Regional myocardial blood flow

Transmural myocardial perfusion

The predilection for subendocardial underperfusion and ischemia is great and must be considered in the management of any patient, especially if there is coronary artery disease or ventricular hypertrophy. Although the mechanisms of subendocardial ischemia remain to be fully defined, they are clearly associated with the transmural distribution of intramyocardial systolic pressures. Even though almost all the myocardium is perfused in diastole, a reduction of diastolic perfusion pressure or duration will result in subendocardial ischemia. The factors that produce subendocardial ischemia are all associated with a reduction or loss of coronary flow reserve, and as our ability to measure flow reserve in humans improves, it is likely that we will be able to select medical or surgical therapy that will minimize or abolish subendocardial ischemia. For example, it will someday become possible to choose a time for valve replacement in an asymptomatic patient to obtain maximal protection of the myocardium or to select the right combination of therapies for the immediate post-operative period so that as much myocardium as possible will be spared. The more we learn to understand the mechanisms of subendocardial ischemia, the sooner will we be able to achieve these desired ends.

Regional blood flow in canine myocardium as determined by local washout of a freely diffusable radioactive indicator

The aim of this study has been to examine the utility of the washout of a freely diffusable radioactive indicator as a measure of regional myocardial blood flow in open-chest anesthetized dogs. The method employed was direct intramyocardial injection of Xenon-133 followed by measurement of its gamma-radiation. The experimental washout curves show, after a short acceleration period, monoexponential washout of the indicator over two decades. We found indications of insignificant veno-arterial shunting by diffusion of the blood flow level measured, insignificant arterial recirculation of the indicator, and minimal radioactive contribution to precordial residue versus time curves arising from right heart or non-myocardial tissue. We suggest that diffusion equilibrium between the tissue in the counting field and the blood leaving it is maintained during the linear down slope of two decades of the clearance curve, and that local blood flow can be calculated from washout rate constant obtained from this part of the curve. The method employing intramyocardial injection of Xenon-133 was found to give the same results as atraumatic epicardial labelling indicating negligible effect of the injection trauma and supporting the validity of the local injection method using small volumes (2-10 microliter).

Assessment of the efficacy of interventions to limit ischemic injury by direct measurement of intramural carbon dioxide tension after coronary artery occlusion in the dog

Although numerous interventions have been shown to exert a salutary effect on the ischemic myocardium, the severity of ischemia generally has been measured by indirect techniques. In the present investigation the effect of ischemia on intramural carbon dioxide tension (PmCO(2)) was measured directly in the open-chest, anesthetized dog with a mass spectrometer during repetitive 10-min coronary artery occlusions separated by 45-min periods of reflow; simultaneously, regional myocardial blood flow in the ischemic area was measured by (127)Xenon washout. In all dogs the increase in PmCO(2) from before to 10 min after the first occlusion (DeltaPmCO(2)) exceeded that during subsequent occlusions. In those dogs not receiving an intervention (controls), DeltaPmCO(2) during the third occlusion was similar to that during the second occlusion. When propranolol, hyaluronidase, and nitroglycerin were administered to different groups of dogs before the third occlusion, each caused significantly smaller elevations in DeltaPmCO(2) than those occurring during the control second occlusion, and the combination of all three interventions induced the smallest increase in DeltaPmCO(2). Regional myocardial blood flow rose with hyaluronidase and was unchanged with propranolol, nitroglycerin, and the three drugs in combination. In contrast to these beneficial interventions, isoproterenol infused with the third occlusion caused a higher DeltaPmCO(2) than during the control second occlusion. It is concluded, first, that interventions that modify the severity of ischemia can be evaluated by measuring intramural carbon dioxide tension; second, that propranolol, hyaluronidase, and nitroglycerin reduce ischemic injury, whereas isoproterenol increases it; and third, that the combination of propranolol, hyaluronidase, and nitroglycerin exerts an additive beneficial effect on ischemia.

