Regional myocardial perfusion rates in patient with coronary artery disease

Pathophysiologic studies of the pulmonary and coronary circulations in man

Studies of the pulmonary circulation in normal man, performed with external radiation detectors, have shown that pulmonary blood volume is about 10% of total blood volume. Pulmonary blood volume was unchanged in patients with acute or chronic left atrial hypertension and in normal persons during expansion of total blood volume in spite of marked increases in pulmonary vascular pressures. However, pulmonary blood volume was greatly increased in patients with polycythemia rubra vera and a large total blood volume and in patients with a left to right shunt but normal pulmonary intravascular pressure. Studies of regional myocardial perfusion with injection of xenon-133 solution into the left coronary artery revealed localized areas of ischemia distal to stenotic lesions even when the patient was at rest. During angina produced by pacing, more severe ischemia occurred, thus suggesting that functional factors reduce local perfusion below resting levels. In patients with "variant" angina, intravenous injection of thallium-201 chloride during spontaneous attacks has revealed large cold areas in myocardial scintigrams not present under control conditions, thus suggesting severe transmural reduction of perfusion in heart muscle corresponding to S-T segment elevation in the electrocardiogram.

Regional myocardial blood flow during hyperemia induced by contrast agent in patients with coronary artery disease

Regional myocardial specific blood flow (regional specific flow) was measured at rest and during contrast hyperemia after the intracoronary injection of xenon-133. The changes in regional specific flow were transient, resulting in some compromise in one of the underlying restraints of the inert gas washout method, namely, the presence of a steady state. Therefore, to determine the clinical utility of this technique, regional specific flow values obtained with this method were correlated with the presence and severity of coronary artery disease as assessed from the coronary arteriogram and left ventriculogram. Regional specific flow during contrast hyperemia was 186+/- 11 (mean +/- 1 standard error of the mean) ml/min per 100 g in control patients and 115+/-5 in patients with coronary artery disease. There was an inverse relation between regional specific flow during contrast hyperemia and the percent coronary stenosis when the stenosis was 40 percent or greater (r = 0.70, P less than 0.001). Regional specific flow was significantly less in patients with asynergy (77 +/- 10 ml/min per 100 g) than in patients with normal ventricular function (105 +/- 5) distal to coronary stenoses of greater than 75 percent. Thus regional specific flow measured during contrast hyperemia using the xenon washout technique and the Anger camera differentiated patients with normal coronary arteriograms from those with coronary artery disease. With this technique, good correlation was shown between regional specific flow and the percent coronary stenosis and presence of ventricular wall abnormalities. The information obtained with this method may provide prognostic information concerning suitability for surgical intervention.

Studies of regional myocardial blood flow: results in patients with left anterior descending coronary artery disease

Measurements of regional myocardial blood flow have been performed rapidly and safely in man at the time of coronary arteriography. Xenon-133 was injected into the coronary artery and estimates of myocardial capillary perfusion were made by computer analysis of the multiple precordial tracer washout curves recorded with a scintillation camera. Blood flow rates/100 g/min in different areas of the heart were calculated by the Schmidt-Kety formula, using an assumed partition coefficient, and were related to the coronary vascular lesions by landmarks provided by the arteriograms. The flow significance of lesions was assessed by making measurements at rest and during interventions that increase coronary blood flow. Perfusion was also estimated in areas supplied by collateral vessels, and regions of scar were detected from the initial distribution of peak tracer activity. In patients with less than 50% obstructions apparent on coronary arteriograms and in those with greater than 50% isolated left anterior descending lesions average mean left ventricular (LV) myocardial perfusion values were not reduced below values found in patients with normal coronary arteries and normal cardiac function. However, in patients with significant two-vessel disease (LAD + right, LAD + circ) mean LV perfusion was significantly reduced. Average regional myocardial perfusion distal to significant lesions was not selectively reduced below the remainder of the ventricle unless the lesions were 100% obstructions. However, both total and distal regional myocardial perfusion increased less in 12 patients with greater than 50% lesions than in 12 others with normal arteriograms or less than 50% lesions. Subnormal flow responses in all of the former group were associated with angina pectoris compared with no angina in the latter. The studies indicate the potential utility of the measurements of regional myocardial blood flow in the evaluation of patients with ischemic heart disease who are potential candidates for myocardial revascularization procedures.

