The Q1 deflection of the electrocardiogram in bundle branch block and axis deviation

An initial downward, or Q, deflection in Lead I is very uncommon in human left branch block. When this component occurs in an electrocardiogram otherwise characteristic of this conduction defect, a lesion of the ordinary muscle of the ventricular septum should be suspected, and a full set of precordial leads should be taken.A Q deflection in Lead I occurs in about one-half of all cases of left axis deviation, regardless of the criteria employed in selecting examples of this electrocardiographic abnormality. Left axis deviation accompanied by inversion of the T waves in Lead I may sometimes be due to incomplete left bundle branch block when Q₁ is absent, but it is almost never due to this cause when this deflection is present.The incidence of Q₁ in right branch block is similar to its incidence in left axis deviation. In right axis deviation, this deflection is extremely rare.     

Reversal in direction of the QRS complex of experimental right bundle-branch block with change in the heart's position

It can be demonstrated that the contour of experimentally produced right bundle-branch block is modified by changing the heart's position. The direction of QRS can be reversed in Leads I or III, or in both, by moving the heart's apex from left to right of the body's long axis, especially when the heart is at the same time rotated on its own long axis. This shift alone may change a seeming right to a seeming left bundle-branch block or vice versa, depending on whether the classical or Wilson's terminology is used, as is shown in the illustrations of this report. This last observation explains the apparent discrepancies between the electrocardiographic and the autopsy diagnosis of the branch involved in bundle-branch block.It is recommended that no attempt be made to designate the bundle-branch involved; instead in man all such cases should be called intraventricular block of the bundle-branch type.     

The electrocardiogram in apparently healthy men and the risk of sudden death.

The purpose of this study was to determine whether electrocardiographic abnormalities detected on a routine examination in men without clinical evidence of heart disease predicted sudden death in the absence of pre-existing clinical manifestations of heart disease. The Manitoba study consists of a cohort of 3983 men with a mean age at entry of 30.8 years who have been followed with regular examinations including electrocardiograms since 1948. During the 30 year observation period, 70 cases of sudden death have occurred in men without previous clinical manifestations of heart disease. The prevalence of electrocardiographic abnormalities before sudden death was 71.4% (50/70). The frequency of abnormalities was 31.4% (22) major ST segment and T wave abnormalities, 15.7/ (11) ventricular extrasystoles, 12.9% (nine) left ventricular hypertrophy (voltage criteria), 7.1% (five) complete left bundle-branch block, and 5.7% (four) pronounced left axis deviation. When these electrocardiographic findings in men without clinical manifestations of heart disease were related prospectively to incidence of sudden death each one except pronounced left axis deviation was a significant predictor of sudden death. Two of the variables were examined in more detail. Increased severity of primary T wave abnormalities and the association of ST segment and T wave abnormalities with increased QRS voltage further increased sudden death risk. The combination of ventricular extrasystoles with either ST-T abnormalities or left ventricular hypertrophy much increased the risk of sudden death. Thus these data indicate that electrocardiographic abnormalities detected on routine examination in men without clinical evidence of heart disease are significantly related to the occurrence of sudden death.     

The form of the electrocardiogram in experimental myocardial infarction: I. Septal infarcts and the origin of the preliminary deflections of the canine levocardiogram

Ligation of the septal branch of the left coronary artery in the dog is usually followed by infarction of a large part of the ventricular septum. Immediately after this vessel is obstructed the electrocardiogram shows displacement of the RS-T segment of the ventricular complex. Later, disturbances of intraventricular or atrioventricular conduction develop; right bundle-branch block occurred in all three of our experiments. In one instance the right branch block complexes were not strikingly different from those usually obtained after the right branch of the His bundle has been cut, in spite of the fact that a large part of the septal muscle was dead.In right bundle-branch block the precordial electrocardiograms may be characteristic in every respect when the standard electrocardiograms are not. Under these circumstances precordial leads are of great value in locating the conduction defect. When the potential variations of the precordium are small, the precordial electrodes should not be paired with a single electrode, but with a central terminal connected through like resistances of 5000 ohms or more to all three extremity electrodes.The R deflection of the levocardiogram is not abolished by infarction of the septum but is frequently absent in Lead I after ligation of the anterior descending and in Lead III after the ligation of the circumflex branch of the left coronary. This deflection is not of septal origin. The muscle responsible for the preliminary deflections of the levocardiogram is widely distributed, and it is probable that most of the endocardial surface of the left ventricle is active before the first summit of the levocardiogram is written.     

