Bundle branch and intraventricular block in acute coronary artery occlusion

Diagnosis of coronary artery disease with Tl-201 SPECT in patients with left bundle branch block: importance of alternative interpretation approaches for left anterior descending coronary lesions

Left bundle branch block (LBBB) is a strong predictor of mortality in the presence of coronary artery disease (CAD). Noninvasive evaluation of CAD in these patients has some difficulties. Exercise-induced electrocardiographic ST segment changes are nondiagnostic, and several scintigraphic studies have reported false-positive anteroseptal and septal perfusion defects up to 80%. The authors aimed to assess the diagnostic accuracy of thallium-201 (Tl-201) exercise myocardial single photon emission computerized tomography (SPECT) in comparison with coronary angiography (CAG) for detection of CAD in patients with LBBB. Seventy-seven consecutive patients suffering from chest pain with complete and permanent LBBB were included in the study. All patients (40 women, 37 men, mean age = 54 +/- 7 years) were studied with Tl-201 exercise SPECT and coronary angiography. Tl-201 exercise SPECT for diagnosis of left anterior descending (LAD) artery lesions was interpreted by using three different approaches: method A (conventional approach), method B (involvement of anterior and septal wall regardless of apical wall), and method C (apical approach: involvement of anterior septal and apical wall). Methods A and B gave a sensitivity of 100% each but a specificity of 47% and 56%, respectively. Although method C gave a higher value of specificity than that of methods A and B (98% vs 47% and 56%, respectively p < 0.05), the sensitivity of method C significantly decreased in respect to methods A and B (33% vs 100% p < 0.01). Isolated septal defects were evaluated separately. Isolated septal defects on exercise Tl-201 SPECT were detected in 11 patients, and none of them had CAD according to CAG results. Isolated septal wall involvement had a sensitivity of 0% and a specificity of 74%. The sensitivity and specificity of Tl-201 SPECT for diagnosis of CAD in the right coronary and left circumflex artery territories were 91% and 89%, respectively. In conclusion, the apical approach increased the specificity and decreased the sensitivity of the test. Isolated septal defects seem to have no value for diagnosis of CAD in patients with left bundle branch block.

BUNDLE-BRANCH BLOCK: AN EPIDEMIOLOGIC STUDY

As part of an inclusive health examination of the population of Tecumseh, Michigan, electrocardiograms were recorded from 8,641 persons of all ages, 87.9 per cent of those living in the study area. Eighteen persons, twelve men and six women, had complete right bundle-branch block and a like number, composed of six men and 12 women, had left. All affected persons were past 20 years of age and 67 per cent were past 60.

Twenty-five of the 36 persons had no clinical evidence of valvular heart disease, angina pectoris, or myocardial infarction.

Bundle-branch block occurred mostly in the older age groups where there was a high prevalence of hypertension, hypercholesteremia, hyperglycemia, and obesity, although these conditions were no more frequent among the affected persons than among others of the same age and sex.

Improved identification of coronary artery disease in patients with left bundle branch block by use of dobutamine stress echocardiography and comparison with myocardial perfusion tomography

This study compared the efficacy of dobutamine stress testing using 2-dimensional echocardiography and perfusion tomography for the noninvasive identification of coronary artery disease (CAD) in patients with left bundle branch block (LBBB). Twenty-four patients with permanent, complete LBBB (11 with previous myocardial infarction) were studied prospectively with dobutamine echocardiography and perfusion tomography. The presence of > 50% luminal diameter coronary stenosis was compared with the presence of dobutamine-induced fixed or reversible perfusion defects, and with resting or dobutamine-induced abnormalities of wall thickening. For each test, the left anterior coronary artery territory was compared with the circumflex and/or right coronary artery. Significant CAD was found in the left anterior descending coronary artery in 12 patients; all (100%) were identified by perfusion imaging, and 10 (83%, p = NS) by 2-dimensional stress echocardiography. In the 12 patients without left anterior descending CAD, scintigraphy was also positive in all (specificity: 0%), and echocardiography in only 1 (specificity: 92%, p < 0.01). The diagnostic accuracy was 50% and 87% (p < 0.05), respectively. This low specificity of perfusion tomography was improved by requiring an associated apical defect to indicate left anterior descending CAD and was corrected by restricting the diagnosis of coronary disease to those patients with partially reversible defects. In the circumflex and/or right coronary artery territory, sensitivity and specificity were similar using both techniques. We conclude that dobutamine-stress echocardiography is a specific and accurate test for the noninvasive identification of CAD, even in the left anterior descending artery territory of patients with LBBB.

