Changes in plasma catecholamine concentrations in patients with coronary heart disease during pacing and physical exercise

QT hysteresis index improves the power of treadmill exercise test in the screening of coronary artery disease

BACKGROUND

QT hysteresis phenomenon exists in healthy subjects, and is more exaggerated in patients with coronary artery disease (CAD) and long QT syndrome. The purpose of this study was to establish an appropriate method to evaluate the magnitude of QT hysteresis, and assess the value of QT hysteresis index in the treadmill exercise test (TET) in predicting CAD. METHODS AND RESULTS: A total of 138 subjects with suspected CAD and referred for TET and selective coronary angiography (SCA) were divided into positive (n=77) and negative (n=61) SCA groups. Dynamic ECG were recorded during TET. QT/RR curves were constructed and QTp (Q-Tpeak) and QTe (Q-Tend) hysteresis indices were calculated for each subject. SYNTAX score in the positive SCA group was determined. The QTp and QTe hysteresis indices in the positive SCA group were significantly higher than in the negative SCA group. The combination of QTe hysteresis index and conventional TET criteria had the highest sensitivity and negative predictive value according to receiver operating characteristic curve, and was an independent predictor on multivariate logistic regression. QT hysteresis indices significantly correlated with SYNTAX score in the positive SCA group.

CONCLUSIONS

QTe hysteresis index enhances the specificity of predicting CAD in TET. It improves the diagnostic value of TET for CAD significantly when combined with conventional criteria and is associated with the severity of CAD.

Persistent endocrine stress response in patients undergoing cardiac surgery

To investigate the endocrine stress response in patients undergoing major surgery with general anesthesia using a balanced technique with sufentanil, isoflurane and midazolam up to the second postoperative day, blood levels of cortisol, epinephrine, norepinephrine, prolactin and growth hormone were determined in 68 males for elective coronary artery bypass grafting (CABG) surgery. Intraoperatively, during extracorporeal circulation none of the measured parameters were significantly increased compared to preoperative values. The endocrine response of patients with perioperative epinephrine medication (n = 32) was not significant different to patients that did not receive exogenous epinephrine (n = 36). On the evening of the day of surgery, levels of cortisol (3 fold), epinephrine (4.7 fold), norepinephrine (1.7 fold) and growth hormone (16.5 fold) were significantly increased. Compared to preoperative values levels of cortisol (3.3 fold), growth hormone (5.5 fold) and norepinephrine (1.8 fold) remained elevated up to the evening of the second postoperative day. In conclusion, the endocrine stress response in patients undergoing CABG-surgery under general anesthesia with sufentanil, midazolam, isoflurane is intraoperatively prevented by anesthesia. Although hemodilution or hormone degradation might be responsible for the lack of an increase in endocrine parameters during CPB, this study indicates that a balanced technique with isoflurane, sufentanil and midazolam is more effective in blocking the endocrine stress response than previously described anesthetic techniques. In the early postoperative period, a sharp increase in cortisol, epinephrine, norepinephrine and growth hormone occurred suggesting that the predominant endocrine stress response begins in the intensive care unit with end of anesthesia. The postoperative elevated levels of cortisol, growth hormone and norepinephrine indicate a persisting stress-response for more than two days after surgical trauma.

Systemic and cardiac neuroendocrine activation and severity of myocardial ischemia in humans

OBJECTIVES

The purpose of this study was to assess the effect of different degrees of ischemia on circulating and cardiac neurohormones and vasotone.

BACKGROUND

Neuroendocrine activation and subsequent systemic vasoconstriction may complicate ischemia. Whether this relates to severity of ischemia and subsequent cardiac dysfunction, and whether neurohormonal balance in the ischemic area changes, is unknown.

METHODS

Fifty-six normotensive patients with coronary artery disease were evaluated during incremental atrial pacing. On the basis of ST segment changes, patients were classified in a nonischemic (n = 11) or ischemic group (n = 45), the latter patients were subsequently classified as lactate (n = 28) or nonlactate (n = 17) producing, to identify neurohormonal changes in the effluent of the ischemic myocardium.

