Myocardial release of lactate, inosine and hypoxanthine during atrial pacing and exercise-induced angina

Microneedle-based interstitial fluid extraction for drug analysis: Advances, challenges, and prospects

Similar to blood, interstitial fluid (ISF) contains exogenous drugs and biomarkers and may therefore substitute blood in drug analysis. However, current ISF extraction techniques require bulky instruments and are both time-consuming and complicated, which has inspired the development of viable alternatives such as those relying on skin or tissue puncturing with microneedles. Currently, microneedles are widely employed for transdermal drug delivery and have been successfully used for ISF extraction by different mechanisms to facilitate subsequent analysis. The integration of microneedles with sensors enables in situ ISF analysis and specific compound monitoring, while the integration of monitoring and delivery functions in wearable devices allows real-time dose modification. Herein, we review the progress in drug analysis based on microneedle-assisted ISF extraction and discuss the related future opportunities and challenges.

Detection of intraoperative myocardial ischaemia--a comparison among electrocardiographic, myocardial metabolic, and haemodynamic measurements in patients with reduced ventricular function

This study determined the sensitivity and specificity of haemodynamic and ECG monitors to detect the development of intraoperative myocardial ischaemia utilizing myocardial lactate production as the standard. In 29 patients with reduced ejection fraction (0.27-0.50) undergoing coronary artery revascularization, measurements were made at the awake, post-induction, post-intubation, first skin incision, post-sternotomy, pre-protamine, immediately post-cardiopulmonary bypass, and skin suture intervals. At each interval, measurement of a haemodynamic profile (including pulmonary artery occlusion (PAOP) and central venous (CVP) pressures, heart rate, and pressure rate quotient); myocardial lactate extraction and flux; changes in ST segments in ECG leads, V5 and II utilizing a Siemens 1280 intraoperative monitor, and a Marquette 8500 Holter monitor utilizing leads V5, V2, and AVF were made. "Ischaemia" was considered to be present when myocardial lactate production (MLP) occurred, PAOP or CVP increased by 5 mmHg above the baseline value, the pressure rate quotient was < 1, or ST segment deviation (> 1 mm) occurred in any lead for > 1 min. Variables positive when MLP was positive were the pressure rate quotient (sensitivity 32.8%, specificity 71.9%), CVP (sensitivity 10.9%, specificity 92.6%), and PAOP (sensitivity 1.6%, specificity 99.2%). Holter monitoring had a 100% positive predictive value but poor sensitivity (1.6%). The ECG (Lead V5 + II) measures of ischaemia were insensitive (17.5%) and relatively non-specific (87.7%). We conclude that, in this patient group and using myocardial lactate production as the standard, the pressure rate quotient, elevations in CVP or PAOP, or ST segment changes are insensitive measures of intraoperative myocardial ischaemia.

The use of HPLC to evaluate the variations of blood coronary adenosine levels during percutaneous transluminal angioplasty

Although it is well established that adenosine is released during acute ischemia, little is known of the behaviour of adenosine levels following treatment of coronary lesion by percutaneous transluminal coronary angioplasty (PTCA). Using high performance liquid chromatography, we measured intracoronary adenosine levels before and 5 min after PTCA in ten patients with one-vessel disease and a significant (> 70%) coronary stenosis. Adenosine levels decrease in all patients after PTCA. Nevertheless, more studies are now necessary to evaluate the possible predictive value (with regard to restenosis) of coronary adenosine levels after PTCA.

Anaesthesia for coronary artery surgery--a plea for a goal-directed approach

The purpose of the current literature review was to examine whether changes in current anaesthetic techniques are warranted for patients undergoing coronary artery surgery in light of recent information presented in the literature. The objectives of a cardiac anaesthetic technique are to maintain haemodynamic stability and myocardial oxygen balance, minimize the incidence and severity of ischaemic episodes, be aware of cardiopulmonary bypass-induced pharmacokinetic changes, and facilitate early tracheal extubation if appropriate. Many techniques have been utilized. Provided attention is paid to the details of managing myocardial oxygen supply and demand, none has emerged as superior in preventing intraoperative myocardial ischaemia. Silent myocardial ischaemia (i.e., ischaemia occurring in the absence of haemodynamic aberrations) is common throughout the perioperative period and may occur even in the presence of an appropriately used anaesthetic technique. The incidence and severity appear to be greatest in the postoperative period when the effects of anaesthesia are dissipating. The use of high-dose opioid anaesthesia may no longer be the most appropriate technique to facilitate the anaesthetic objectives. The role of pain management in altering the incidence of ischaemia requires further study. Increased waiting lists for cardiac surgery and ever-diminishing resources should prompt a re-evaluation of early extubation (i.e., within eight hours) as a method of improving utilization of scarce ICU resources. It is suggested that this should be possible with currently available agents to achieve the anaesthetic objectives. Future suggestions for research in this area are made.