A new approach to the assessment of tomographic thallium-201 scintigraphy in patients with left bundle branch block

To determine whether a new approach to interpretation could improve the accuracy of thallium-201 single photon emission computed tomography (SPECT) for detection of left anterior descending coronary artery disease in patients with left bundle branch block, 69 patients were evaluated. Forty-four had angiographically proved coronary artery disease; the remaining 25 were considered to have a "low" (mean 13.5 +/- 6.4%, range 3.4% to 24.9%) likelihood of disease before thallium-201 scintigraphy. The conventional scintigraphic criterion for detection of left anterior descending artery disease (septal, anterior or apical defects) was compared with a new criterion that required the apex to be abnormal to indicate left anterior descending disease. The normalcy rates in the low likelihood patient group were significantly improved by using the new approach, from 16% to 80% (p less than 0.0001) by visual analysis and from 24% to 64% (p = 0.003) by quantitative SPECT polar map analysis. The sensitivity for left anterior descending disease was similar for the conventional and the new method by visual (100% vs. 94%) and quantitative (100% vs. 83%) analyses. In contrast, the specificity was significantly improved by using the new approach, from 14% to 79% (p = 0.0006) by visual analysis and 14% to 64% (p = 0.007) by quantitative analysis. In conclusion, septal and anterior thallium-201 SPECT defects are common in patients with left bundle branch block without coronary artery disease, resulting in low specificity for left anterior descending artery disease. The normalcy rates and accuracy for detection of left anterior descending coronary artery disease were significantly better when an apical defect was used as the criterion for disease.

Conduction defects in acute myocardial infarction in the Chinese in Hong Kong

In order to delineate the conduction defects complicating acute myocardial infarction in the Chinese, 636 Chinese patients admitted into one of the three medical units of a general hospital in Hong Kong in the period 1973-80 were reviewed. A relatively high incidence of conduction defects was observed, including atrioventricular block (11.3%), right bundle branch block (12.7%) and left bundle branch block (3.3%). Right bundle branch block (whether isolated or combined with left fascicular block) and atrioventricular block complicating anterior Q-wave infarction were ominous, with a high incidence of pump failure, cardiogenic shock and cardiac arrhythmias. These are markers of massive infarction. Atrioventricular and bundle branch blocks complicating inferior Q-wave infarction were benign. Left bundle branch block appeared to be a more chronic lesion, with moderate mortality, and isolated left anterior hemiblock did not adversely affect the short-term outcome. These results conform well to the patterns seen in Western series. The high incidence of conduction defects, in particular right bundle branch block and atrioventricular block complicating anteroseptal infarction, indicates a more serious clinical spectrum of acute myocardial infarction in the Chinese, and could have contributed to a higher hospital mortality in the Chinese series.

