Provocation of bradycardia and hypotension by isoproterenol and upright posture in patients with unexplained syncope

Article Abstract:

Syncope is a brief loss of consciousness induced by lack of adequate blood flow to the brain. It is a common clinical condition, with a number of possible causes. Low blood pressure (hypotension) and slow heart beat (bradycardia) are believed to be most often responsible. To test the involvement of hypotension and bradycardia in causing syncope, a test was devised that utilized a catecholamine drug (isoproterenol) to bring about a reduction in blood pressure and a slowing of heart output. The test was administered to 24 patients with recurrent syncope and 18 normal subjects. Measurement of the electrical activity of the cardiovascular system (electrophysiology) was made before inducing test conditions. An "upright tilt" test, in which the body position was tilted to 80 degrees off the horizontal for up to ten minutes was conducted with and without isoproterenol. Arterial pressure and electrocardiographic measurements were continuously monitored. The tilt test alone (that is, without isoproterenol) was able to induce bradycardia or hypotension in 5 of the 24 patients but none of the normal subjects. The combination of isoproterenol and the tilt test brought about syncope in: 9 of the 11 patients whose electrophysiologic and tilt tests were negative; 1 of the 8 patients with a positive electrophysiologic test but negative tilt test; and 2 of the control subjects. In contrast, in 8 patients with positive electrophysiologic tests and in the 18 control subjects, isoproterenol actually increased heart rate and caused only a slight drop in arterial pressure. The authors conclude that isoproterenol in conjunction with the upright tilt test can be useful in identifying patients who are susceptible to recurrent syncope caused by hypotension and bradycardia.

Research, Causes of, Complications and side effects, Physiological aspects, Fainting, Bradycardia, Hypotension, Isoproterenol

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Longitudinal electrophysiologic assessment of asymptomatic patients with the Wolff-Parkinson-White electrocardiographic pattern

Article Abstract:

Ventricular fibrillation is the usual cause of the sudden death of asymptomatic patients with Wolff-Parkinson-White syndrome. The low rate of cardiac events in asymptomatic patients and the difficulty of diagnosing those who will have ventricular fibrillation renders their treatment problematic. Electrophysiologic studies of 29 asymptomatic patients with the Wolff-Parkinson-White pattern reveals that a significant number lose their capacity for preexcitation and anterograde conduction over the accessory pathway. Most who lost the capacity were older.

Analysis, Case studies, Electrocardiography, Sudden death, Wolff-Parkinson-White syndrome

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