Inosine--a natural modulator of contractility and myocardial blood flow in the ischemic heart?

The energetic role of inosine (INO) remains controversial. The aim of the present study was first to test whether endogenous INO consumption/production correlates with regional myocardial contractile performance and second to test whether locally increased levels of INO influence contractility and blood flow in severely ischemic myocardium. Fentanyl-anesthetized dogs with implanted sonomicrometry crystals and independently perfused left anterior descending coronary arteries were studied. Two relatively load-independent indexes of regional myocardial contractility derived from left ventricular pressure-segment length loops were used: the regional stroke work-end-diastolic segment length relationship (Wr/L(ed)) and the end-systolic pressure-segment length relationship (Plv/L(es)). Very good correlations between myocardial contractile performance (as measured by the slope of the regional Wr/L(ed) relationship) and endogenous INO consumption/production under both nonischemic and ischemic conditions were found. Ischemia severely depressed contractility, significantly shifting rightward the Wr/L(ed) and Plv/L(es) relationships. INO infused into the left anterior descending bypass, in a concentration of 600 to 800 mumol/L, partially restored contractile performance as evidenced by a significant leftward displacement of both relationships. Wr, measured at a common maximum L(ed), increased significantly by 61 +/- 5%. Border-zone collateral flow (microspheres) increased by 35 +/- 7% within the endocardial segments and by 34 +/- 9% in the epicardial segments, but no increase in flow in the ischemic region was measureable. With the current emphasis on recanalization with thrombolytic therapy and considering the apparent safety of INO, this naturally occurring nucleoside might prove to be a useful adjunctive agent in the treatment of acute myocardial ischemia.

Systemic and coronary hemodynamic effects of bepridil in patients with depressed left ventricular function

To assess the effects of oral bepridil therapy (10-14 days) on cardiac performance and myocardial energetics in the presence of depressed left ventricular function, systemic and coronary hemodynamic effects and neurohumoral effects were evaluated in 7 patients with coronary artery disease and reduced ejection fraction at control, submaximal, and maximal pacing rates during atrial pacing stress. After bepridil therapy, arterial, right atrial, and left ventricular filling pressures as well as systemic vascular resistance and left ventricular stroke work index did not change, suggesting no deleterious effects of bepridil on cardiac performance in patients with reduced ejection fraction. Rate-pressure product, myocardial oxygen consumption, coronary sinus blood flow, myocardial lactate extraction, and catecholamine balance remained unchanged. Development of angina during pacing showed a variable response to bepridil. We conclude that despite its potential negative inotropic effect, bepridil does not exert deleterious effects on hemodynamics or left ventricular performance. The mechanism for its beneficial antianginal effect may be due to favorable redistribution of myocardial blood flow to ischemic zones; no clear effect on anginal threshold or sympathetic tone could be demonstrated in these patients.

Evaluation of the metabolic compensation after treadmill test in patients with peripheral occlusive arterial disease

Patterns of release of lactate, hypoxanthine, and arginine into the bloodstream after a standardized treadmill test (twelve minutes, 1.6-2.8 mph, inclination 0,5,10,15%) were recorded in 21 consecutive patients with stage II peripheral arterial occlusive disease. Heart rate, systolic blood pressure, ankle blood pressure, and ankle/brachial systolic blood pressure ratio (A/B ratio), as well as plasma lactate, plasma hypoxanthine and serum arginine were recorded before and at fifteen to thirty-minute intervals for up to two hours after the treadmill test. Immediately after the treadmill test, lactate levels (36.6 +/- 3.7 mg/L) and hypoxanthine levels (2.73 +/- 0.19 mmol/L) were significantly (p less than 0.001) increased but returned to preexercise levels after thirty and sixty minutes, respectively. Arginine levels did not change significantly. Ankle blood pressure (57 +/- 5 mm Hg) and A/B ratio (0.40 +/- 0.04) were significantly (p less than 0.001) decreased after exercise, while heart rate and systolic blood pressure were increased. These parameters returned to normal as well within a half hour after exercise. Absolute walking distance correlated significantly (p less than 0.01) with the postexercise systolic blood pressure (r = -0.62), ankle pressure (r = 0.63) and A/B ratio (r = 0.72). Induced hypoxanthine and lactate production intercorrelated significantly positively (r = 0.57, p = 0.007) but were independent of the absolute walking distance. In contrast with lactate, hypoxanthine production correlated significantly with postexercise ankle pressure (r = 0.49, p = 0.02) and exercise-induced fall in A/B ratio (r = 0.66, p = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of stress-induced ST elevation and negative T-wave normalization studied by serial cardiokymogram in patients with a previous myocardial infarction

