Increased myocardial perfusion at rest and diminished perfusion reserve in patients with angina and angiographically normal coronary arteries.

Angiographically normal coronary arteries are found in a substantial number of patients evaluated for angina pectoris. One third to one half of such patients demonstrate abnormalities of myocardial perfusion or metabolism when evaluated with invasive techniques. This study was designed to determine whether angina in such patients is attributable to abnormalities of perfusion at rest, maximal perfusion or vasodilator reserve and whether any identified abnormalities were global or regional in nature. Positron emission tomography was performed with oxygen-15-labeled water (H2(15)O) and oxygen-15-labeled carbon monoxide (C15O) before and after intravenous dipyridamole to assess regional myocardial perfusion and perfusion reserve in absolute terms in 16 normal subjects and 17 patients with chest pain and angiographically normal coronary arteries. Eight of the 17 patients had a myocardial perfusion reserve less than 2.5 (the lower limit of normal in studies with positron emission tomography, as well as with other techniques) and 9 of 17 patients had a normal response. In the patients with an impaired perfusion reserve, perfusion at rest was significantly higher than that measured in normal subjects (1.61 +/- 0.38 versus 1.25 +/- 0.28 ml/g per min, p less than 0.02) and maximal flow and perfusion reserve were significantly reduced (2.26 +/- 0.92 versus 4.62 +/- 1.58 ml/g per min and 1.4 +/- 0.5 versus 3.8 +/- 1.1, respectively; p less than 0.001 for both comparisons). Abnormalities of perfusion and perfusion reserve were spatially homogeneous without detectable regional disparities. Thus, nearly half of patients with chest pain and normal coronary arteries have abnormalities of myocardial perfusion that are detectable noninvasively with positron emission tomography and H2(15)O.

Noninvasive estimation of regional myocardial oxygen consumption by positron emission tomography with carbon-11 acetate in patients with myocardial infarction.

We previously demonstrated in experimental studies that myocardial oxygen consumption (MVO2) can be estimated noninvasively with positron emission tomography (PET) from analysis of the myocardial turnover rate constant (k) after administration of carbon-11 (11C) acetate. To determine regional k in healthy human subjects and to estimate alterations in MVO2 accompanying myocardial ischemia, we administered [11C]acetate to five healthy human volunteers and to six patients with myocardial infarction. Extraction of [11C]acetate by the myocardium was avid and clearance from the blood-pool rapid yielding myocardial images of excellent quality. Regional k was homogeneous in myocardium of healthy volunteers (coefficient variation = 11%). In patients, k in regions remote from the area of infarction was not different from values in myocardium of healthy human volunteers (0.061 +/- 0.025 compared with 0.057 +/- 0.008 min-1). In contrast, MVO2 in the center of the infarct region was only 6% of that in remote regions (p less than 0.01). In four patients studied within 48 hr of infarction and again more than seven days after the acute event, regional k and MVO2 did not change. The approach developed should facilitate evaluation of the efficacy of interventions designed to enhance recovery of jeopardized myocardium and permit estimation of regional MVO2 and metabolic reserve underlying cardiac disease of diverse etiologies.

Assessment of myocardial oxidative metabolic reserve with positron emission tomography and carbon-11 acetate.

We have previously demonstrated that positron emission tomography (PET) with [11C]acetate allows noninvasive regional quantification of myocardial oxidative metabolism. To assess the metabolic response of normal myocardium to increased work (oxidative metabolic reserve), clearance of myocardial 11C activity after administration of [11C]acetate i.v. was measured with PET in seven normal subjects at rest and during dobutamine infusion. At rest, clearance of 11C was monoexponential and homogeneous. The rate constant of the first phase of 11C clearance, k1, averaged 0.054 +/- 0.014 min-1 at a rate-pressure produce (RPP) of 7329 +/- 1445 mmHg X bpm. During dobutamine infusion, RPP increased by an average of 141% to 17,493 +/- 3582 mm Hg Z bpm. Clearance of 11C became biexponential and remained homogeneous. k1 averaged 0.198 +/- 0.043 min-1 with a mean coefficient of variation of 16%.. k1 and RPP correlated closely (r = 0.91; p less than 0.001), and the slope of the k1/RPP relation remained consistent in all subjects (1.48 +/- 0.42). These findings suggest that PET with [11C]acetate and dobutamine stress may provide a promising approach for evaluation of regional myocardial oxidative metabolic reserve in patients with cardiac diseases of diverse etiologies and for assessment of the efficacy of interventions designed to enhance the recovery of metabolically comprised myocardium.

Developing strategies for improving the diagnostic and management efficacy of medical consultations.

To determine the clinical effects of internists' consultations to surgeons and other non-internists, we studied a random sample of 250 consultations provided by the Yale Medical Service to patients admitted on non-medical services during 1978-1979. We found that consultations changed or confirmed a diagnosis in 82% (205), and changed or confirmed a management plan in 69% (172). We also found that the diagnostic or management effects could be enhanced by several features of the way the consultation is performed: rapid response to the request for consultation; frequent follow-up notes by the consulting medical team; and detailed specifications of dosage and duration in recommendations for pharmacologic therapy.