How to prevent ICD shocks: part I

A 63-year-old male with non-ischaemic cardiomyopathy due to a hereditary autosomal-dominant desmin mutation (left ventricular ejection fraction 30%) and a history of persistent atrial fibrillation and flutter since 1990 received an implantable cardioverter-defibrillator (ICD, Medtronic ® Virtuoso DDD ICD) in December 2006. He was known with a first-degree atrioventricular block, intermittent second-degree atrioventricular block, Mobitz type I, while taking low-dose sotalol (40 mg twice daily). In September 2007, he visited our outpatient ICD clinic because of two shocks ( Figure 1 ). He complained of a small decrease in exercise tolerance. Physical examination revealed basal pulmonary rales. Figure 2 shows the cardiac compass trends. At the time of the shocks, he was treated with enalapril 10 mg twice daily, bumetanide 1 mg daily, sotalol 40 mg twice daily, and acenocoumarol. His pacing mode was DDD lower rate 40 bpm and upper rate 130 bpm. The detection border for atrial arrhythmias started above 171 bpm, without therapies. The detection and therapies for ventricular arrhythmias started above 200 bpm. Therapies for ventricular arrhythmias included anti-tachycardia pacing during discharge and five shocks thereafter (first shock 25 J, second, third, fourth, and fifth shocks 35 J). Analysis of the ICD after the shocks showed a normal impedance of the atrial (368 ohm) and RV lead (536 ohm), and the amount of ventricular pacing was 28%. Were there adequate shocks? Was the first shock effective? What happened before the first shock? What was the atrial rhythm before and after the first shock? How to interpret the cardiac compass trend? How can we possibly prevent (part of the) shocks in the future? For answers see page 1126 PLOT. The cardiac compass trends.