Seventeen patients with a previous myocardial infarction were studied during pacing to characterize the clinical correlates of ST elevation, to analyze the relation between ST elevation and negative T-wave normalization and to investigate the mechanism of these electrocardiographic changes. Myocardial ischemia was evaluated by measurement of blood lactate, and wall motion was analyzed using cardiokymographs concurrently and serially. Results show that ST elevation and negative T-wave normalization were most marked in leads containing abnormal Q waves, that ST elevation greater than or equal to 1 mm during pacing was associated with a significant increase in left ventricular end-diastolic pressure and deterioration of left ventricular wall motion and that the magnitude of ST elevation and negative T-wave normalization was significantly correlated, but the latter appeared earlier and more markedly. In addition, there was no significant correlation between the extent of either ST elevation or negative T-wave normalization and myocardial lactate production. Thus, ST elevation and negative T-wave normalization are caused by abnormal left ventricular wall motion rather than myocardial ischemia. Negative T-wave normalization is a more sensitive marker of abnormal wall motion than ST elevation in patients with a previous myocardial infarction.

Biochemical indicators of myocardial ischaemia during coronary artery bypass grafting

Metabolic indicators of myocardial ischaemia were measured in coronary sinus blood in six patients undergoing coronary artery bypass grafting (CABG). Five arterial and coronary sinus blood samples were taken in each case--one before cardiopulmonary bypass (CPB), and three during and one after CPB. Moderate hypothermia with topical cardiac cooling and cold cardioplegia were used. Myocardial infarction occurred perioperatively in two patients. Myocardial lactate production was not found before CPB in any patient, but it was common during CPB. Adenosine, inosine and hypoxanthine were released into the coronary sinus blood, but their release did not correlate significantly with lactate production. Myocardial noradrenaline production showed positive correlation with lactate levels (p less than 0.05). Release of adrenaline from the myocardium during CABG was also demonstrated. Myocardial catecholamine production was especially seen in the patients with myocardial infarction. Myocardial catecholamine release seemed to be the most sensitive of the studied biochemical indicators of myocardial ischaemia during CABG.

Myocardial release of hypoxanthine and lactate during percutaneous transluminal coronary angioplasty

The response of myocardial lactate and hypoxanthine metabolism during percutaneous transluminal coronary angioplasty was studied in a series of 15 patients undergoing this procedure. A minimum of 4 balloon inflations was performed per patient with an average duration per occlusion of 49 +/- 11 seconds (mean +/- standard deviation) for a total occlusion time of 192 +/- 40 seconds. Thermodilution coronary venous blood flow measured in the great cardiac vein decreased from control values of 72 +/- 4 ml/min (mean +/- standard error of the mean) to 47 +/- 10 ml/min with the fourth coronary occlusion (p less than 0.005). Arteriovenous lactate and hypoxanthine showed peak differences during the reactive hyperemia after the first 2 occlusions which did not increase after subsequent occlusions. Within minutes after the procedure, lactate and hypoxanthine efflux was no longer seen, demonstrating the reversibility of the metabolic disturbances after repeated ischemia. The results of this study indicate that there is no permanent alteration in lactate or hypoxanthine metabolism after percutaneous transluminal coronary angioplasty with 4 coronary occlusions of 40 to 60 seconds' duration, with a total occlusion time of 192 +/- 40 seconds.

Release of adenosine and lactate from human hearts during atrial pacing in patients with ischemic heart disease

Thirty-eight patients treated by atrial pacing were divided into three groups (Group I, patients with neither coronary stenosis nor anginal pain during pacing; Group II, patients with no coronary stenosis but having anginal pain during pacing; Group III, patients with coronary stenosis). The concentrations of adenosine and lactate were measured in the coronary sinus blood and in the arterial blood before, during, and after atrial pacing. During atrial pacing, significant levels of adenosine were released from the heart of patients in Group III, whereas significant lactate release was observed in Groups II and III. In Group II, the concentration of adenosine in coronary sinus blood appeared to increase during pacing, but not significantly. There was no significant correlation between the release of adenosine and that of lactate. A significant release of adenosine due to atrial pacing may be observed only in patients with coronary artery disease.

