Electrocardiographic diagnosis of myocardial infarction in cases of complete left bundle branch block

Diagnosis of myocardial infarction and ischemia in the setting of bundle branch block and cardiac pacing

The diagnosis of myocardial infarction (MI) in the presence of left bundle branch block (LBBB) or during ventricular pacing (VP) is challenging because of inherent changes in the sequence of ventricular depolarization and repolarization associated with both conditions. Although LBBB and right ventricular (RV) pacing may both produce abnormalities in the ECG, it is often possible to diagnose an acute MI (AMI) or an old MI based on selected morphologic changes. Primary ST-segment changes scoring 3 points or greater according to the Sgarbossa criteria are highly predictive of an AMI in patients with LBBB or RV pacing. The modified Sgarbossa criteria are useful for the diagnosis of AMI in patients with LBBB; however, these criteria have not yet been studied in the setting of RV pacing. Although changes of the QRS complex are not particularly sensitive for the diagnosis of an old MI in the setting of LBBB or RV pacing, the qR complex and Cabrera sign are highly specific for the presence of an old infarct. Diagnosing AMI in the setting of biventricular (BiV) pacing is challenging. To date there is minimal evidence suggesting that the traditional electrocardiographic criteria for diagnosis of AMI in bundle branch block may be applicable to patients with BiV pacing and positive QRS complexes on their ECG in lead V1. This report is a careful review of the electrocardiographic criteria facilitating the diagnosis of acute and remote MI in patients with LBBB and/or VP.

Electrocardiographic Diagnosis of Myocardial Infarction during Left Bundle Branch Block

The electrocardiographic diagnosis of myocardial infarction (MI) in the presence of left bundle branch block (LBBB) has long been considered problematic or even almost impossible. Many proposed ECG markers in the old literature have now been discarded. However, the advent of reperfusion therapy has generated greater interest in the ECG diagnosis of acute MI in LBBB where ST-segment deviation is the only useful sign. As such, the ST-segment criteria cannot be used to rule out MI, but they can help to rule it in. Criteria for old MI (based on QRS changes) have not been reevaluated for almost 20 years and continue to exhibit low sensitivity, but high specificity.

Interobserver agreement in the electrocardiographic diagnosis of acute myocardial infarction in patients with left bundle branch block

STUDY OBJECTIVE

To determine the interobserver agreement between cardiologists and emergency physicians in the ECG diagnosis of acute myocardial infarction (AMI) in patients with left bundle branch block (LBBB) using the ECG algorithm previously described by Sgarbossa et al.

METHODS

Using the Sgarbossa ECG algorithm, 4 cardiologists and 4 emergency physicians independently interpreted a test set of 224 ECGs with LBBB, of which 100 ECGs were from patients with an evolving AMI. A subset of 25 ECGs was reinterpreted by each reader to test intraobserver agreement for AMI as well as interobserver agreement for the degree of ST-segment deviation. Agreement rates for AMI were estimated using the kappa statistic. In addition, the sensitivity and specificity for diagnosing AMI were determined for each reader, using the Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries (GUSTO I) enzyme criteria for AMI as the gold standard. The study was conducted at 3 university-affiliated medical centers. The test set contained ECGs from 100 patients enrolled in the GUSTO I trial with LBBB on their initial ECG and an evolving AMI confirmed by serum cardiac enzyme changes, and 124 control patients from the Duke Databank for Cardiovascular Disease who had stable, angiographically documented coronary artery disease and LBBB.

RESULTS

There was excellent interobserver agreement (kappa=0.81, 95% confidence interval [CI] 0.80 to 0.83) between cardiologists and emergency physicians for diagnosing AMI. Intraobserver agreement kappa values for AMI diagnosis by cardiologists and emergency physicians were 0.81 (95% CI 0.67 to 0.94) and 0.71 (95% CI 0.54 to 0.89). The median sensitivity for diagnosing AMI by cardiologists and emergency physicians was 73% (range 66% to 80%) versus 67% (range 61% to 75%); median specificity was 98% (range 97% to 99%) versus 99% (range 98% to 99%). Spearman rank correlation coefficients for the degree of ST-segment deviation in all 12 leads was 0.86 (95% CI 0.85 to 0.87) among all readers.

CONCLUSION

There is excellent interobserver agreement between cardiologists and emergency physicians for diagnosing AMI when applying the Sgarbossa ECG algorithm to patients with LBBB. Emergency physicians should be able to reliably use this algorithm when evaluating patients.

Diagnosis of acute myocardial infarction in patients with chronic left bundle-branch block. Standard 12-lead ECG compared to dynamic vectorcardiography

Standard 12-lead electrocardiogram (ECG) criteria were evaluated and compared with dynamic vectorcardiography for diagnosing acute myocardial infarction in 33 patients with chronic left bundle-branch block. In 14 patients a clinical diagnosis of acute myocardial infarction was made, but it was found that none of the seven most promising ECG criteria suggested in the literature could alone or in combination diagnose acute myocardial infarction. QRS vector difference evolution showed the same kind of pattern as that for patients with narrow QRS-complex. By using a predefined specific pattern, a diagnostic accuracy of 79% was achieved. The results indicate that dynamic vectorcardiography is a better tool for diagnosing and monitoring acute myocardial infarction in patients with left bundle-branch block than standard 12-lead ECGs taken on admission and after 12-24 h.

