Reproducibility of coronary haemodynamics and cardiac metabolism during pacing-induced angina pectoris

Fatty acid oxidation in the reperfused ischemic heart

Myocardial ATP production is dependent chiefly on the oxidative decarboxylation of glucose and fatty acids. The co-utilization of these and other substrates is determined by both the amount of any given substrate supplied to the heart as well as by complex intracellular regulatory mechanisms. This regulated balance is altered during and after ischemia. During aerobic reperfusion of ischemic myocardium, a rapid recovery of energy production is desirable for the complete recovery of muscle contractile function. It is now clear that the type of energy substrate used by the heart during reperfusion will directly influence this contractile recovery. By increasing the relative proportion of glucose oxidized to that of fatty acids, the mechanical function of the reperfused heart can be improved. However, fatty acid oxidation recovers quickly during reperfusion and dominates as a source of oxygen consumption. These high rates of fatty acid oxidation occur at the expense of glucose oxidation, resulting in a decreased recovery of both cardiac function and efficiency during reperfusion. One contributory factor to these high rates of fatty acid oxidation is a decrease in myocardial malonyl-coenzyme A (CoA) levels. Malonyl-CoA, which is synthesized by acetyl-CoA carboxylase, is an essential metabolic intermediary in the regulation of fatty acid oxidation. A decrease in malonyl-CoA level results in an increase of carnitine palmitoyl transferase-1 mediated fatty acid uptake into the mitochondria. This mechanism seems important in the regulation of fatty acid oxidation in the postischemic heart and is discussed in detail in this review, with reference to specific clinical scenarios of ischemia and reperfusion and options for modulating cardiac energy metabolism.

Atrial natriuretic peptide attenuates pacing-induced myocardial ischemia during general anesthesia in patients with coronary artery disease

Atrial natriuretic peptide (ANP) exerts a dilatory effect on coronary arteries in humans. We investigated the effects of ANP on pacing-induced myocardial ischemia during enflurane anesthesia in patients with coronary artery disease (CAD). In 20 patients with CAD, myocardial ischemia was induced by atrial pacing before and after an i.v. infusion of ANP (50 mg x kg(-1) min(-1), n = 10) or placebo (n = 10). We studied the effects of ANP or placebo on pacing-induced changes in central hemodynamics, myocardial blood flow and regional myocardial indices of lactate uptake (RMLU), and oxygen consumption (RMVO2) and extraction (RMO2E). ST-segment depression was less pronounced during pacing with ANP compared with control pacing (-0.09 +/- 0.01 vs -0.24 +/- 0.02 mV; P < 0.001). RMLU decreased to -11.1 micromol/min during control pacing compared with -0.7 micromol/min during pacing with ANP (P < 0.01). ANP did not affect pacing-induced changes in RMVO2, RMO2E, or the rate pressure product. Placebo did not affect pacing-induced changes in ST-segment depression or RMLU. In conclusion, ANP attenuates ischemic ST-segment depression and lactate release during pacing-induced myocardial ischemia in patients with CAD. The antiischemic effect of ANP was not accompanied by any improvement in the regional myocardial oxygen supply/demand relationship.

IMPLICATIONS

We evaluated the effects of i.v. atrial natriuretic peptide (50 ng x kg(-1) x min(-1)) on pacing-induced myocardial ischemia during general anesthesia in patients with coronary artery disease. In contrast to placebo, atrial natriuretic peptide attenuated ST-segment depression and myocardial lactate production and improved left ventricular function during pacing-induced ischemia.

Long-term outcome of spinal cord electrical stimulation in patients with refractory chest pain

BACKGROUND AND HYPOTHESIS

Treatment of patients with refractory chest pain remains a challenge. In this study, the long-term clinical effects of spinal cord electrical stimulation were evaluated in 10 consecutive male patients (mean age 53.7 years) with chronic chest pain in a prospective observational study.

METHODS

After placement of the electrode in an epidural position and before implantation of the device, patients were subjected to clinical evaluation, including atrial pacing, in order to document significant antianginal effects.

RESULTS

Spinal cord electrical stimulation abolished or improved pacing time to angina by more than 50% in seven of the patients who subsequently had the device implanted. In three of these patients, the system was ineffective after a period of 3-9 months despite paresthesia in the area of anginal pain with electrical stimulation. The effects of treatment remained satisfactory in the remaining patients (40%) after a mean follow-up of 60 (45-72) months. Thus, a long-lasting clinical response was able to be predicted in 57% of the patients.