The significance of electrocardiograms characterized by an abnormally long QRS interval and by broad S-deflections in lead I

Serial precordial leads have been used in an attempt to locate the conduction defect responsible for electrocardiograms characterized by a QRS interval measuring 0.12 second or more and by narrow R-deflections and broad S-deflections in Lead I. In Lead III there is a narrow Q or S deflection synchronous with R in Lead I and a broad upward deflection synchronous with S in the same lead.In cases in which the standard electrocardiogram is of this type precordial leads from the right side of the precordium show a very late chief upstroke; precordial leads from the left side of the precordium show an early chief upstroke approximately synchronous with the peak of R in Lead I. These curves are strikingly similar to those obtained by the same method of leading after section of the right branch of the His bundle in dogs.For this reason it is believed that electrocardiograms of the kind mentioned represent right bundle-branch block in man. There is much less difference in frequency between clinical right and clinical left branch block than has heretofore been supposed.     

The form of the electrocardiogram in experimental myocardial infarction: V. The later effects produced by ligation of the right coronary artery

Infarction of the wall of the canine right ventricle was produced by ligation of the right coronary artery. This operation was carried out aseptically, and the chest wall was restored. After the lapse of a period sufficiently long to cause death of the fatally injured muscle the heart was exposed, and its anterior surface was explored by means of direct leads. A sharp electrode which could be thrust into or through the ventricular wall was used to obtain leads from the ventricular cavities and to determine whether the infarcted ventricular wall contained living muscle.Direct leads from the outer surface of right ventricular infarcts which extended completely through the right ventricular wall yielded curves of the same kind as those obtained in earlier experiments by leading from the surface of left ventricular infarcts of the same kind. Both before and after section of the right branch of the bundle of His, leads from the surface of the infarct and leads from the neighboring part of the right ventricular cavity gave practically identical results.In leads from regions where the infarcted right ventricular wall contained living muscle, the preintrinsic plus deflection of the QRS complex was present but abnormally small. In surface leads from regions where the wall contained no living muscle and in leads from the ventricular cavity this deflection was absent when the cardiac mechanism was normal. When right bundle branch block was induced, a prominent initial downward or plus deflection was present, both in cavity and in surface leads.It has recently been recommended⁹ that in taking direct leads of the kind used in this study the galvanometer connections be so made that relative positivity of the exploring electrode is represented by an upward deflection. In the curves reproduced in this article relative negativity of the exploring electrode is represented by an upward deflection.     

Detection of late arrhythmia and conduction disturbance after correction of tetralogy of Fallot.

The electrocardiographic conduction disturbances were evaluated retrospectively, in relation to prognosis, in 196 patients who underwent correction of tetralogy of Fallot. The follow-up was one to 20 years (mean 10). After surgery complete right bundle-branch block occurred in 187 patients (95%), right bundle-branch block and left axis deviation in 17 patients (9%), and progressive conduction defects, either left axis deviation or right bundle-branch block, developed during follow-up in 21 patients (11%). Nine patients (4.6%) died suddenly and two patients developed complete heart block late after the operation. Though late sudden death or complete heart block occurred in 19 per cent of patients with progressive conduction defects as opposed to 4 per cent of the group with stable conduction defects, the difference was not significant. Twenty-four hour ambulatory electrocardiographic monitoring was performed in 74 patients; 41 per cent had significant (Lown grade 2, 3, or 4) ventricular arrhythmias. The incidence of ventricular arrhythmia in the group with progressive conduction defects (80%) was significantly higher than in the group with stable conduction defects (30%). As occult arrhythmia may be the cause of sudden death, it is important to identify these patients.     

His bundle recordings in right bundle-branch block coexisting with iatrogenic right ventricular pre-excitation

Iatrogenic right ventricular pre-excitation failed to abolish right bundle-branch block in two patients. When `exclusive' His bundle pacing was performed, the QRS complexes, St-V, and St-LVE intervals were similar to the ventricular deflections, H-V, and V-LVE (intervals) recorded during sinus rhythm. `Exclusive' pacing of the ordinary muscle at the right ventricular inflow tract produced a complete left bundle-branch block pattern without abnormal left axis deviation. Pacing of both His bundle and ordinary muscle yielded combination complexes in which the right bundle-branch block pattern persisted.     

