Tachycardia-dependent left posterior hemiblock.

A patient with intermittent tachycardia-dependent left posterior hemiblock is reported. Electrocardiographic patterns of complete and incomplete block were documented. Identification of the electrocardiographic characteristics of intraventricular conduction defects is aided when they are intermittent. The difficulty in diagnosing incomplete left posterior hemiblock, and the possible masking of the signs of previous inferior infarction by left posterior hemiblock are emphasised.     

Left posterior hemiblock in acute myocardial infarction.

Fifteen cases of left posterior hemiblock associated with acute myocardial infaction were studied. In 5 cases the left posterior hemiblock was the only intraventricular conduction defect, while in the other 10 cases it was associated with complete right bundle-branch block. Left posterior hemiblock proved to be an early complication, appearing within a few hours from the onset of the acute episode, and an ominous sign, since hospital mortality rate was 87 per cent. Cause of death was mainly pump failure. In most of these cases ther was electrocardiographic evidence of infarction involving both anterior and inferior ventricular walls. Infarction of most or all of the ventricular septum was a common finding in the cases examined anatomically. Histologically, acute changes involving mainly the posterior septal and midseptal fibres were observed in 6 of the 8 cases studied. On the basis of these findings and of other published findings an alternative physiopathological mechanism for so-called left posterior hemiblock is proposed.     

Left posterior hemiblock in acute myocardial infarction.

Fifteen cases of left posterior hemiblock associated with acute myocardial infaction were studied. In 5 cases the left posterior hemiblock was the only intraventricular conduction defect, while in the other 10 cases it was associated with complete right bundle-branch block. Left posterior hemiblock proved to be an early complication, appearing within a few hours from the onset of the acute episode, and an ominous sign, since hospital mortality rate was 87 per cent. Cause of death was mainly pump failure. In most of these cases ther was electrocardiographic evidence of infarction involving both anterior and inferior ventricular walls. Infarction of most or all of the ventricular septum was a common finding in the cases examined anatomically. Histologically, acute changes involving mainly the posterior septal and midseptal fibres were observed in 6 of the 8 cases studied. On the basis of these findings and of other published findings an alternative physiopathological mechanism for so-called left posterior hemiblock is proposed.     

Transient left posterior hemiblock. Association with acute lateral myocardial infarction

Two cases of transient left posterior hemiblock associated with acute lateral myocardial infarction are reported. The main electrocardiographic features, diagnostic criteria and problems of differential diagnosis are analyzed. The association of left posterior hemiblock with the lateral infarction causes a difficult diagnostic problem. Left posterior hemiblock should be suspected when the ÂQRS direction is about +120 °, with an S₁-Q₃ pattern and a QRS interval within normal limits, provided right ventricular hypertrophy or a vertical heart can be excluded, and provided there is some form of left ventricular disease.     

Shift from left to right axis deviation during ischemia.

A case report of a patient with persistent left anterior hemiblock admitted with acute ischemic heart disease is described. At effort during follow-up evaluation, the patient complained of retrosternal pain when the heart rate was 124 beats/min. No pathological ST-T changes were demonstrated at this time. At 133 beats/min, the precordial pain increased, the QRS axis displayed a marked shift to the right, and ischemic ST-T depression was recorded. In discussing this unreported phenomenon, it is pointed out that left anterior hemiblock does not necessarily represent an anatomical block of the atrioventricular bundle but may simply reflect a relative delay in conduction. In addition, acute ischemia may change the physiological behavior of the system resulting in slower conduction through the posterior rather than through the anterior atrioventricular bundle. The influence of left anterior and left posterior hemiblock on ischemic ST-T changes and on the coronary flow distribution is discussed.     

The fate of patients with intraventricular conduction disturbances complicating acute myocardial infarction.

