Lawrence E. Lamb

Electrocardiographic Findings in 122,043 Individuals

Electrocardiograms on 122,043 apparently healthy male subjects aged 16 years to over 50 years have been studied. Of this group 5,773 subjects (4.72 per cent) had electrocardiographic abnormalities. The more common abnormalities were expressed in terms of rate per thousand subjects for each 5-year age group. This provides a means of relating incidence to age. Each abnormality and its clinical significance is discussed. In 54,668 subjects incidental findings such as notched P waves, amplitude, and wave forms were tabulated.

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.

Effects of lower body negative pressure on the cardiovascular system

Abstract Application of negative pressures ranging between −25 and −80 mm. Hg to the lower half of the supine body produces cardiovascular changes similar to venesection and upright tilting. The heart rate increases between 13 and 67 per cent; central venous pressure decreases by 3 to 6 mm. Hg; cardiac index falls by 20 to 42 per cent; and stroke volume decreases by 28 to 64 per cent. In spite of these changes, systolic and pulse pressures are often well maintained. Calculated peripheral resistance increased significantly between 14 and 34 per cent, during lower body negative pressure; however, due to great individual variability, no significant difference was observed among the various negative pressures. Syncope very similar to that observed secondary to other vasodepressor stimuli is noted with increasing frequency as the amount of negative pressure is increased, i.e., 100 per cent at −80 mm. Hg, 70 per cent at −60, 58 per cent at −40, and none at −25. The cardiac output falls within three minutes atter the onset of negative pressure. The magnitude of the fall does not correlate with the subsequent development of presyncopal symptoms and does not significantly change with further exposure to negative pressure. Inability to maintain an adequate blood pressure in the face of a diminished cardiac output was directly associated with the onset of presyncopal symptoms. The physiologic changes induced by lower body negative pressure are apparently secondary to redistribution of blood volume with pooling in the pelvis and lower extremities, thus diminishing cardiac venous return. Compensatory mechanisms mediated neurogenically maintain adequate circulation to vital organs. The possible origins and controls of these mechanisms are discussed.

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.

Significant cardiac arrhythmias induced by common respiratory maneuvers

Abstract Significant cardiac arrhythmias have been induced by simple respiratory maneuvers, breath holding and hyperventilation. Marked cardiac slowing, passive nodal rhythm and cardiac arrest have been noted. Arrhythmias are apparently initiated by stimulation of pulmonary stretch receptors. Syncope may be precipitated. The case of an aircraft accident involving a pilot with one of these mechanisms is discussed. Examples of various arrhythmias is included. The possible role of this mechanism in sudden unexplained death is pointed up.

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.

Influence of exercise on premature contractions

Abstract 1. 1. A total of 2,160 subjects were studied to determine the influence of exertion upon cardiac arrhythmias. Of this group, 1,851 were studied with a double standard two-step exercise tolerance test. Two hundred eighty-one were studied with a two-step exercise test and before and after treadmill exertion. Twenty-eight were studied from telemetered records of the two-step exercise test as well as the treadmill test before, during and after maximal exertion. 2. 2. Inconsistent responses of premature beats to two-step exercise tests were noted. In certain instances, premature beats disappeared; in other instances they were noted for the first time, and in still other instances they seemed to increase in frequency after exertion. No difference in the clinical picture of the individuals presenting these different types of response was noted. 3. 3. Individuals studied with two-step exercise tests and with before and after treadmill exertion indicated variability of responses. Some subjects had premature contractions before and after one two-step exercise tolerance test and not after a subsequent one. Some subjects showed occurrence of premature contractions after treadmill exertion and not after two-step exercise tests. More commonly, subjects showed premature contractions after a two-step exercise test and none following treadmill exertion. 4. 4. Individuals studied by telemetry methods during acute exertion demonstrated the influence of heart rate upon the occurrence of ectopic premature contractions. Subjects with premature beats before treadmill exercise had no premature contractions when the heart rate became sufficiently rapid, usually 150 beats per minute or above. In only one instance did ventricular premature contractions persist and in an unchanged fashion throughout both twostep exercise and treadmill exertion. The influence of cardiac rate upon ectopic impulses suggests that the occurrence of premature contractions with exercise is influenced by the degree of exertion and its effect upon sinus rate. 5. 5. These studies point out that it is illogical to assume that there is significant underlying heart disease because of the occurrence (which sometimes is strictly by chance) of premature contractions after a two-step exercise test or other forms of exertion unless there is definite supporting clinical evidence such as angina pectoris, valvular disease or other signs of coronary artery disease. The same applies to the observation of apparent increase in premature contractions following physical exertion.