MEASUREMENT OF MYOCARDIAL BLOOD FLOW IN ANIMALS AND MAN BY SELECTIVE INJECTION OF RADIOACTIVE INERT GAS INTO THE CORONARY ARTERIES

CCTA-based CABG SYNTAX Score: a tool to evaluate completeness of coronary segment revascularization after bypass surgery

To describe the updated coronary computed tomographic angiography (CCTA)-based coronary artery bypass graft (CABG) anatomic SYNTAX Score (aSS) and assess its utility and reproducibility for assessing the completeness of revascularization after CABG. The CCTA-CABG aSS is a visual assessment using CCTA post-CABG which quantifies the failure in effectively grafting stenotic coronary segments, and therefore assesses the completeness of surgical revascularization. It is calculated by subtracting the aSS of successfully anastomosed coronary segments from the aSS of the native coronary tree. The inter-observer reproducibility of the CCTA-CABG aSS was evaluated in 45 consecutive patients with three-vessel disease with or without left main disease who underwent a CCTA 30 days (± 7 days) after CABG. The CCTA-CABG aSS was evaluated in 45 consecutive patients with 117 bypass grafts and 152 anastomoses. The median native coronary aSS was 35.0 [interquartile range (IQR) 27.0-41.0], whilst the median CCTA-CABG aSS was 13.0 (IQR 9.0-20.5). The inter-observer level of agreement for the native coronary aSS and the CCTA-CABG aSS were both substantial with respective Kappas of 0.67 and 0.61. The CCTA-CABG aSS was feasible in all patients who underwent CABG for complex coronary artery disease with substantial inter-observer reproducibility, and therefore can be used to quantify the completeness of revascularization after CABG.

The CABG SYNTAX Score - an angiographic tool to grade the complexity of coronary disease following coronary artery bypass graft surgery: from the SYNTAX Left Main Angiographic (SYNTAX-LE MANS) substudy

AIMS

The SYNTAX Score (SXscore) has established itself as an important prognostic tool in patients undergoing percutaneous coronary intervention (PCI). A limitation of the SXscore is the inability to differentiate outcomes in patients who have undergone prior coronary artery bypass graft (CABG) surgery. The CABG SXscore was devised to address this limitation.

METHODS AND RESULTS

In the SYNTAX-LE MANS substudy 115 patients with unprotected left main coronary artery disease (isolated or associated with one, two or three-vessel disease) treated with CABG were prospectively assigned to undergo a 15-month coronary angiogram. An independent core laboratory analysed the baseline SXscore prior to CABG. The 15-month CABG SXscore was calculated by a panel of three interventional cardiologists. The CABG SXscore was calculated by determining the standard SXscore in the "native" coronary vessels ("native SXscore") and deducting points based on the importance of the diseased coronary artery segment (Leaman score) that have a functioning bypass graft anastomosed distally. Points relating to intrinsic coronary disease, such as bifurcation disease or calcification, remain unaltered. The mean 15-month CABG SXscore was significantly lower compared to the mean baseline SXscore (baseline SXscore 31.6, SD 13.1; 15-month CABG SXscore 21.2, SD 11.1; p<0.001). Reproducibility analyses (kappa [k] statistics) indicated a substantial agreement between CABG SXscore measurements (k=0.70; 95% CI [0.50-0.90], p<0.001), with the points deducted to calculate the CABG SXscore the most reproducible measurement (k=0.74; 95% CI [0.53-0.95], p<0.001). Despite the limited power of the study, four-year outcome data (Kaplan-Meier curves) demonstrated a trend towards reduced all-cause death (9.1% vs. 1.8%, p=0.084) and death/CVA/MI (16.4% vs. 7.0%, p=0.126) in the low compared to the high CABG SXscore group.

CONCLUSIONS

In this pilot study the calculation of the CABG SXscore appeared feasible, reproducible and may have a long-term prognostic role in patients with complex coronary disease undergoing surgical revascularisation. Validation of this new scoring methodology is required.

Nitrates and nitrites in the treatment of ischemic cardiac disease

The organic nitrite, amyl of nitrite, was initially used as a therapeutic agent in the treatment of angina pectoris, but was replaced over a decade later by the organic nitrate, nitroglycerin (NTG), due to the ease of administration and longer duration of action. The administration of organic nitrate esters, such as NTG, continues to be used in the treatment of angina pectoris and heart failure since the birth of modern pharmacology. Their clinical effectiveness is due to vasodilator activity in large veins and arteries through an as yet unidentified method of delivering nitric oxide (NO), or a NO-like compound. The major drawback is the development of tolerance with NTG, and the duration and route of administration with amyl of nitrite. Although the nitrites are no longer used in the treatment of hypertension or ischemic heart disease, the nitrite anion has recently been discovered to possess novel pharmacologic actions, such as modulating hypoxic vasodilation, and providing cytoprotection in ischemia-reperfusion injury. Although the actions of these 2 similar chemical classes (nitrites and organic nitrates) have often been considered to be alike, we still do not understand their mechanism of action. Finally, the nitrite anion, either from sodium nitrite or an intermediate NTG form, may act as a storage form for NO and provide support for investigating the use of these agents in the treatment of ischemic cardiovascular states. We review what is presently known about the use of nitrates and nitrites including the historical, current, and potential uses of these agents, and their mechanisms of action.