RESULTS

Angina occurred in 55%, 82% and 82% of patients in the nonischemic, lactate- and nonlactate-producing groups, respectively. Baseline hemodynamic variables and neurohormones were comparable in all groups, as were heart rate, rate-pressure product and coronary hemodynamic variables during pacing. In lactate producers, contractility did not improve, relaxation deteriorated, left ventricular filling pressure increased and cardiac output decreased during pacing, indicating more severe ischemia compared with that in nonlactate producers. Neurohormones did not change in the nonischemic group. In contrast, arterial and coronary venous catecholamines increased significantly more in lactate producers than in nonlactate producers (arterial norepinephrine by 68% vs. 36%, respectively). Moreover, arterial angiotensin II increased in lactate producers from a baseline mean +/- SEM of 6.8 +/- 0.9 to 9.7 +/- 1.6 pmol/liter (p < 0.05), accompanied by a sustained 23% increase in systemic resistance and arterial pressures. In lactate producers, baseline net cardiac norepinephrine release changed to net uptake during pacing (-0.05 +/- 0.02 vs. 0.06 +/- 0.05 nmol/min, p < 0.05). Epinephrine uptake increased in all patients with ischemia, albeit more in lactate producers.

CONCLUSIONS

Circulating catecholamines and renin-angiotensin levels are activated, and systemic vasotone is increased in relation to the degree of ischemia. Cardiac epinephrine uptake increases, whereas net baseline norepinephrine release from the ischemic myocardium changes to net uptake. Modulation of this neurohormonal activation may provide an alternative mode to limit ischemia.

The role of heart rate in myocardial ischemia and infarction: implications of myocardial perfusion-contraction matching

The pathophysiology of myocardial ischemia traditionally has been attributed to disturbances of oxygen demand, as observed in classic effort-induced angina pectoris, or to a primary disruption of coronary blood supply, as in unstable angina or acute myocardial infarction. Laboratory research eliciting various types of perfusion-contraction matching has challenged such a historical distinction between supply and demand-induced determinants of myocardial ischemia. A growing number of clinical studies analyzing the role of heart rate in the course of coronary heart disease suggest the possibility that a common perfusion-contraction scheme may underlie these diverse clinical manifestations. During experimental myocardial ischemia, produced by a low coronary blood flow, regional perfusion-contraction matching exists in which the energy demands and regional contraction are reduced to match the diminished myocardial substrate supply. Heart rate is a major factor influencing transmural blood flow distribution and regional function, because when coronary vasodilation is maximal there is an inverse relation between the level of heart rate and subendocardial perfusion. Thus, in experimental regional ischemia, increasing heart rate reduces subendocardial flow and contraction, whereas slowing of heart rate causes improvement of contraction associated with increased subendocardial blood flow, accompanied by a decrease in outer wall blood flow. Also, "interventricular steal" of blood from the left ventricle by the right ventricle during ischemia can be reversed by slowing the heart rate in the presence of regional ischemia. Improvement of contraction by heart rate slowing is more than would be expected on the basis of the increase in subendocardial perfusion alone, reflecting a combination of decreased oxygen demand and increased oxygen supply, and separate curves relating blood flow per minute to contractile function are observed at different heart rates. However, when perfusion is normalized for heart rate by expressing subendocardial blood flow in units per beat, a single relation is observed at different heart rates. This observation supports the concept of a close coupling between subendocardial blood flow per beat and regional performance, or perfusion-contraction matching, during various levels of ischemia. Based on these principles, it can be predicted that exercise-induced regional ischemia in the presence of coronary stenosis will be attenuated by several mechanisms when heart rate is slowed using either a beta-blocking agent, or a specific bradycardic drug.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of beta 1-blockade on myocardial substrates early after a coronary operation