Regional myocardial perfusion during atrial pacing in patients with coronary artery disease

Regional myocardial perfusion (RMP) was measured with 133xenon and a multiple-crystal scintillation camera at rest and during atrial pacing in 24 patients with normal coronary arteriograms or less than 50% lesions, Group I, and in 24 with significant (greater than 50% lesions) left coronary artery disease (CAD), Group II. Pacing induced increases in the double product (DP) of heart rate and systolic blood pressure, an index of myocardial oxygen consumption, were not different for Groups I and II. In Group I average mean LV perfusion rate was subnormal at rest but rose from 49 to 73 ml/100 g-min during pacing to 150/min without angina. A response index (RI), (deltaMP X 10(3)/deltaDP), averaged 2.93. Twenty patients in Group II developed angina during pacing. The average mean LV perfusion rose less than in Group I, from 48 to 64 ml/100 g-min (P less than 0.05) and the average RI, 1.76, was lower (P less than 0.01). In 19 of these patients, average RMP distal to the major coronary lesion increased from 46 to 58 ml/100 g-min; this increase during pacing was significantly less than in the remainder of the LV of 48 to 66 ml/100 g-min (P less than 0.05). Average regional RIs were 1.39 and 2.18, respectively. In three patients the presence of collaterals termed adequate by radiological criteria was not associated with preferential decreases in the distal regional RI. The data support the hypothesis that in some patients with CAD, angina pectoris results when an obstructive coronary lesion restricts the total or regional myocardial blood flow response to an increased rate of myocardial oxygen consumption.

Evaluation of perfusion with the 81Rb-81mKr generator

The development of the 81Rb-81mKr generator-delivery system has made available an ultrashort (13-sec) half-life radionuclide for continuous, constant-rate delivery as a gas, or as an isotonic, nonionic solution in 5% dextrose and water. This system has been evaluated and applied to the scintigraphic imaging of various organs and anatomic regions by intravenous and intraarterial infusion and by inhalation and deglutition. This diffusible, noble gas is inert chemically and biologically. When the gas is administered intraarterially, the volume of tissue being perfused may be defined with the scintillation camera. The 13-sec half-life is of a similar magnitude to the rate of capillary exchange, producing a heterogeneous image with steady-state administration in which the intensity of detectable radioactivity is proprotional to the time of diffusion into the tissue. This system appears capable of defining the rate of capillary exchange and the moment-to-moment changes brought about by vasoactive stimuli in specific organs.

Regional differences in lactate concentration in experimental myocardial infarction

Lacate concentrations were measured in blood from (a) coronary veins within ischaemic myocardium and (b) veins nearer to the coronary vein, for periods of up to 2 1/2 hours after ligation of the left anterior descending artery in dogs. Concentrations at (a) were three to four times higher than at (b), while blood sampled simultaneously from two veins at (a) yielded similar concentrations of lactate. At 2 1/2 hours after ligation the veno-arterial difference of lactate concentration in blood from (a) was about one half of the difference at 15 minutes. Lactate concentration at (a) was approximately twice as great when the area of ischaemic myocardium drained by the vein was large (18 not equal to 1% of heart weight) than when it was small (6 not equal to 1% of heart weight). No close correlation was apparent between the height of epicardial ST-segment elevation and the level of lactate release. These experiments extend previous observations that changes in lactate concentration at a given site may reflect changes in venous dilution, rather than in the rate of production of lactate, and emphasize that caution is necessary in interpretation of changes in concentrations of metabolites in coronary sinus blood after acute myocardial infarction in man.

The relationship between regional myocardial perfusion at rest and arteriographic lesions in patients with coronary atherosclerosis