The partial incidence and the early and late mortality were studied in 104 patients with acute myocardial infarction complicated by intraventricular conduction defects. Right bundle branch block and left anterior hemiblock had a greater incidence than the other conduction anomalies, while the hospital mortality was greater for the complete right bundle branch block combined with left anterior or posterior hemiblock, followed in order by complete left bundle branch block. Late morality was higher in cases with complete right bundle branch block combined with left posterior hemiblock and also in cases with focal block or left bundle branch block indicating a poor prognosis for these patients. For the rest sub-groups of patients late mortality was relatively low indicating the possibility of long survival after passing the acute phase. However, longer periods of observation are desirable for further estimation of their ultimate prognosis.     

Vectorcardiographic study of aberrant conduction anterior displacement of QRS: another form of intraventricular block.

Aberrant ventricular conduction was induced in 44 subjects by introduction of atrial premature beats through a transvenous catheter-electrode. Multiple patterns of aberrant ventricular conduction were obtained in 32 patients and, in the whole group, 116 different configurations were recorded. Of these, 104 showed a classical pattern of mono- or biventricular conduction disturbance. The pattern frequencies were as follows: right bundle-branch block, 28; left anterior hemiblock combined with right bundle-branch block, 21; left anterior hemiblock, 17; left posterior hemiblock combined with right bundle-branch block, 12; left posterior hemiblock, 10; complete left bundle-branch block, 10; and incomplete left bundle-branch block, 6. The remaining 12 configurations could not be classified into the usual categories of intraventricular blocks. In 7 of them, the alterations only consisted of trivial modifications of the QRS contour. In the other 5 instances, aberrant conduction manifested itself by a conspicuous anterior displacement of the QRS loop, with increased duration of anterior forces. The latter observation is worthy of notice, as it indicates that, in the differential diagnosis of the vectorcardiographic pattern characterized by prominent anterior forces, conduction disturbances should be considered a possible aetiological factor in addition to right ventricular hypertrophy, and true posterior wall myocardial infarction.     

Transient right axis deviation with left posterior hemiblock and junctional rhythm during acute myocardial infarction

One of the most common causes of hemiblocks is coronary artery disease, and there is a particularly frequent association between anteroseptal myocardial infarction and left anterior hemiblock. Changing Axis Deviation has been reported during acute myocardial infarction also associated with atrial fibrillation. Isolated left posterior hemiblock is a very rare finding but the evidence of transient right axis deviation with a left posterior hemiblock pattern has been reported during acute anterior myocardial infarction as related with significant right coronary artery obstruction and collateral circulation between the left coronary system and the posterior descending artery. We present a case of transient changing axis deviation, transient right axis deviation, transient left posterior hemiblock pattern and transient junctional rhythm too in a 61-year-old Italian man with acute myocardial infarction and a significant left anterior descending coronary artery stenosis.     

Electrocardiographic abnormalities in alcoholic cardiomyopathy. A study of 65 patients.

Electrocardiograms of 65 patients with alcoholic cardiomyopathy seen over a five-year period were reviewed. ST segment and T wave abnormalities, left ventricular hypertrophy, biatrial enlargement, left atrial enlargement, premature ventricular contractions, prolonged PR interval, and left anterior hemiblock are the most frequently encountered abnormalities. A combination of left ventricular hypertrophy and biatrial enlargement with or without left anterior hemiblock is most specific, Atrial flutter or fibrillation, pathologic Q waves, and bifascicular block are not uncommon findings, while isolated right atrial or right ventricular abnormalities, and isolated posterior hemiblock or right bundle branch block are rare. Electrocardiographic changes are in general similar to those seen in any diffuse cardiomyopathy and reflect biventricular involvement.     

Transient left posterior hemiblock during Prinzmetal's angina culminating in acute myocardial infarction

A 49-year-old man had transient left posterior hemiblock during Prinzmetal's angina with inferior ST-segment elevations; subsequently, left posterior hemiblock reappeared associated with acute inferior myocardial infarction. The electrocardiographic and electrophysiologic aspects of these findings are discussed.     

