This patient with a left bundle branch block (LBBB) on her baseline electrocardiogram (ECG) should undergo vasodilator nuclear perfusion imaging. In patients with baseline ECG abnormalities such as preexcitation, LBBB, a paced rhythm, or baseline ST-segment depression greater than 1 mm, ECGs obtained during stress testing cannot be appropriately interpreted, and standard exercise treadmill testing is therefore not appropriate. Instead, these patients must undergo stress testing with additional imaging, such as nuclear perfusion imaging or stress echocardiography.

When myocardial perfusion imaging is used to evaluate patients with LBBB, a vasodilator study using an agent such as adenosine or dipyridamole is necessary instead of an exercise study. This is because perfusion defects that are not related to obstructive coronary artery disease (CAD) can be seen in the septum with exercise. Radiotracers are distributed with blood flow, and when the coronary arteries fill during diastole, the delay in contraction of the septum with LBBB can impair filling and create a defect in the septum in the absence of obstructive CAD. However, vasodilators produce hyperemia and a flow disparity between myocardium supplied by the stenotic vessel as compared with the unobstructed vessel that is not affected by the delay in septal contraction related to LBBB. For this reason, an exercise nuclear perfusion study would not be appropriate in this patient.

Coronary artery calcium scoring quantifies the amount of calcium in the walls of the coronary arteries and correlates well with plaque burden in the coronary arteries. It is an anatomic study with fairly high sensitivity for detecting occlusive CAD, although the frequency of false-negative results (significant CAD with a low CAC score) is not known. Therefore, CAC scoring is more frequently used for risk stratification in patients with intermediate risk for atherosclerotic cardiovascular disease. Another anatomic study, coronary CT angiography, is an emerging technology that has high correlation with findings on invasive coronary arteriography and may be increasingly useful in evaluating for occlusive CAD.