Myocardial scintigraphy as a supplementary diagnostic tool in heart disease

Myocardial scintigraphy with cesium-131 and thallium-201 was performed in 191 patients. Previous myocardial infarctions localized to the anterior and lateral wall of the left ventricle were correctly diagnosed with both radionuclides. Inferior and posterior infarctions were only detected when thallium was used. In patients with non-informative ECG changes like bundle branch block, non-specific ST-T changes or with atypical symptoms, myocardial imaging made an essential contribution to the establishment of a correct diagnosis. The potential value of myocardial imaging in patients with valvular heart disease and in cardiomyopathy is described.

Estimation of coronary flow reserve by intracoronary administration of nicorandil: comparison with intracoronary administration of papaverine

We investigated the usefulness of the intracoronary administration of nicorandil (NIC) compared with that of papaverine (PAP) in the evaluation of coronary flow reserve (CFR) in 17 patients, including 10 patients with old myocardial infarction and 7 patients with angina pectoris. CFR was measured with a Doppler guidewire inserted into the distal site of the left anterior descending coronary artery during intracoronary administration of 10 mg PAP, and of 0.5 mg, 1.0 mg, 2.0 mg, and 3.0 mg NIC. We examined the changes in heart rate (HR), mean blood pressure (mBP), the total score of QTc interval on a 12-lead electrocardiogram (sigma QTc), and ST-T segment, before and after drug administration. CFR was significantly lower during administration of 0.5 mg (1.9 +/- 0.9) and 1.0 mg (2.2 +/- 0.9) NIC than during administration of PAP (2.6 +/- 1.1) (P < 0.01). There was no significant difference in the CFR during administration of 2.0 mg (2.6 +/- 1.0) or 3.0 mg (2.5 +/- 1.0) NIC and that observed during administration of PAP. The CFR during administration of PAP was significantly correlated with that during administration of 2.0 mg NIC (r2 = 0.72, P < 0.0001) and 3.0 mg NIC (r2 = 0.70, P < 0.0001). PAP, but not NIC, significantly altered the HR, mBP, and sigma QTc. Inverted T waves were observed in 14 patients, and elevation of the ST segment was observed in 4 patients during administration of PAP (including 1 patient with ventricular tachycardia). The administration of 0.5 mg to 2.0 mg NIC was not associated with ST-T segment changes, except in 1 patient, but inverted T waves were observed in 2 patients and depression of the ST segment was observed in 2 patients during administration of 3.0 mg NIC. Intracoronary administration of NIC is useful and safe for evaluating the CFR. The appropriate dose for measuring CFR is 2.0 mg nicorandil.

The measurement of blood flow in humans using radioactive tracers

Since the first description of the movement of blood around the body by William Harvey, the accurate measurement of blood velocity has provided a major challenge for medical science. This review looks at the contribution made by techniques using radioactive tracers. Initially consideration is given to the fundamental problem of how to measure the amount of radiotracer in an organ with sufficient accuracy, using both single-photon and positron-emitting tracers. The various models used to link tracer behaviour with blood flow are then discussed and the article closes with a detailed review of the clinical applications of blood flow measurements.

Hemodynamic effects in dogs of nitrous oxide-meperidine and meperidine, respectively, in comparison with nitrous oxide

The aim of this investigation on dogs, was to examine the hemodynamic effects of nitrous oxide (N2O) plus meperidine and of meperidine with room air ventilation, respectively, compared with those of N2O on its own. When meperidine (bolus dose 3 mg.kg-1 and continued infusion 4 mg.kg-1.h-1) was added to 80% N2O, mean arterial blood pressure fell from about 20 to 10 kPa (150 to 75 mmHg), as a result of a decrease in peripheral vascular resistance, but no compensatory changes in cardiac output were seen. When N2O was withdrawn, during continued meperidine infusion, cardiac output and stroke volume increased, while peripheral resistance remained low. Coronary vasodilation was noted when meperidine was added to N2O, and persisted when N2O was withdrawn. In the pulmonary circulation a different response was found. Here, no effects were observed when meperidine was added to N2O, while pressure and resistance decreased when N2O was withdrawn and meperidine continued.