Differing time courses between delta lactate and mitochondrial respiration during coronary occlusion and after reperfusion in canine hearts

The present study was designed to clarify whether or not a difference between arterial and venous lactate (delta lactate) levels is useful for evaluation of mitochondrial function in ischemia-reperfused myocardium. In the first experiment, 12 dogs were divided into 2 groups: 10-min occlusion of the left anterior descending coronary artery (LAD) followed by 10-min reperfusion, or 30-min occlusion followed by 40-min reperfusion, were performed. The lactate levels in the femoral artery and the great cardiac vein were measured enzymatically. delta Lactate was reversed immediately after occlusion. Ten min and 20 min were required for the recovery of delta lactate in the 10-min-occlusion with 10-min-reperfusion, and 30-min-occlusion with 40-min-reperfusion groups, respectively. In the second experiment, 36 dogs were divided into 6 groups: 10-min occlusion of LAD; 10-min occlusion with 10-min reperfusion; 30-min occlusion; and 30-min occlusion with 10-, 20-, or 40-min reperfusion were performed. Mitochondria from normal and occluded or reperfused areas were prepared, and the respiratory function of the mitochondria was measured polarographically. No significant decreases in the mitochondrial function were observed in the 10-min-occlusion, and 10-min-occlusion with 10-min-reperfusion groups. On the other hand, respiratory function of mitochondria was impaired by 30-min occlusion and was not improved by 10- or 20-min reperfusion. Significant recovery in the mitochondrial function was observed after 40-min reperfusion. That is, differing recovery time courses between delta lactate and the mitochondrial function were observed.

Effect of pressure-controlled intermittent coronary sinus occlusion on pacing-induced myocardial ischemia in domestic swine

This study tested the hypothesis that pressure-controlled intermittent coronary sinus occlusion (PICSO) would be useful in ameliorating myocardial ischemia under conditions characterized by preserved, but reduced (relative to demand), myocardial blood flow. Studies were conducted in closed-chest, sedated domestic swine prepared with an artificial stenosis that reduced luminal diameter of the animal's left anterior descending coronary artery by 80%. Measurements of hemodynamics, regional myocardial blood flow, and oxygen, lactate, and nucleoside metabolism were obtained in 10 animals (1) before placement of stenosis, (2) 30 min after insertion of stenosis, (3) after 30 and 60 min of PICSO, and (4) 30 min after discontinuation of PICSO. Two groups of control animals were studied to observe the natural history of metabolic markers of ischemia. Control group I consisted of four animals studied concurrently and subjected to the same protocol except for the fact that PICSO was not applied. Control group II consisted of eight additional animals studied as a group. A specially designed balloon-tipped catheter positioned in the proximal portion of the animal's great cardiac vein was used to provide PICSO. Heart rate was controlled by atrial pacing (rate, 145 beats/min) through the study. After placement of the stenosis, flow in endocardial and transmural layers distal to the stenosis declined significantly (p less than .01) vs control. Application of PICSO failed to increase arterial inflow distal to the stenosis in any myocardial layer. Myocardial aerobic metabolism was adversely affected by stenosis and changed from consumption of lactate, inosine, and hypoxanthine before stenosis to production at 30 min after stenosis. Although PICSO was associated with reduced production and a return toward consumption of lactate, inosine, and hypoxanthine, a similar pattern of changes in lactate, inosine, and hypoxanthine metabolism was observed in control animals over a comparable period of time. In addition, regional myocardial oxygen extraction and consumption were not changed vs poststenosis levels by PICSO. However, in comparison with controls, PICSO did accelerate the rate of resolution of myocardial ischemia as assessed by lactate metabolism. At 30 min of PICSO (or sham) the change vs poststenosis was +33.6 +/- 25.0 mumol/min/100 g in the PICSO but only +6.7 +/- 29.7 in the control group (p = .05). We conclude, therefore, that even though PICSO did not alter the final level of myocardial ischemia under conditions modeled in this study it did accelerate its rate of resolution, an effect that may be beneficial clinically.