Bundle branch block in patients with chronic coronary artery disease: angiographic correlates and prognostic significance

The onset of bundle branch block during acute myocardial infarction is indicative of ischemia in the distribution of the left anterior descending coronary artery. However, whether patients with chronic coronary artery disease and bundle branch block have a predominance of left anterior descending artery lesions is not known. Similarly, the prognostic implications of bundle branch block have been studied primarily in the setting of acute myocardial infarction, and the independent prognostic implications of bundle branch block in patients with chronic coronary artery disease are not known. The electrocardiograms (ECGs) of 15,609 patients with chronic coronary artery disease who underwent coronary and left ventricular angiography as part of the Coronary Artery Surgery Study (CASS) were reviewed, and 522 patients with bundle branch block were identified. Patients with bundle branch block had both more extensive coronary artery disease and worse left ventricular function than did patients without bundle branch block. However, no particular location of coronary artery stenosis or left ventricular wall motion abnormality predominated in patients with bundle branch block. During a follow-up period of 4.9 +/- 1.3 years, 2,386 patients died. Actuarial probability of mortality at 2 years in patients with left bundle branch block was more than five times that in patients without bundle branch block (p less than 0.0001), and in patients with right bundle branch block the mortality rate was approximately twice that in patients without bundle branch block (p less than 0.0001). Stepwise Cox regression analysis showed that left bundle branch block, but not right bundle branch block, was a strong predictor of mortality, independent of degree of heart failure, extent of coronary disease and other variables (p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

The pathologic correlates of the electrocardiogram: complete left bundle branch block

To assess whether gross pathologic differences exist between hearts with left bundle branch block (LBBB) and left-axis deviation (LAXD) and those with LBBB and a normal frontal plane axis, we examined 70 hearts with LBBB in a series of 1410 sequential dissections (5%). Thirty-two hearts had LAXD and 34 had normal axes on the correlative ECG. Left ventricular enlargement occurred frequently (93%). No significant differences were found in age distribution, left ventricular weight, coronary anatomy or infarct location. Quantitative analysis revealed larger inferoposterolateral and apical infarcts in hearts with LBBB and LAXD (p less than 0.01). The accuracy of various electrocardiographic signs of left ventricular enlargement and myocardial infarction in the presence of LBBB was assessed. Voltage criteria and QRS duration poorly define anatomic chamber enlargement. Anterior infarction is suggested by a q or pathological Q wave in lead I, a q wave in leads I, V5 and V6, or notched S waves in V3 or V4. Pathologic q waves or ST shifts in the inferior leads have high diagnostic specificity but low sensitivity for inferior infarction.

Frequency and significance of conduction defects in acute myocardial infarction

The frequency of intraventricular conduction defects was determined in 556 consecutive patients with proven acute myocardial infarction. Complete left bundle branch block was present in 23 patients and carried a high mortality rate (61 per cent). Complete right buldle branch block was the rarest defect to be seen in isolation (8 patients) and carried a lower mortality rate (38%). Lone left anterior hemiblock was present in 72 patients and was associated with a low mortality rate (13 per cent); left posterior hemiblock occurred in 32 patients (mortality rate 19 per cent). In a further 59 patients right bundle branch block with left anterior or posterior hemiblock in addition was present and these patients had a high mortality rate which was greater than isolated right bundle branch block or hemiblock alone. Complete atrioventricular block developed in 51 patients, 26 of whom had prior evidence of intraventricular conduction defect. Despite the use of temporary transvenous pacing, mortality in patients who developed complete heart block was significantly increased whether or not an intraventricular conduction defect was already present. The significance of these findings for the management of patients with myocardial infarction is discussed.

Heart block complicating acute inferior wall myocardial infarction

Heart block was noted in 60 (35 complete and 25 second-degree) of 410 patients with acute inferior wall myocardial infarction. This group with heart block was compared to a control group of 30 patients with acute inferior wall infarction without heart block. The incidences of prior myocardial infarction and hypertension, in addition to the highest level of serum creatine phosphokinase and a maximum degree of ST-segment elevation in the inferior leads, were all greater in patients with heart block, as compared to the controls. The incidences of various complications, including dizziness and syncope, transient hypotension, cardiogenic shock, and congestive heart failure, were also higher in the group with heart block, while sinus nodal distrubances and atrial arrhythmias occurred with equal frequency. The mortality in those with heart block was 28 percent compared to 13 percent for the control. It is concluded that patients with heart block complicating acute inferior myocardial infarction have a greater amount of myocardial necrosis, a higher incidence of complications, and a higher mortality. Insertion of a temporary pacemaker should be considered when specific indications are present and not routinely.