Measurements of mean left ventricular (LV) and regional myocardial blood flow rates were made at rest in 161 patients with 133Xe and a multiplecrystal scintillation camera. Myocardial perfusion rates were correlated with assessments of the degree of coronary artery disease made from the arteriograms obtained during the same studies. In patients with normal coronary arteries without heart failure, the presence of hypertension, aortic stenosis, or aortic insufficiency was not associated with changes in mean LV perfusion from the control value of 61+/-7 ml/100 g-min. However, mean LV perfusion was significantly reduced in patients with normal coronary arteries who had cariomyopathy and impaired ventricular performance. Mean LV perfusion was not significantly different from control values in patients with "mild" coronary artery disease (less than 50% obstruction) or in patients with significant isolated disease (greater than 50% obstruction) of the left anterior descending (lad) artery. Significant reductions in mean LV perfusion were found in patients with greater than 50% obstruction of two coronary arteries (LAD + right or LAD + circumflex) and in patients with triple-vessel disease. The average perfusion rate for regions distal to LAD obstructions in patients with isolated LAD disease was not lower than the LAD perfusion in control patients, but was significantly reduced in patients with LAD + right coronary artery disease (43+/-14 ml/100 g-min). In the latter group average perfusion distal to the LAD lesion was significantly lower than the average regional perfusion rate for the remainder of the LV. However, the mean blood flow rate for the remainder of the LV was also significantly lower than control values despite the lack of significant circumflex disease. The data demonstrate that the presence of radiographically "mild" or significant isolated LAD coronary disease is not associated with reductions in mean LV perfusion at rest, but that mean LV perfusion is reduced in the presence of significant disease of two or three coronary artieries. None of the patients experienced angina during the resting studies and most had clinical evidence of ventricular failure. The observation of depressed LV perfusion in this group, as in the patients with cardiomyopathy, raises the possibility that a lowered resting blood supply may be adequate for a reduced level of performance of a diseased ventricle. The lack of selective reductions of regional perfusion at rest in the majority of the patients with LAD lesions suggests that regional myocardial blood flow must be measured during an intervention which increases myocardial oxygen consumption in order to assess the physiological significance of lesions which are observed at coronary arteriography.

Measurement of regional myocardial blood flow in man: description and critique of the method using xenon-133 and a scintillation camera

A method has been devised to measure regional myocardial blood flow in man. The approach consists of selective injection of xenon-133 into a coronary artery and the external monitoring of radioisotope washout curves from multiple areas of the myocardium with a multiple crystal scintillation camera. Rate constants of isotope washout are calculated using a monoexponential model, and the capillary blood flow rates in multiple regions of the heart are calculated by the Kety formula. The pattern of perfusion rates is related to the coronary arteriogram obtained in the same study. Myocardial perfusion patterns obtained in patients with and without coronary artery disease and during atrial pacing are given, as well as examples of results obtained in myocardial aneurysms, in regions of ischemic myocardium supplied by collateral vessels and after tracer injection into an aortocoronary bypass graft. Advantages of the method are discussed along with limitations related to the tracer, the scintillation camera, the form of mathematical analysis and the three dimensional nature of the heart.

Effects of nitroglycerin on the major determinants of myocardial oxygen consumption. An angiographic and hemodynamic assessment

A direct and quantitative study of the effects of sublingually administered nitroglycerin on the major determinants of myocardial oxygen consumption was carried out in 10 patients, 7 with coronary artery disease. Left ventricular wall tension, estimates of the contractile state and heart rate were studied directly using simultaneous pressure measurements and angiographically obtained volume determinations. The peak systolic left ventricular wall tension decreased 15 percent after administration of nitroglycerin, suggesting a diminished myocardial oxygen requirement. Increased myocardial oxygen requirements were suggested by the occurrence of both positive chronotropic and inotropic effects. Heart rate increased 15 percent. The mean circumferential fiber shortening velocity increased 26 percent and the ejection fraction 30 percent; these findings, in association with a 23 percent reduction in left ventricular end-diastolic volume, were considered consistent with an increase in the contractile state. The mechanism of action of nitroglycerin seems to relate best to the decrease in systolic wall tension. The end-diastolic tension decreased 57 percent, suggesting the possibility that diastolic coronary blood flow may be augmented by diminished extravascular resistance to flow.

Regional myocardial blood flow measurements before and after coronary bypass surgery. A preliminary report

Myocardial blood flow in 16 patients before and after coronary bypass surgery in conjunction with coronary angiography, left ventricular function measurement, and graded exercise test. Radioactive 133-Xe was injected into the coronary artery or bypass graft and the washout was recorded by an Anger camera. Myocardial blood flow increased in 11 out of 14 patients and decreased in three patients. The average flow was 55 (plus or minus 6) preoperatively and 96 (plus or minus 10) ml 100 g/min postoperatively. Increase of blood flow occurred in both the bypassed left anterior descending coronary artery (LAD) region and the nonbypassed left circumflex coronary artery (LCIR) region. The postoperative flow increase and the absolute postoperative flow values are higher with saphenous vein than with mammary artery grafts. Statistically significant correlation is not found between myocardial blood flow changes and exerice tolerance. The volume measurements (end diastolic volume, stroke volume, ejection fraction) remained unchanged.

