Diagnosis of coronary artery disease by estimation of coronary sinus lactate

Cardiac release and kinetics of cytokines after elective bare metal coronary stenting

The study was designed to assess the cardiac release kinetics of the cytokines interleukin-1ß (IL-1ß), interleukin-6 (IL-6) and tumor-necrosis-factor-α (TNF-α) in patients with significant stenosis of the ramus interventricularis anterior. Ten patients were treated by bare metal stent implantation, 11 patients who underwent a diagnostic coronary angiography without intervention served as a control group. Cytokines paired blood samples were withdrawn from the coronary sinus and a peripheral vein immediately before and 1, 2, 6 h after the intervention. Myocardial ischemia was monitored by means of cardiac lactate metabolism and 12-lead electrocardiogram. After coronary intervention IL-6 gradually increased from a common baseline level of 1.34 ± 1.56 pg/ml to a maximum of 10.58 ± 5.7 pg/ml in the peripheral vein and 15.81 ± 6.98 pg/ml in the coronary sinus within 6 h with persistent higher levels in the coronary sinus indicating coronary IL-6 release. After 12 h the peripheral venous concentration of IL-6 returned to baseline levels. Neither in the study group for IL-1ß and TNF-α nor in the control group for any cytokine level significant changes were found. Myocardial ischemia was excluded in all patients. Uncomplicated percutaneous coronary intervention (PCI) was followed by a significant cardiac IL-6 release due to endothelial injury and not to myocardial ischemia.

Microvascular angina: assessment of coronary blood flow, flow reserve, and metabolism

Microvascular angina (MVA) is an often overlooked cause of significant chest pain. Decreased myocardial perfusion secondary to dysregulated blood flow in the microvasculature can occur in the presence or absence of obstructive epicardial coronary artery disease. The corresponding myocardial ischemia and angina is now a well-established diagnosis, made by detection of decreased coronary flow reserve (CFR). Although low CFR and MVA are associated with poor prognosis, there is initial evidence for reversibility of this abnormal vascular regulation with aggressive medical therapy and control of associated risk factors. Current assessment of MVA is carried out predominantly during cardiac catheterization; however, noninvasive techniques to assess CFR are being developed, including PET, MRI, and CT modalities. Quantitative tracer techniques or imaging of metabolic disturbances reflecting ischemia will likely enhance diagnostic approaches for such patients as well as allow more frequent monitoring of response to therapy.

Clinical significance of myoglobin and troponin-T in short-lasting severe myocardial ischemia

BACKGROUND

Myoglobin, cardiac troponin-T and creatine phosphokinase are biochemical indicators of acute coronary syndromes, however, the clinical significance in myocardial ischemia is not well established. Our aim was to elucidate their release kinetics in a well-defined short-lasting myocardial ischemia.

METHODS

A coronary sinus lactate study with incremental atrial pacing was performed in 27 patients with significant coronary stenosis. Troponin-T, myoglobin and creatine phosphokinase samples were withdrawn from the coronary sinus and a peripheral vein before, 1, 5, 10, 30, 45 min and 1, 2, 3, 6, 12 h after pacing.

RESULTS

Pacing stress induced a severe myocardial ischemia with a duration of 5.8+/-1.6 min, angina pectoris in 22/27, significant ST-segment depressions in 25/27 patients (0.34+/-0.11 mV) and a frank cardiac lactate production of 37.6+/-19.9%. Serum troponin-T levels as well as creatine phosphokinase were normal at baseline and remained unchanged. A transient rise of myoglobin after 1 h with a peak coronary sinus concentration after 2 h (101.5+/-39.0 microg/l) and peripheral venous concentration (90.5+/-32.5 microg/l) after 3 h (134.3% and 120.7%, respectively, of the upper normal limit, p<0.002) followed myocardial ischemia. In a control group of 20 patients without heart disease all variables remained unchanged.

CONCLUSIONS

Severe short-lasting myocardial ischemia did not enhance troponin-T or creatine phoshokinase concentrations, whereas a transient slight cardiac release of myoglobin with a delay of 1 h and a coronary sinus peak concentration after 2 h was detected. This may be due to a rapid reperfusion effect on ischemic myocardium or minor damaged single myocardial cells.