Transient tachycardia- and bradycardia-dependent left anterior and left posterior hemiblocks. Effects of isoproterenol

Tachycardia- and bradycardia-dependent, left anterior and left posterior hemiblocks as transient phenomena were registered in two patients spontaneously, and especially as a consequence of isoproterenol infusion. A chronic trifascicular type of A-V block was present in the first case, whereas in the second case a bradycardia-dependent left posterior hemiblock was registered during an acute myocardial infarction. In the first patient the isoproterenol effects were: (1) a shortening of the refractoriness and an increase of the conduction velocity in the injured fascicle, (2) an increase in the slope of phase-4 depolarization on the left posterior fascicle, and (3) a presumably shifting toward zero of the threshold potential on the left anterior fascicle. Isoproterenol effects disappeared from 30 to 40 min after it was discontinued. In the second case the bradycardia-dependent left posterior hemiblock was registered during very fast heart rates (150 beats min). This finding supports the view that enhanced phase-4 depolarization is the main factor in the development of bradycardia-dependent intraventricular blocks in the course of acute myocardial ischemia.     

Atrioventricular and intraventricular conduction in hyperkalemia

Twelve patients exhibited electrocardiographic evidence of fascicular block during hyperkalemia. Isolated left posterior hemiblock occurred in four, isolated left anterior hemiblock in two, right bundle branch block with left anterior hemiblock in two, right bundle branch block with left posterior hemiblock in one, left bundle branch block with abnormal left axis deviation in two and advanced atrioventricular block in one. In all seven patients with sinus rhythm the P-R interval shortened after correction of hyperkalemia. Electrophysiologic studies using His bundle recording and atrial pacing in one patient revealed intraatrial conduction delay and marked prolongation of conduction time in the His-Purkinje system. It is concluded that conduction defects in the specialized intraventricular conduction system are common in hyperkalemia and result in electrocardiographic patterns of fascicular block.     

Quantitative study of left bundle branch fibrosis in left anterior hemiblock: A stereologic approach

Serial sectioning of the interventricular septum was carried out in 16 hearts, 8 from elderly subjects with no conduction disturbance and 8 from patients with chronic left anterior hemiblock. The histologic slides were studied stereologically, and the relative density of fibrosis was quantitatively assessed by the point counting technique at various levels of the main subdivisions of the left bundle branch system.Statistical analysis revealed the following: (1) Although some fibrosis was found in the control hearts, the density of fibrosis was consistently and significantly greater throughout the conduction system in patients with left anterior hemiblock. (2) In the group with hemiblock, the relative density of fibrosis tended to increase significantly from the posterior ramification to the midseptal fibers and, finally, to the anterior fascicle. (3) Among the eight patients with hemiblock, fibrosis appeared to be evenly distributed throughout the conduction system in four. It was predominantly located in the anterior and midseptal fibers in one patient and showed an increasing severity from the posterior to the midseptal and anterior fibers in the remaining three patients.From this quantitative study, it is concluded that left anterior hemiblock is a reliable sign of left bundle branch disease but that the underlying lesions are more widely distributed than would be from the expected electrocardiographic terminology since they were found predominantly in the anterior ramifications in only half of the studied cases.     

Acute inferior wall myocardial infarction associated with complete atrioventricular block and left posterior hemiblock.

Three cases of acute inferior wall myocardial infarction associated with complete atrioventricular block and junctional escape rhythm showing left posterior hemiblock are presented. The triad appears to consitiute a distinct syndrome. It is postuated that the subsidiary pacemaker is situated either in the bundle of His or the proximal part of the anterior division of the left bundle-branch.     

Acute inferior wall myocardial infarction associated with complete atrioventricular block and left posterior hemiblock.

Three cases of acute inferior wall myocardial infarction associated with complete atrioventricular block and junctional escape rhythm showing left posterior hemiblock are presented. The triad appears to consitiute a distinct syndrome. It is postuated that the subsidiary pacemaker is situated either in the bundle of His or the proximal part of the anterior division of the left bundle-branch.     