CONCLUSION

Spinal cord electrical stimulation is one of the few therapeutic options in inoperable patients with refractory chest pain.

Pain perception and brain evoked potentials in patients with angina despite normal coronary angiograms

OBJECTIVE

To evaluate the role of nociception in patients with angina despite normal coronary angiograms and to investigate whether any abnormality is confined to visceral or somatosensory perception.

METHODS

Perception, pain threshold, and brain evoked potentials to nociceptive electrical stimuli of the oesophageal mucosa and the sternal skin were investigated in 10 patients who had angina but normal coronary angiograms, no other signs of cardiac disease, and normal upper endoscopy. Controls were 10 healthy volunteers. The peaks of the evoked potential signal were designated N for negative deflections and P for positive. Numbers were given to the peaks in order of appearance after the stimulus. The peak to peak amplitudes (P1/N1, N1/P2) were measured in microV.

RESULTS

(1) Angina pectoris was provoked in seven patients following continuous oesophageal stimulation. (2) Distant projection of pain occurred after continuous electrical stimulation of the oesophagus in four patients and in no controls. (3) Patients had higher oesophageal pain thresholds (median 16.3 mA v 7.3 mA, P = 0.02) to repeated stimuli than controls, whereas the values did not differ with respect to the skin. There were no intergroup differences in thresholds to single stimuli. (4) Patients had substantially reduced brain evoked potential amplitudes after both single oesophageal (P1/N1, median values: 7.2 microV, controls: 29.0 microV; N1/P2: 16.5 microV, controls: 66.0 microV; P < 0.001 for both) and skin (N1/P2: 13.5 microV; controls: 76.0 microV; P < 0.001) stimuli despite the similar pain thresholds.

CONCLUSION

Central nervous system responses to visceral and somatosensory nociceptive input are altered in patients who have angina despite normal coronary angiograms.

Hemodynamic tolerability and anti-ischemic efficacy of high dose intravenous diltiazem in patients with normal versus impaired ventricular function

OBJECTIVES

This study was designed to compare the acute systemic and coronary hemodynamic effects of high doses of intravenous diltiazem in patients with normal versus impaired left ventricular function, investigate the safety of this drug and compare its anti-ischemic potential in these two patient groups during pacing-induced stress.

BACKGROUND

Because coronary hemodynamic effects and negative inotropic properties of diltiazem are dose related, high dose intravenous diltiazem may improve anti-ischemic efficacy but may not be tolerated in patients with impaired cardiac function.

METHODS

High dose intravenous diltiazem, 0.4 mg/kg for 5 min followed by 0.4 mg/kg for 10 min, was administered to 23 normotensive patients with coronary artery disease, 11 (group A) with normal and 12 (group B) with impaired ventricular function (ejection fraction < 45%) during two identical arterial pacing stress tests performed 30 min before (pacing test I) and immediately after diltiazem (pacing test II).

RESULTS

Diltiazem was well tolerated despite high peak plasma levels, 869 +/- 152 micrograms/liter (group A) and 926 +/- 169 micrograms/liter (group B). It resulted in immediate but similar reductions in systemic resistance from 1,321 +/- 136 (control value) to 963 +/- 113 dynes.s.cm-5 (group A) and from 1,267 +/- 106 to 865 +/- 58 dynes.s.cm-5 (group B) and in mean arterial pressure from 107 +/- 3 to 93 +/- 4 mm Hg (group A) and from 103 +/- 4 to 86 +/- 4 mm Hg (group B), at 5 min after diltiazem (all p < 0.05 vs. control value). Diltiazem improved stroke output from 36 +/- 3 (control value) to 46 +/- 4 ml/beat per m2 in group B and from 44 +/- 4 (control value) to 49 +/- 5 ml/beat per m2 in group A, an effect that was significantly greater and more prolonged in group B than in group A. Although neither heart rate nor contractility was affected in either group, left ventricular end-diastolic pressure increased in group A (9 +/- 2 mm Hg to 12 +/- 1 mm Hg, p < 0.05) but not in group B. Despite similar reductions in coronary resistance and improvements in coronary flow, diltiazem consistently reduced myocardial oxygen extraction, but only in group B. Also, the anti-ischemic effects of diltiazem were more pronounced in group B. During pacing test II, myocardial lactate extraction normalized in group B (7 +/- 5% vs. -6 +/- 12% [pacing test I]) but not in group A, contractility indexes improved more and the increase in left ventricular filling pressure was reduced to a greater extent in group B. Moreover, the ischemia-induced increase in arterial pressures, observed in both groups during pacing test I, was prevented in group B but recurred in group A during pacing test II.