Quantification of infarction in cross sections of canine myocardium in vivo with positron emission transaxial tomography and 11C-palmitate

To assess myocardial infarction quantitatively in 15 mm thick transverse sections of the canine heart in vivo we utilized a new technique, positron emission transaxial tomography (PETT) and cyclotron-produced 11C-palmitate (11C-P) injected intravenously. Results were compared to regional myocardial creatine phosphokinase (CPK) depletion, diminished 14C-palmitate accumulation in tissue extracts, and infarction estimated morphometrically 48 hours after coronary occlusion. CPK activity and 14C-P content declined in parallel in transmural biopsies (N=44) from normal and ischemic zones (r=.92) in six dogs; and infarct in 10 mm thick cross sections of the entire left ventricle estimated morphometrically (N=26) in six other animals correlated with CPK depletion in contiguous 2.5 mm thick slices (r=.92). When the percentage of infarction in 15 mm thick cross sections was assessed tomographically in six other dogs 48 hours after coronary occlusion with 11C-P injected intravenously, results correlated with infarction in corresponding cross sections from the same hearts estimated morphometrically (r=.97, N=9) and by analysis of CPK depletion (r=.93, N=9). Thus, PETT permits estimation of infarction in cross sections of the left ventricle in vivo after intravenous injection of 11C-palmitate.

Particulate myocardial perfusion scintigraphy: its clinical usefulness in evaluation of coronary artery disease

The determination of myocardial viability is a crucial parameter in the evaluation of a patient with coronary artery disease. Particulate myocardial perfusion scintigraphy (PMPS) is one of several methods available for this determination. A brief comparison between PMPS and two other commonly used methods is described in this review. The technique and analysis are described and applied to 194 patients with 366 surgically bypassed regions. The patients are analyzed for postoperative regional wall function and for total ventricular function as expressed by ejection fraction. PMPS is a highly accurate and unique study for clinically predicting myocardial viability.

Myocardial blood flow in congestive and hypertrophic cardiomyopathy: relationship to peak wall stress and mean velocity of circumferential fiber shortening

Myocardial blood flow/unit mass (MBF) and the determinants of myocardial oxygen consumption were measured in seven control subjects (group I) and 15 patients (pts) with cardiomyopathy (CM), group II (group IIa-congestive CM: 10 pts; group IIb-hypertrophic CM: 5 pts). In group I left ventricular (LV) MBF was 64 +/- 8 (SD) ml/100g-min; it was significantly lower in IIa (45 +/- 15 ml/100g-min, P less than 0.01) and IIb (39 +/- 7 ml/100g-min, P less than 0.01). However, calculated total LV flow (LV mass X MBF) was increased in the two CM groups. In nine CM pts, LV MBF increased in response to atrial pacing from 41 +/- 7 to 63 +/- 13 ml/100g-min. In group IIa, calculated peak wall stress was normal (4.39 +/hortening (MVcf) was significantly reduced (0.53 +/- 0;18 vs 1.26 +/- 0.12 circum/sec, P less than 0.01). In IIb, MVcf was normal but peak stress was significantly reduced (2.80 +/- 0.75 vs 4.51 +/- 1.10 dynes/cm2 X 10(5), P less than 0.05). Multiple regression analysis based on all pts yielded, MBF - 16.9 MVcf + 9.30 Stress + 0.26 Heart Rate - 26.4 (r=0.79). The data indicate that MBF is reduced in CM patients and the regression analysis suggests that MBF in these 22 pts with normal coronary arteriograms was determined largely by heart rate, peak stress, and ventricular performance.

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.

The effect of aortocoronary bypass grafts on myocardial blood flow reserve and treadmill exercise tolerance

Twenty-five patients had myocardial blood flow reserve determinations (percentage increase in myocardial blood flow with stress), treadmill exercise tests and coronary and bypass cineangiography pre- and postaortocoronary bypass surgery. Twenty of the patients had the postoperative studies performed three months after operation, three at two months and two at five and six months, respectively.

Eleven of the 25 patients had all significant coronary artery obstructions (75% or greater) bypassed and all grafts were open at the time of restudy. Preoperatively, blood flow reserve had been abnormal in nine and all had positive treadmill tests. Postoperatively, all eleven patients had normal myocardial blood flow response to stress and treadmill tests were negative in ten (one patient was not restudied on the treadmill).

In six patients, no patent grafts could be demonstrated. These patients continued to show abnormal blood flow reserve and positive treadmill studies.

Eight of the 25 patients had partial revascularization in that some grafts were open, some closed, and some significantly occlusive lesions were not bypassed. Four of these eight patients had normal flow and treadmill studies and the remainder continued to have an abnormal response to one or both of the measurements.

