Changing P wave polarity. Intermittent posterior internodal conduction.

Spontaneous changes of P-wave polarity without change in heart rate were noted on the resting electrocardiogram of a patient admitted because of chest pain. Intracardiac and His bundle electrograms were compatible with a sequence of activation from high to low right atrium with both positive and negative P waves in lead aVR. The decrease in the P-His interval with positive P waves in lead aVR is consistent with selective conduction via the posterior internodal pathway.

Permanent pacing in disorders of sinus node function.

Thirty-three patients with disorders of sinus node function treated with permanent endocardial pacemakers were evaluated. Study of the underlying heart rate and rhythm was accomplished by external inhibition of pacemakers. The development of stable atrial fibrillation was documented in 7 out of 29 patients studied and effectively terminated the syndrome of sinus node dysfunction. Embolic complications appeared to be an important factor in the morbidity and mortality in patients with changing supraventricular rhythms. Pacemaker therapy effectively controlled syncopal episodes due to bradycardia, but recurrent episodes of tachycardia and problems associated with this remained unaffected.