Keith H. Averill

Electrocardiographic findings in 67,375 asymptomatic subjects

Abstract The electrocardiograms obtained from 67,375 asymptomatic healthy adult men have been studied to determine the incidence of electrocardiographic abnormalities. There were 2,527 electrocardiographic abnormalities in 2,499 subjects, representing 3.7 per cent of the total population surveyed. The age distribution curve for the total abnormalities was almost identical to the age distribution curve for the sampled population. With increasing age, there was a significant increase in incidence of non-specific T wave changes, ventricular ectopic beats, right bundle branch block, and possible myocardial infarction, and a significant decrease in incidence of simple atrial rhythm and wandering pacemaker. There was no significant difference in incidence among the various age groups for those records showing supraventricular ectopic beats, first degree A-V block or the WPW syndrome. The subjects with A-V dissociation were concentrated in the younger age groups, with twenty-seven of the thirty-three subjects with this abnormality being less than twenty-five years of age. The electrocardiograms obtained from 410 Negro officers in the Air Force had a 9 per cent abnormality rate compared to a 3.1 per cent abnormality rate for the non-Negro population. The source of this increased abnormality rate was found in the increased incidence of T wave changes and first degree A-V block.

Electrocardiographic findings in 67,375 asymptomatic subjects. IV. Wolff-Parkinson-White syndrome.

Abstract One hundred nine new cases of the WPW syndrome are presented. One hundred six were discovered as the result of an electrocardiographic survey of 67,375 asymptomatic healthy adult men producing an occurrence rate of 1.6 per thousand. There was an equal distribution among the various age groups; none was thought to have underlying organic heart disease and the incidence of paroxysmal tachycardia was approximately 12 per cent. The electrocardiographic characteristics, the instability of intraventricular excitation and the intermittent nature of the anomalous excitation are discussed. The experimental production of normal excitation is discussed with particular reference to the effects of varying vagal tone at various levels of the conduction system and to the value of intravenous administration of atropine sulfate. The vectorcardiographic characteristics are presented. The variability and lability of the S-T segments and T waves are stressed with respect to both spontaneous changes and those following various maneuvers. The probable congenital nature of the true WPW syndrome is stressed and the usual benign clinical nature discussed. This study casts serious doubt on the concept of an acquired WPW syndrome.

Electrocardiographic findings in 67,375 asymptomatic subjects: VII. Atrioventricular block∗

Abstract Observations from the electrocardiographic data of 350 subjects with first degree A-V block and from clinical studies of 139 subjects from this group are presented. First degree A-V block in a large, healthy population occurred at an incidence rate of 5.2 per thousand. A-V conduction time was greater than 0.24 second in 20 per cent of this group, indicating that a precise value which separates the normal from the abnormal A-V conduction time does not exist. Although the significance of the prolonged P-R interval can be determined only by individual clinical evaluation, there is no doubt that the P-R interval can be markedly prolonged in some subjects who are otherwise normal. In the present series only five of 139 were found to have evidence of organic disease. In the majority of subjects first degree A-V block was still present at the time of clinical evaluation several months after its discovery. Despite its tendency to persist, the prolonged P-R interval exhibited marked lability both spontaneously and during procedures that altered vagal and sympathetic influences. The effect of administration of atropine, standing and exercise on the A-V conduction time was compared. In nearly all, the P-R interval could be reduced to normal by one or more of these procedures. Instability of the A-V conduction mechanism was often demonstrable, particularly in those with the longest P-R intervals. Cardiac arrhythmias such as A-V dissociation, blocked sinus impulses, atrial rhythm, nodal escape beats and A-V dissociation could often be induced by stress. In three subjects, transient second degree A-V block with Wenckebach periods appeared either spontaneously or in response to respiratory maneuvers. While these changes could be related to alterations in vagal tone, individual responses were not always predictable and the response of the P-R interval to such alterations frequently seemed independent of the sinus node response. Observation of one case of second degree A-V block, apparently due to myocarditis, and one case of complete A-V block, presumably congenital, are included.