The relationship between treadmill exercise response, myocardial blood flow reserve, and graft patency was significant at the 0.005 level for patients with all grafts open or closed. No significant correlation was obtained between any of the measurements in those patients with partial revascularization.

The data indicate that successful aortocoronary bypass grafting provides myocardial revascularization as reflected in a return to normal of the myocardial blood flow reserve and response to treadmill stress testing.

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.

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.

Regional myocardial perfusion rates in patient with coronary artery disease

Regional myocardial perfusion rates were estimated from the myocardial washout of (133)Xenon in 24 patients with heart disease whose coronary arteriograms were abnormal and 17 similar subjects whose coronary arteriograms were judged to be normal. Disappearance rates of (133)Xe from multiple areas of the heart were monitored externally with a multiple-crystal scintillation camera after the isotope had been injected into a coronary artery and local myocardial perfusion rates were calculated by the Kety formula. The mean myocardial perfusion rates in the left ventricle exceeded those in the right ventricle or atrial regions in subjects without demonstrable coronary artery disease. In this group there was a significant lack of homogeneity of local perfusion rates in left ventricular myocardium; the mean coefficient of variation of left ventricular local perfusion rates was 15.8%. In the patients with radiographically demonstrable coronary artery disease, a variety of myocardial perfusion patterns were observed. Local capillary blood flow rates were depressed throughout the myocardium of patients with diffuse coronary disease but were subnormal only in discrete myocardial regions of others with localized occlusive disease. Local myocardial perfusion rates were similar to those found in the group with normal coronary arteriograms in patients with slight degrees of coronary disease and in those areas of myocardium distal to marked coronary constrictions or occlusions which were well supplied by collateral vessels. In subjects with right coronary disease, the mean right ventricular perfusion rates were significantly subnormal; in seven subjects of this group perfusion of the inferior left ventricle by a dominant right coronary artery was absent or depressed. The average mean left ventricular perfusion rate of 12 subjects with significant disease of two or more branches of the left coronary artery was significantly lower than that of the group with normal left coronary arteriograms. In the patients with abnormal left coronary arteriograms, the average coefficient of variation of local left ventricular perfusion rates was significantly increased (24.8%). The studies provide evidence that coronary artery disease is associated with increased heterogeneity of local myocardial perfusion rates. They indicate that radiographically significant vascular pathology of the right or left coronary artery may be associated with significant reductions of myocardial capillary perfusion in the region supplied by the diseased vessel.

Determination of the site, extent, and significance of regional ventricular dysfunction during acute myocardial infarction

Infarct site, extent, and the degree of associated asynergy are major determinants of the hemodynamic consequences of myocardial infarction. Although conventional electrocardiography and vectorcardiography are routinely employed in assessing the location and size of infarction, they are relatively nonspecific. The newer techniques of high-frequency electrocardiography and isopotential mapping offer promise but have yet to undergo systematic evaluation. A rough measure of the extent of infarction is obtained from serum enzyme measurements. However, they furnish no information with regard to localization.

The region of infarction may be detected by precordial scanning following the intravenous or intracoronary injection of a radioisotope. The infarct may be revealed as an area of decreased perfusion (cold spot) or as an area to which a specific radioactive label is bound (hot spot). With the availability of newer radionuclides such as 43 potassium and the use of computer techniques, a more precise means of localizing and quantifying myocardial infarction may become available.

Optimal definition of asynergy is obtained with contrast angiography. However, the risk of this procedure has limited its use, to date, in acute myocardial infarction. Apex- and kinetocardiography, chest X-ray, and fluoroscopy often suggest regional ventricular dysfunction, but these techniques are not sufficiently specific. Newer noninvasive methods for objectively evaluating regional ventricular dysfunction are ECG-gated cardiac scintiphotography and radarkymography. With ECG-gated scintiphotography, end-diastolic and end-systolic cardiac isotope images are obtained following intravenous injection of 99m technetium-albumin. From these images, assessment of asynergy and extent and location of infarct can be made. With radarkymography, heart-wall motion is assessed and quantitated by tracking segments of the cardiac silhouette visualized on a cinefluorogram. These techniques are ideally suited to the acutely ill patient. Echocardiography is another noninvasive technique with potential application to the study of asynergy. However, at present, only posterior-wall motion can be measured.