Myocardial lactate metabolism in relation to preoperative regional wall motion and to early functional recovery after coronary revascularization

OBJECTIVE

To evaluate myocardial lactate metabolism as a marker of functional status after surgical coronary revascularization.

DESIGN

Single-center, prospective, cohort study.

SETTING

Tertiary care teaching hospital.

PARTICIPANTS

Fifty patients with stable angina, ejection fraction >0.40, undergoing coronary artery bypass surgery for multiple-vessel disease.

MEASUREMENTS AND MAIN RESULTS

Before (T1) and 30 minutes (T2) after coronary artery bypass grafting, the authors simultaneously sampled blood from artery and coronary sinus to determine myocardial lactate dynamics and performed transesophageal echocardiography (TEE) to assess segmental wall motion. Wall motion score index (WMSI) was calculated with an online/offline comparison. At T2, WMSI improved from 1.40 +/- 0.31 to 1.17 +/- 0.23 (p = 0.0001). Preoperatively, 2 patterns of lactate balance were found: 39 patients were lactate extractors (17% +/- 10%) and 11 were lactate producers (-11% +/- 11%). At T2, lactate metabolism was shifted towards a pattern opposite to the baseline: delta lactate extraction was -8% +/- 16% in extractors at T1 versus 7% +/- 9% in producers at T1 (p = 0.003). Changes in WMSI were not correlated with changes in lactate utilization. No single preoperative variable predicted postoperative WMSI or its changes from baseline. Cardiopulmonary bypass (CPB) time was the only significant predictor of postoperative lactate extraction by multivariate regression (r = -0.46, p = 0.001): at T2, patients in the highest CPB time quartile showed frank lactate production (-6% +/- 13%) when compared with those in the lowest quartile (15% +/- 11%, p = 0.005). However, postoperative WMSI was similar in different CPB time groups.

CONCLUSIONS

Myocardial lactate metabolism pattern is not associated with functional status before and early after successful coronary revascularization. CPB time was the only significant predictor of postoperative lactate extraction. Measurement of lactate does not appear to be a valuable tool to assess the coupling of myocardial regional function and metabolism in the setting of coronary artery surgery and mild-to-moderate functional impairment.

An ultrafiltration catheter for monitoring of venous lactate and glucose around myocardial ischemia

Early detection of myocardial ischemia is of major importance in critical-care medicine. Changes of lactate or glucose levels in the cardial venous efflux may be useful parameters. We succeeded in integrating an ultrafiltration membrane in a cardiac catheter for continuous sampling. The ultrafiltrate was analyzed outside the body, resulting in a lag-time of about 24 min. Biosensors in a flow-injection analysis system were used for minute by minute sample analyses. The coronary sinus of pigs was catheterized to monitor the effects of 5, 15 or 45 min ischemia by coronary artery obstruction or myocardial stress by dobutamine infusion. A total of 27 h was monitored. The intravascular response time was 1.33+/-0.61 min (10-90%). Linear regression in vivo of blood and ultrafiltrate samples was 0.977 for lactate and 0.994 for glucose. Lactate levels rose 0.38+/-0.10 mM above baseline within 5 min after ischemia. Reperfusion was clearly marked by a promptly peaking lactate release (maximum 9.27 mM). Myocardial stress by dobutamine increased glucose but not lactate levels. Once, a wall effect was noted at the catheter tip. In vivo semi-continuous myocardial monitoring of absolute lactate and glucose concentrations was thus achieved by an ultrafiltration catheter. Ischemia and reperfusion can be detected very early by a lactate level rise. Further, development of the ultrafiltration catheter will be focused on the diagnostic potential of lactate monitoring for patients.

Exercise-induced myocardial ischemia in isolated coronary artery ectasias and aneurysms ("dilated coronopathy")

OBJECTIVES

The purpose of our study was to evaluate the clinical significance of isolated coronary artery ectasias or aneurysms (CEA).

BACKGROUND

It has been postulated that altered coronary blood flow in CEA predisposes patients to the development of myocardial ischemia (CI) and infarction.

