EFFECTS OF STRONG PULSED MAGNETIC-FIELDS ON THE CARDIAC ACTIVITY OF AN OPEN-CHEST DOG

The heart of an open chest dog was stimulated by strong magnetic field s which were damped sinusoidal pulses with the one-cycle period of 1.4 7 ms. Stimulation effects were detected by electrocardiograph (ECG) an d arterial blood pressure as a function of the strength of the field, the triggering point in the cardiac cycle, and the position of a stimu lating coil. The threshold for arrhythmias was a minimum for the stimu li triggered at the apex of the T wave and on the P wave in the ECG. P remature ventricular and premature atrial contractions occurred accord ing to whether the coil was placed over the ventricles or the atria. V entricular defibrillation can not be attained by the magnetic stimulus with the Bur density of 9.2 T which was the maximum field used.