32 Permanent cardiac pacemaker/implantable cardioverter-defibrillator
Salient features
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).
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.
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