Transthoracic Coronary Doppler for Coronary Flow Velocity Reserve
Background: Myocardial perfusion imaging (MPI), using single photon emission computed tomography (SPECT) is a validated method for detecting coronary artery disease. Transthoracic Doppler echocardiography (TTDE) of flow at rest and during adenosine provocation has previously been evaluated in selected patient groups. We therefore wanted to compare the diagnostic ability of TTDE in the left anterior descending coronary artery (LAD) to that of MPI in an unselected population of patients with chest pain referred for MPI. Our hypothesis was that TTDE with high accuracy would identify healthy individuals and exclude them from the need for further studies, enabling invasive investigations to be reserved for patients with a high probability of disease.
Methods: Sixty-nine patients, 44 men and 25 women, age 61 ± 10 years (range 35–82), with a clinical suspicion of stress induced myocardial ischemia, were investigated. TTDE was performed at rest and during adenosine stress for myocardial scintigraphy.
Results: We found that coronary flow velocity reserve (CFVR) determined from diastolic measurements separated normal from abnormal MPI findings with statistical significance. TTDE identified coronary artery disease, defined from MPI, as reversible ischemia and/or permanent defect, with a sensitivity of 60% and a specificity of 79%. The positive predictive value was 43% and the negative predictive value was 88%. There was an overlap between groups which could be due to abnormal endothelial function in patients with normal myocardial perfusion having either hypertension or diabetes.
Conclusion: TTDE is an attractive non-invasive method to evaluate chest pain without the use of isotopes, but the diagnostic power is strongly dependent on the population investigated. Even in our heterogeneous clinical cardiac population, we found that CFVR>2 in the LAD excluded significant coronary artery disease detected by MPI.

Coronary artery disease (CAD) is the most common cause of death in the western world, despite advances in medical, interventional and surgical treatments. The diagnosis of coronary disease is often based on patient symptoms and an exercise test. However, the sensitivity for the detection of ischemia using exercise in combination with electrocardiography is low, in the range of 60%. Myocardial perfusion imaging (MPI) in combination with stress increases sensitivity to about 85% without compromising specificity. If verification bias (where the selection process results in a higher prevalence of disease than in a clinical population) is taken into account, exercise stress testing as well as other non-invasive testing could have a sensitivity as low as 40% and specificity of 80%. The drawback of scintigraphy is exposure to radiation. Echocardiography is inexpensive, widely available, non-invasive and, in combination with Doppler, flow velocity in the epicardial coronary vessels can be interrogated. The method is demanding for the operator but could become a widely available and inexpensive diagnostic modality, especially if combined with pharmacological stress.

Gould et al have shown that resting coronary blood flow does not decrease until coronary artery diameter is reduced by 85%. The coronary flow reserve, however, begins to decrease already with a 30–45% reduction of the arterial diameter. In healthy coronary arteries, adenosine provokes an increase in coronary flow 3–6 times the resting value. Coronary flow velocity reserve (CFVR) is defined as the ratio between coronary flow velocities during maximal hyperaemia and at rest. CFVR has been used as an index of normality in studies of pathological processes such as coronary obstructive disease and endothelial dysfunction. Previous studies have produced encouraging results for the diagnosis of significant coronary stenoses. Since the method so far has been applied mainly in selected patient populations, we wanted to study if it could be applied in a routine clinical setting, where patients with coronary artery disease as well as with various cardiovascular conditions that are associated with endothelial dysfunction present with chest pain. Thus, in contrast to most previous studies, patients with previous revascularization, surgical valve procedures, non-sinus rhythm, artificial pacemaker, bundle branch block, hypertension, cardiomyopathy and diabetes mellitus were also included. In this clinical population we set forth to assess transthoracic coronary Doppler echocardiography (TTDE) compared to our standard MPI method.