The utility of 12-lead Holter monitoring in patients with permanent atrial fibrillation for the identification of nonresponders after cardiac resynchronization therapy.

OBJECTIVES: This study sought to determine the incidence of ineffective capture using 12-lead Holter monitoring and to assess whether this affects response to cardiac resynchronization therapy (CRT). BACKGROUND: Cardiac resynchronization therapy is used in patients with atrial fibrillation (AF), prolonged QRS duration, and heart failure in the setting of ventricular dysfunction. The percentage of ventricular pacing is used as an indicator of adequate biventricular (BiV) pacing. Although device counters show a high pacing percentage, there may be ineffective capture because of underlying fusion and pseudo-fusion beats. METHODS: We identified 19 patients (age 72 +/- 8 years, ejection fraction 18 +/- 5%), with permanent AF who underwent CRT. All patients received digoxin, beta-blockers, and amiodarone for rate control; device interrogation showed >90% BiV pacing. Patients had a 12-lead Holter monitor to assess the presence of effective (>90% fully paced beats/24 h) pacing. At 12 months post-CRT, the New York Heart Association functional class was reassessed and an echocardiogram was obtained and compared with pre-CRT. RESULTS: Only 9 (47%) patients had effective pacing. The other 10 (53%) patients had 16.4 +/- 4.6% fusion and 23.5 +/- 8.7% pseudo-fusion beats. Long-term responders (> or =1 New York Heart Association functional class improvement) to CRT had a significantly higher percentage of fully paced beats (86.4 +/- 17.1% vs. 66.8 +/- 19.1%; p = 0.03) than nonresponders. CONCLUSIONS: Pacing counters overestimate the degree of effective BiV pacing in patients with permanent AF undergoing CRT therapy. Only patients with complete capture responded clinically to CRT. These findings have important implications for the application of CRT to patients with permanent AF and heart failure.

Sudden cardiac death and the role of medical therapy.

Sudden cardiac death (SCD) accounts for more than 300,000 deaths annually in the United States. The goal of medical therapy in patients considered to be at high risk (coronary artery disease, post myocardial infarction, structural heart disease and congestive heart failure) involves treating the disease state as well prevention of potentially lethal arrhythmias. Treatment with angiotensin receptor inhibitors, beta blockers and statins has been shown to improve survival in this high risk group. The use of anti-arrhythmic drugs has been studied and found to lack efficacy and has potential for adverse effects. The role of omega-3 fatty acids in preventing sudden death continues to evolve.

Clinical significance of pacemaker-detected atrial high-rate episodes.

PURPOSE OF REVIEW: Pacemakers currently being implanted offer several advanced diagnostic features. Among these is the ability to store counters and intracardiac electrograms of individual atrial high-rate episodes, which are a surrogate of atrial fibrillation. As the majority of these episodes are brief and asymptomatic, their clinical significance remains to be determined. The purpose of this review is to provide a better understanding of the clinical significance of pacemaker-detected atrial high-rate episodes. RECENT FINDINGS: Follow-up after dual-chamber pacemaker implantation demonstrates that nearly 30% of patients without a known history of atrial fibrillation develop an atrial high-rate episode lasting 5 min or more. Patients experiencing such an episode are at a twofold increased risk of stroke and death. An important risk factor for developing an atrial high-rate episode is a high burden of right ventricular pacing, suggesting that ventricular pacing should be minimized whenever possible. SUMMARY: Atrial high-rate episodes are frequently observed in patients after dual-chamber pacemaker implantation and can be associated with adverse outcomes. Ongoing studies seek to determine whether the overall burden of these episodes correlates with the risk of thromboembolism, especially in patients without a history of atrial fibrillation, which would help guide decision-making regarding the initiation of anticoagulation.