VENTRICULAR rates in excess of 300 beats per minute occur not infrequently during bouts of paroxysmal tachycardia in infants and young children.1 Indeed, Silverman and Race2 have reported a heart rate of 365 beats per minute in a 5-week-old infant. Heart rates in the vicinity of 300 beats per minute occur very rarely in persons past puberty with paroxysmal tachycardia; we have been able to find only five such cases with electrocardiographic confirmation in the literature.3 As might be anticipated, the exact nature of a tachycardia, whether auricular, nodal, or 1: 1 atrial flutter, is difficult to ascertain by clinical or electrocardiographic means when the heart rate is extremely rapid; generally the tachycardia is labeled supraventricular (or ventricular) with little further effort or, indeed, ability to elucidate its exact nature.
Prinzmetal and his associates4 have recently presented evidence that auricular tachycardia and auricular flutter are fundamentally a result of the