METHODS

Sixty-seven patients with bilateral nonobstructive CEA without associated cardiac defects ("dilated coronaropathy") were derived from 16,341 cardiac catheterizations between 1986 and 1997. Ectasias were defined as luminal dilation of 1.5- to 2.0-fold, aneurysms of >2.0-fold of normal limits. Eleven of 25 patients presented with myocardial infarction due to an occlusion of the infarct vessel. In 42 patients without infarction (study group), exercise-induced CI was investigated.

RESULTS

A corresponding CI was documented in 32 of 42 patients in a coronary sinus lactate study (reduced lactate extraction 5.6 +/- 4.1%) and in 29 of 40 patients in an ergometry (0.25 +/- 0.06 mV ST depressions). The results differed significantly from a control group of 29 patients without heart disease (p < 0.001). Nitroglycerin (0.8 mg) provoked a further significant deterioration of CI in the 32 of 42 developing a frank cardiac lactate production (-2.6 +/- 6.8%, p < 0.001). The metabolic extent of CI was significantly correlated to the coronary diameters of the proximal and middle segments of left anterior descending artery and the middle segment of left circumflex artery (r = 0.87, p < 0.001). Stigmata of an impaired coronary blood flow such as delayed antegrade filling, segmental backflow phenomenon and local deposition of dye were found significantly more often with increasing coronary diameters (p < 0.04).

CONCLUSIONS

"Dilated coronaropathy" is an entity of nonobstructive, ischemic coronary artery disease. Nitroglycerin is of no therapeutic benefit but leads to an aggravation of exercise-induced CI.

Myocardial lactate extraction during repeated fibrillation/defibrillation episodes in defibrillator implantation testing

Intraoperative testing with several fibrillation/defibrillation episodes (FDEs) is routinely performed during defibrillator implantation. Testing is considered safe even in patients with severe cardiac impairment, provided the recovery timespans and number of FDEs are adapted to the individual patient. Myocardial lactate extraction (MLE) was examined in two testing protocols. In 30 patients with coronary artery disease defibrillator implantations were performed under intravenous anesthesia. A percutaneous catheter was positioned into the coronary sinus (CS) underfluoroscopy. Two groups were randomly formed: group A (n = 20, mean number of FDEs: 4.2/patient) with 2 minutes waiting time between FDEs, and group B (n = 10, mean number of FDEs 4.1/patients) with 10 minutes between FDEs. Defibrillation pulses were released 15 seconds after T wave shock induced fibrillation. To estimate MLE, arterial and CS blood samples were collected before and after each FDE. After the last FDE, samples were obtained after 5, 10, and up to 20 minutes. In group A, MLE fell from a baseline value of 29.6% +/- 3.6% before the FDEs to 7.8% +/- 5.4% immediately after the episodes. MLE recovered to 27.2% +/- 6.5% within 1 minute and overshot to 35.6% +/- 5.8% within 5 minutes. In group B, MLE decreased from 37.6% +/- 7.5% to 15.1% +/- 8.1% immediately after each FDE and rose to its original value (33.6 +/- 7.8) within the 5-minute recovery period. MLE decreased immediately after each FDE, and recovered within 1 minute even in poor left ventricular function. For full MLE recovery a 2-minute wait between episodes is sufficient, if the total number of FDEs does not exceed four.

Cardiac release and kinetics of endothelin after uncomplicated percutaneous transluminal coronary angioplasty

This study was designed to assess the release kinetics of endothelin after percutaneous transluminal coronary angioplasty (PTCA) and to prove the coronary endothelium as the source of the endothelin release. Twenty-seven patients with single-vessel coronary artery disease underwent PTCA. Endothelin, troponin T, myoglobin, and creatine phosphokinase paired blood samples were withdrawn from the coronary sinus and a peripheral vein before the balloon maneuver and at 1, 5, 10, 30, 45 minute(s), and at 1, 2, 3, 6, 12, and 24 hour(s) after the last balloon maneuver. Myocardial ischemia was monitored by means of cardiac lactate metabolism and 12-lead electrocardiogram. Thirteen patients who underwent a diagnostic cardiac catheterization served as a control group. In the left coronary artery, PTCA (n = 19) endothelin concentrations increased from 4.1 pg/ml as a common mean baseline level before intervention to 13.9 +/- 2.6 pg/ml (mean +/- SD) in the coronary sinus and 7.9 +/- 2.2 pg/ml (mean +/- SD) in the peripheral vein at 1 minute after the intervention (p <0.001). The levels remained elevated for 3 hours with higher coronary sinus than peripheral venous concentrations due to persistent cardiac endothelin release. PTCA of the right coronary artery (n = 8) also led to an instantaneous endothelin increase from a mean concentration of 4.4 before intervention to 8.3 pg/ml after intervention with identical coronary sinus and peripheral venous levels (p <0.001). Endothelin levels gradually decreased to normal within 6 hours. No patient developed a measurable myocardial ischemia or a myocardial infarction. In the control group all parameters remained unchanged. Uncomplicated PTCA was followed by a significant cardiac endothelin release that seems to indicate endothelial injury and not myocardial ischemia.

