Atrial fibrillation with sinus node dysfunction

The only effective treatment for symptomatic sinus node dysfunction is cardiac pacing. Despite two decades of clinical investigation, the optimal pacing mode, pacing system and site of ventricular stimulation for bradycardia support for sinus node dysfunction remain uncertain. Selection of pacing mode may be important for the clinical outcomes of quality of life, pacemaker syndrome, atrial fibrillation, heart failure, thromboembolism, and mortality in patients with sinus node dysfunction. 

Gillis AM, Koehler J, Morck M, et al. High atrial antitachycardia pacing therapy efficacy is associated with a reduction in atrial tachyarrhythmia burden in a subset of patients with sinus node dysfunction and paroxysmal atrial fibrillation. Heart Rhythm 2005 2 791-6. 

Hermida JS, Kulbala M, Lescure EX, et al. Atrial septal pacing to prevent atrial fibrillation in patients with sinus node dysfunction results of a randomized controlled study. Am Heart J 2004 148 312-7. 

The causes of syncope in patients with Alzheimer s disease treated with donepezil have been reported in 16 consecutive patients (12 women, 4 men) with Alzheimer s disease, mean age 80 years, who underwent staged evaluation, ranging from physical examination to electrophy-siological testing (54). The mean dose of donepezil was 7.8 mg/day and the mean duration of donepezil treatment at the time of syncope was 12 months. Among the causes of syncope, carotid sinus syndrome (n = 3), complete atrioventricular block (n = 2), sinus node dysfunction (n = 2), and paroxysmal atrial fibrillation (n = 1) were diagnosed. No cause of syncope was found in six patients. Non-invasive evaluation is recommended before withdrawing cholinesterase inhibitors in patients with Alzheimer s disease and unexplained syncope. 

Ajmaline occasionally causes cardiac dysrh5dhmias (SEDA-17, 219). Of 1995 patients who were given ajmaline 1 mg/kg intravenously during an electrophysiological study, 63 developed a supraventricular tachydysrhythmia (atrial flutter, fibrillation, or tachycardia), and seven an atrioventricular re-entrant tachycardia (2). Those most at risk were older patients, those with underlying cardiac disease, and those with a history of dysrhythmias or sinus node dysfunction. 

Sweeney MO, Hellkamp AS, Ellenbogen KA, et al. Adverse effect of ventricular pacing on heart failure and atrial fibrillation among patients with normal baseline QRSd in a clinical trial of pacemaker therapy for sinus node dysfunction. Circulation 2003 23 2932-7. 

Some individuals exhibit an impaired heart rate response to increased metabolic demand. Patients in sinus rhythm may have sinus node dysfunction, leading to decreased maximal sinus rates with exertion. Patients in chronic atrial fibrillation may have a slow ventricular response that does not increase adequately with exertion. In both these cases, the heart rate response to exertion may be blunted, a condition termed chronotropic incompetence. The definitions of chronic incompetence are varied It is sometimes defined as failure to achieve 75% of the maximal predicted heart rate. Relative chronic incompetence refers to a blunted heart rate response at lower levels of exertion and is more difficult to define. 

Fig. 9 J A patient with the bradycardia-tachycardia form of sinus node dysfunction. On conversion from atrial fibrillation to sinus rhythm there is a 3.8 s pause.

---