Relation between coronary artery stenosis and myocardial purine metabolism, histology and regional function in humans

In 54 patients undergoing elective or emergency aortocoronary bypass grafting, angiographic and electrocardiographic changes were studied. Five patients with unstable angina and five patients with evolving myocardial infarction were included. High energy phosphate metabolism and the histologic appearance of the myocardium were analyzed in transmural biopsy specimens acquired at the time of surgery. In patients without anterior infarction on the electrocardiogram, severe stenosis of the left anterior descending coronary artery resulted in a reduction of anterior wall motion that was associated with a partial depletion of the adenylate pool. Mitochondrial function, however, remained intact: the adenosine diphosphate/adenosine triphosphate ratio, the energy charge and the creatine phosphate/adenosine triphosphate ratio were in the normal range. Histologic assessment demonstrated viable myocardium with a high incidence of atrophic cells. In evolving myocardial infarction, 170 minutes of acute coronary artery obstruction resulted in anterior wall akinesia associated with a decrease of the sum of the adenylates to 52% and of creatine phosphate to 16% of their normal value (p less than 0.05). The nucleosides accumulated; their major fraction (91%) was inosine. The adenosine diphosphate/adenosine triphosphate ratio increased from 0.14 +/- 0.04 to 0.49 +/- 0.20 (p less than 0.01) and the energy charge decreased from 0.924 +/- 0.021 to 0.660 +/- 0.169 (p less than 0.01). Ultrastructure examination revealed irreversible cell damage in at least the subendocardial layer. These results suggest that the energetic base of reduced contractility due to severe coronary artery stenosis is different from that in acute coronary obstruction.(ABSTRACT TRUNCATED AT 250 WORDS)

Enalaprilat, a new parenteral angiotensin-converting enzyme inhibitor: rapid changes in systemic and coronary hemodynamics and humoral profile in chronic heart failure

Systemic and coronary hemodynamic, metabolic and humoral effects of a new intravenous angiotensin-converting enzyme inhibitor, enalaprilat, were evaluated in 14 patients with chronic heart failure. Onset of hemodynamic action occurred within 15 minutes and persisted for 6 hours. At the time of peak effect, there was a significant reduction in mean arterial pressure (-21%) and pulmonary capillary wedge pressure (-33%). Systemic vascular resistance decreased by 32% and stroke volume index increased by 20%. These systemic hemodynamic changes indicate improved left ventricular function. There was a substantial sustained reduction in rate-pressure product initially without a change in coronary sinus blood flow or myocardial oxygen consumption. There was also reduced myocardial oxygen extraction and augmented coronary sinus oxygen saturation at 30 minutes and 1 hour. In three patients, abnormal myocardial lactate extraction, present before enalaprilat, changed to uptake after enalaprilat, indicating amelioration of myocardial ischemia that was not clinically manifest. Systemic catecholamine levels and myocardial catecholamine balance did not change. Plasma renin activity increased and plasma aldosterone decreased. These findings suggest that enalaprilat produces inhibition of the angiotensin-converting enzyme and consequent beneficial systemic hemodynamic changes in heart failure. In some patients with heart failure, silent myocardial ischemia at rest can occur and can be alleviated with enalaprilat. Decreased myocardial oxygen extraction, increased coronary sinus oxygen saturation and lack of expected decrease in coronary sinus blood flow despite reduced rate-pressure product suggest transient coronary vasodilation by enalaprilat.

Cardiovascular effects of adenosine

The results, briefly summarized above, indicate that adenosine could be a physiologically important modulator of several aspects of cardiovascular regulation. Most cells are equipped with adenosine receptors. These receptors are of at least two subtypes which can be defined by the relative agonist potency. At these adenosine receptors, methylxanthines, including caffeine and theophylline, act as competitive antagonists. The role of adenosine antagonism, as a mechanism behind the cardiovascular effects of these xanthines, was recently reviewed (Fredholm, 1984). The concentrations of adenosine are low during resting conditions, but may be raised substantially by, for example, hypoxia, ischaemia and increased mechanical or biochemical work. The adenosine levels can also be raised by drugs, including uptake inhibitors such as dipyridamole. Already the concentrations of adenosine that occur during basal conditions are sufficient to produce significant effects, for example, on blood-flow. When the concentrations are raised the importance of endogenous adenosine becomes even greater. Adenosine may not only be of physiological significance but may also be pharmacologically important. First, there are several drugs that may act by affecting the levels of adenosine or by influencing its receptors. Second, the possibility exists that adenosine itself could be used clinically. For example, adenosine may be an attractive alternative to sodium nitroprusside or nitroglycerin when controlled hypotension is to be achieved. Adenosine may also be used to preserve blood platelets during extracorporal circulation or to produce selective regional vasodilatation. Both the physiological and pharmacological aspects are subject to intense study in several laboratories.