Cardiac release and kinetics of endothelin after severe short-lasting myocardial ischemia

OBJECTIVES

The aim of this study was to investigate the release kinetics of endothelin after induced short-lasting myocardial ischemia.

BACKGROUND

Endothelin is an endothelium-derived vasoactive peptide. Unequivocal proof of its cardiac release in ischemic syndromes has not yet been demonstrated.

METHODS

A coronary sinus study with atrial pacing was performed in 23 patients with coronary artery disease. Endothelin (ET), cardiac troponin-T (TnT), myoglobin (Mb) and creatine kinase (CK) samples were withdrawn from the coronary sinus and a peripheral vein before and 1, 5, 10, 30 and 45 min and 1, 2, 3 and 6 h after pacing. The appearance of angina pectoris, abnormal cardiac lactate metabolism and ST segment depression were further criteria for myocardial ischemia.

RESULTS

In the study group, pacing stress induced severe ischemia (mean duration +/- SD 6.1 +/- 1.2 min), with a maximum of 0.34 +/- 0.12-mV ST segment depression in 21 of 23 patients and angina pectoris in 22 of 23. The maximal cardiac lactate production was 42.8 +/- 17.3% (p < 0.03). TnT and CK levels in the total group were normal; in 14 of 23 patients a transient elevation of Mb with a maximum after 3 h was detected (86.4 +/- 27.1 micrograms/liter, p < 0.03). The ET concentrations increased significantly (p < 0.001) in the coronary sinus (from 4.6 +/- 0.8 [baseline] to 12.9 +/- 2.7 pg/ml at 1 min after cessation of pacing) and the peripheral vein, respectively (from 4.7 +/- 0.7 [baseline] to 8.3 +/- 2.1 pg/ml at 1 min). ET further remained elevated for 1 h with persisting higher coronary sinus than peripheral venous concentrations, indicating cardiac ET release. In a control group of 18 patients without heart disease, all variables were unchanged.

CONCLUSIONS

Short-lasting severe myocardial ischemia was associated with significant ET release of cardiac origin that lasted up to 1 h.

Vasodepressor syncope due to subclinical myocardial ischemia

INTRODUCTION

Vasodepressor syncope is a common cause of syncope, but the initiating event that triggers the vasodepressor response remains incompletely understood. Although ischemia due to acute right coronary occlusion may precipitate hypotension and bradycardia through the Bezold-Jarisch reflex, an ischemic precipitant for the common vasodepressor faint has not been previously identified. In the present study, we present evidence for a causal relationship between myocardial ischemia and vasodepressor syncope.

METHODS AND RESULTS

Two patients referred for evaluation of syncope underwent upright tilt table testing with either ST segment monitoring, sestamibi scintigraphy and echocardiography during the tilt test, or coronary angiography. Both patients had positive tilt table tests during the control study. Patient 1 was documented to have reproducible ischemic ECG changes during atypical chest pressure induced by upright tilt, despite a normal coronary angiogram with ergonovine provocation. Subsequent tilt testing with simultaneous sestamibi perfusion imaging and echocardiography revealed reversible anterolateral hypoperfusion corresponding with anterolateral hypokinesis during upright tilt that preceded syncope. Ischemic ECG changes during incremental rapid atrial pacing further suggested ischemia on the basis of microvascular disease. Follow-up tilt testing on verapamil was negative. Patient 2 developed ischemic ECG changes during the recovery phase of an exercise stress test, which was followed by a vasodepressor response and frank syncope. Coronary angiography revealed a 90% distal right coronary artery stenosis that was successfully dilated, after which follow-up tilt table testing off all other medication was negative.

