From the Guidelines
The development of a new Left Bundle Branch Block (LBBB) during a stress test should be considered a positive result, indicating potential myocardial ischemia, and pharmacologic stress testing is preferred over exercise stress testing for patients with LBBB. This is because the tachycardia induced during exercise can result in reversible septal defects even in the absence of left anterior descending artery disease, leading to low specificity of exercise myocardial perfusion imaging in the presence of LBBB, as reported in the 2009 ACCF/AHA focused update 1.
Key Points to Consider
- The specificity of exercise myocardial perfusion imaging in the presence of LBBB is low, reported to be 33% 1.
- Pharmacologic stress testing with either perfusion scintigraphy or dobutamine stress echocardiography (DSE) has higher sensitivity and specificity compared to exercise stress testing for detecting coronary artery disease in patients with LBBB 1.
- The use of vasodilators in patients with LBBB has a sensitivity of 98%, a specificity of 84%, and a diagnostic accuracy of 88% to 92% 1.
- Exercise should not be combined with dipyridamole in patients with LBBB, and synthetic catecholamines will also yield false-positive results 1.
Management and Further Evaluation
- When a patient develops new LBBB during exercise, the test should be terminated immediately, and the patient should be evaluated for coronary artery disease.
- Management typically includes referral for further cardiac evaluation, which may include coronary angiography or other imaging studies to assess for coronary artery disease.
- It's essential to distinguish between new LBBB that develops during stress versus pre-existing LBBB, as the latter makes interpretation of other ECG changes during stress testing more challenging and may necessitate alternative imaging modalities like nuclear perfusion imaging or stress echocardiography for accurate assessment.
From the Research
New Left Bundle Branch Block and Stress Test Results
- A new Left Bundle Branch Block (LBBB) may not necessarily indicate a positive result in a stress test, as the relationship between LBBB and stress test outcomes is complex and influenced by various factors 2, 3, 4, 5.
- Studies have shown that LBBB can be associated with coronary artery disease (CAD), but the diagnostic accuracy of stress tests in patients with LBBB is limited 3, 4, 5.
- Dobutamine stress echocardiography has been found to be a useful diagnostic tool for identifying CAD in patients with LBBB, with high sensitivity and specificity 4, 5.
Diagnostic Accuracy of Stress Tests in LBBB Patients
- Exercise stress echocardiography has been found to have limited diagnostic accuracy in patients with resting LBBB, with a low specificity for significant obstructive coronary artery disease 3.
- Dobutamine stress echocardiography, on the other hand, has been found to be a more accurate diagnostic tool for identifying CAD in patients with LBBB, with high sensitivity and specificity 4, 5.
- The diagnostic accuracy of stress tests in patients with LBBB can be influenced by various factors, including the presence of coronary artery calcium and the severity of CAD 2, 6.
Clinical Implications of New LBBB
- A new LBBB can be associated with poorer long-term outcomes in patients with ST-elevation myocardial infarction (STEMI), including higher rates of new myocardial infarction, revascularization, and mortality 6.
- Early identification and management of factors such as reduced left ventricular ejection fraction (LVEF) and timely hospital admission can improve prognosis in patients with new-onset LBBB 6.