Electrocardiographic diagnosis of evolving acute myocardial infarction in the presence of left bundle-branch block. GUSTO-1 (Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries) Investigators

BACKGROUND

The presence of left bundle-branch block on the electrocardiogram may conceal the changes of acute myocardial infarction, which can delay both its recognition and treatment. We tested electrocardiographic criteria for the diagnosis of acute infarction in the presence of left bundle-branch block.

METHODS

The base-line electrocardiograms of patients enrolled in the GUSTO-1 (Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries) trial who had left bundle-branch block and acute myocardial infarction confirmed by enzyme studies were blindly compared with the electrocardiograms of control patients who had chronic coronary artery disease and left bundle-branch block. The electrocardiographic criteria for the diagnosis of infarction were then tested in an independent sample of patients presenting with acute chest pain and left bundle-branch block.

RESULTS

Of 26,003 North American patients, 131 (0.5 percent) with acute myocardial infarction had left bundle-branch block. The three electrocardiographic criteria with independent value in the diagnosis of acute infarction in these patients were an ST-segment elevation of 1 mm or more that was concordant with (in the same direction as) the QRS complex; ST-segment depression of 1 mm or more in lead V1, V2, or V3; and ST-segment elevation of 5 mm or more that was disconcordant with (in the opposite direction from) the QRS complex. We used these three criteria in a multivariate model to develop a scoring system (0 to 10), which allowed a highly specific diagnosis of acute myocardial infarction to be made.

CONCLUSIONS

We developed and validated a clinical prediction rule based on a set of electrocardiographic criteria for the diagnosis of acute myocardial infarction in patients with chest pain and left bundle-branch block. The use of these criteria, which are based on simple ST-segment changes, may help identify patients with acute myocardial infarction, who can then receive appropriate treatment.

ECG diagnosis of acute myocardial infarction in the presence of left bundle-branch block in patients undergoing continuous ECG monitoring

It is common knowledge that the ECG diagnosis of completed myocardial infarction in the presence of left bundle-branch block (LBBB) is extremely difficult and often impossible. More than 50 rules have been proposed as criteria for interpreting Q-wave equivalents superimposed on the QRS complex in the presence of LBBB. However, because of misinterpretation of the available literature, physicians frequently recommend that patients with chest pain in the presence of LBBB receive thrombolytic therapy or urgent coronary arteriography on the basis of the assumption that acute injury and ischemia cannot be interpreted in the presence of LBBB. Unfortunately, many physicians fail to realize that although completed infarction is difficult to confirm in the presence of LBBB, ongoing ischemia and injury can be detected in the presence of LBBB and may be seen as often as they are in the presence of normal cardiac conduction. A deflection of the J point (and ST segment) in the direction of the major QRS complex or an elevation of the ST segment of more than 7 to 8 mm opposite the direction of the major QRS complex has been demonstrated to have a sensitivity of more than 50% in detecting acute injury, with a specificity of more than 90%. During the first half of an ongoing prospective study of the use of continuous 12-lead ECG monitoring in the emergency department, we encountered five patients with final diagnoses of acute myocardial infarction in the presence of LBBB who demonstrated significant ECG changes while undergoing continuous ST-segment monitoring with frequent serial ECGs. The five different locations of the infarcts in these five patients were posterior, posterolateral, inferior, anterior, and anterolateral. We present these patients' cases to demonstrate the ECG characteristics of acute injury in the presence of LBBB.

Quantification of ST-segment changes during coronary angioplasty in patients with left bundle branch block

Electrocardiographic manifestations of ischemia are difficult to interpret in the presence of left bundle branch block (LBBB). Recently developed techniques allow continuous computerized digital analysis of ST segments that can be zeroed to the patient's own baseline electrocardiogram even if that baseline is abnormal conduction. With use of this technology, ST-segment changes during balloon coronary occlusion were compared in 10 patients with LBBB versus an age-, sex-, and coronary anatomy-matched population of 20 control subjects with normal baseline conduction. ST-segment deviation of greater than or equal to 1 mm from baseline was present in 80% of patients with LBBB and in 75% of control patients (difference not significant). There was no significant difference between patients with LBBB versus control patients in maximal ST-segment deviation (2.6 +/- 1.7 vs 2.0 +/- 1.0 mm) or in ST-segment deviation measured after 60 seconds of occlusion (2.4 +/- 1.3 vs 1.8 +/- 1.1 mm). ST-segment deviation reached 1 mm more quickly in patients with LBBB (33 +/- 11 seconds) than in control subjects (60 +/- 36 seconds) (p = 0.003). It is concluded that ST-segment analysis is feasible in patients with LBBB using digital self-referenced ST analysis and may provide important clinical information regarding the presence of myocardial ischemia.