Clinical and anatomic implications of intraventricular conduction blocks in acute myocardial infarction

The electrocardiogram in 480 patients with acute myocardial infarction showed right bundle-branch block (RBBB) with normal QRS axis in 18 patients (3.7%), left bundle-branch block (LBBB) in 31 (8%), RBBB and left anterior hemiblock (LAH) in 23 (4.8%), RBBB and left posterior hemiblock (LPH) in four (1%), LAH alone in 20 (4%), LPH in one (0.2%), and no evidence of intraventricular conduction (I-V) disturbance in 383 (80%). Eighteen of the 97 patients with I-V block showed 1° A-V block, and seven of the 18 (39%) showed abrupt progression to high-grade A-V block, while only six of 79 (8%) without 1° A-V block showed similar progression.

Cause of death in patients with I-V block was cardiac failure and/or shock in 92%; only three instances of primary asystole occurred. The incidence of complete heart block was higher in the I-V disease group (15%) than in the group without block (5%), but not significantly. Patients with LAH or RBBB and LAH usually had occlusion of the left anterior descending artery with extensive septal infarction, while patients with RBBB or LBBB had a more variable pattern of vessel involvement. Presence of I-V block in patients with acute myocardial infarction implies a hectic clinical course with poor prognosis, but does not justify prophylactic temporary transvenous intracardiac pacing except perhaps in the subgroup with associated 1° A-V block.

Observations on heart block during continuous electrocardiographic monitoring in myocardial infarction

Complete heart block (CHB) was observed in 24 of 350 patients with myocardial infarction who were studied under conditions of continuous electrocardiographic monitoring. CHB occurred predominantly in posterior and anteroseptal infarctions. In posterior infarction CHB was observed in patients who also developed first degree (1°) and types I and II second degree (2°-I and 2°-II) atrioventricular (A-V) block but not bundle-branch block (BBB). In anteroseptal infarction CHB was found in patients with BBB, occasionally in patients with 2°-II A-V block, but not in patients with 1° and 2°-I A-V block. Right BBB with a Q wave in lead V 1 was the usual form of BBB observed in patients with CHB and anteroseptal infarction. One mechanism for sudden death in anteroseptal infarction is the abrupt development of CHB following the onset of BBB. Evidence is presented attributing CHB to a lesion in the A-V node in posterior infarction and to bilateral BBB in anteroseptal infarction.

Bundle-branch block in acute myocardial infarction

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Electrocardiographic diagnosis of myocardial infarction in the presence of left bundle-branch block

It is generally accepted that most myocardial infarctions are obscured on the electrocardiogram by left bundle-branch block. The number of published cases in which this could be evaluated, however, is small, and the case reports are scattered. We have studied 30 cases of myocardial infarction with left bundle-branch block in which the location of the infarction could be determined with certainty, by autopsy, or by a previous electrocardiogram with normal intraventricular conduction. Twenty such published cases have also been collected. Electrocardiographic abnormalities have been correlated with infarctions in different locations. The possible specificity of these abnormalities is discussed.

The changing electrocardiogram in Wilson block

The significance of the Wilson variety of right bundle-branch block was investigated on the basis of serial electrocardiographic changes seen in almost half of the series. Wilson block may originate from both anteroseptal and posterior infarction; in the former it may form a solitary relic without prognostic significance; in the latter it denotes extensive septal involvement. It may modify the injury pattern of anterior infarction and may abolish the signs of posterior infarction; cardiac infarction may approximate it to the classic form of right bundle-branch block. Except in two patients, less than 4 per cent of the series, it was related to pathologic causes; it should therefore be regarded as a sign of organic heart disease.