Sinus node dysfunction treatment

Many individuals, particularly those who partake in regular vigorous exercise, have heart rates less than 60 bpm. For those individuals, sinus bradycardia is normal and healthy, and does not require evaluation or treatment. However, some individuals develop symptomatic sinus node dysfunction. In the absence of correctable underlying causes, idiopathic sinus node dysfunction is referred to as sick sinus syndrome,12 and occurs with greater frequency with advancing age. The prevalence of sick sinus syndrome is approximately 1 in 600 individuals over the age of 65 years.12... 

Treatment of sinus node dysfunction involves elimination of symptomatic bradycardia and possibly managing alternating tachycardias such as AF. Asymptomatic sinus bradyarrhythmias usually do not require therapeutic intervention. 

Ideally, if symptomatic sinus node dysfunction occurs in the presence of drugs known to impair sinus node function, the first treatment is to discontinue the offending drug [29]. However, this is typically not feasible in patients with heart failure who are dependent on several medications to improve long-term outcomes, or may need antiarrhythmic drug therapy for symptomatic arrhythmias. Accordingly, the treatment usually becomes a question of whether to apply pacing to increase heart rate. This is further complicated by the appropriate pacemaker prescription once the decision to pace has been made. 

Benditt DG, Sakaguchi S, Goldstein MA, et al. Sinus node dysfunction, pathophysiology, clinical features, evaluation, and treatment. In Zipes DP, Jalife J, eds. Cardiac electrophysiology from cell to bedside. 2nd ed. Philadelphia WB Saunders, 1995 1215-47. 

Perrild H, Hegedus L, Baastrup PC, et al. Thyroid function and ultrasonically determined thyroid size in patients receiving long-term lithium treatment. Am J Psychiatry 1990 147 1518-1521. Rosenquist M, Bergfeldt H, Aili H, et al. Sinus node dysfunction during long-term lithium treatment. Br Heart J 1993 70 371-375. 

The authors discussed the difficulty of the differential diagnosis between lithium intoxication and other neurological disorders, such as strokes. What they did not discuss was the possibility that the presentation was caused by sinus node dysfunction, which has been reported as a complication of lithium treatment. 

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. 

Lemery R, Talajic M, Nattel S, Theroux P, Roy D. Sinus node dysfunction and sudden cardiac death following treatment with encainide. Pacing Clin Electrophysiol 1989 12(10) 1607-12. 

The safety of oral propafenone in the treatment of dysrhythmias has been studied retrospectively in infants and children (40). There were significant electrophysiolo-gical adverse effects and prodysrhythmia in 15 of 772 patients (1.9%). These included sinus node dysfunction in four, complete atrioventricular block in two, aggravation of supraventricular tachycardia in two, acceleration of ventricular rate during atrial flutter in one, ventricular prodysrhythmia in five, and unexplained sjmcope in one. Cardiac arrest or sudden death occurred in five patients (0.6%) two had a supraventricular tachycardia due to Wolff-Parkinson-White syndrome the other three had structural heart disease. Adverse cardiac events were more common in the presence of structural heart disease and there was no difference between patients with supraventricular and ventricular dysrhythmias. 

Sinus node dysfunction was initially described in the early 1900s, and is the primary indication for pacemaker implantation in industrialized countries. The only effective treatment for symptomatic sinus node dysfunction is cardiac pacing. However, despite the widespread use of pacing therapy for this group of patients, the optimal pacing mode, pacing system and site of ventricular stimulation for sinus node dysfunction remains controversial. The available data for the diagnosis and treatment of sinus node dysfunction are reviewed in this chapter. 

The only effective treatment for symptomatic sinus node dysfunction due to an intrinsic cause is pacing. Treatment of the condition is directed at symptoms. However, as every clinician knows, correlation of symptoms with a specific arrhythmia is not always possible in a condition with an episodic nature. 

Atropine can be used in the differential diagnosis of S-A node dysfunction. If sinus bradycardia is due to extracardiac causes, atropine can generally elicit a tachy-cardic response, whereas it cannot elicit tachycardia if the bradycardia results from intrinsic causes. Under certain conditions, atropine may be useful in the treatment of acute myocardial infarction. Bradycardia frequently occurs after acute myocardial infarction, especially in the first few hours, and this probably results from excessive vagal tone. The increased tone and bradycardia... 

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