Left bundle-branch block with right axis deviation—a unique aberrancy during supraventricular tachycardia

A tachycardia with left bundle-branch block morphology and right axis deviation points to the diagnosis of ventricular tachycardia. Conversely, any supraventricular tachycardia with left bundle-branch block is typically associated with a normal or leftward QRS axis. We present the case of a 34-year-old man showing atrioventricular nodal reentrant tachycardia with left bundle-branch block/right axis deviation as an exception to this rule.     

The electrocardiogram and cardiac state in active sickle-cell anemia

The problem of sickle-cell anemia heart disease was studied in twenty-five carefully chosen cases of active sickle-cell anemia. The pathologic changes were studied in nine others. The problem of heart disease in patients with sicklecell anemia was discussed from the clinical, pathologic, and electrocardiographic points of view.The electrocardiograms were analyzed in the routine manner.The disease occurred in young adults, and it was frequently confounded with rheumatic or congenital heart disease.An outstanding feature of the cardiac disease was cardiac enlargement, which occurred in 95 per cent of the cases. The enlargement involved for the most part the left ventricle, the right ventricle, and the pulmonary conus. In no instance was undue enlargement of the left auricle observed.Systolic and diastolic murmurs occurred at the aortic, pulmonic, and mitral areas. A thrill occurred in one case.Dyspnea on exertion was a frequent complaint, but orthopnea was uncommon. The pathologic specimens showed arteritis of the pulmonary, pericardial, and coronary arteries in one case, and mild pulmonary thrombosis in six of the nine subjects autopsied.Routine analysis of the electrocardiogram showed nothing characteristic of sickle-cell anemia heart disease. Significant changes in the electrocardiogram were seen in 20 per cent of the cases when single electrocardiograms were studied in the routine manner. Serial electrocardiograms showed very few changes over periods of approximately four years.Definite right axis deviation occurred in only one case, although enlargement of the pulmonary conus or right ventricle was encountered in 73 and 88 per cent of the cases, respectively.Premature beats were encountered in only two cases. No other cardiac arrhythmias, other than sinus arrhythmia, were seen.The P waves shoed about the same degree of notching as is encountered among normal subjects.The P-R interval surpassed the upper limit of normal in 12 per cent of the cases. Complete A-V block and bundle branch block were not present in this series.Only 4 per cent of the patients had a low T wave in Lead I.     

On axis deviation in human bundle branch block

Fifty-four cases with records showing both normal intraventricular conduction and bundle branch block have been collected; 192 records were available, ninety showing bundle branch block, ninety-two showing normal intraventricular conduction, and ten showing both bundle branch block and normal conduction.The axis deviation has been measured in each record and the average position of the electrical axis of QRS during normal conduction compared with that during bundle branch block.When right or left bundle branch block appeared or disappeared there was a significant change in the direction of the electrical axis of QRS (15° or more) in less than one-half of the cases, and the average change was 12° to the left in left bundle branch block and 12° to the right in right bundle branch block.When a significant change of axis was associated with the appearance of bundle branch block, the direction of the change was always to the left when the block was of the left bundle branch and, except in one case, to the right when the right bundle branch was blocked.Even in cases in which a significant change of axis was found, the general pattern of the bundle branch block electrocardiogram conformed closely to the pattern with normal intraventricular conduction.Factors, other than the bundle branch block, that might have caused a shift of the electrical axis have been discussed; it is believed that they did not materially influence the averaged results.It is concluded that the axis deviation and the general pattern of the electrocardiogram are not greatly modified by the appearance of bundle branch block, and that the axis deviation associated with right and left bundle branch block is due principally to the position of the electrical axis of QRS before the bundle branch block appeared.Certain implications arising from this conclusion have been briefly discussed.     

A study of the QRS complex of Lead III in left axis deviation

In 431 records showing the major deflection upward in Lead I and downward in Lead III, the QRS configuration in 419 could be grouped into seven distinct types. While four of these types (A, B, C, D) appear to occur in various degrees and types of cardiac displacement, the frequency with which disease accompanies them varies greatly, especially with changes in the Q and S components. Other types of curves (E and G), apparently not related to cardiac displacement, appear much more frequently in diseased than in normal individuals. However, a larger series of these curves is necessary in order to evaluate them accurately. Group E does not rightfully fall into the group of left axis deviation.     

A clinicopathological study on the electrical axis of the heart in 1,000 autopsy cases.