Cardiovascular effects of adenosine in man; possible clinical implications

The results summarized above indicate that adenosine is a physiologically relevant modulator of the cardiovascular system in man. The levels of adenosine are low during resting conditions, but may increase during conditions of oxygen and/or substrate deficiency. Already the basal concentration seems to be sufficient to affect regional flow in vital organs such as the heart. Several drugs may act by increasing the levels of adenosine or by influencing its receptors. In addition, adenosine may be used in many clinical situations as a vasodilator, antiaggregatory compound as well as an antiarrythmic agent. Its effect is easy to control due to the extremely short plasma half-life. The dose range for the clinical effects are summarized in Table 6. Both the physiological and pharmacological aspect of adenosine are subject to intense study in several laboratories.

Effects of a selective thromboxane synthetase inhibitor, dazoxiben, and of acetylsalicylic acid on myocardial ischemia in patients with coronary artery disease

Thromboxane A2 (TxA2) may aggravate myocardial ischemia by inducing vasoconstriction and platelet aggregation in small coronary vessels, whereas prostacyclin (PGI2) counteracts these effects. Acetylsalicylic acid (ASA) inhibits the formation of TxA2 as well as PGI2, whereas dazoxiben, a thromboxane synthetase inhibitor, reduces TxA2 formation selectively. In 25 patients with coronary artery disease, 2 identical atrial pacing stress tests were performed: before and after the administration of dazoxiben (200 mg) in 15 patients and before and after ASA (250 mg) in 10. The ischemic response, quantified by coronary sinus and aortic lactate levels and by ST depression, was significantly reduced after administration of dazoxiben (p less than 0.02) but not after ASA. Heart rate at rest, myocardial extraction of free fatty acids and the arteriovenous oxygen difference was unaffected by medication. Both drugs reduced TxB2 levels to the same extent, whereas collagen-induced aggregation was more reduced after ASA than after dazoxiben. The effect of dazoxiben on ischemia was probably a result of inhibited TxA2 and preserved PGI2 production, which increased blood flow to ischemic regions.

Abnormalities in myocardial perfusion during tachycardia in dogs with left ventricular hypertrophy: metabolic evidence for myocardial ischemia

This study tested the hypothesis that in the chronically hypertrophied left ventricle pacing stress may cause abnormalities of perfusion that result in myocardial ischemia. Left ventricular hypertrophy (LVH) was produced by banding the ascending aorta of 10 dogs at 6 weeks of age, and studies were carried out after the animals had reached adulthood and when mean left ventricular/body weight ratio was 74% greater than in eight control dogs. Myocardial blood flow was measured with microspheres during pacing at 100, 200, and 250 beats/min, while aortic and coronary sinus blood samples were obtained for determination of concentrations of lactate and the adenosine metabolites inosine and hypoxanthine. In the control dogs, increasing heart rates were associated with an increase in mean myocardial blood flow while subendocardial flow was maintained at a level equal to or greater than subepicardial flow. Myocardial lactate uptake ranged from +60% to -5%, and adenosine metabolites were not detected in coronary sinus blood (less than 0.5 microM/l). In four dogs that underwent aortic banding no production of lactate or adenosine metabolites was observed at any heart rate; in these animals subendocardial flow was maintained at a level equal to or greater than subepicardial flow at all pacing rates. The remaining six dogs with LVH demonstrated net lactate production significantly greater than control during pacing at 250 beats/min; five of these six animals also produced adenosine metabolites.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in left ventricular volumes and ejection fraction during atrial pacing in patients with coronary artery disease: assessment with radionuclide ventriculography