Myocardial imaging with indium- 113m- and technetium-99m-macroaggregated albumin. New procedure for identification of stress-induced regional ischemia

Regional coronary blood flow distribution was studied by myocardial imaging after intracoronary injection of technetium-99m- and indium-113m-macroaggregated albumin at rest and during coronary hyperemia induced by intracoronary injection of Hypaque-M, 75 percent. The four- to five-fold increase in coronary flow after injection of radiographic contrast material was similar in magnitude to that occurring with maximal exercise stress. Experimentally, resting coronary blood flow and regional distribution of radioactive particles remains normal in spite of coronary stenosis of up to 85 percent. Less severe stenosis causes flow and distribution abnormalities only during periods of increased flow, and the degree of maldistribution is directly related to the physiologic severity of the stenosis. Of 49 patients with suspected coronary artery disease, 10 had no significant lesions by coronary arteriography and all had normal images at rest and during coronary hyperemia. Thirty-seven of 39 patients with significant obstructive coronary artery disease had abnormal images at rest or during contrast agent-induced hyperemia, or both. Patients with significant coronary artery disease without previous infarction usually demonstrated abnormalities in flow distribution only during coronary hyperemia. Patients with previous infarction demonstrated resting perfusion abnormalities that often became more abnormal during hyperemia. This technique provides a new method for assessing the physiologic effects of coronary stenosis in conjuntion with coronary arteriography.

Radionuclides and the patient with coronary artery disease

The emergence in the past 20 years of nuclear medicine as a distinct diagnostic discipline has been a major clinical advance. The relatively rapid evolution from the small laboratory limited primarily to the study of thyroid disease to the large unit in which radioactive tracers (radionuclides) are utilized to evaluate structure and function of most organ systems has been accelerated by major advances in instrumentation, new radioactive tracers and application of computer techniques. Application of these radionuclide techniques to the study of coronary artery disease has been quite recent, and has in part been limited by the need for a coordinated effort between the cardiologist and the specialist in nuclear medicine. However, realization of the potential usefulness of these techniques has fostered an increasingly productive liaison between the two specialties. The potential advantages of these radionuclides in evaluating patients with cardiovascular disease is twofold: first, they may permit the noninvasive or atraumatic acquisition of data that might otherwise be obtained only at the time of cardiac catheterization; second, and perhaps more important, they may permit the acquisition of physiologic measurements or observations not attainable by more conventional modes of study. Functionally, these techniques can be divided into those that evaluate cardiac performance and those that evaluate coronary blood flow, regional myocardial perfusion and myocardial viability.

Quantitative evaluation of coronary perfusion in man

The usefulness and limitations of currently available techniques for quantitating coronary flow in ischemic heart disease are summarized. There are appreciable difficulties in assessing coronary flow solely from an arteriographic evaluation of the epicardial arteries. There is a considerable reserve mechanism for vasodilation at the arteriolar level, and a proximal occlusive lesion produces a reduction in flow only after this distal reserve has been exhausted. In addition, small increments in the severity of established lesions sometimes cause profound reductions in flow. The development of clinically useful flow measurements has been impeded by methodological problems related to nonuniformity of flow within the left ventricle in coronary artery disease. Validation of specific techniques for abnormal situations is difficult but possible and should probably be a prerequisite to the clinical application of any technique. When a methodologically appropriate technique is employed, average left ventricular flow per unit weight is found to be reduced systematically at rest in patients with double- and triple-vessel disease. This reduction is a group difference, however, and is not always evident in individual patients. Accordingly, more recent measurements have concentrated on the assessment of regional perfusion, and two general approaches, selective venous sampling and selective precordial sampling are illustrated. While only preliminary measurements of regional flow are available, it is clear that these measurements offer a more sensitive tool for detecting abnormalities of flow in individual patients and thereby for contributing to the management of specific clinical problems. Measurements of regional flow need to be performed during stress as well as at rest. For the future, there is also need for techniques which can assess transmural variations of flow in man and relate measurements of regional flow to regional oxygen demand. Because of the complexity of current techniques which are methodologically adequate, measurements of coronary flow will, for the immediate future, probably remain confined to clinical centers which have a special interest in them. The effort in these centers will hopefully include significant emphasis on the refinement of existing techniques so that they are more widely applicable.