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

Whether myocardial infarction (MI) can be diagnosed electrocardiographically in the presence of left bundle branch block (LBBB) is controversial. Our study sought to test the reliability of ECG criteria for diagnosing MI in patients with LBBB. Among 985 patients presenting within 18 hours of the onset of ischemic chest pain, 35 had complete LBBB. Acute MI was identified by serial MB-creatine kinase (CK) elevations and prior MI was determined by previously documented ECG and/or enzyme changes. Among those with LBBB, 24 patients had acute and/or prior MI, while 11 had neither. Eleven ECG criteria previously proposed for detecting MI in the presence of LBBB were evaluated. In patients presenting with ischemic chest pain and complete LBBB, presence of any one of the following ECG criteria was highly specific (90% to 100%) and predictive (85% to 100%) for acute or prior MI: Q waves in at least two of leads I, aVL, V5, or V6; R wave regression from V1 to V4; notching of the upstroke of the S wave in at least two of leads V3, V4, or V5, and primary ST-T wave changes in two or more adjacent leads.

ECG diagnosis of acute myocardial infarction in patients with bundle branch block

The ECG diagnosis of myocardial infarction in the setting of bundle branch block is one that most physicians find difficult and that many erroneously believe to be impossible. Two case reports of a patient with right bundle branch block and of a patient with left bundle branch block are presented to illustrate instances in which the ECG diagnosis of myocardial infarction was both possible and essential. Methods for detecting ECG changes that indicate acute myocardial injury in the patient with bundle branch block are presented and applied to these cases.

Accuracy of localization of acute myocardial infarction by 12 lead electrocardiography

Until recently, ECG accuracy in localizing acute myocardial infarction (AMI) could be assessed only by comparing the ECGs with autopsy findings. This approach, however, preselected patients, including only those who died. It is possible that this postmortem group of patients would be different from the whole population of patients with AMI. Myocardial imaging with 99mTc-pyrophosphate offers the advantage of directly localizing the region of injured myocardium in the acute phase of AMI. In 34 patients with confirmed AMI and focal uptake of 99mTc-pyrophosphate, serial ECGs were obtained and interpreted by two independent observers. The sensitivity and specificity of serial ECGs in determining the location of AMI in the five left ventricular (LV) wall segments were determined: (1) in the anterior wall sensitivity was 86.7% and specificity was 89.5%; (2) in the lateral wall sensitivity was 73.7% and specificity was 80.0%; (3) in the high lateral wall sensitivity was 80.0% and specificity was 87.5%; (4) in the inferior wall sensitivity was 87.5% and specificity was 100%; (5) in the "true" posterior wall sensitivity was 83.3% and specificity was 86.4%. Overall, in the 170 LV wall segments (five per patient) examined, scans localized with a sensitivity of 81.9% and a specificity of 88.8%. After four patients with LBBB were excluded, sensitivity increased to 87.1%. Overall, localization of AMI by serial ECG was accurate in 85.9% of the 34 patients included in the study.

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.

Evaluation of criteria for diagnosis of myocardial infarction: study of 256 patients with intermittent left bundle branch block

In an attempt to elucidate the specificity and sensitivity of atypical findings during left bundle branch block (LBBB) with respect to myocardial infarction (MI), we analyzed ECGs from patients with intermittent LBBB obtained by mail solicitation of cardiologists. The group consisted of 256 patient files fulfilling the following criteria: 1) complete LBBB present on one or more 12-lead ECGs, and 2) at leat one 12-lead ECG taken subsequent to a LBBB tracing exhibiting absence of LBBB (non-LBBB). The sensitivity of atypical LBBB for predicting presence of MI was 0.41, the specificity 0.64, and the accuracy 0.59. No specific atypical finding was significantly better than any other in predicting MI. We conclude that atypical findings present during LBBB are of little value in predicting the presence of MI (as diagnosed by significant Q waves present during non-LBBB conduction).

Correlation of electrocardiographic and pathologic findings in healed myocardial infarction

A correlative study in 50 cases of healed myocardial infarction compared the 12 lead electrocardiogram with pathologic observations. The electrocardiogram was interpreted according to established Minnesota codes with some modifications. The following conclusions were reached: (1) The electrocardiogram underestimates the extent of myocardial infarction. (2) When a healed myocardial infarct at a specific location is recognized with electrocardiographic criteria, it is likely that there are unrecognized infarcts involving other areas of the left ventricle. (3) Infarctions involving the lateral and inferobasal areas are frequently unrecognized. (4) The electrocardiogram is more likely to miss myocardial infarcts in patients with multiple, than in those with single, electrocardiographically diagnosed infarcts. (5) Apical myocardial infarction does not appear to have specific electrocardiographic findings, other than those related to general infarct localization by electrocardiogram, particularly in patients with anteroseptal or anterolateral infarction. (6) Abnormal Q waves, generally thought to indicate transmural myocardial infarction, are frequently found in subendocardial infarction. (7) The simplified electrocardiographic classification of myocardial infarct site (anteroseptal, inferior, anterolateral) used in this study is preferable to more detailed classifications previously suggested by others.