A high adrenergic strain during reperfusion after ischemia impedes functional recovery. Conversely, adrenergic blockade may be beneficial during reperfusion. This study was undertaken to find out if early postoperative high-dose infusion of the selective beta 1-blocking agent metoprolol tartrate has additional effects on metabolic variables related to myocardial energy supply/demand balance compared with those obtained with a late preoperative oral dose. The study included 21 male patients undergoing coronary bypass grafting. All patients received an oral dose of metoprolol before the operation. After the operation, patients were randomized to a control group or a group receiving intravenous infusion of metoprolol. Myocardial uptake of oxygen and substrates was determined before and during atrial pacing. Metoprolol reduced arterial concentrations of free fatty acids, reduced myocardial uptake of free fatty acids, and enhanced myocardial uptake of lactate. During paced tachycardia, the metoprolol concentration correlated negatively with myocardial uptake of free fatty acids (r = -0.80; p < 0.001) and positively with myocardial uptake of lactate (r = 0.53; p < 0.05). It is concluded that postoperative infusion of metoprolol induces myocardial metabolic changes compatible with an improved energy supply/demand balance.

Systemic neurohumoral activation and vasoconstriction during pacing-induced acute myocardial ischemia in patients with stable angina pectoris

To identify the effect of myocardial ischemia on systemic neurohormones and vascular resistance, 32 untreated, normotensive patients with coronary artery disease underwent incremental atrial pacing until angina. Arterial and coronary venous lactate and arterial values of catecholamines and angiotensin II were determined at control, at maximal pacing rates, and at 1, 2, 5 and 30 minutes after pacing. Based on pacing-induced ST-segment depression (greater than or equal to 0.1 mV) or myocardial lactate production, or both, patients were selected as ischemic (n = 25) or nonischemic (n = 7). Baseline clinical and hemodynamic data were comparable. During pacing, chest pain was similar (20 ischemic vs 7 nonischemic patients). Also, hemodynamic measurements were comparable, except for contractility, which did not improve, and left ventricular end-diastolic pressure, which significantly increased in ischemic patients. Moreover, during ischemia arterial pressures increased significantly (13%) and systemic resistance increased from 1,470 +/- 60 (control) to 1,632 +/- 76 dynes.s.cm-5 5 minutes after pacing (p less than 0.05) in ischemic but not in nonischemic patients. Pacing did not affect neurohormones in nonischemic patients. In contrast, norepinephrine in ischemic patients increased significantly from 1.7 +/- 0.2 (control) to 2.6 +/- 0.3 (maximal pacing) and to 3.0 +/- 0.4 nmol/liter (1 minute after pacing), whereas angiotensin II levels increased from 6.2 +/- 1.4 (control) to 9.3 +/- 2.1 pmol/liter (1 minute after pacing, p less than 0.05). Epinephrine only increased during maximal rates (0.9 +/- 0.1 vs 0.6 +/- 0.1 nmol/liter at control, p less than 0.05). Thus, myocardial ischemia activates circulating catecholamines and angiotensin II, accompanied by systemic vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Paradoxical narrowing of atherosclerotic coronary arteries induced by increases in heart rate

Vasodilation in normal and vasoconstriction in atherosclerotic coronary arteries have been observed in response to complex stimuli such as exercise and the cold pressor test. To study a single parameter that changes during these activities, and to better understand the pathophysiology of ischemia associated with increases in heart rate, we studied coronary vasomotion and blood flow response to increasing heart rate alone, produced by atrial pacing, with quantitative angiographic and Doppler flow-velocity measurements in 15 patients. In five patients with angiographically smooth coronary arteries (group 1), tachycardia produced progressive dilation of the epicardial artery with increases in cross-sectional area (CSA) of +15.5 +/- 3.4%, +22.4 +/- 2.1%, +28.5 +/- 3.3%, and +30.6 +/- 2.2% at 90, 110, 130, and 150 beats/min, respectively. In contrast, in five patients with mild angiographic narrowings (group 2), coronary segments failed to dilate with progressive tachycardia (-6.3 +/- 2.0%, -8.3 +/- 2.0%, -12.5 +/- 2.0%, and -11.4% at 90, 110, 130, and 150 beats/min, respectively), and progressive loss of luminal area was observed in five patients with severe angiographic narrowings (group 3) (-34.4 +/- 3.4%, -49.6 +/- 2.2%, -59.2%, and -72.8% at 90, 110, 130, and 150 beats/min, respectively). Coronary blood flow increased significantly with tachycardia in group 1 (+44.5 +/- 10.2%, +86.0 +/- 24.6%, +105.8 +/- 29.3%, and +137.5 +/- 46.0%), increased slightly in group 2 (+7.8 +/- 3.2%, +9.4 +/- 4.4%, +8.4 +/- 3.9%, and +10.0%), and decreased significantly in group 3 (-31.8 +/- 6%, -42.6 +/- 10.7%, -61.0%, and -70.0%). We conclude that an isolated increase in heart rate in patients with normal coronary arteries results in a modest increase in flow and vasodilation. In early atherosclerosis, the flow increase is blunted and dilation is replaced with paradoxical loss in luminal size. In patients with stenoses, further loss in luminal size occurs accompanied by a decrease in coronary blood flow. Thus, increasing heart rate alone in the setting of coronary stenoses could produce myocardial ischemia by a reduction in coronary supply, as well as by an increase in oxygen demand.