Indomethacin attenuates the constriction of canine epicardial coronary arteries to acetylcholine in the absence of endothelium: contribution of platelets to vasoconstriction in vivo

This study was designed to evaluate the in vivo effect of acetylcholine on endothelial-damaged canine epicardial coronary arteries and the potential contribution of platelets to those acetylcholine-induced responses. Changes in left anterior descending artery cross-sectional area were determined by quantitative angiography in the closed chest anesthetized dog. Baseline cross-sectional area of the left anterior descending artery was not changed by removal of the endothelium by balloon-tipped catheter. Increased constrictor tone produced by prostaglandin F2 alpha was comparable in endothelium-intact and endothelium-removed vessels, supporting an endothelium-independent mechanism for prostaglandin F2 alpha in vivo. Acetylcholine produced anterior descending artery vasodilation with the endothelium intact; a comparable maximal dilator response was also obtained in the presence of increased constrictor tone (prostaglandin F2 alpha). In contrast, acetylcholine produced vasoconstriction of the anterior descending artery when the endothelium was removed. To evaluate the mechanism of acetylcholine-induced vasoconstriction in endothelium-removed vessels, the same protocol was completed in the presence of the platelet inhibitor indomethacin. Indomethacin did not alter baseline cross-sectional area or the dilator response to acetylcholine in endothelium-intact vessels. In contrast, the constrictor response in endothelium-removed vessels was antagonized, and a dilator response comparable with that in endothelium-intact vessels was produced by acetylcholine. The results of this study provide an experimental basis for the observations in human studies in which apparently atherosclerotic vessels constrict in response to acetylcholine. Removal of the endothelium in vivo abolishes the dilator response to acetylcholine and converts the acetylcholine response to vasoconstriction or vasospasm.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperosmotic mannitol and collateral blood flow to ischemic myocardium

Elevation of extracellular osmolality reduces the extent of myocardial and endothelial cell swelling that accompanies acute ischemia, and the reduction of cell swelling is associated with an increase in collateral blood flow to the ischemic area. However, little is known about the effects of hyperosmolality on the vascular resistance of the collateral coronary vasculature. We compared the effects of hyperosmolar mannitol with those of nitroglycerin and dipyridamole on the vascular resistance of large collateral coronary vessels and of the small arterial vasculature in an isolated heart model of regional ischemia. Elevation of osmolality by mannitol increased collateral blood flow to the ischemic region through at least two mechanisms. First, increasing osmolality resulted in dilation of large arterial conductance vessels, similar to that produced by nitroglycerin. In addition, mannitol produced an effect on the coronary circulation at a microvascular level which, per se or in combination with its effect on larger collateral conductance vessels, increased collateral blood flow to ischemic regions.

Impaired coronary vasodilator reserve in the immediate postcoronary angioplasty period: analysis of coronary artery flow velocity indexes and regional cardiac venous efflux

The ratio of peak hyperemic/basal mean coronary flow velocity, an index of coronary vasodilator reserve, immediately after coronary angioplasty normalizes in less than 50% of patients. To evaluate other indexes of coronary vasodilator capacity, both intracoronary arterial velocity and cardiac venous efflux were measured at rest and during vasodilator-induced coronary hyperemia (intracoronary nitroglycerin and papaverine) before and after angioplasty in 27 patients; 17 patients had measurements of intracoronary velocity alone and 10 had thermodilution measurements of great cardiac vein flow. Coronary flow velocity responses were also measured in 6 angiographically normal segments in patients undergoing angioplasty and in 10 normal left coronary artery segments in patients with normal coronary arteries or isolated right coronary artery disease. Despite significant angiographic (72 +/- 12 to 23 +/- 11% diameter narrowing) and hemodynamic (49 +/- 12 to 19 +/- 12 mm Hg aortocoronary gradient) improvement, coronary vasodilator reserve ratios for both arterial velocity and venous flow after angioplasty were only minimally affected. Angioplasty did not significantly increase rest coronary vein flow or artery flow velocities, but did result in significantly higher papaverine responses after angioplasty. Mean and phasic coronary velocity, diastolic coronary flow velocity integral and measured great cardiac vein flow ratios were significantly lower when compared with those in 16 angiographically normal coronary artery segments. These data indicate that maximal hyperemic coronary flow velocity is increased after angioplasty, but the reserve ratios, calculated by any of several flow velocity indexes, remain minimally improved. Angiographic correlations (percent coronary diameter, absolute diameter or cross-sectional area) with variables of coronary blood flow or velocity suggest that no single variable is useful in assessing angioplasty results. However, postangioplasty arterial mean velocity and diastolic flow velocity integral are nearly normalized in most patients, whereas relative changes remain attenuated. These findings are important in studies assessing coronary vasomotor responses in patients with atherosclerotic coronary disease, especially after angioplasty.

Cardiac nuclear medicine, present status, future hopes as seen from the view of a cardiologist

The present techniques of nuclear medicine that are used in cardiology are critically evaluated. They are used mainly for the assessment of coronary circulation (measurement of regional flow and perfusion), on the determination of left ventricular muscle function (radionuclear ventriculography) and on the study of cardiac metabolism. The last-mentioned technique is unique insofar as (except for magnetic resonance imaging) there is no other method available to analyse myocardial metabolism noninvasively in living man. Of immense practical importance is the diagnosis and quantitation of the abnormal coronary flow and perfusion, as coronary artery disease is one of the major diseases of the Western world. Finally, the value of nuclear imaging techniques is compared with that of other nonnuclear methods. In present-day medicine, with its increasingly high costs, the value of nuclear techniques must be assessed very carefully.