Average coronary blood flow per unit weight of left ventricle in patients with and without coronary artery disease

Average left ventricular flow per unit mass (F/W) has been evaluated at rest in 20 normal individuals and 26 patients with arteriographically proven, advanced coronary artery disease, using inert gas techniques modified to take into account methodological problems presented by heterogeneous perfusion within the ventricle. Preliminary studies in a canine model in which corornary flow could be measured directly before and after coronary occlusion indicated (1) that inert gas techniques utilizing venous sampling are suitable for abnormal situations when appropriately long periods of saturation and desaturation, and careful resolution of prolonged venous-arterial differences, are employed; and (2) that traditional inert gas methods are not adequate when F/W is abnormally heterogeneous. Using helium as a tracer, coronary disease patients showed a systematic reduction, in comparison to normal individuals, in average left ventricular F/W at rest (54 ± 11 vs 70 ± 13 ml/min/100 g, P < 0.01). Simultaneous studies with traditional nitrous oxide and krypton techniques did not show this difference because of the methodological limitations of these techniques in the presence of abnormally heterogeneous F/W. We conclude: (1) that useful, accurate measurements of F/W can be obtained in coronary disease if appropriate methodological precautions are taken; and (2) that appreciable portions of the left ventricle have an abnormally low F/W, even at rest, in patients with advanced coronary disease.

Measurement of regional cerebral blood flow with 133xenon and a multiple-crystal scintillation camera

A method was devised to measure gray and white matter cerebral blood flow simultaneously in multiple regions of the brain using 133 Xenon and a multiple-crystal scintillation camera. Following magnification cerebral arteriography, 133 Xe was injected into the internal carotid artery and the washout of tracer was monitored with a scintillation camera which consists of 294 individually collimated NaI (TI) crystals. These data, obtained from each crystal overlying the brain, were processed by a weighted least-squares nonlinear regression technique. The blood flow rates of the rapid and slow compartments were calculated by the Kety-Schmidt formula along with 95% confidence limits for each measurement.

In four patients, local increases or decreases in regional cerebral flow were correlated with areas of pathology. In one patient with a cerebral arteriovenous malformation, regions of local shunting of tracer were identified. Application of a three-compartment analysis to these curves permitted estimation of the magnitude of shunting along with gray and white matter flow in the lesion. The increased discrimination provided by the multiple-crystal camera and the estimates of measurement accuracy obtained by this mathematical analysis may facilitate more precise localization of regional blood flow abnormalities in intracranial disease.

Rest and exercise potassium-43 myocardial perfusion imaging for the noninvasive evaluation of aortocoronary bypass surgery

Sixteen patients undergoing aortocoronary bypass surgery were evaluated with rest and exercise potassium-43 ( 43 K) myocardial imaging and contrast angiography an average of 5.5 months postoperatively. The results of 43 K imaging allowed the division of these patients into two groups. Group 1 consisted of patients in whom there was either normalization or significant improvement in postoperative images when compared to abnormal preoperative studies (five patients), or patients in whom preoperative imaging was not accomplished but whose postoperative images both at rest and exercise showed a normal homogenous pattern of 43 K distribution (four patients). All patients in this group had at least one patent bypass graft, and 13 of 16 total grafts were patent. Group 2 consisted of seven patients in whom postoperative rest and exercise 43 K studies were either not significantly different from preoperative evaluation, or had worsened. Of these patients, three experienced intraoperative infarction, two demonstrated significant distal native coronary disease, and one had a single occluded graft. In both groups there was good correlation between the anatomic sites of graft patency or occlusion and the location of either increased perfusion or lack thereof on the 43 K image. Perfusion abnormalities occurring in the presence of occluded grafts, or improvement in perfusion occurring in the presence of patent grafts were best appreciated by comparison of exercise images. Abnormalities occurring in the presence of infarction were detected at rest as well. Thus, in this initial group of patients, 43 K rest and exercise myocardial imaging appeared to offer a sensitive noninvasive means of evaluating the results of aortocoronary bypass surgery.