CONCLUSIONS

These two cases illustrate a previously unrecognized causality between myocardial ischemia and clinical vasodepressor syncope, and demonstrate that subtle manifestations of myocardial ischemia, associated with either atypical angina or silent ischemia, can provoke syncope.

17-beta-Estradiol therapy lessens angina in postmenopausal women with syndrome X

OBJECTIVES

We sought to investigate the hypothesis that estrogen replacement therapy ameliorates symptoms in postmenopausal women with syndrome X.

BACKGROUND

Syndrome X (angina pectoris, positive findings on exercise electrocardiography and normal results on coronary angiography) frequently occurs in menopausal women. This observation, in conjunction with the known vasoactive properties of estrogens, suggests that estrogen depletion may contribute to the pathogenesis of syndrome X in some women.

METHODS

Twenty-five postmenopausal patients with syndrome X completed a double-blind, placebo-controlled study of the effect of 17-beta-estradiol cutaneous patches (100 micrograms/24 h) on the frequency of chest pain and on exercise tolerance. Patients were randomly assigned to receive either placebo or 17-beta-estradiol patches for 8 weeks and were then crossed over to the other treatment.

RESULTS

During the placebo phase, patients had a mean of 7.3 episodes of chest pain/10 days. A reduction to 3.7 episodes/10 days was observed during the 17-beta-estradiol phase (p < 0.05). No significant differences were observed between the effects of 17-beta-estradiol and placebo on exercise duration or the results of other cardiologic investigations.

CONCLUSIONS

Estrogen replacement reduces the frequency of chest pain and may be a useful new therapeutic option for treating postmenopausal women with syndrome X.

Influence of radiofrequency catheter ablation on myocardial metabolism

We investigated the change of the arterial-coronary sinus lactate difference before and after radiofrequency ablation to assess the influence of radiofrequency ablation on myocardial metabolism. Sixteen patients underwent radiofrequency catheter ablation and blood sampling. The patients were further divided into two groups according to the energy received, group 1 (n = 8) with lower energy and group 2 (n = 8) with higher energy. The postpacing arterial-coronary sinus lactate difference was significantly higher than that 1 min after ablation (0.18 +/- 0.16 vs. -0.08 +/- 0.14 mmol/l, P < 0.01). The mean arterial-coronary sinus lactate difference obtained at 3 min, 5 min and 10 min increased gradually and finally approximated the postpacing lactate difference. The arterial-coronary sinus lactate difference 1 min after ablation of group 2 was significantly lower than that of group 1 (-0.03 +/- 0.14 vs. -0.13 +/- 0.14 mmol/l, P < 0.01). The arterial coronary sinus lactate differences of group 2 obtained at 3 min, 5 min and 10 min were also lower than those of group 1. However, the difference between the two groups decreased with time. This finding suggests that radiofrequency energy has an influence on the myocardial metabolism and higher energy causes more metabolic alteration than lower energy.

Myocardial metabolism in ischemic heart disease: basic principles and application to imaging by positron emission tomography

The human heart in the fasting state extracts FFA, glucose, lactate, pyruvate, and ketone bodies from the systemic circulation. Of these substrates, FFA utilization accounts for the greater part of oxygen consumption and energy production. The oxidative use of lipid (FFA) and carbohydrate (glucose and lactate) fuels is reciprocally regulated through the operation of Randle's cycle. Feeding, by increasing both insulin and glucose concentration, shifts myocardial metabolism towards preferential carbohydrate usage, both for oxidative energy generation and for glycogen synthesis. During conditions of reduced oxygen supply, the oxidation of all substrates is decreased while anaerobic metabolism is activated. In patients with coronary artery disease and stable angina pectoris, lactate release in the CS can be demonstrated during pacing stress. However, this occurs in only 50% of patients, and no relationship can be demonstrated between lactate production and the severity of ischemia. In patients with chronic angina, a significant release of alanine in the CS and an increased myocardial uptake of glutamate could be demonstrated at rest and following pacing. These two phenomena result from increased transamination of excess pyruvate to alanine with glutamate serving as NH2 donor. In addition, release of citrate (a known inhibitor of glycolysis) in the CS can be demonstrated following pacing in patients with stable angina. The introduction of PET has made it possible to study regional myocardial perfusion and metabolism in humans noninvasively. Two basically different patterns of myocardial glucose utilization have been observed in patients with coronary artery disease studied at rest using 18F-flurodeoxyglucose. In patients with stable angina on exercise but studied at rest, regional myocar- dial glucose utilization was homogeneously low and comparable with that of a group of normals. In contrast, in patients with unstable angina, myocardial glucose utilization at rest was increased even in the absence of symptoms and ECG signs of acute ischemia. In patients with stable angina, a prolonged increase in glucose uptake could be demonstrated in the post-ischemic myocardium in the absence of perfusion abnormalities, and a state of chronic metabolic ischemia is proposed. PET imaging has also allowed prospective differentiation between viable and nonviable segmental function in patients with recent myocardial infarction and in those undergoing coronary artery surgery; in both cases viable segments have relatively maintained glucose uptakes, whereas nonviable segments have depressed glucose uptakes.