Electrocardiographic findings in 67,375 asymptomatic subjects. III. Ventricular rhythms.

Abstract An electrocardiographic analysis of 67,375 healthy, asymptomatic men has been conducted and the incidence of various types of ventricular rhythms determined. All known forms of ventricular rhythm were detected except ventricular flutter and ventricular fibrillation. Four hundred nineteen cases of premature ventricular contractions were noted (0.6 per cent), of which twenty-two were interpolated and one multifocal. Bigeminy, trigeminy and quadrigeminy were each noted in a few subjects. There was a twofold increase in the rate of premature ventricular contractions per 1,000 subjects in the forty to forty-four year age group as compared to the younger age groups, and a threefold increase above forty-five years of age. The average heart rate of subjects with numerous premature ventricular contractions was the same as that of subjects with rare premature beats, indicating that heart rate is not a significant determinant of the frequency of ectopic ventricular beats. The ratio of premature ventricular contractions originating in the right ventricle (QRS pattern of left bundle branch block) to those from the left ventricle (QRS pattern of right bundle branch block) was 3 to 1. There was a fourfold increase in the rate per 1,000 of the former from the youngest to the oldest age group, but no increase in rate of the latter with age. There were eighteen subjects with ventricular parasystole (0.03 per cent) and one with ventricular tachycardia. Four subjects with idioventricular rhythm with A-V dissociation were presented. These demonstrate the passive assumption of control of cardiac excitation by a ventricular focus upon slowing or failure of the sinus node. This occurred in preference to either an atrial or nodal focus which in most subjects are active under such circumstances.

Electrocardiographic Findings in 67,375 Asymptomatic Subjects VI. Right Bundle Branch Block*

Abstract Complete right bundle branch block was noted in 106 subjects in a survey of 67,375 apparently healthy men. The rate per thousand below the age of forty was 1.5 contrasted to a rate of 2.9 per thousand past the age of forty. Complete right bundle branch block could not be correlated with an increase in clinical factors thought to be associated with an increased incidence of coronary artery disease. The body weight, blood cholesterol and phospolipid levels and blood pressure were similar in the normal group as compared to the subjects with complete right bundle branch block. The initial 0.08 second QRS vector was more often normally oriented even in the presence of complete right bundle branch block, suggesting that the initial events of ventricular excitation are relatively unaltered in the presence of uncomplicated right bundle branch block. The T waves were normal in all, suggesting that the presence of right bundle branch block does not significantly alter the order of ventricular recovery. S-T segment changes were noted infrequently after a double Master exercise test. The significance of these findings should be evaluated in terms of anticipated long term follow-up studies. In contradistinction to left bundle branch block, right bundle branch block is frequently seen in apparently healthy persons and unless other evidence of heart disease is present or the subject is in the older age group with a previously normal electrocardiogram it should not be accepted as diagnostic evidence of significant underlying heart disease.

Electrocardiographic findings in 67,375 asymptomatic subjects: VIII. Non-specific T wave changes∗