Differential H1- and H2-receptor-mediated histamine responses of canine epicardial conductance and distal resistance coronary vessels

The contributions of histamine (H1 or H2) receptor-mediated responses and, therefore, the effects of histamine blocking agents are unclear with regard to regulation of proximal epicardial and distal resistance coronary arteries. This study was designed to evaluate the effects of selective H1- and H2-receptor antagonists on epicardial and resistance vessels in the closed chest dog model. Histamine, diphenhydramine (H1 blocker), and cimetidine (H2 blocker) were infused into the left anterior descending coronary artery (LAD), and responses were studied by quantitative coronary angiography and flow measurements (133Xe washout). Histamine infusion alone produced a significant dilation of the proximal LAD (13% above control) only at the highest dose (45 micrograms/min), while LAD flow was increased by 128%. In the presence of H1 blocker, histamine produced significantly greater epicardial dilation (55% above control). The flow response curve was shifted to the right in the presence of H1 blocker, but the flow attenuation was overcome by the highest histamine dose. In contrast, the H2 blocker attenuated both epicardial dilation (6% below control) and flow response (31% above control) to the highest histamine dose. Results support a differential regulation of proximal epicardial and distal resistance vessels to histamine with epicardial arteries demonstrating H1-mediated vasoconstriction and H2-mediated vasodilation and distal resistance vessels showing H1- and H2-mediated vasodilation. In addition, these findings suggest that H1 blockade may antagonize histamine-related vasoconstriction and vasospasm, while H2 blockers may permit unopposed H1-mediated vasoconstriction of epicardial arteries and also limit resistance vessel vasodilatory responsiveness in the presence of elevated tissue histamine, as may occur in atherosclerotic coronary artery disease.

Blood velocity measurements during selective coronary angiography before and after percutaneous transluminal coronary angioplasty

The velocity of blood flowing down a coronary artery may provide an index of myocardial perfusion, independent of the need for measuring the amount of myocardium supplied by a vessel. The velocity of the leading edge of contrast material was therefore measured before and after percutaneous transluminal coronary angioplasty in 15 patients utilizing digitized images from routine coronary angiography. The velocity (mean +/- SD) before percutaneous transluminal coronary angioplasty in the 15 patients was 11.9 +/- 6.0 cm/s, increasing to 21.7 +/- 8.7 cm/s after (P less than 0.01). There was a correlation between the percent change in velocity and the change in percent stenosis before and after percutaneous transluminal coronary angioplasty (r = 0.65; P less than 0.001). The mean absolute interobserver and intraobserver variabilities for the velocity measurements were 2.1 and 1.8 cm/s, respectively. Measurement of coronary flow velocity from data obtained at the time of routine coronary angiography is an easily performed reproducible technique, which may be used to assess the results of an intervention such as percutaneous transluminal coronary angioplasty.

Measurement of myocardial blood flow by ultrafast computed tomography

Myocardial blood flow was analyzed by radioisotope-labeled microspheres and ultrafast computed tomography (CT) in 16 closed-chest, anesthetized dogs. The first set of 10 dogs had CT and microsphere measurements before and after chromonar-induced increases in myocardial blood flow. A second set of six dogs had flows measured at control and during temporary reductions in regional flow produced by balloon cuff occlusion of the left anterior descending coronary artery. All dogs had four-slice, 20-instance CT scans after injection of a medium bolus (0.35 ml/kg) of contrast medium into a femoral vein simultaneous with injection of microspheres into the left atrium. CT myocardial flow was calculated as the change in myocardial CT numbers divided by the area from a blood pool time-density curve. A wide range of myocardial blood flows was produced as determined by microspheres (0 to 6.7 ml/min/g). Global flow of the first set of dogs was shown to have excellent correlation (r = .95, n = 17) for a limited range (.4 less than X less than 1.4 ml/min/g) of flows. Regional flows of these measurements demonstrated less correlation (r = .63, n = 110) but extended the range of flow to 1.7 ml/min/g. At higher flows (greater than 2.5 ml/min/g) the correlation for global and regional flows was not significantly different than zero. Regional ischemic flow correlation extended the linear range of flow to 0 ml/min/g (r = .62, n = 17). These results show that CT can measure myocardial blood flow over a limited but clinically relevant range of flows defined as slightly above normal to ischemic. These results indicate that another preparation of CT flow measurement must be sought for quantification of myocardial perfusion values significantly above normal.