CONCLUSIONS

High dose intravenous diltiazem is well tolerated, augments coronary flow and improves left ventricular pump function, particularly in patients with preexisting ventricular dysfunction. As its anti-ischemic effects also appear more pronounced in the latter group, high dose diltiazem may be particularly useful when ventricular function is depressed, for example, during prolonged ischemia at rest.

Antiischemic and metabolic effects of glutamate during pacing in patients with stable angina pectoris secondary to either coronary artery disease or syndrome X

The effects of glutamate on anginal threshold, cardiac metabolism and hemodynamics were studied in 11 patients with stable angina pectoris, positive stress test results, and pacing-induced myocardial lactate release due to coronary artery disease (CAD) (n = 9) or syndrome X (n = 2). Data were obtained before, during and after 2 identical periods of coronary sinus pacing, the second being preceded by an intravenous injection of monosodium glutamate 1.2 (n = 7) or 2.5 (n = 4) mg/kg body weight. After glutamate administration, pacing time to onset of angina increased from mean +/- standard deviation 103 +/- 53 to 166 +/- 71 seconds (p less than 0.01) and ST-segment depression after pacing decreased from 2.3 +/- 1.0 to 1.6 +/- 1.1 mm (p less than 0.01). Arterial glutamate concentration increased 60% (p less than 0.01) after the low dose and 150% (p less than 0.01) after the high dose of glutamate. Regardless of dose, myocardial glutamate uptake increased by 25% (p less than 0.01). Pacing-induced cardiac release of lactate diminished 50% (p less than 0.05), whereas the releases of xanthine and hypoxanthine were unchanged by glutamate. Arterial free fatty acids decreased 20% (p less than 0.01). Circulating levels and cardiac exchanges of alanine, glucose and citrate were unchanged. Glutamate did not influence heart rate, arterial blood pressure, coronary blood flow, coronary vascular resistance or myocardial oxygen consumption. One patient complained of short-lasting burning sensations after receiving the high glutamate dose. In conclusion, augmented provision of glutamate enhances pacing tolerance in stable angina, presumably by a metabolic improvement of cardiac energy production during ischemia.

Effects of intravenous glutamate on substrate availability and utilization across the human heart and leg

To study the effect of monosodium glutamate on hemodynamics and on substrate metabolism in cardiac and skeletal muscle, an intravenous (IV) dose of 1.2, 2.5, or 5.0 mg/kg body weight was administered to 27 patients during arterial-coronary sinus catheterization (15 patients) or arterial-femoral vein catheterization (13 patients). Data were obtained for 25 minutes after the injection. Arterial glutamate concentrations increased 2.5-5 fold in a dose-related manner. Glutamate administration reduced arterial levels of free fatty acids by 25% (P less than .001), of lactate by 13% (P less than .05), and of alanine by 6% (P less than .05). Arterial glucose increased by 10% (P less than .001) and arterial insulin was increased threefold (P less than .01). Myocardial uptake of free fatty acids decreased by 25% (P less than .001), whereas uptakes of glutamate and glucose increased by 60% (P less than .001) and 100% (P less than .001), respectively. Cardiac release of citrate increased transiently (P less than .05), whereas consumption of lactate and releases of alanine were unchanged by the glutamate. Across the leg, the arteriovenous differences of glutamate were elevated threefold to eightfold (dose-related) (P less than .001), and that of glucose was doubled (P less than .01). The release of citrate increased (P less than .01). Arterial-femoral vein gradients of free fatty acids, lactate, and alanine remained unchanged. Heart rate, blood pressure, coronary sinus flow, coronary vascular resistance, and cardiac oxygen uptake were unmodified by glutamate. Six patients complained of short-lasting burning sensations after the highest glutamate doses. In conclusion, glutamate administration stimulates insulin secretion and changes substrate availability and utilization in human cardiac and skeletal muscle from free fatty acids toward glucose and glutamate.