Jacques Melin

Exercise echocardiography is an accurate and cost-efficient technique for detection of coronary artery disease in women

OBJECTIVESnThis study compared the accuracy and cost implications of using exercise echocardiography and exercise electrocardiography for detection of coronary artery disease in women.nnnBACKGROUNDnThe specificity of exercise electrocardiography in women is lower than in men. Exercise echocardiography accurately identifies coronary artery disease in women, but its utility in place of exercise electrocardiography is unclear.nnnMETHODSnOne hundred sixty-one women without a previous Q wave infarction underwent exercise echocardiography and coronary angiography. Positive findings were a new or worsening wall motion abnormality on the exercise echocardiogram and ST segment depression > 0.1 mV at 0.08 s after the J point on the exercise electrocardiogram (ECG).nnnRESULTSnCoronary artery stenosis > 50% diameter narrowing was present in 59 patients; the sensitivity (mean +/- SD) of exercise echocardiography was 80 +/- 3%. In 48 patients with an interpretable ECG, the sensitivity of exercise echocardiography was 81 +/- 4%, and that of the exercise ECG was 77 +/- 3% (p = 0.50). In 102 patients without coronary artery disease, the overall specificity of exercise echocardiography was 81 +/- 4%. In 70 patients with an interpretable ECG, the specificity of exercise echocardiography (80 +/- 3%) exceeded that of the exercise ECG (56 +/- 4%, p < 0.0004). The accuracy of exercise echocardiography was also greater than exercise electrocardiography (81 +/- 5% vs. 64 +/- 6%, p < 0.005). Exercise echocardiography stratified significantly more patients of intermediate (20% to 80%) pretest disease probability into the high (> 80%) or low (< 20%) posttest probability group. In women without a previous exercise ECG, the specificity of exercise echocardiography continued to exceed that of exercise electrocardiography (80 +/- 3% vs. 64 +/- 3%, p = 0.05). Exercise echocardiography had the best balance between accuracy and cost for the diagnosis of coronary artery disease in women.nnnCONCLUSIONSnExercise echocardiography is more specific than exercise electrocardiography for diagnosis of coronary artery disease in women and is a cost-effective approach to the diagnosis of coronary artery disease because of the avoidance of inappropriate angiography.

Comparative ability of dobutamine and exercise stress in inducing myocardial ischaemia in active patients.

OBJECTIVE--To compare the ability of dobutamine and exercise stress to induce myocardial ischaemia and perfusion heterogeneity under routine clinical circumstances. DESIGN--86 active patients without previous myocardial infarction were studied by dobutamine and exercise stress protocols and coronary angiography. During both tests patients underwent electrocardiography, digitised echocardiography, and perfusion scintigraphy using Tc-99m methoxybutylisonitrile (MIBI) single photon emission computed tomography. MAIN OUTCOME MEASURE--Coronary disease defined as an ST segment depression of > or = 0.1 mV, a resting or stress induced perfusion defect, or a resting or stress induced wall motion abnormality on exercise and dobutamine stress testing. RESULTS--Dobutamine stress was submaximal in 51 patients because of ingestion of beta adrenoceptor blocking agents on the day of the test (n = 25) or failure to attain the peak dose owing to side effects (n = 28). Exercise was limited in 23 patients by non-cardiac symptoms. The peak heart rate with dobutamine was less than that attained with exercise (105 (25) v 132 (24) beats/min, P < 0.0001); the response to maximal dobutamine stress significantly exceeded that to submaximal stress. Peak blood pressure was greatest with exercise (206 (27) v 173 (25) mm Hg, P < 0.001), values at maximal and submaximal dobutamine stress being comparable. Electrocardiographic evidence of ischaemia was induced less frequently by dobutamine than exercise (32% v 77% of the 56 patients with significant coronary disease, P < 0.01), as was abnormal wall motion (54% v 88%, P < 0.001). Ischaemia was induced more readily with maximal stress of either type; thus the sensitivities of dobutamine and exercise echocardiography were comparable only in patients undergoing a maximal dobutamine testing (73% v 77%, NS). Perfusion heterogeneity was induced in 58% of patients with coronary disease at submaximal dobutamine stress, 73% at maximal dobutamine stress, and 73% at exercise stress (NS). Among 30 patients without coronary stenoses, normal function was obtained in 83% of echocardiography studies with dobutamine and in 80% with exercise (NS). Normal perfusion was identified in 70% of these patients at exercise MIBI, and 68% at dobutamine stress (NS). CONCLUSIONS--In a group of patients studied under normal clinical circumstances antianginal treatment and inability to complete the stress protocol are frequent and compromise the capacity of dobutamine stress to induce ischaemia. In contrast, the induction of perfusion heterogeneity is less susceptible to submaximal stress.

Methodological Issues in Regional Myocardial Perfusion Imaging with Positron Emission Tomography

Positron emission tomography (PET) is currently the only technique available that permits the quantification of regional myocardial blood flow in vivo. Absolute PET measurements of nutrient tissue flow and flow reserve1 have contributed significantly to the understanding of the mechanisms of various cardiac disorders such as ischemic heart disease, cardiac hypertrophy or microcirculatory disorders.2 However these quantitative measurements are demanding and are currently performed adequately in a limited number of laboratories with particular expertise in instrumentation and tracer modelling. This chapter deals with several aspects of PET methodology in the evaluation of myocardial perfusion.

Assessment of Myocardial Perfusion by PET

Several tracer approaches have been proposed for the assessment of myocardial perfusion with positron emission tomography (PET) in the clinical setting. These include nitrogen-13 (13N) labelled ammonia, oxygen-15 (15O) labelled water, rubidium-82 (82Rb) and potassium-38 (38K). These tracers require a local cyclotron for production, except for 82Rb which may be delivered directly to the patient from an on-site generator. There are two specific clinical applications of PET that have been proposed for the evaluation of patients with coronary artery disease (CAD) [1-3]. The first is the noninvasive detection of CAD and estimation of the severity of the disease. This is performed using a PET perfusion agent at rest and during pharmacologic vasodilation. A unique application of PET is the noninvasive calculation of absolute regional myocardial perfusion at rest and during vasodilation in humans using [15O]water or [13N]ammonia. However, most centers rely on the qualitative interpretation of 82Rb or [13N]ammonia images for the detection of CAD and the assessment of its severity. The second clinical application of PET is the assessment of myocardial viability in CAD patients with left ventricular dysfunction. The most common approach is to determine whether metabolic activity assessed by 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) is preserved in regions with reduced perfusion, thus indicating tissue viability.

Myocardial Hibernation: Blood Flow and Metabolism

The term “hibernation” was employed for the first time by Diamond et al. in 1978 1 to describe the chronic wall motion abnormalities of patients with coronary artery disease but no previous myocardial infarction and their reversibility upon revascularization. The overall concept of myocardial hibernation was subsequently developed by Rahimtoola23 and popularized by Braunwald and Rutherford.4 In his 1989 description of the syndrome, Rahimtoola postulated that myocardial hibernation resulted from the “relatively uncommon response to reduced myocardial blood flow at rest whereby the heart downgrades its myocardial function to the extent that blood flow and function are once again in equilibrium, and as a result, neither myocardial necrosis or ischemic symptoms are present.” 2

Myocardial blood flow quantitation with positron emission tomography

Dynamic Positron Emission Tomography (PET) with the use of appropriate tracers is the only technique available thus far that permits quantitation of regional myocardial blood flow (MBF) in absolute terms, i.e. ml/min/g of tissue. This review discusses some of the contributions of PET measurements of MBF to the understanding of the pathophysiology of coronary artery disease.