Effect of aortocoronary bypass surgery on coronary circulation and myocardial metabolism during atrial pacing

Eleven patients with coronary heart disease, in whom at least one of several bypass grafts to the left coronary artery was patent, were selected for the study. The hemodynamics, coronary sinus blood flow, myocardial oxygen consumption, and myocardial lactate metabolism were evaluated at rest and during atrial pacing stress test before and after surgery. There were no significant improvements in the cardiac index, pulmonary arterial end-diastolic pressure, and left ventricular ejection fraction after aortocoronary bypass surgery. However, significant improvement of coronary sinus blood flow, myocardial oxygen consumption, and myocardial lactate extraction and consumption were found during postoperative atrial pacing compared with the preoperative findings. These results suggest that successful bypass grafting may improve myocardial lactate metabolism in ischemic lesions and contribute to the postoperative relief of angina.

Effect of pacing-induced myocardial ischemia on platelet activation and fibrin formation in the coronary circulation

The effect of pacing-induced myocardial ischemia on platelet activation and fibrin formation was investigated in seven patients with severe proximal lesions of the left anterior descending coronary artery to determine if acute ischemia activates the coagulation system. Fibrin formation was assessed from plasma levels of fibrinopeptide A. Platelet activation was assessed by levels of platelet factor 4, beta-thromboglobulin and thromboxane B2. Plasma levels were measured before, during and after acute myocardial ischemia induced by rapid atrial pacing. Blood samples were collected from the ascending aorta and from the great cardiac vein through heparin-bonded catheters. The occurrence of anterior myocardial ischemia was established by electrocardiography and by myocardial lactate extraction. No significant transmyocardial gradients in the levels of fibrinopeptide A, platelet factor 4, beta-thromboglobulin or thromboxane B2 were found at rest, during ischemia or in the recovery period, and levels in the great cardiac vein did not change in response to ischemia. These data indicate that pacing-induced myocardial ischemia does not result in release of fibrinopeptide A, platelet factor 4, beta-thromboglobulin or thromboxane B2 into the coronary circulation, and imply that acute ischemia does not induce platelet activation or fibrin formation in the coronary circulation.

Effort angina without coronary obstruction in a patient with Takayasu's aortitis: a case report

Angina occurring in patients with Takayasu's aortitis is attributed to the narrowing of the coronary ostium and/or aortic regurgitation. We treated a patient with Takayasu's aortitis with effort angina, in whom there was no obstruction of the ostium or aortic regurgitation. Treadmill exercise stress test revealed significant ST depression in leads V4-6, II, III and aVF with chest pain. Examinations of lactate in coronary sinus as well as arterial blood suggested the occurrence of myocardial ischemia during atrial pacing. The DPTI/TTI index was decreased and the left ventricular end-diastolic pressure was increased during angina. It is considered that the reduced coronary perfusion pressure resulted from a low diastolic aortic pressure and the elevated left ventricular end-diastolic pressure decreased the DPTI/TTI index and contributed to the development of subendocardial ischemia.