Preservation of endothelial cell structure and function by intracoronary perfluorochemical in a canine preparation of reperfusion

To determine the effect of intracoronary perfluorochemical on endothelial cell structure and function, 16 dogs were randomized to receive either low-dose (15 ml/kg) intracoronary perfluorochemical (Fluosol-DA) or saline after 90 min of proximal occlusion of the left anterior descending coronary artery (LAD). The animals underwent reperfusion for 60 min with the introduction of perfluorochemical or saline 5 to 10 min after the onset of reperfusion. Endothelium-dependent coronary vasodilatory reserve was determined in vivo both at baseline and 1 hr after reperfusion by infusion of acetylcholine and then serotonin into the distal LAD bed in 12 animals (six in each group). Both agonists significantly increased regional flow measured by 133Xe washout in the two groups before occlusion, but at 1 hr after reperfusion only animals given perfluorochemical demonstrated a significant increase in flow. Vasodilatory reserve was assessed in vitro with cumulative dose-response curves to acetylcholine on LAD rings proximal and distal to the snare in all animals. These studies demonstrated a significant reduction in endothelial cell-mediated relaxation of epicardial arterial segments in the ischemic segment of control but not treated animals. Light microscopy revealed the presence of neutrophils within vessels in the ischemic zones in control animals only. Electron microscopy showed capillary obstruction by endothelial cell protrusions and neutrophil and red cell plugging in control animals in the ischemic region but an intact endothelium and predominantly unobstructed capillaries in treated animals. These findings suggest that the structural and functional endothelial damage after reperfusion may be prevented by the administration of intracoronary perfluorochemical after the onset of reperfusion.

Effects of thromboxane analog U46619 on endothelial damaged canine coronary arteries in vivo

We studied the effects of the thromboxane analog, U46619, infused into the left anterior descending (LAD) artery of intact dogs before and after producing endothelial denudation of the mid portion of the LAD. Proximal artery cross-sectional area (CSA) decreased by 47% with 0.1 microgram/min infusion of U46619 with intact and denuded endothelium, while resting CSA reduced spontaneously following denudation. Coronary resistance vessels demonstrated a marked constrictor response to U46619 with a rise in resistance and a fall in flow and myocardial O2 consumption. U46619 produces significant narrowing of proximal epicardial coronary arteries as well as resistance coronary vessels. This effect could cause ischemia in patients with moderate coronary atherosclerosis.

Blood flow of experimental liver metastases in rat as evaluated by the locally injected 133-Xenon washout

The investigations on blood flow in liver metastases are interesting from both a pathophysiological and a therapeutic point of view. Available data, however, are few and not definitive, as these studies are complex and difficult to perform. In a group of 25 Sprague-Dawley rats, in which liver metastases of Walker-256 carcinoma had been implanted, the blood flows in a metastasis and in the normal liver surrounding it were determined by means of the locally injected 133-Xenon washout. Thirteen sham-operated rats were a control group. Blood flow in the metastases was decreased as a group compared to that in the normal liver surrounding metastases and to that in liver of sham-operated rats. Small metastases showed normal or increased blood flow, large ones decreased or stagnant blood flow. Moreover, a significant inverse correlation was found between blood flow and diameter of metastasis. It is concluded that liver metastases of Walker-256 carcinoma show a decrease in blood flow which is related to the size of metastasis.

Myocardial perfusion after aortocoronary bypass surgery: measurements at rest and after administration of isoproterenol

This study examined quantitative regional myocardial perfusion (RMP) measured by the washout of 133Xe at rest and after an isoproterenol challenge in 50 patients (group I) studied 8 to 14 days after they underwent saphenous vein bypass grafting to the left coronary artery, and compared this with RMP measured in the native left coronary artery in 14 patients (group II) with significant coronary artery disease and in 12 normal subjects (group III). The double product of the heart rate and aortic systolic pressure was used as an indicator of demand. The statistical significance of group comparisons was analyzed with Dunn's multiple comparisons among means test. Analysis of the data showed no significant difference among the groups with respect to aortic systolic pressure. In subjects at rest, heart rate was lower in groups II and III than in group I, and double product was lower in group II than in group I. After isoproterenol, both heart rate and double product were lower in group II compared with groups I and III, but there was no significant difference between groups I and III with respect to heart rate or double product. Mean resting RMP in group II was lower than in group I; however, results of other group comparisons were insignificant for resting parameters. After isoproterenol, mean flow (ml/100 g/min) in group I was similar to flow in group III (130 +/- 24 vs 139 +/- 26). In contrast, the average flow response after isoproterenol was significantly less in group II when compared with that in group I (105 +/- 20 vs 130 +/- 24) and with that in group III (105 +/- 20 vs 139 +/- 26). Because of differences in levels of demand with isoproterenol, the change in flow was normalized to the percent increase in double product. These data showed results similar to those above, i.e., normalized RMP in patients with coronary artery disease was significantly lower than that in normal subjects (82 +/- 41 vs 119 +/- 57) and in revascularized patients (82 +/- 41 vs 105 +/- 54). However, there was no significant difference between normal subjects and patients who had undergone surgery. To further evaluate the relationship of flow response to demand parameters, we plotted RMP/double product vs resistance. The data revealed a significant correlation between these variables in all groups both in subjects at rest and after isoproterenol.(ABSTRACT TRUNCATED AT 400 WORDS)

