Complete Heart Block in an Experienced Pilot

Abstract

The purpose of this communication is to report the finding of complete heart block, probably of congenital origin, in an experienced pilot. A normal G tolerance, a normal response to both strenuous exercise and anoxia, together with a lack of referable symptoms while in the air indicated his capacity to perform flying duties efficiently within the limits to which he was exposed.In 1945, an apparently healthy flying instructor, aged 23, was referred for special investigation because of bradycardia and an apical systolic murmur found at the time of his annual aircrew medical examination. Apart from admitting some recent lack of energy he had been in good health since entering the service. He was one of three normal children, born of healthy Canadian parents. He had been active in sport, and had fainted but once, following an injury. His tonsils and adenoids had been removed for nasal obstruction when he was 8 years old. He had not been subject to sore throats and there was no history suggestive of rheumatic fever. His mother first became aware of his slow pulse when he was 10 years old. In 1941, at the age of 19, he was passed medically fit for aircrew duties with the Royal Canadian Air Force. Before this, he had worked for a short period in an explosives factory, blending cordite.Early in his airforce career, he was a member of an experimental group used in a study of the cardiovascular response to strenuous exercise. Because of his slow pulse and freedom from distress after exercise he was thought to possess better than average physical fitness. He had flown a total of 1850 hours, of which 350 hours were logged in the past twelve months. He had never blacked out, although his vision became dimmed on rare occasions when performing tight manceuvres. The heart rates documented during his four years of service varied from 46 to 56 beats a minute.No heart murmurs were reported.Physical examination showed a healthy well-built young man-height 66 inches, weight 139 pounds, pulse rate 48 beats a minute, blood pressure 130/68 mm. Hg. There was a faint systolic murmur at the apex transmitted to the midline which was best heard in the left lateral position and varied with respiration. In the supine position, a pulmonary systolic murmur was also heard. The liver edge was just palpable. Physical examination was otherwise normal. Blood sedimentation rate 7 mm. (Westergren). The heart was normal in size and contour by X-ray. The electrocardiogram showed complete heart block and was substantially the same as one taken ten years later (Fig. 3). Because of the early age at which bradycardia was recognized, the relatively rapid ventricular rate (Campbell, 1943) and the absence of other cause, it was concluded that his heart block was probably of congenital origin.Further cardiograms were recorded with the pilot in various positions, after exercise and following the subcutaneous injection of atropine sulphate, 1/50th of a grain. In no instance did the ventricular rate exceed 60 beats a minute while the atrial rate, 83 at rest, rose...