Increased coronary sinus lactate concentration during pacing induced angina pectoris after clinical improvement by glyceryl trinitrate

Ten patients with stable angina pectoris and obstructed coronary arteries (greater than 75% reduction in diameter) were studied before and during two periods of pacing, the second of which was preceded by sublingual administration of glyceryl trinitrate (mean dose 0.78 mg). Coronary sinus blood flow measurements and aortocoronary sinus blood sampling for metabolite determinations were carried out. Although the rate of pacing was increased by 10 beats/minute after glyceryl trinitrate administration, the onset of angina was delayed in eight patients during pacing. Drug administration decreased coronary sinus blood flow by 42% and myocardial oxygen uptake by 41% during pacing and induced a shift in mean lactate extraction towards a net release (from 3.1% to -12.6%). It increased the number of patients producing lactate from three to five. Glyceryl trinitrate administration decreased myocardial glucose uptake throughout the study, decreased lactate extraction during recovery, and increased the aortocoronary sinus citrate gradient at rest and during recovery, while the exchange of free fatty acids remained unchanged. A decrease in aortocoronary sinus lactate difference during pacing after glyceryl trinitrate administration correlated positively with the fall in coronary sinus blood flow. The metabolic data do not indicate an augmented myocardial lactate production after glyceryl trinitrate administration. A decrease in coronary sinus blood flow seems, therefore, to be of primary importance in explaining the elevated coronary sinus lactate concentration. Our finding that coronary sinus lactate concentration increased during pacing after glyceryl trinitrate administration despite clinical improvement questions the validity of its use as a quantitative index of ischaemia.

Therapy of coronary vasoconstriction in patients with coronary artery disease

Patients with obstructive coronary artery disease and stable, exertional angina respond to the alpha adrenergic stimulus of the cold pressor test with an inappropriate increase in coronary vascular resistance. The clinical significance of this abnormal response and its possible role in the pathogenesis of ischemic heart disease are discussed. Comparison of the anti-anginal agents currently in use of undergoing investigation suggests that the calcium antagonists may be the most effective therapy for coronary vasoconstriction. Nifedipine, 10 mg buccally, successfully prevented the increase in coronary vascular resistance during the cold pressor test in 10 of 10 patients, whereas the response in placebo-treated patients was unaltered. This dose of nifedipine was without effect on systemic hemodynamics or myocardial oxygen consumption, suggesting a selective antivasoconstrictor effect on the coronary vasculature.

Antianginal and myocardial metabolic properties of verapamil in coronary artery disease

To determine the metabolic cost of administering an experimental calcium antagonist, verapamil, to patients with coronary artery disease, 12 such patients were studied at rest and during stress with atrial pacing before and after intravenous treatment with verapamil (bolus dose of 0.1 mg/kg body weight, followed by infusion at 0.005 mg/kg per min). The mean (+/- standard deviation) aortic pressure at rest (98 +/- 22 mg Hg), coronary sinus blood flow (88 +/- 17 ml/min) and myocardial oxygen consumption (10.7 +/- 2.4 ml O2/min) decreased to 88 +/- 20 mm Hg (p < 0.0004), 77 +/- 14 ml/min (p < 0.03) and 8.8 +/- 2.5 ml O2/min (p < 0.01), respectively, after administration of verapamil. With atrial pacing, these values were 105 +/- 25 mm Hg, 151 +/- 50 ml/min and 18.5 +/- 6.4 ml O2/min, respectively, before infusion of verapamil, and then decreased to 87 +/- 14 mm Hg (p < 0.006), 107 +/- 31 ml/min (p < 0.0002) and 13.3 +/- 4.4 ml O2/min (p < 0.001) during infusion. Angina occurred in all patients with atrial pacing before verapamil (threshold to pain: 93 +/- 67 seconds). After verapamil, the threshold to pain in six patients increased to 191 +/- 183 seconds; and no pain was experienced by the remaining six (p < 0.0005). Before administration of verapamil lactate extraction decreased from 24 +/- 9 to 10 +/- 11 percent (p < 0.0002) during atrial pacing, and 9 (75 percent) of the 12 patients exhibited electrocardiographic S-T segment depressions. After administration of verapamil lactate extraction normalized to 22 +/- 9 percent during atrial pacing, and the electrocardiogram reverted to baseline in all but one patient. These findings indicate that verapamil decreases left ventricular myocardial metabolic demands, and concomitantly greatly increases the threshold to angina.