We conclude that more than one quarter of ICD patients experience complications during a mean follow-up of almost 4 years, although serious complications such as intraoperative death or ICD system infections are rare in patients with nonthoracotomy ICD systems. Recognition of these complications is the prerequisite for advances in ICD technology and management strategies to avoid their recurrence.

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Heart block during sleep has been described in up to 10% of patients with obstructive sleep apnoea. The aim of this study was to determine the relationship between sleep stage, oxygen desaturation and apnoea-associated bradyarrhythmias as well as the effect of nasal continuous positive airway pressure (nCPAP)/nasal bi-level positive airway pressure (nBiPAP) therapy on these arrhythmias in patients without electrophysiological abnormalities. Sixteen patients (14 males and two females, mean age 49.6+/-10.4 yrs) with sleep apnoea and nocturnal heart block underwent polysomnography after exclusion of electrophysiological abnormalities of the sinus node function and atrioventricular (AV) conduction system by invasive electrophysiological evaluation. During sleep, 651 episodes of heart block were recorded, 572 (87.9%) occurred during rapid eye movement (REM) sleep and 79 (12.1%) during nonrapid eye movement (NREM) sleep stages 1 and 2. During REM sleep, the frequency of heart block was significantly higher than during NREM sleep: 0.69+/-0.99 versus 0.02+/-0.04 episodes of heart block x min(-1) of the respective sleep stage (p<0.001). During apnoeas or hypopnoeas, 609 bradyarrhythmias (93.5%) occurred with a desaturation of at least 4%. With nCPAP/ nBiPAP therapy, apnoea/hypopnoea index (AHI) decreased from 75.5+/-39.6 x h(-1) to 3.0+/-6.6 x h(-1) (p<0.01) and the number of arrhythmias from 651 to 72 (p<0.01). We conclude that: 1) 87.9% of apnoea-associated bradyarrhythmias occur during rapid eye movement sleep; 2) the vast majority of heart block episodes occur during a desaturation of at least 4% without a previously described threshold value of 72%; and 3) nasal continuous positive airway pressure or nasal bi-level positive airway pressure is the therapy of choice in patients with apnoea-associated bradyarrhythmias.

Background-Arrhythmia risk stratification with regard to prophylactic implantable cardioverter-defibrillator therapy is a completely unsolved issue in idiopathic dilated cardiomyopathy (IDC). Methods and Results-Arrhythmia risk stratification was performed prospectively in 343 patients with IDC, including analysis of left ventricular (LV) ejection fraction and size by echocardiography, signal-averaged ECG, arrhythmias on Holter ECG, QTc dispersion, heart rate variability, baroreflex sensitivity, and microvolt T-wave alternans. During 52Ϯ21 months of follow-up, major arrhythmic events, defined as sustained ventricular tachycardia, ventricular fibrillation, or sudden death, occurred in 46 patients (13%). On multivariate analysis, LV ejection fraction was the only significant arrhythmia risk predictor in patients with sinus rhythm, with a relative risk of 2.3 per 10% decrease of ejection fraction (95% CI, 1.5 to 3.3; Pϭ0.0001). Nonsustained ventricular tachycardia on Holter was associated with a trend toward higher arrhythmia risk (RR, 1.7; 95% CI, 0.9 to 3.3; Pϭ0.11), whereas ␤-blocker therapy was associated with a trend toward lower arrhythmia risk (RR, 0.6; 95% CI, 0.3 to 1.2; Pϭ0.13). In patients with atrial fibrillation, multivariate Cox analysis also identified LV ejection fraction and absence of ␤-blocker therapy as the only significant arrhythmia risk predictors. Conclusions-Reduced LV ejection fraction and lack of ␤-blocker use are important arrhythmia risk predictors in IDC, whereas signal-averaged ECG, baroreflex sensitivity, heart rate variability, and T-wave alternans do not seem to be helpful for arrhythmia risk stratification. These findings have important implications for the design of future studies evaluating prophylactic implantable cardioverter-defibrillator therapy in IDC.

The incidence and cause of electrocardiographically documented spontaneous implantable cardioverter defibrillator (ICD) discharges for a rhythm other than ventricular tachycardia (VT) or fibrillation (VF) (unnecessary shocks) were determined in 241 patients who underwent ICD implantation between March 1983 and November 1991. During follow-up of 24 +/- 20 months, 54 of 241 patients (22%) received a total of 132 unnecessary ICD shocks confirmed by Holter or telemetry monitoring or stored electrograms (Egs) from the ICD. The rhythm preceding these unnecessary ICD shocks was atrial fibrillation in 30 patients, sinus or supraventricular tachycardia (SVT) in 11 patients, antitachycardia pacing triggered by atrial fibrillation or SVT resulting in VT in 5 patients, nonsustained VT in 3 patients, and normal sinus or pacemaker rhythm in 10 patients. Unnecessary ICD discharges occurred most frequently during the first week after implantation or generator replacement (18 of 54 patients [33%]). Unnecessary ICD discharges could be documented more often by stored Egs in patients with devices with Eg storage capability (Ventritex Cadence, 19 of 54 patients [35%]) than by Holter or telemetry monitoring in patients with devices without Egs storage capabilities (34 of 193 patients [18%], P < 0.01), despite a shorter mean follow-up duration of 14 +/- 9 months versus 26 +/- 21 months, respectively. Only six of 54 patients (11%) in whom unnecessary ICD discharges occurred had recurrent unnecessary shocks during 22 +/- 20 months of follow-up after treatment directed at the cause of the first episode or device reprogramming to preclude non-VT rhythm detection.(ABSTRACT TRUNCATED AT 250 WORDS)

The majority of patients receive shocks during long-term follow-up. The occurrence of appropriate or any spontaneous shocks during follow-up is not associated with increased arrhythmic or total mortality consistent with effective prevention of sudden cardiac death with ICD therapy in this high-risk patient population. Although low ejection fraction is the strongest predictor of both shock occurrence and mortality during follow-up, no easy algorithm can be derived from the analyzed clinical characteristics to predict which patients will benefit most from ICD implantation.

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