Quantification of regional myocardial blood flow in vivo with H215O

Using H215O (half-life = 2.1 min) we demonstrated that a modification of the tissue autoradiographic approach permitted quantitation of myocardial blood flow in open-chest dogs by direct assay of myocardial tissue and that noninvasive estimation with positron-emission tomography (PET) delineated relative myocardial blood flow in intact dogs. In open-chest anesthetized dogs, the single-pass extraction fraction of H215O averaged 96 +/- 5% at flows of 80 to 100 ml/100 g/min. This high extraction fraction did not differ significantly over the range of 12 to 238 ml/100 g/min. Myocardial blood flow calculated after a 60 sec intravenous infusion of H215O and direct analysis of tissue correlated well with results obtained with microspheres (r = .94, n = 9 dogs). Subsequently the approach was adapted for preliminary use with PET. Estimation of myocardial content of radiolabeled H2O after intravenous infusion of 20 to 30 mCi of H215O was corrected for vascular pool radioactivity with the use of tomographic data obtained after administration of C15O by inhalation to label red blood cells. Tomograms obtained in vivo in six dogs with either normal or reduced regional blood flow correlated closely with the tomographically detectable distribution of 68Ga-labeled microspheres (r = .93) and with postmortem microsphere distribution (r = .95). The technique accurately reflects myocardial blood flow. With the use of PET, rapid sequential noninvasive estimation of relative regional myocardial blood flow has been demonstrated that should ultimately permit improved objective assessment of nutritional blood flow in patients in response to medical and surgical interventions designed to augment perfusion.

Effects of intraaortic balloon counterpulsation on myocardial blood flow in patients with severe coronary artery disease

The purpose of this study was to test the hypothesis that myocardial blood flow distal to a critical stenosis would increase during intraaortic balloon counterpulsation. Accordingly, 13 patients with severe coronary artery disease were studied at the time of elective preoperative insertion of an intraaortic balloon catheter. Hemodynamic measurements and measurements of myocardial blood flow were made before and during counterpulsation. Myocardial blood flow was measured with a xenon-133 washout technique. Compared with control measurements, the heart rate decreased from 87.8 +/- 18.8 to 82.8 +/- 13.4 beats/min (p = 0.02) and systolic arterial pressure decreased from 112.1 +/- 17.9 to 97.8 +/- 14.8 mm Hg (p = 0.004) during counterpulsation. Diastolic arterial pressure increased from 72.2 +/- 10.1 to 120.2 +/- 21.4 mm Hg (p = 0.00002) during counterpulsation. Myocardial blood flow for the entire group decreased from 48.8 +/- 14.1 to 42.6 +/- 11.0 ml/100 g per min (p = 0.008). Regional flows in the left anterior descending and circumflex distributions also decreased. Left anterior descending artery blood flow decreased insignificantly from 51.5 +/- 14.4 to 47.4 +/- 11.7 ml/100 g per min (p = not significant), while circumflex flow decreased from 50.7 +/- 12.2 to 41.1 +/- 8.9 ml/100 g per min (p = 0.008). When normalized for the rate-pressure product, myocardial blood flow was 53 +/- 16 X 10(-4) at rest and 55 +/- 12 X 10(-4) (p = not significant) during counterpulsation.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of regional myocardial perfusion using collimated miniature radiation detectors and the method of 133-xenon washout

A new approach to the measurement of local myocardial perfusion based on the application of highly-collimated miniature cadmium telluride radiation detectors to measure washout of 133-Xenon from well-defined tissue volumes is presented. Single-hole collimators with length/diameter ratios of 1 (L = 4 mm, D = 4 mm) and 4 (L = 12 mm, D = 3 mm) were employed as prototype designs. The probe field of view was characterized theoretically using a spherical model of the myocardium in conjunction with experimental point source response measurements for each collimator. Method evaluation using two medium resolution collimators (L/D = 1) was effected by performing left main and circumflex coronary artery perfusion studies at controlled but variable flows in the dog heart. An excellent correlation (r greater than 0.99) between actual and estimated perfusion determined from 65 washout curves over the flow range 0.38 to 3.18 ml/min/gm was demonstrated. The ability to resolve regional flow differences was verified by measuring tracer washout from circumflex and left anterior descending regions of the myocardium, using two high resolution collimators (L/D = 4), in a preparation where the left main coronary artery was cannulated and a snare was placed around the circumflex coronary artery to selectively reduce flow to that region.