At the time of surgery regions of infarction may be localized by means of chemical indicators (fluoroscein), isotope techniques, or epicardial electrocardiographic mapping. Recently much has been learned about the hemodynamics of myocardial infarction. Through the use of the techniques described, further insight into regional ventricular abnormality and extent and localization of myocardial infarction could be obtained. With this information better approaches to therapy and prognosis could be developed.

Many students of the coronary circulation must have noted that the ventricular zone affected by ligating a large coronary branch not only appears cyanotic and dilated, but that it seems to alter in its mode of contraction. The detailed and sequential changes in contraction are not easily followed by the unaided eye and so far have not been recorded myographically. The reasons for this were the lack of an adequate and suitable myograph and a technique for the application of one to a limited ventricular surface so that records obtained represent, at least reasonably well, changes in muscle length and not predominantly artifacts due to position changes, thrusts and vibrations of the vigorously beating ventricle. 1

Effects of nitroglycerin on regional myocardial blood flow in coronary artery disease

Regional myocardial blood flow before and after sublingual nitroglycerin was measured in 10 patients with coronary artery disease. During thoracotomy, (133)Xe was injected directly into the subepicardium in diseased regions of the anterior left ventricular wall, and washout rates were recorded with a scintillation counter. All disappearance curves were closely approximated by two exponential decays analyzed as two parallel flow systems by the compartmental method. The appearance of a double exponential decay pattern in diseased regions suggests that the slow phase was associated with collateral blood flow, although nonhomogeneous myocardium-to-blood partition coefficients for xenon cannot be excluded. Nitroglycerin increased the rapid phase flow in 9 of 10 patients and the slow flow in 7 of 10 patients. Average flow increased in 9 of the 10 patients (P < 0.01). Mean rapid phase flow in the control state was 110 ml/100 g per min and after nitroglycerin increased to 132 ml/100 g per min (P < 0.01); slow phase flow increased from 12 ml/100 g per min to 15 ml/100 g per min (P < 0.05). It is concluded that, under these conditions, nitroglycerin improves perfusion in regions of diseased myocardium in patients with coronary artery disease.

Regulation of coronary blood flow

Coronary blood flow is dependent upon arterial pressure, diastolic time, and small vessel resistance. The system is regulated to achieve a low flow high oxygen extraction and low myocardial Po(2). This setting is sensitive to change in oxygen needs. Regulation of blood flow occurs primarily through local intrinsic regulation, most likely through production of vasodilating metabolites in response to minimal degrees of ischaemia. Local regulation appears to dominate over remote regulation in most circumstances. Blood flow distribution to the myocardium is depth dependent as well as regional in variation. Both types of distribution of blood flow are profoundly disturbed in the presence of obstructive coronary atherosclerosis. This results in either concentric myocardial shells or patchy transmural zones of selective ischaemia with clear-cut but local abnormalities in metabolism and performance.

Coronary heart disease. Differential hemodynamic, metabolic, and electrocardiographic effects in subjects with and without angina pectoris during atrial pacing

Right atrial pacing was performed in 41 subjects with coronary heart disease. Twenty developed angina pectoris during pacing, while 21 did not. The extent of coronary artery disease, as judged by selective cinearteriography, was similar in the two groups. Both had significant increases in heart rate and pressure-time per minute, but there was no significant difference in either of these parameters between groups. Among the hemodynamic parameters measured, the only statistically significant change was in the cardiac index which fell slightly but significantly in the angina group. There were no differences in myocardial oxygen extraction either within each group or between groups. In the angina group, however, 14 of 20 subjects exhibited abnormal myocardial lactate metabolism during pacing. The mean change was highly significant (P < 0.01). In the nonangina group, eight of 21 subjects had abnormal lactate metabolism during pacing and the mean change was significant (P < 0.05). There was no correlation between abnormal lactate metabolism and electrocardiographic evidence of myocardial ischemia in either group. Sublingual nitroglycerin, given to five subjects with angina while pacing was continued, resulted in prompt relief of symptoms, but abnormal lactate metabolism and ST-segment depression were unaffected after 10 min. By contrast, when anginal symptoms were relieved in five subjects by cessation of pacing, symptomatic improvement was accompanied by marked improvement in lactate metabolism after 10 min. Although angina pectoris appears to be related statistically to subnormal left ventricular function and abnormal lactate metabolism, there is significant individual variation.