The present study was performed to determine the utility of radionuclide ventriculography (RNV) in conjunction with atrial pacing in the identification of individuals with coronary artery disease. Accordingly, left ventricular end-diastolic volume index, end-systolic volume index, ejection fraction, and regional wall motion were measured with radionuclide ventriculography before and during atrial pacing in 37 patients: 27 with and 10 without (control subjects) coronary artery disease. In the control subjects, pacing caused a decrease in end-diastolic volume index (77 +/- 19 [mean +/- SD] ml/M2 at rest, 50 +/- 18 ml/M2 at peak pacing; p less than 0.001), a decrease in end-systolic volume index (34 +/- 14 ml/M2 at rest, 19 +/- 9 ml/M2 at peak pacing; p less than 0.001), an increase in ejection fraction (0.61 +/- 0.11 at rest, 0.66 +/- 0.11 at peak pacing; p = 0.006); and no deterioration in wall motion. In 16 patients with coronary artery disease who developed ECG and/or metabolic evidence of ischemia during pacing, end-diastolic volume index decreased (87 +/- 26 ml/M2 at rest, 69 +/- 24 ml/M2 at peak pacing; p less than 0.001), end-systolic volume index was unchanged (43 +/- 20 ml/M2 at rest, 44 +/- 21 ml/M2 at peak pacing; p = NS), ejection fraction decreased (0.55 +/- 0.12 at rest, 0.40 +/- 0.14 at peak pacing; p less than 0.001), and new wall motion abnormalities developed in 14. In 11 patients with coronary artery disease but no ECG or metabolic evidence of ischemia, pacing caused a decrease in end-diastolic volume index (80 +/- 26 ml/M2 to 61 +/- 31 ml/M2; p less than 0.001), a decrease in end-systolic volume index (36 +/- 17 ml/M2 to 28 +/- 20 ml/M2; p = 0.002), no change in ejection fraction (0.60 +/- 0.11 to 0.60 +/- 0.13; p = NS), and new wall motion abnormalities in four. Although the specificity of these scintigraphic measurements for the identification of patients with coronary artery disease was excellent (1.0), the combined sensitivity of all scintigraphic measurements was high only if ECG or metabolic evidence of ischemia was present: 0.94 in patients with evidence of ischemia but only 0.36 in those without ischemia. Thus radionuclide ventriculography during incremental atrial pacing is useful in the identification of patients with coronary artery disease only if ischemia is induced.

Symptomatic, electrocardiographic, metabolic, and hemodynamic alterations during pacing-induced myocardial ischemia

Atrial pacing has been used to assess the physiologic impact of coronary artery disease (CAD). Several variables have served as markers of pacing-induced myocardial ischemia, but their specificities and sensitivities are unknown. Accordingly, in 28 patients, incremental atrial pacing was performed. Of the 28, 10 had no CAD. The left ventricular ejection fraction (LVEF) (by gated equilibrium blood pool scintigraphy) increased in this group (0.60 +/- 0.11 [mean +/- standard deviation] before pacing to 0.67 +/- 0.13 at peak-pacing, p = 0.002). In no patient did left ventricular end-diastolic pressure increase by greater than 5 mm Hg. No patient had lactate production, and 2 (20%) had electrocardiographic S-T segment depression greater than or equal to 0.1 mV. Four (40%) had chest pain with atrial pacing. In the remaining 18 patients with CAD, atrial pacing caused a decrease in LVEF greater than or equal to 0.05 (0.46 +/- 0.10 to 0.33 +/- 0.09, p less than 0.001) and new segmental wall motion abnormalities in all, indicating pacing-induced myocardial ischemia. Only 8 (44%) had an increase in left ventricular end-diastolic pressure of greater than 5 mm Hg, and only 9 (50%) had lactate production. Ten (56%) had ischemic electrocardiographic changes, and 12 (67%) had chest pain. Thus, the electrocardiographic, metabolic, and hemodynamic alterations that may accompany pacing-induced ischemia are specific but relatively insensitive markers of ischemia. In contrast, chest pain during atrial pacing is a nonspecific occurrence, appearing with similar frequency in normal subjects and patients with CAD and pacing-induced ischemia.

Myocardial lactate and adenosine metabolite production as indicators of exercise-induced myocardial ischemia in the dog

To determine the value of lactate and the adenosine metabolites inosine and hypoxanthine as indicators of myocardial ischemia, we measured the levels of these metabolites in arterial and coronary sinus blood of nine chronically instrumented dogs subjected to exercise stress before and during reversible circumflex coronary artery occlusion. The degree of circumflex bed hypoperfusion was measured by 15-mu microspheres and the reduction in circumflex coronary flow was measured with a proximal flow probe. Adenosine metabolites, although below the level of accurate detection in our laboratory in arterial blood (i.e., 0.5 microM/l), were detected in coronary sinus blood (range 2.7--18.7 microM/l) in 26 of 33 studies with partial circumflex occlusion when circumflex flow was reduced to less than 80% of that seen during exercise without occlusion and when only subendocardial perfusion was reduced. Global left ventricular flow and transmural flow in nonischemic beds did not correlate with positive studies. Myocardial lactate extraction was a less accurate test for determining circumflex bed hypoperfusion. Thus, myocardial production of adenosine metabolites is a sensitive qualitative test of exercise-induced ischemia responding to a modest fall in coronary flow when only subendocardial hypoperfusion is present.