Total and effective coronary blood flow in coronary and noncoronary heart disease

There are no data available concerning total coronary blood flow to the whole heart (CBF) in man. "Effective" or "nutrient" coronary blood flow to the whole heart (MBF), supposedly a measure of flow through exchanging channels of the coronary circulation, has been measured but its validity has not been established. Accordingly, CBF and MBF were measured in 9 normal subjects, 26 patients with coronary heart disease (CHD), and 19 with noncoronary, mostly valvular heart disease (NCHD), by coincidence counting 84Rb technique. Two methods were used: single bolus (24 cases) and continuous infusion (30 cases). Various other parameters including myocardial oxygen utilization (MVO2) and lactate extraction ratio were determined. In the normal subjects CBF (386 +/- 77 ml/min) was significantly higher (P < 0.05) than in CHD (288 +/- 124 ml/min) and NCHD (292 +/- 111 ml/min). Likewise the normal MBF (380 +/- 81 ml/min) was significantly higher (P < 0.01) than in CHD (251 +/- 105 ml/min) as well as NCHD (258 +/- 104 ml/min). The myocardial Rb extraction ratio epsilon Rb) was significantly lower in normal subjects (39 +/- 9%) than in CHD (50 +/- 7%) and NCHD (52 +/- 11%) and this supports the view that epsilon Rb is flow-dependent. In both CHD and NCHD there was significant diminution of MVO2 as well as CBF. In CHD this was accompanied by a significant anaerobic trend but in NCHD it was not. It might therefore appear that in CHD, MVO2 is determined by perfusion whereas in NCHD, perfusion is determined by MVO2. In comparing CBF with MBF by paired observation testing, there was no significant difference in the normals (P > 0.3), whereas the differences were significant in CHD (P < 0.01) and NCHD (P < 0.02). This was merely a reflection of a reduced ratio of myocardial to total body epsilon Rb in CHD and NCHD, and available evidence indicates that this may be an expression of depressed transport of Rb+ rather than true shunting.

Intraoperative coronary collateral function in patients with coronary occlusive disease. Nitroglycerin responsiveness and angiographic correlations

To elucidate the direct influence of nitroglycerin on coronary collateral function in patients and to clarify the relation between angiographic appearance and functional performance of coronary collaterals, we measured retrograde flow and peripheral coronary pressure (PCP) before and after nitroglycerin in patients undergoing saphenous vein bypass. Measurements were made via the distally (but not proximally) attached vein graft while the coronary artery receiving the graft was totally occluded proximal to the site of graft attachment. Nitroglycerin (100 to 150 mcg bolus and 100 mcg/min) was infused into the ascending aorta in 29 patients. Baseline measurements revealed: aortic pressure mean 79 mm Hg, PCP 30 mm Hg, retrograde flow 2.7 ml/min, and collateral resistance 28.5 mm Hg/ml/min. Following nitroglycerin, mean aortic pressure decreased 18% but retrograde flow was not consistently changed; thus collateral resistance fell significantly (average 28%, P < 0.05). Similarly, collateral resistance fell (mean 50%) in eight individuals in whom aortic pressure changes were attenuated by altering systemic flow. If calculated as a fraction of aortic pressure, PCP increased 9.9% ( P < 0.02), a finding consistent with enhanced collateral flow. Our results suggest that nitroglycerin can diminish resistance to collateral flow despite severe multivessel involvement. Comparison of baseline data with preoperative angiography revealed a correlation between the size and extent of coronary collaterals and physiologic evidence of collateral function. Thus, angiographic appearance of coronary collaterals accurately predicts collateral function during bypass surgery.

Differentiation of physiologically significant coronary artery lesions by coronary blood flow measurements during isoproterenol infusion

At cardiac catheterization, the effect of isoproterenol on coronary blood flow was compared in six patients with normal coronary arteries and normal left ventricular function, and eight patients with angiographically defined coronary lesions. Coronary blood flow was measured by selective coronary artery injection of xenon-133 and external monitoring of disappearance curves with a dual probe, digital scintillation counter. Resting values did not differ in the two groups. In the normal group isoproterenol increased mean coronary blood flow 93 ml/100 g/min (152%) and cardiac output 2.3 liters/min (42%); coronary resistance/100 g decreased 60 ± 4% ( sem ), while total peripheral resistance decreased 29 ± 4%. In the coronary disease group coronary blood flow increased 20 ml/100 g/min (33%) and cardiac output increased 2.8 liters/min (62%); coronary resistance decreased 26 ± 9% and total peripheral resistance decreased 37 ± 4%. In all normal patients the percent increase in coronary blood flow markedly exceeded the percent increase in cardiac output and the percent fall in coronary resistance markedly exceeded the percent fall in total peripheral resistance. In six of the eight patients with coronary lesions the percent increase in coronary blood flow was less than the percent increase in cardiac output and the fall in coronary resistance was less than the fall in total peripheral resistance. Thus measurement of coronary blood flow, cardiac output, and aortic pressure before and during isoproterenol infusion may permit differentiation of those subjects with physiologically significant coronary obstructions.