Measurement of systolic and diastolic flow rates in the coronary artery system by x-ray densitometry

The reliability of a modified videodensitometric and photodensitometric sampling technique for measuring phasic flow rates in the coronary artery system was examined. Electromagnetic flow measurements were performed in a circulatory model with continuous and pulsatile flow and intraoperatively in aortocoronary bypass grafts; cineangiograms were made simultaneously. Based on the front velocities of injected boluses of contrast medium, the densitometric measurement overestimated the electromagnetically measured flow systematically by about 20%. Systolic and diastolic flow rates in aortocoronary bypass grafts and coronary arteries determined from biplane cineangiograms in 34 patients generally revealed the typical pulsatile flow pattern familiar from electromagnetic and ultrasonic flow measurements. Flow velocities in unstenosed coronary arteries were nearly identical before and after branchings of the vessels, whereas the corresponding flow rates were higher in proximal than in distal segments. The identical flow velocities in different branches of the same vessel and the low variability of this parameter in different patients may be a suitable index of the effect of stenoses on coronary arterial blood flow.

Relationship between segmental thallium-201 uptake and regional myocardial blood flow in patients with coronary artery disease

The relationship between the spatial distribution of thallium-201 in myocardial perfusion scintigrams and the distribution of left ventricular regional myocardial blood flow was examined in 25 patients undergoing coronary arteriography. Thallium-201 myocardial scintigrams were obtained after symptom-limited exercise and after a 4 hr delay. Regional myocardial blood flow was measured by the xenon-133 clearance method in patients at rest and during rapid atrial pacing to a double product comparable with that achieved during exercise stress testing. Patterns of regional thallium-201 activity and regional myocardial blood flow, recorded in similar left anterior oblique projections, were compared for left ventricular segments supplied by the left anterior descending (LAD) and left circumflex (CIRC) arteries. In 11 patients without significant lesions of the left coronary artery (group 1), thallium-201 was homogeneously distributed in the LAD and CIRC distributions in scintigrams taken during peak exercise; these scintigrams correspond to homogeneous regional myocardial blood flow in the LAD and CIRC regions during pacing-induced stress. In 14 patients with significant lesions of the left coronary artery (group 2), ratios of regional thallium-201 activity in the LAD and CIRC distributions of exercise scintigrams correlated well (r = .84) with ratios of regional myocardial blood flow measured during rapid pacing. Background subtraction altered the relationship between relative thallium-201 uptake and regional myocardial blood flow, causing overestimation of the magnitude of flow reduction on exercise scintigrams. These data indicate that: (1) in patients with normal left coronary arteries, thallium-201 is homogeneously distributed to the left ventricle, reflecting the homogeneous distribution of regional myocardial blood flow over a wide range of mean left ventricular flow rates and (2) in patients with significant lesions of the left coronary artery, the relative spatial distribution of thallium-201 activity in exercise perfusion scintigrams reflects the distribution of regional myocardial blood flow.

Left ventricular myocardial blood flow in multivessel coronary artery disease

The relationship between resting left ventricular (LV) myocardial blood flow (MBF) and hemodynamic determinants of myocardial oxygen consumption was investigated in 15 patients with multivessel coronary artery disease (CAD) and in 10 patients with normal coronary arteriograms. Mean LV MBF per unit mass of tissue was measured with a multicrystal scintillation camera from the regional clearance rates of xenon-133 injected into the left main coronary artery. Peak LV wall stress, mean velocity of circumferential fiber shortening (Vcf), rate of ejection during the first third of systole (1/3 SV), LV ejection fraction (EF), and the ratio of peak LV systolic pressure to LV end-systolic volume were measured by contrast left ventriculography. Mean LV MBF per unit mass was significantly reduced (48 +/- 11 vs 67 +/- 12 ml/100 g.min; p less than 0.01) in patients with multivessel CAD. However, none of the patients with CAD experienced chest pain or had electrocardiographic evidence of myocardial ischemia during the resting MBF measurements. Ejection phase indexes were lower in the patients with CAD: LVEF (56 +/- 10% vs 64 +/- 7%, p less than 0.05); 1/3 SV (35 +/- 3 vs 44 +/- 4%, p less than 0.05); and mean Vcf (1.05 +/- 0.30 vs 1.19 +/- 0.27 circ/sec, NS). LV wall thickness (9.8 +/- 1.9 vs 7.5 +/- 1.4 mm, p less than 0.01) and LV mass index (94 +/- 32 vs 64 +/- 17 g/m2, p less than 0.05) were significantly increased in the patients with CAD, accounting for the reduction in peak LV wall stress (276 +/- 73 vs 373 +/- 91 dyn-cm-2 x 10(-3), p less than 0.05) observed in these patients. Multiple regression analysis indicated that indexes of three of the major determinants of myocardial oxygen consumption explained 65% of the variation in MBF in patients with CAD: peak LV stress, mean Vcf and heart rate. After adjustment for these three indexes, the average LV MBF rates were not significantly different in the two patient groups (54.8 +/- 1.8 vs 57.6 +/- 2.3 ml/100 g.min). In both groups, resting LV MBF/beat correlated most highly with peak LV wall stress (r = 0.79). Thus, the reduction in LV MBF per unit mass observed in patients with multivessel CAD at rest is related to lower levels of hemodynamic variables that determine myocardial oxygen consumption. Peak LV wall stress is the most important hemodynamic variable determining the level of resting MBF in patients with and without CAD.