DIAGNOSIS OF INFERIOR MYOCARDIAL INFARCTION IN THE PRESENCE OF LEFT ANTERIOR HEMIBLOCK

Inferior myocardial infarction results in Q waves in the inferior leads of the electrocardiogram (ECG). Left anterior hemiblock results in initial r waves in these leads. Thus the diagnosis of one in the presence of the other is difficult. It has been reported that inferior infarction can be diagnosed in the presence of left anterior hemiblock when there is a q wave or q equivalent in lead II, and that part of the inferior wall must be spared, to result in the initial r waves of left anterior hemiblock in leads III and aVF. We examined these concepts in 18 patients with such an ECG, by means of resting myocardial perfusion (thallium-201) scintigraphy. In 15 there were defects in the inferior left ventricular wall consistent with inferior infarction. In all of these patients there was sparing of part of the inferior wall: in nine, sparing of the posterior part, and in six, sparing of the anterior part. We conclude that in apparently isolated left anterior hemiblock, a q wave or q equivalent in lead II is an important sign, indicating the likelihood of associated inferior infarction.     

Incidence and prognostic significance of intraventricular block in acute myocardial infarction.

In 404 consecutively admitted patients with their first myocardial infarction (MI), intraventricular block (IV) was a complication in 124 (31%). The following types of block were encountered: 21 (5%) had left bundle-branch block (LBBB), 73 (18%) left anterior hemiblock (LAH), 13 (3%) left posterior hemiblock (LPH); 7 (2%) right bundle-branch block (RBBB); 9 (2%) RBBB + LAH, and 1 (0.3%) RBBB + LPH. Patients with IV block at the time of admission did not develop total atrioventricular block more frequently in the acute phase of MI (0-30 days) or in the follow-up period (3-5 years) than patients without IV block. During the acute phase, only patients with RBBB with or without hemiblock showed significantly higher mortality than patients without IV blocks. The other types of IV block did not influence the short-term prognosis. Among patients who survived the acute phase, significantly lower long-term survival rates were found in patients with LBBB compared to patients without IV block, whereas the presence of LAH did not affect the long-term prognosis.     

Trifascicular block with asynchronous intraventricular recovery and "supernormal" AV conduction

The authors present a case of trifascicular block: complete right bundle branch block, tachycardia-dependent left anterior hemiblock, and bradycardia-dependent left posterior hemiblock. There is, in addition, a complicating independent AV junctional rhythm that is in most instances not affected by the conducted sinus impulses. Occasionally, however, this focus is discharged by very early sinus impulses that are unexpectedly conducted to the ventricles (a manifestation of "supernormal" conduction). A complex electrocardiographic pattern results from the interplay of the aforementioned mechanisms.     

急性心肌梗塞并发室内传导障碍与近期预后

本文分析127例急性心肌梗塞(AMI)病例,其中无室内传导障碍(NIVCD)91例,并发室内传导障爵(IVCD)36例(28%)。住院期(6～8周)病死率:NIVCD者15.4%,IVCD者33.3%,差异显著(P<0.025),合并IVCD者的病死率高于NIVCD者两倍。     

Significance of hemiblock of the left branch during exercise

There have been few reports of exercise induced left branch hemiblock. In order to assess its frequency and significance, a retrospective study of 8684 patients was undertaken: 24 cases (11 anterior and 13 posterior) were recensed. Nineteen of these patients had typical effort angina, 3 had a history of myocardial infarction and 3 had aortiocoronary bypass surgery. Twenty patients developed ST-T wave abnormalities included 11 ST segment depressions. Four patients refused coronary angiography: 3 of these patients had probable coronary artery disease (typical effort angina, positive exercise stress tests and in 1 case, inferior wall hypofixation during myocardial scintigraphy). Twenty patients underwent coronary angiography. In 2 patients, the exercise stress test was performed under Class IC antiarrhythmic therapy; 1 had a normal coronary angiogram and the other had patient coronary bypass graft. A control exercise stress test after withdrawal of drug therapy was negative in these 2 cases. The other 18 patients had significant coronary artery disease. The recording of left branch hemiblock during exercise stress testing would seem to indicate severe coronary artery narrowing (greater than or equal to 90% in 15 cases; greater than or equal to 80% in 3 cases) and left anterior hemiblock is indicative of left main coronary or proximal left anterior descending artery disease. In this series, medical therapy did not make exercise-induced left branch hemiblock regress, in contrast to aortocoronary bypass surgery and angioplasty.