Abstract An electrocardiographic analysis of 67,375 asymptomatic healthy men on flying status with the U. S. Air Force has revealed the presence of 581 subjects with non-specific T wave changes in their routine electrocardiogram. Complete clinical evaluation of 226 subjects failed to reveal any increase of heart disease or family history of heart disease over what might be expected from a similar analysis of randomly selected men from the same population with normal electrocardiograms. The types of T wave changes were categorized into nine basic patterns. An attempt to correlate these patterns with any characteristic of the subject or other features of his electrocardiogram was unrevealing. Comparison of the group with non-specific T wave changes with a series of 6,000 normal electrocardiograms (1,000 from each five-year age group of the adult population) revealed many striking differences. The body weights and heart rates of the group with the abnormality were slightly higher than in those with normal values, and the percentage of overweight subjects in each age group was markedly larger. The T wave amplitude in leads I, aVF, V 2 and V 6 was approximately half that of comparable values in the normal series when each lead was compared separately and when sums of leads in the same plane were compared. There was an increase in the incidence of non-specific T wave changes in the older age groups. This is likely due to increased cardiac disease expected at these ages. A complete clinical evaluation was conducted on 226 of the 581 subjects with non-specific T wave changes. There were 121 (53.3 per cent) subjects whose fasting tracing was normal in all respects. In these, T wave changes were often artificially induced following ingestion of 100 gm. of glucose in solution, following orthostasis and with deep inspiration. These T wave changes mimicked the original abnormality seen on the routine survey electrocardiogram. Obesity was a factor in the production of non-specific T wave changes in several subjects, but the presence of obesity did not preclude normal fasting electrocardiograms. There were twenty-five subjects, whose T wave abnormality was attributed to increased heart rate and/or anxiety. Because of the extreme T wave changes which are possible in susceptible subjects under such benign conditions as the postprandial state, respiration or minor anxiety, it is believed that T wave changes found in any routine electrocardiogram should be carefully considered as potentially physiologic. A diagnosis of heart disease on the basis of isolated T wave changes in the absence of clinical correlation or other more specific electrocardiographic findings is not justified.

Electrocardiographic findings in 67,375 asymptomatic subjects: V. Left bundle branch block∗

Abstract As a result of routine electrocardiograms taken on 67,375 apparently healthy subjects from the U. S. Air Force flying population, only thirteen examples of complete left bundle branch block were found. The majority of the thirteen subjects had a significant past history that suggested an acquired defect of the heart. This study points up the fact that complete left bundle branch block in a healthy population is a rare finding (1 in 5,000). Complete left bundle branch block was found in twelve other men during examination for other reasons. They are not included in the statistics of the survey but they do present important evidence concerning the etiology of asymptomatic left bundle branch block. This study presents evidence that left bundle branch block is the result of cardiac disease and is evidence of cardiac disease. In certain instances the cardiac involvement may be minimal, creating no major adverse effects.

Intermittent right bundle branch block without apparent heart disease

Abstract The pertinent literature on intermittent complete bundle branch block is critically reviewed. It is pointed out that the majority of cases reported are of intermittent left bundle branch block. Four cases of intermittent complete right bundle branch block without apparent heart disease are reported. Critical heart rate appeared to be the dominant feature determining whether complete bundle branch block was present or not. Vectorcardiograms during normal conduction and complete right bundle branch block demonstrated conclusively that the changes in conduction were confined to the terminal QRS interval in contradistinction to the excitation in left bundle branch block. The low incidence of intermittent complete right bundle branch block is apparent in that only the four reported cases were found in an electrocardiographic survey of approximately 70,000 asymptomatic subjects. For comparison two cases of intermittent left bundle branch block in the presence of heart disease are included. It is suggested that intermittent right bundle branch block may not have the same significance as intermittent left bundle branch block. Studies on intermittent right bundle branch block reveal fundamental information on the excitation process in complete right bundle branch block.

Electrocardiographic findings in 67,375 asymptomatic subjects: II. Supraventricular arrhythmias∗

Abstract Of 67,375 healthy members of the Air Force flying population, 861 subjects had supraventricular arrhythmias discovered by a routine electrocardiogram. These included 328 subjects with atrial rhythm, 329 with supraventricular premature contractions, 158 with wandering pacemaker, thirty-three with A-V dissociation, nine with nodal rhythm, five with atrial fibrillation, and five with sinus arrest with nodal escape. Increased vagal tone, common to youth, appears to be the greatest cause of atrial rhythm (sometimes called upper nodal rhythm with A-V block), wandering pacemaker, sinus arrest with nodal escape, A-V dissociation and perhaps nodal rhythm. A high incidence of these abnormalities occurs below the age of twenty-five years and the incidence drops sharply past this age. This is in contradistinction to premature contractions which occur at the same rate per thousand subjects through all age groups of the survey.