The electrical axis of the heart in 1,000 aged people more than 56 years of age was classified as normal axis in 58%, left axis deviation in 17.4%, mild left axis devaition in 21.9%, and right axis deviation in 2.7%. Pathological examination disclosed that left axis deviation was associated with myocardial infarction in 20%, right bundle branch block in 16%, but showed no significant relationships with coronary sclerosis, myocardial fibrosis and cardiac hypertrophy. Right axis deviation was associated with right bundle branch block in 66.7% and right ventricular hypertrophy in 22.2%     

Left anterior fascicular block: electrocardiographic criteria for its recognition in the presence of inferior myocardial infarction.

Although the vectorcardiographic criteria for recognizing left anterior fascicular block in the presence of inferior myocardial infarction are well established, comparable electrocardiographic criteria have not been studied. From vectorcardiographic criteria, it was hypothesized that in patients with left axis deviation but without bundle branch block the presence of a deep negative terminal deflection (S wave) in lead II accompanied by a positive terminal deflection (r wave) in lead aVR should indicate left anterior fascicular block whether or not inferior infarction is present. The electrocardiograms of 75 patients with unequivocal vectorcardiographic evidence of either left anterior fascicular block or inferior infarction, or both, were reviewed. Of the 47 patients who met strict vectorcardiographic criteria for left anterior fascicular block, 44 (94 percent) showed the predicted electrocardiographic pattern, including 24 of 26 (92 percent) who had both this conduction defect and inferior myocardial infarction. There was only one patient with vectorcardiographic evidence of inferior myocardial infarction alone with the findings of left axis deviation and the electrocardiographic pattern of combined infarction and fascicular block (that is, only one false positive). Thus, if bundle branch block is excluded, the proposed electrocardiographic pattern permits recognition of left anterior fascicular block whether or not there is coexistent inferior myocardial infarction.     

The electrocardiogram in late middle life

Within the limits of our experience we may state:The following findings, some of which we have previously considered of doubtful significance, are not pathological.Diphasic or iso-electric P-waves in Lead I or inverted P-waves in Lead III, if they become upright on deep inspiration; slurring of QRS complexes, especially in Lead III and slight to moderate notching of R with the QRS interval below 0.10 seconds, “transverse heart,” isolated left axis deviation, moderate inversion of T-III (this last finding is very common).On the other hand, the following findings were not present in this series and must therefore be looked upon with suspicion.Indeterminate or inverted P-waves in Leads I or II, inverted P-waves in Lead III, if they do not become upright on deep inspiration. Inversion of T-waves in Leads I or I and II, or iso-electric T-waves in Leads I or II if they do not become upright on deep inspiration. A P-R interval exceeding 0.20 seconds, a QRS interval exceeding 0.10 seconds, or an S-T interval exceeding 0.34 or 0.36 seconds (the upper limit seems slightly uncertain).It is seen that for the proper evaluation of a doubtful finding deep inspiration and sometimes change in position may be necessary in any lead. Such thorough investigation should always be done when the electrocardiographic findings may be the determining factor in the diagnosis.This material does not indicate whether an isolated right axis deviation is definitely a pathological sign or whether the inverted wave in a transverse heart is always an S-wave.There do not seem to be any characteristic “age-changes” in the electrocardiogram.     

Changes in the electrocardiogram in status asthmaticus

The aim of this study, based on the electrocardiographic analysis of 42 patients in status asthmaticus, is to define the basic criteria which may be used as a basis for electrocardiographic differential diagnosis. The following ECG changes were observed: the pulmonary "p" wave is common, sometimes with exaggerated amplitude in peripheral leads, however, in the precordial leads, the voltage of the "p" wave is reduced; most cases have a vertical heart with clockwise rotation and mild right axis deviation, S1 Q2 Q3 and the transitional zone displaced to the left. Ten cases also had a S1 S2 S3 appearance and three cases showed Q1 Q2 Q3, simulating myocardial infarction; there is poor progression of the R wave in the precordial leads and marked persistence of the S wave in the left precordial leads. In some cases, a QS complex dominates the right precordial leads. A variation in the amplitude of the QRS with the respiratory rhythm is often seen in V1 and V2; ventricular repolarization shows a lowered J point with an upward oblique ST segment in the peripheral leads. However, in the precordial leads, the repolarization is normal except for three cases which presented a frank hypokalaemia. The mechanism of these electrocardiographic changes appears to depend on the vertical position of the heart caused by over expansion of the lungs and pulmonary arterial hypertension. The elements of the electrocardiographic differential diagnosis with myocardial infarction and pulmonary embolism are discussed.