Electrophysiologic effects on combined autonomic blockade in patients with sinus node disease.

Abstract

SUMMARY Thirty-two patients were studied before and after i.v. administration of 0.150.20 mg/kg of propranolol. Twenty-one of the 32 underwent combined autonomic blockade with the additional infusion of 0.04 mg of atropine. Twenty other patients with sinus node disease underwent electrophysiologic studies both before and after i.v. administration of 0.04 mg of atropine alone. Spontaneous cycle length, maximal corrected sinus node recovery time, sinoatrial conduction time, secondary pauses and intrinsic heart rate were measured. Secondary pauses were more common in those with abnormal intrinsic heart rates, and they did not correlate with changes in maximal corrected sinus node recovery time or sinoatrial conduction time. In patients with normal intrinsic heart rate, abnormal test measurements usually returned to normal after combined blockade (hypervagotonia); however, some patients showed a new abnormality after propranolol that was not reversible with atropine (catecholamine-dependent). Abnormal test responses in patients with abnormal intrinsic heart rate persisted or increased after combined blockade. We conclude that patients with sinus node disease may be categorized as (1) those with intrinsic sinus node disease; (2) those with normal intrinsic sinus node function but either relative hypervagotonia or catecholamine dependency; and (3) those with abnormal intrinsic sinus node function affected by vagal or catecholamine factors.CLINICAL EVALUATION of patients with electrocardiographic evidence of sinus node dysfunction is difficult because of the interplay of intrinsic sinus node disease and autonomic nervous system tone.'-6 Jordan et al.? suggested that measurement of the intrinsic heart rate might be of value for distinguishing patients with disturbances of autonomic nervous system tone from those with intrinsic sinus node dysfunction. One of the objectives of our report is to extend their observations of the relative contribution of sympathetic and vagal influences in patients with symptomatic sinus node disease.Recently, Benditt et al.6 described the secondary pause (2°P) phenomenon or abnormal prolongation of postpacing cycles 2-10 in patients with sinus node disease. They demonstrated that evaluation of postpacing cycles 2-10 increased the value of atrial pacing tests in that patients with sinus node dysfunction may show the 2°P phenomenon in the presence of normal sinus node recovery time and sinoatrial conduction time (SACT). The role of autonomic tone in unmasking or suppressing this phenomenon has not been studied in detail, and such information might clarify the mechanisms of the 2°P phenomenon.

Pulmonary Vein Isolation for Atrial Fibrillation in Patients with Symptomatic Sinus Bradycardia or Pauses

“…Sick sinus syndrome is associated with adverse long‐term outcomes, including high rates of syncope, heart failure, and stroke 26,27 . Although it is occasionally attributed to the use of medications known to suppress sinoatrial electrical activity or delay AV nodal conduction, 7–12 or to heightened vagal tone, 28–30 in at least 50% of patients with sick sinus syndrome the problem is thought to be intrinsic to the sinus node and atrial myocardium 31 . A number of etiologies have been thought to explain the occurrence of sinus node dysfunction.…”

Clinical Characteristics of Hypervagotonic Sinus Node Dysfunction

“…SND results in syncope, dizziness and lightheadedness, and it may be caused by sinus node disease and various extrinsic conditions such as drug, decreased blood flow to the sinus node and autonomic imbalance 3 , 4 ) .…”

“…The resting electrocardiography (ECG) of the 32 patients showed sinus bradycardia, sinus pause, sinoatrial exit block or tachycardia-bradycardia. Hypervagotonic SND was defined if the sinus cycle length, sinus node recovery time (SNRT) and/or sinoatrial conduction time (SACT) returned to normal after the administration of atropine (0.04 mg/kg) 3 ) . Those patients were excluded that had taken beta blockers, calcium channel blockers, antiarrhythmic drugs, or if they had a positive head-up tilt test.…”

Cardiac Arrhythmias During Epinephrine-Propranolol Infusions for Measurement of In Vivo Insulin Resistance

“…Our observations suggest that important but asymptomatic cardiac rhythm disturbances can develop during the infusion of propranolol, epinephrine, glucose, and insulin for measurement of in vivo insulin resistance. In view of these findings, we believe that alternative measures of insulin resistance should be considered in patients with abnormal electrocardiograms, particularly if sinus node dysfunction is present, 19 or with histories suggestive of coronary artery disease and that all subjects undergoing this test should have continuous cardiac monitoring. Finally, we would terminate the test promptly if second degree atrioventricular block, idioventricular rhythm, ventricular tachycardia, or other potentially serious rhythm disturbances were observed.…”