Treatment of vasospastic angina pectoris at rest with nitroglycerin ointment: a short-term controlled study in the coronary care unit

The effectiveness of nitroglycerin ointment in vasospastic angina pectoris at rest was evaluated in 10 patients selected for study. The study was performed after a 24 hour control period, and a randomized single-blind crossover experimental design was followed. Two percent nitroglycerin ointment (15 mg) or placebo ointment was administered every 6 hours for a period of 48 hours each; the first treatment period was followed by a second in which each preparation was used for a 24 hour period. All patients were hospitalized in the coronary care unit; an objective evaluation was carried out using a multichannel electrocardiographic recording to assure recognition of the painless ischemic episodes. Coronary angiography showed critical stenosis of one or two vessels in 9 of the 10 patients; spasm was demonstrated in 3. Results of the ergonovine test were positive in nine of nine patients. Nitroglycerin ointment produced a significant reduction in the mean daily number of episodes during the first (12.5 +/- 3.9 versus 0.5 +/- 0.4, p less than 0.02) as well as the second treatment period (10.6 +/- 3.8 versus 0.6 +/- 0.4, p less than 0.02). These results demonstrate that nitroglycerin ointment provides effective, long-lasting protection against angina due to coronary spasm.

Intravenous xenon- 133 for the determination of radionuclide first pass right ventricular ejection fraction

The use of intravenous xenon- 133 for determination of radionuclide first pass right ventricular ejection fraction is described. First pass determinations of right ventricular ejection fraction were made with both xenon- 133 and technetium-99m in 13 subjects (15 right ventricular ejection fraction determinations); results obtained with xenon- 133 show an excellent correlation (r = 0.98, p less than 0.002) with results obtained using technetium-99m. Because of rapid pulmonary elimination of xenon- 133 from the body, the use of this radioisotope allows multiple first pass right ventricular ejection fraction determinations within a short period of time, without significant radiation exposure for the patient.

Quantitative difference in "critical" stenosis between right and left coronary artery in man

Coronary artery stenoses that limit blood flow below demand are considered critical. In this comparative study we investigated whether the same degree of stenosis in either the proximal third of the right coronary artery (RCA) or the proximal third of the left anterior descending artery (LAD) causes critical flow reduction. Lesions were quantified from 35-mm cinefilms in multiple projections using a vernier caliper. These morphometric measurements were correlated with various manifestations of critical flow reduction, such as angina pectoris, development of collateral vessels and segmental wall motion abnormalities. In 13 patients with anginal pain and isolated RCA stenosis, the mean degree of obstruction was 63% area stenosis, which was significantly lower (p < 0.05) than that measured in 17 symptomatic patients who had isolated obstructions of the LAD (77% area stenosis). In patients with an identical degree of obstruction (78%) in either the LAD or RCA, collateral vessels were angiographically demonstrable in 53% of the RCA stenoses but in only 29% of the LAD stenoses. Furthermore, when the stenoses were less than 63% in the RCA and LAD, regional wall motion abnormalities were more frequently (p < 0.05) associated with RCA than with LAD stenoses. These observations indicate that a significantly smaller percent area of stenosis is critical in the RCA than in the LAD.

Assessment of regional blood flow by intravenous injection of 99m-technetium-pertechnetate

A general method for computation of regional blood flow from time-activity curves obtained after intravenous injection of 99m-TC pertechnetate is presented. The method is based on the well-known principle of Meier and Zierler, but, it also considers the dispersion of an intravenously injected activity-bolus as well as the recirculation of the nondiffusible tracer. The problems arising from the use of a nondiffusible indicator concerning the partition coefficient lambda are discussed. This method of blood flow determination is adopted for measurements of cerebral blood flow and some first results are discussed.

Quantitative aspects of myocardial perfusion imaging

Myocardial perfusion measurements have traditionally been performed in a quantitative fashion using application of the Sapirstein, Fick, Kety-Schmidt, or compartmental analysis principles. Although global myocardial blood flow measurements have not proven clinically useful, regional determinations have substantially advanced our understanding of and ability to detect myocardial ischemia. With the introduction of thallium-201, such studies have become widely available, although these have generally undergone qualitative evaluation. Using computer-digitized data, several methods for the quantification of myocardial perfusion images have been introduced. These include orthogonal and polar coordinate systems and anatomically oriented region of interest segmentation. Statistical ranges of normal and time-activity analyses have been applied to these data, resulting in objective and reproducible means of data evaluation.