Effects of methoxamine and phenylephrine on left ventricular contractility in rabbits.

The end-systolic pressure-volume relation is employed to evaluate left ventricular contractility. In clinical studies, pharmacologic vasoconstriction is used to increase left ventricular systolic pressure to assess pressure-volume relations. However, the effect of vasoconstrictors on the ventricular contractile state is not well characterized. The effects of methoxamine and phenylephrine on systemic arterial pressure and left ventricular contractility in rabbits were studied with three protocols. In protocol 1, anesthetized rabbits (n = 10) were injected with incremental doses of methoxamine and phenylephrine intravenously. Methoxamine (4 mg) increased the mean arterial pressure by 50 +/- 12% (mean +/- SE) (n = 5, p = 0.001). Phenylephrine (0.2 mg) increased mean arterial pressure by 82 +/- 14% (n = 5, p = 0.004). In protocol 2, isolated blood-perfused hearts were injected with incremental doses of these drugs in the ascending aorta in amounts approximately equal to the concentrations injected in the intact rabbits. Methoxamine (2 mg) reduced isovolumic peak systolic left ventricular pressure by 43 +/- 9% (n = 7, p = 0.003), whereas phenylephrine (0.1 mg) increased the isovolumic pressure by 24 +/- 9% (n = 7, p less than 0.05). These responses indicated an enhanced contractile state with phenylephrine and a reduced contractile state with methoxamine. Pretreatment with propranolol blunted the effect of phenylephrine on isovolumic pressure (n = 6, p less than 0.02). In protocol 3, cross-circulation experiments allowed study of the effect of these drugs on isovolumic left ventricular pressure in the isolated heart and simultaneously on the systemic arterial pressure in the intact anesthetized rabbit (support rabbit).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of maximal medical therapy on refractoriness of unstable angina pectoris.

A group of 125 patients with unstable angina were studied over a 5-year period to define the incidence of refractory unstable angina in the current era of 5-drug medical therapy with intravenous heparin, aspirin, nitrates, calcium antagonists and beta blockers. All patients had greater than 20 minutes of chest pain at rest with reversible electrocardiographic changes occurring in the absence of myocardial infarction. Patients were considered refractory only if chest pain continued despite treatment with maximal 5-drug therapy. At the time of transfer to the center, 65 patients continued to have ischemic chest pain at rest and were considered "medically refractory" by their referring physicians. A more aggressive medical regimen was used, and 54 patients (83%) were rendered chest pain-free. Of the 11 truly refractory patients (8.8%), coronary arteriography revealed an increased likelihood of left main or 3-vessel disease (7 of 11 vs 26 of 114; p = 0.01). In-hospital treatment strategies for the 114 patients stabilized with medical therapy included continued medical therapy (n = 37), coronary angioplasty (n = 46) and bypass grafting (n = 31). The rate of myocardial infarction or death in patients managed medically was 3%. Coronary angioplasty in medically stabilized patients was complicated by an abrupt closure rate of 26%, and a 17% rate of myocardial infarction, death or need for emergency bypass grafting. Medically stabilized patients undergoing bypass grafting had a 9% rate of myocardial infarction or death. Unstable angina truly refractory to current, maximal medical therapy is infrequent (8.8%).(ABSTRACT TRUNCATED AT 250 WORDS)

Emergent percutaneous cardiopulmonary bypass in patients having cardiovascular collapse in the cardiac catheterization laboratory.

Percutaneous cardiopulmonary bypass (PCB) was instituted in 30 initially stable patients who developed either cardiac arrest refractory to resuscitation (n = 7) or cardiogenic shock (mean arterial blood pressure < 50 mm Hg unresponsive to fluid resuscitation or vasopressors) (n = 23) after a catheterization laboratory complication. Events leading to collapse included abrupt closure during percutaneous transluminal coronary angioplasty (PTCA) (n = 22), complications from diagnostic cardiac catheterization (n = 6), left ventricular perforation during mitral valvuloplasty (n = 1), and right ventricular perforation during pericardiocentesis (n = 1). PCB was initiated within 20 minutes of cardiovascular collapse in 83% of patients (arrest: 21 +/- 13 minutes [range 10 to 50]; and shock: 17 +/- 6 minutes [range 10 to 30]). Mean arterial blood pressure increased on PCB from 0 to 56 mm Hg in patients with cardiac arrest and from 37 to 63 mm Hg in those with cardiogenic shock at mean PCB flow rates of 2.5 to 5.0 liters/min. Subsequent therapy on PCB included emergent cardiac surgery (n = 14), PTCA (n = 13) and medical therapy (n = 3). Six patients (20%) survived to hospital discharge (3 with cardiac surgery, 2 with PTCA, and 1 with medical therapy). All 7 patients with refractory cardiac arrest died despite further interventions on PCB, whereas 6 of 23 (26%) with cardiogenic shock survived to hospital discharge. Thus, in response to cardiovascular collapse in the catheterization laboratory, PCB does not salvage patients who do not regain a stable cardiac rhythm. PCB can stabilize patients who develop cardiogenic shock for further interventions which are lifesaving in only a minority of patients.

Update in nuclear cardiology.

Imaging techniques for the noninvasive detection and evaluation of coronary artery disease continue to develop. New techniques for the quantification of myocardial blood flow by positron-emission tomography, new approaches to metabolic imaging, and new gamma camera technology have the potential to expand the scope of cardiac nuclear medicine in many facilities. Determination of the best and most cost-effective method of assessing myocardial viability in patients with advanced coronary artery disease remains of key interest with research directed at alternative 201Tl imaging protocols, fatty acid metabolism, and viability assessment with the new 99mTc-based myocardial perfusion radiopharmaceuticals. The assessment of endothelial function and determination of coronary flow reserve with 13N-ammonia positron-emission tomography may aid in the identification of preclinical atherosclerosis, and in monitoring disease progression and response to therapy. New information in radionuclide perfusion imaging in young and elderly patients and in those with interventricular conduction disturbances may allow for more accurate identification of coronary artery disease. The role of radionuclide imaging in patients with dilated cardiomyopathy continues to evolve with the development of radiolabeled chemicals of the adrenergic nervous system and their analogues, which will be helpful in the stratification of disease severity. These new imaging techniques promise to increase the accuracy of nuclear cardiology for detection of disease, assessment of function, and prognosis.