Haemodynamic response to myocardial ischaemia during unrestricted activity, exercise testing, and atrial pacing assessed by ambulatory pulmonary artery pressure monitoring

Ambulatory pulmonary artery pressure monitoring by means of a transducer tipped catheter with a simultaneous frequency modulated electrocardiogram and a miniaturised tape recorder was used to study the haemodynamic implications of ST segment depression in patients with coronary artery disease. Nineteen male patients (mean (SD) age 58 (11) years) with clinical and angiographic evidence of coronary artery disease were studied together with six controls. Changes in the ST segment and pulmonary artery diastolic pressure during treadmill exercise, atrial pacing, and unrestricted ambulant activity were analysed. During exercise, pulmonary artery diastolic pressure rose significantly in patients with coronary artery disease but not in the controls. One patient with ST depression greater than 1 mm did not have a rise in pulmonary artery diastolic pressure on exercise; two had a rise in pulmonary artery diastolic pressure with no ST segment change despite severe angina. The pulmonary artery diastolic pressure tended to rise before or simultaneously with the onset of ST segment depression. The haemodynamic response to atrial pacing was similar in normal controls and patients with coronary artery disease. During ambulatory monitoring there were 29 episodes of ST segment depression all of which were associated with a rise in pulmonary artery diastolic pressure and chest pain. The onset of ST segment depression occurred before a rise in pulmonary artery diastolic pressure in 11 episodes, was simultaneous with it in 11, and followed it in seven episodes. During exercise and ambulatory monitoring there was a correlation between the magnitude of ST segment depression and the rise in pulmonary artery diastolic pressure. Pain was a late feature during exercise, atrial pacing, and anginal episodes. This technique for the first time allows the relation between ST segment changes and haemodynamic alterations in left ventricular function to be assessed in ambulant patients with coronary artery disease.

Alterations of beta-adrenoceptors subsequent to myocardial infarction

Elevations and reductions of the number of beta-adrenoceptor binding sites are dependent on the strength and the duration of receptor interaction with respective agonists. In the paper presented here, results obtained by the authors concerning biosynthesis, storage and release of catecholamines following experimentally induced infarction of the myocardium in rats are compared with those of other authors for other species. Principally, storage and release of noradrenaline from ischemic hearts do not differ with the mode of inducing tissue hypoxia (stopped-flow ischemia, coronary artery ligation, occlusion of the great cardiac vein), nor for various species (rat, dog, guinea-pig). Differences are, however, present in the results of several beta-adrenoceptor binding studies performed after experimental myocardial infarction. Following acute infarction, an increase in the number of beta-adrenoceptor binding sites is generally observed, which is explained on the basis of an externalization of receptors from the cytoplasm ot the sarcolemmal membrane. Results pertaining to 2-3 days after infarction are not uniform: in guinea-pig hearts a marked drop in the number of beta-adrenoceptors has been reported, a mild rise in the number has been detected in the left and right ventricle of rat hearts. These divergent observations could arise from the experimental protocol employed, for instance in the binding assay and in the pretreatment given to the hearts prior to assay.