John Hay, a highly respected physician of Liverpool, England, (Fig, I ) and a disciple of Sir James Mackenzie, was the first to discover a form of second degree atrioventricular (AV) block that is now known as Mobitz type I1 AV b1ock.l Hay was born near Liverpool on November 25,1873, the eldest son of Scottish parents; his father was a notable architect.*. He studied medicine at the University College of Liverpool, a division of Victoria University of Manchester, where he was considered a brilliant student, gaining a diploma in 1895. The next year he obtained the Manchester degrees of Bachelor of Medicine and Bachelor of Surgery with honors, and in 1901 the M.D. degree from Victoria University. His postgraduate training included studies in physiology, anatomy, and pathology. From 1900 to 1903, he was house physician at the Liverpool Royal Infirmary. In 1904, he was granted an additional M.D. degree from the University of Liverpool, and the next year was appointed to the staff of the Stanley Hospital of Liverpool. He soon became a friend and admirer of James Mackenzie, the pioneer of British cardiology, who was the first to use the sphygmogram, a small kymographic pulse wave recorder of the venous and arterial pulses, to study unexplained disturbances of cardiac rhythm in a large series ofpatients. Hay frequently visited Mackenzie in Bumley, learning how to apply Mackenzie's technique to study his own patients and discussing the interpretation of the findings. The Discovery of m e II Atrioventricular Block On October 19, 1905, in the Stanley Hospital, Hay examined a 65-year-old man who had been aware of a slow pulse rate for 8 years and of dyspnea on exertion for 2% years. At cardiac fluoroscopy that day, he noted a heart rate of 80 beats per minute (beatdmin) that suddenly decreased to 40 beatdmin. "During the long pauses which now occurred, the ventricles were seen to remain motionless."l From the simultaneous radial arterial sphygmogram and jugular phlebogram recorded the same day (Fig. 2), Hay noted that the a waves and radial arterial pulse remained stable initially, but after six consecutive normal cycles, the seventh, ninth, and eleventh a waves were not followed by c wave or radial pulse, and the ventricularrate declined from 80 to 40 beatdmin. The a-c jugular wave interval, that is, the time between the atrial wave and the carotid pulse, an indirect measurement of atrioventricular (AV) conduction time, did not change after a pause, and each pause was equal to two atrial pulse wave intervals. ' Hay believed that the heart block demonstrated in Figure 2 was not due to depression of conductivity since the a-c intervals remained normal. He reasoned that the pauses were due to the failure of the ventricle to respond to a stimulus. He explained:We are compelled, therefore, to conclude that the . . . function of excitability is the one impaired. Depression of excitability exists in the patient. . . in the musculature of the ventricle; the consequence is that a stimulus normally produced and normally conducted...
