiological benefits in selected patients.
Choice of chamber configuration
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Single-chamber atrial pacing is indicated in patients with SA disease without AV block.
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Ventricular pacing is indicated in patients with continuous AF and bradycardia.
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Dual-chamber pacing is most often used for second- or third-degree AV block.
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In dual-chamber pacing, the atrial electrode detects spontaneous atrial activity and triggers ventricular pacing. This preserves AV synchrony and allows the ventricular rate to rise with the sinus node rate during exercise or other stress.
Benefits of dual-chamber pacing
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Compared with single-chamber ventricular pacing, dual-chamber pacing provides superior haemodynamics and better effort tolerance.
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It is associated with a lower prevalence of atrial arrhythmias in patients with SA disease.
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It avoids pacemaker syndrome: a fall in blood pressure and dizziness caused by loss of AV synchrony in patients who have a single ventricular pacemaker but remain in sinus rhythm.
Pacing-mode examples
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AAI denotes a system that paces and senses the atrium and inhibits pacing when spontaneous activity is sensed.
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Most dual-chamber pacemakers use DDD mode. Ventricular pacing is triggered by a sensed sinus P wave and inhibited by a sensed spontaneous QRS complex.
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A fourth letter, R, indicates a rate-response function. AAIR denotes an atrial demand pacemaker with rate response.
Rate response and diagnostic information
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Rate-responsive pacemakers are used for chronotropic incompetence, in which patients cannot increase their heart rate during exercise.
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Their sensors trigger an increase in heart rate in response to movement or increased respiratory rate. Sensor sensitivity and the maximum paced heart rate are programmable.
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Pacemakers store diagnostic information about heart-rate trends and episodes of tachyarrhythmia, such as AF or VT.
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The illustrated devices include single-chamber and dual-chamber pacemakers, a cardiac resynchronisation therapy pacemaker (CRT-P), and a cardiac resynchronisation therapy defibrillator (CRT-D).