Derangements in myocardial purine and pyrimidine nucleotide metabolism in patients with coronary artery disease and left ventricular hypertrophy

Studies in animal models of myocardial ischemia and left ventricular hypertrophy have demonstrated a number of derangements in purine and pyrimidine nucleotide content of myocardium that are postulated to play a role in the pathogenesis of muscle dysfunction in these disorders. The present study examined myocardium of patients with coronary artery disease, left ventricular hypertrophy, or neither of these two abnormalities, to determine whether derangements in purine and pyrimidine nucleotide metabolism occur in humans. In patients with coronary artery disease, endocardial content of ATP, GTP, UTP, CTP, and creatine phosphate was reduced and ranged between 60% and 86% of the amount found in the epicardium. In patients without coronary artery disease or ventricular hypertrophy, endocardial content of these nucleotides was equal to or greater than that of epicardium. Endocardial and epicardial content of inosine was increased in patients with coronary artery disease, and after vein bypass grafting inosine content fell to the levels observed in myocardium of patients with normal coronary arteries. In patients with left ventricular hypertrophy, endocardial content of ATP, GTP, UTP, CTP, and creatine phosphate was also reduced and ranged between 64% and 88% of the epicardial content. In contrast to results obtained in patients without left ventricular hypertrophy, epicardial content of GTP, UTP, and CTP was increased by 131%, 123%, and 132% in hypertrophied myocardium. Thus the changes noted in myocardial nucleotide content in patients are similar to those noted in animal models of occlusive coronary disease and ventricular hypertrophy. These results suggest that the pathophysiological abnormalities in nucleotide metabolism noted in animal models also occur in human myocardium.

Myocardial release of citrate and lactate during atrial pacing-induced angina pectoris

Arterio-coronary sinus (A-Cs) differences of plasma citrate, glucose, free fatty acids and blood lactate were measured in 19 patients with coronary artery disease (CAD) and in eight control subjects exposed to atrial pacing. Among patients with CAD 11 showed a myocardial release of lactate during pacing (lactate producers, LP) while myocardial lactate extraction was unchanged in the remaining eight patients (lactate non-producers, LNP). In patients with CAD, (A-Cs) plasma citrate differences became increasingly negative during recovery from pacing, values at rest and at 3-5 min of recovery were: -5 +/- 2 mumol/l (mean +/- SD) vs. -12 +/- 5 mumol/l in LP (P less than 0.001) and -6 +/- 3 mumol/l vs. -8 +/- 4 mumol/l in LNP (P less than 0.01). In controls, (A-Cs) citrate difference varied inversely, from -8 +/- 4 mumol/l at rest to -2 +/- 4 mumol/l at 3-5 min of recovery (P less than 0.001). An increasingly negative (A-Cs) plasma citrate difference during recovery from pacing-induced angina pectoris is suggested to reflect a wash-out of accumulated citrate from ischaemic heart cells; and is proposed as a more sensitive marker of ischaemia in man than a myocardial release of lactate.

Myocardial release of lactate, inosine and hypoxanthine during atrial pacing and exercise-induced angina

The coronary venous efflux of lactate, inosine and hypoxanthine during pacing-induced angina has been compared with myocardial extraction of the catabolites during exercise-induced angina. Inosine and hypoxanthine were analyzed by enzyme assay after separation by column chromatography. Myocardial lactate extraction at rest (15 +/- 9%, mean +/- SD) was converted to production levels (-34 +/- 26%) during pacing-induced angina (p less than 0.0005) and increased (24 +/- 13%) during exercise (p less than 0.05). The arterial values at rest (850 +/- 330 mumol/1) were unchanged during pacing and increased five-fold during exercise (4380 +/- 1860 mumol/1). The mean myocardial inosine extraction at rest (33 +/- 10%) was transformed to release values (-41 +/- 30%) during pacing (p less than 0.0005) as well as during exercise (-20 +/- 27%) (p less than 0.0005). The hypoxanthine extraction at rest (25 +/- 11%) decreased during pacing (-7.8 +/- 29%) (p less than 0.0025) and exercise (10 +/- 25%) (NS). The slight increase of arterial inosine and hypoxanthine values was not significant. Myocardially produced lactate, a sensitive marker of pacing-induced ischemia, was obscured by elevated arterial concentrations during exercise. However, inosine significantly correlated with lactate during pacing, and was useful in detecting ischemic myocardial energy deficiency during exercise-induced angina.