Regional myocardial blood flow in patients with residual anterior and inferior transmural infarction

Regional myocardial perfusion rates were estimated in ten patients with a residual transmural anterior wall infarction and ten patients with a residual transmural inferior infarction. The results in these two groups of patients were compared to the regional myocardial perfusion patterns obtained in 25 patients with normal coronary arteriograms who failed to demonstrate any electrocardiographic evidence of a myocardial infarction. Clearance rates of xenon-133 from multiple areas of the heart were monitored externally with a multiple-crystal scintillation camera following selective injection of the isotope into either coronary artery. Local myocardial blood flow rates were calculated by the Kety formula.

In patients with normal coronary arteriograms, mean myocardial perfusion rates in the left ventricle (62 ml/l00g/min) exceeded flow rates in the right ventricle and atrium. There was slight inhomogeneity of local perfusion rates but no significant differences among major subregions (anterior descending, diagonal, or circumflex) within the left ventricle.

In the group with an anterior transmural infarction, myocardial blood flow rates were significantly depressed (44 ml/l00g/min) and asynergy was present in the region of the left ventricle supplied by the anterior descending artery, which was >80% narrowed. Diminished capillary blood flow was found in the right ventricular region in the patients with an inferior transmural infarction and right coronary artery narrowing of >80%. There was no evidence of nutrient flow to the inferior surface of the left ventricle after right coronary 133 Xe injection.

The data indicate that myocardial perfusion was reduced in regions of the heart which correspond to the electrocardiographic and angiographic location of residual transmural infarction. The perfusion rates observed in areas showing electrocardiographic evidence of transmural infarction and regional ventricular asynergy, although subnormal, were surprisingly high and suggested the presence of residual viable myocardial cells.

Measurement of regional myocardial perfusion in man with 133 xenon and a scintillation camera

A method was devised to quantitate regional capillary perfusion in the human heart by measuring the clearance constants (k) of Xenon-133 washout from multiple areas of the myocardium with a multiple-crystal scintillation camera. In 17 subjects, (133)Xe was injected into the right or left coronary artery or both and counts per second (cps) were recorded simultaneously on magnetic tape from each of 294 scintillation crystals viewing the precordium through a multichannel collimator. Data were processed by a digital computer. Crystals detecting the myocardial washout of (133)Xe were distinguished from those monitoring pulmonary excretion by positioning radioactive markers at the cardiac margins, and by a computer printout of the peak cps recorded by each crystal and its time after isotope injection into the coronary artery. The slopes of the initial segment of the multiple (133)Xe curves obtained in each study were calculated by the method of least squares using a monoexponential model. Myocardial blood flow rates in the cardiac regions viewed by the individual crystals were calculated (assuming a blood to myocardium partition coefficient of 0.72) along with the SD of every flow measurement. The pattern of myocardial perfusion rates so obtained was superimposed over a tracing of the subject's coronary arteriogram. Scintiphotographs showing the arrival and washout of isotope from various regions of myocardium and the area of tissue perfused by each coronary artery were obtained by replaying the data tape on an oscilloscope. Significant regional variations in local myocardial perfusion rates were observed in hearts with normal coronary arteries. When capillary flow measurements from crystals overlying the various cardiac chambers were averaged in each subject, the mean myocardial blood flow rate of the left ventricle in 17 patients, 64.1 +/-13.9 (SD) ml/100 g.min, significantly exceeded that of the right ventricle, 47.8 +/-10.9 ml/100 g.min, and of the right atrial region, 33.6 +/-10.3 ml/100 g.min. The approach may facilitate more objective assessment of: myocardial capillary perfusion in patients with angina pactoris, the pharmacology of antianginal drugs, and the efficacy of surgical procedures to revascularize ischemic myocardium.