Myocardial Perfusion Scan with Pharmacologic Stress
For an older patient with stable angina and LBBB on ECG, the first next diagnostic test should be a myocardial perfusion scan with pharmacologic stress (dipyridamole or adenosine), not exercise stress testing or direct angiography. 1, 2
Why Pharmacologic Stress Perfusion Imaging is the Answer
Exercise stress testing is contraindicated in patients with LBBB because it produces false-positive septal defects and uninterpretable ECG changes, making the test diagnostically useless. 3, 1, 2 The American College of Physicians guidelines explicitly state that exercise ECG testing should not be performed when complete left bundle-branch block is present on resting ECG (level of evidence: B). 3
The American College of Cardiology/American Heart Association/American College of Physicians provide a Grade I recommendation (moderate-quality evidence) that pharmacologic stress with radionuclide myocardial perfusion imaging should be used for risk assessment in patients with stable ischemic heart disease who have LBBB, regardless of ability to exercise. 2
Technical Specifications
Dipyridamole or adenosine are the preferred pharmacologic agents for stress myocardial perfusion imaging in LBBB patients, as they dilate normal coronary arteries more than obstructed ones, producing regional perfusion differences without the mechanical stress-related artifacts seen with exercise or dobutamine. 1, 2
Single-photon emission computed tomography (SPECT) with images obtained at rest and during pharmacologic stress is the recommended imaging technique, using tracers such as ²⁰¹Thallium or ⁹⁹ᵐTechnetium-labeled compounds (sestamibi or tetrofosmin). 1
Dobutamine stress echocardiography should be avoided in LBBB patients as it produces false-positive results in the septal region. 1, 2
Why Not Direct Angiography?
Coronary angiography should be performed after non-invasive testing has suggested significant coronary artery disease that may benefit from revascularization. 2 Proceeding directly to invasive testing exposes patients to procedural risks and costs without the benefit of non-invasive risk stratification. 2
Normal results on pharmacologic stress myocardial perfusion scanning indicate a low likelihood of significant coronary artery disease, making coronary angiography usually not indicated as a subsequent test. 1
Additional Considerations for Older Patients
The Duke treadmill score does not work well in elderly persons, particularly those older than 75 years of age, providing additional rationale for using pharmacologic stress imaging in this older patient population rather than exercise testing. 1
Diagnostic Performance
Research demonstrates that exercise (+dipyridamole) myocardial SPECT has a high positive predictive value (93% for LAD stenosis, 96% for left circumflex stenosis, 89% for right coronary artery stenosis) and specificity (83%, 91%, and 69% respectively) for the diagnosis of coronary stenosis in patients with LBBB. 4
Visual improvement in anteroseptal and apical myocardial perfusion between stress and rest studies indicates significant LAD stenosis in patients with LBBB. 5