Visual assessment of regional myocardial perfusion utilizing radioactive xenon and scintillation photography

A method was devised to visualize the areas of left ventricle supplied by various coronary arterial branches utilizing scintillation photography and an inert radioactive gas which distributes instantaneously between coronary blood and perfused myocardial cells. From 1 to 5 millicuries of 133 Xe dissolved in saline solution was injected through a catheter into the anterior descending or posterior circumflex branch of the left coronary artery of 15 dogs. Scintillation images produced during arrival and washout of 133 Xe in the various regions of the heart were recorded by an image intensifier scintillation camera and high speed television monitor and were reproduced on Polaroid film during replay of the videotape on an oscilloscope. The resulting scintiphotographs defined the region of the left ventricle supplied by the coronary arterial branch. In nine of the dogs acute myocardial infarctions were produced by occluding one or the other branch of the left coronary artery. When 133 Xe was injected again into the coronary artery proximal to the occlusion, that area of the left ventricle that was deprived of nutrient blood flow was no longer visualized on the gamma-ray scintiphotograph. The results indicate that regional myocardial perfusion may be dynamically visualized in the intact animal.

Effects of heterogeneous myocardial perfusion on coronary venous H2 desaturation curves and calculations of coronary flow

The present investigation was intended to evaluate myocardial inert gas desaturation curves for manifestations of heterogeneous coronary perfusion. The test gas was hydrogen (H(2)) and blood H(2) analyses were performed with a gas chromatograph capable of detecting small but prolonged venous-arterial H(2) differences produced by areas of reduced flow. Curves were initially obtained after 4-min left ventricular infusions of H(2)-saturated saline in six patients with arteriographically proven coronary artery disease, three patients with normal coronary arteries, and nine closed-chest dogs. The dogs were studied before and after embolic occlusion of a portion of the left coronary artery. Although the slopes of their semilogarithmically plotted venous desaturation curves varied with time before embolization, they showed more distinct deviations from single exponentials after embolization (after H(2) concentrations had fallen below 15% of their initial values). The human curves divided similarly, those from coronary artery patients deviating appreciably from single exponentials. A similar separation was also evident in studies of coronary venous-arterial H(2) differences after 20 min of breathing 2% H(2): data were obtained in four dogs before and after coronary embolization, and in three normal patients, and five patients with coronary artery disease. Additional data indicated that the findings were not the result of right atrial admixture in sampled coronary venous blood, although admixture occurred frequently when blood was sampled in the first 2 cm of the coronary sinus (as seen in the frontal projection). Finally, average coronary flows calculated from a given set of data varied significantly with different methods of calculation. Areas of below-average flow seemed likely to be overlooked when single rate constants of desaturation, relatively insensitive analytical techniques, or relatively short periods of saturation and (or) desaturation are employed.

Mechanisms of angina in aortic stenosis

The pathophysiology of cardiac pain in pure aortic stenosis has primarily been ascribed to an augmented left ventricular demand outstripping energy supply. This report provides evidence that not only is the energy demand increased but the supply in terms of coronary vascular reserve may be impaired, particularly in response to stress. Hemodynamic and coronary circulatory changes were studied in 18 patients with aortic stenosis during standard isoproterenol infusion. It was not possible to differentiate any patient with or without angina pectoris or patients with or without coronary artery disease on a basis of change in any measure of left ventricular dynamics. On the other hand, differences did occur in the mechanisms of energy delivery during isoproterenol stress: (1) In group A (aortic stenosis without angina or coronary artery disease), coronary flow increased normally, myocardial oxygen extraction decreased, and myocardial lactate production occurred in only one of seven patients. This suggested that energy supply was, generally, adequate to demand. (2) In group B (critical aortic stenosis with angina but no coronary disease), coronary flow rose insignificantly, myocardial oxygen extraction actually increased in three of five patients, and abnormal glycolysis occurred in all patients. This suggested that little or no reserve for increased coronary flow existed and that compensatory mechanisms had to be summoned. (3) In group C (aortic stenosis with angina and coronary artery disease), coronary flow rose normally, myocardial oxygen extraction decreased normally, but abnormal lactate metabolism occurred in most patients. This suggested adequate overall coronary reserve but evidence of regional ischemia.