Relative roles of preload increase and coronary constriction in ergonovine-induced myocardial ischemia in stable angina pectoris

Angina pectoris associated with ST segment elevation in the absence of epicardial coronary arterial obstruction. Case reports

Two cases are presented in which angina pectoris associated with ST segment elevation occurred during either an ergonovine provocation test or coronary angioplasty, despite the absence of epicardial coronary artery obstruction. In both cases, no epicardial coronary spasm, thromboembolic occlusion, coronary air embolus, vessel dissection, or side-branch occlusion was observed. These findings suggest that transmural myocardial ischemia without epicardial coronary artery obstruction can occur owing to abnormalities of the coronary microcirculation. Microvascular vasoconstriction leading to transmural myocardial ischemia may be induced by ergonovine or by the release of potent vasoconstrictors from disrupted coronary lesions during angioplasty.

Sequence and magnitude of ventricular volume changes in painful and painless myocardial ischemia

Stimulation of left ventricular stretch receptors has been proposed as a possible mechanism for the occurrence of cardiac pain. Changes in left ventricular volume were continuously assessed in 12 patients during 11 spontaneous (two painful) and 12 ergometrine-induced (nine painful) ischemic attacks with a precordial scintillation probe and blood pool labeling with technetium-99m. In all ischemic episodes, spontaneous or induced, painful or painless, severe dilatation of the left ventricle was consistently observed. These changes always preceded the onset of ST segment shifts and occurred long before pain, when present. The maximum increase in end-diastolic volume was slightly greater in painful than in painless episodes, 38 +/- 8.0% versus 28 +/- 12.4%, but no significant difference was observed in the rate of volume change or in the maximum increase of end-systolic volume (133 +/- 50% and 110 +/- 27.3%), stroke volume (-28 +/- 15% and -25 +/- 12.4%), or ejection fraction (-32 +/- 8.7% and -26 +/- 6.0%). Although the maximum end-diastolic volume achieved is greater in painful episodes, this effect cannot be separated from that of duration, and, furthermore, there was no significant difference in end-diastolic volume at the moment chest pain began. Thus, in patients with angina at rest, transient asymptomatic ST segment shifts are consistently associated with large changes in left ventricular volume, similar to those observed during painful episodes. The rate and extent of acute left ventricular dilatation do not appear to be factors directly causing anginal pain.

Preferential venoconstriction by cyclooxygenase inhibition in vivo without attenuation of nitroglycerin venodilation

Because prostacyclin is a rather potent venodilator in vivo, we analyzed the effect of cyclooxygenase inhibition on venous tone in 14 anesthetized dogs during ganglionic and beta-adrenergic blockade and atraumatic conditions. Effective vascular stiffness (a reciprocal of effective vascular compliance) as a variable of integrated venous tone was 0.30 +/- 0.01 mm Hg.kg/ml (n = 35) and was augmented up to twofold by diclofenac (1, 3, and 10 mg/kg i.v.), ibuprofen (6 and 60 mg/kg), or indomethacin (5 mg/kg) parallel to augmentations in central venous pressure, while the rise in arterial pressure was less than half of the increase induced by equivenoconstrictor dosages of norepinephrine. After preconstriction by indomethacin or diclofenac, nitroglycerin (1.5 micrograms/kg/min) lowered effective vascular stiffness (by 24 +/- 2% or 23 +/- 5%, respectively), similarly as during preconstriction by norepinephrine (by 24 +/- 4%). Long-term cyclooxygenase inhibition (diclofenac 2 x 1 mg/kg/day for 4 days) did not modify arterial pressure, heart rate, or hematocrit levels in conscious dogs at rest, but it lowered plasma volume to 52.5 +/- 1.9 ml/kg (sham treatment: 59.1 +/- 1.6 ml/kg, p less than 0.05, n = 4). In conclusion, venoconstriction by clinical dosages of cyclooxygenase inhibitors does not interfere with the venodilator action of nitroglycerin and is compensated chronically by adjustments of plasma volume.