Answer: If the patient is able to exercise and achieve his or her target heart rate, single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) is generally preferred. Asthma may be a contraindication for administering adenosine and related pharmacologic stress agents to obtain a hyperemic response for stress imaging. Asthma also can be a contraindication to administer beta blockers to have heart rate control for coronary computed tomography angiogram (CTA). However, if a dual source CT scanner is available, diagnostic coronary CTA may be obtained without the use of beta blockers.

In a patient with inhaler-dependent asthma, dobutamine cardiovascular magnetic resonance (CMR) could be a good option. Dobutamine stress echocardiography is known to have limitations in the setting of left bundle-branch block (LBBB), and it can be expected that dobutamine CMR might be similarly limited. However, dobutamine CMR might be the only safe option if the patient is inhaler dependent and unable to exercise to achieve their target heart rate. Results of a study presented at the 2011 American Heart Association Scientific Sessions demonstrated the prognostic value of dobutamine CMR in patients with known CAD and peripheral vascular disease (Figure 1). This study included 215 consecutive patients with CAD and peripheral arterial disease who had undergone dobutamine CMR in a 4-year period.² Sixty-five patients had early revascularization and were excluded from analysis. The remaining 140 patients were followed for a mean of 39 ± 18 months. Fifty-two patients (37%) experienced stress-induced wall motion abnormalities (WMA) during testing, and 15 cardiac events were reported. In multivariate analysis of clinical data, stress-induced WMA on dobutamine CMR (HR = 5.8; 95% CI, 1.6-21.3; P = .008) was an independent predictor of late cardiac events. Patients without inducible WMA demonstrated a good prognosis, with a 48-month event-free survival of 95.5%.

The nature of the ECG abnormality must also be taken into consideration. The presence of baseline ECG abnormalities, such as electronically paced ventricular rhythm or left bundle-branch block (LBBB), may interfere with interpretation of exercise ECG testing. For example, patients with nonspecific ST-T changes are considered to have non-diagnostic stress ECG responses. Exercise or pharmacologic stress SPECT MPI may still be useful in this case for identifying areas with ischemia. SPECT MPI with pharmacologic stress perfusion is preferred when there is a LBBB.

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Answer: This is a patient who has been experiencing pressure-like chest discomfort lasting for 15-20 minutes with walking or when she gets emotional. She has hypertension that is reasonably controlled with beta-blockers. She cannot achieve target heart rate walking, and her acoustic windows are poor.

Her physician ordered a pharmacologic stress SPECT MPI, which showed fixed antero-septal and apical perfusion defect that was somewhat reversible. In an obese patient, we have to consider the possibility that these results might reflect breast attenuation, but the reversibility cannot be disregarded.

So let’s consider the non-invasive options first. Both first-pass myocardial perfusion MRI and PET are excellent options with good positive and negative predictive values. A 60-year-old woman is unlikely to have coronary artery calcification, so one could consider just performing a calcium score and ending if the score was zero. However, in a series of over 10,000 patients in the CONFIRM trial, cardiovascular events were observed in symptomatic patients with a zero calcium score over a median of 2.1 years follow-up (Figure 2).^3,4 It is therefore reasonable to perform a coronary CTA.⁵ It has been shown in multicenter studies to have very high negative predictive value for CAD. If the test is negative, one may safely assume that there is a non-coronary cause for the patient’s symptoms.

The question is what to do if the patient has a positive coronary CTA, as the positive predictive value is only modest for detecting significant stenoses. Certainly, it would be reasonable to perform a coronary angiogram at this point. While coronary CTA has a modest predictive value for detecting a significant stenosis, it has a high positive predictive value for detecting the presence of atherosclerotic plaque. On this basis, one could consider treating the patient medically, similar to the approach taken in the COURAGE trial, providing that no significant stenosis was seen in the left main coronary artery.⁶ This proposal is the basis of the ongoing Randomized Evaluation of Patients with Stable Angina Comparing Utilization of Diagnostic Examinations (RESCUE) trial.⁷ The RESCUE trial will test cardiac CTA or MPI in diagnosing cardiac disease in patients with stable angina or angina equivalent. The diagnostic imaging results will guide subsequent therapy. Participants with abnormal findings will be considered for optimal medical therapy or diagnostic invasive coronary angiography and possible revascularization depending on extent and location of disease. The trial is expected to enroll 4,300 patients without prior revascularization over a 2-year follow-up; results will be available in late 2013.

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Answer: In addition to his dyspnea on exertion, we know that this patient is moderately overweight but has no other risk factors for cardiovascular disease. He has had a stress echocardiogram that showed a mild decrease in left ventricular systolic function with stress, but normal at rest. In many ways, this situation is very straightforward, as the patient clearly has a positive test for ischemia. It would be reasonable to perform coronary angiography as the next step.⁸ If a less aggressive approach is desired, a coronary CTA could also be performed.⁵

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