R.Charles Curry

Coronary arterial responses to graded doses of nitroglycerin

The potential benefit from coronary dilatation induced by nitroglycerin is thought to be limited in patients with ischemia by blood pressure reduction, heart rate increase and coronary artery disease. Because recent work with other vasodilators suggests multiple vascular receptor sites with various degrees of responsiveness, coronary dilator and systemic responses to graded doses of nitroglycerin were examined in 13 patients. High resolution, 105 mm photospot film coronary angiograms, using 4.5 or 6 inch image intensification, was performed before and after administration of cumulative doses of sublingual nitroglycerin (75 to 450 μg). A calibrated optical system was used to measure coronary arterial diameter. Small doses of nitroglycerin (75 to 150 μg) increased the diameter of the left anterior descending coronary artery by 10 and 20 percent (mean), that of the left circumflex artery by 9 and 22 percent, and that of collaterally filled vessels by 18 and 28 percent, respectively (all values significantly [P < 0.01] different from measurements before nitroglycerin). No significant change in heart rate or mean aortic pressure occurred. Doses of nitroglycerin to 450 μg produced only modest additional increases in coronary arterial diameter (left anterior descending artery 9 percent, left circumflex artery and collaterally filled vessels 7 percent). Heart rate increased 5 beats/min and blood pressure decreased 11 mm Hg with 450 μg of nitroglycerin (both P < 0.01). These data suggest that dilator receptors of both large left coronary arteries and vessels filled by collateral vessels respond to very small doses of nitroglycerin without significant changes in heart rate or blood pressure.

Left main coronary artery stenosis: Clinical spectrum, pathophysiology, and management

Abstract Atherosclerosis is the major cause of LMCAS. Isolated LMCAS occurs only rarely. Marked narrowing of the LMCA is usually indicative of severe, diffuse coronary atherosclerosis. Physiologically significant LMCAS is present in less than 15% of patients with symptomatic ischemic heart disease. Angina pectoris is the most common symptom in patients with LMCAS. The incidence of unstable angina is higher in these patients when compared to patients without LMCAS. Stress testing may help identify patients with LMCAS if the following criteria are met: (1) greater than 2 mm ST segment depression. (2) prolonged duration of ST segment change after exercise, (3) blunted or decreased heart rate response to exercise, and (4) ST segment change suggesting ischemia at a low heart rate. Coronary angiography provides definitive anatomic description of the location, length, and severity of LMCAS. The procedure can be performed at low risk if proper precautions are taken. Experimentally, 85% reduction in diameter of the LMCA is required to reduce resting coronary blood flow. Parameters of LV function begin to deteriorate at this level and progress as the degree of narrowing increases. General principles of good medical therapy for patients with ischemic heart disease also apply to patients with LMCAS. However, it is important to exercise caution when using agents that lower blood pressure. Patients with LMCAS who are in an unstable state should be hospitalized, monitored, and treated vigorously with pharmacologic agents. If pain persists, intraaortic balloon counterpulsation can be tried as a temporizing measure. Prognosis of medically treated patients with LMCAS is influenced adversely by poor ventricular function, coexistent disease of the right coronary artery, and severity of the narrowing in the left main coronary artery. When surgery is being considered, intraaortic balloon counterpulsation can be useful adjunct in patients with continuing chest pain. However, in the usual patient with LMCAS who is responsive to pharmacologic agents, intraaortic balloon counterpulsation is not necessary. Survival of patients with LMCAS treated surgically is better than that of comparable medically treated patients. However, there are subsets of high- and low-risk patients related to ventricular function, degree of narrowing of the LMCA, and associated disease of other coronary vessels. We conclude that current aggressive medical therapy has eliminated the need for emergency or urgent coronary artery surgery in all but a few patients with LMCAS and persistent symptoms. However, despite the initial success of medical management, the long-term prognosis in these patients is poor. At the present time, surgery should be considered in all symptomatic patients with ≥50% LMCAS.

Variability of electrocardiographic responses to repeated ergonovine provocation in variant angina patients with coronary artery spasm

We reviewed our experience with serial ergonovine provocative tests for coronary artery spasm (CAS) in ten variant angina patients with angiographically proved CAS. Of the 26 ergonovine tests performed in the ten patients, only four patients exhibited reproducible ECG response to ergonovine. The remaining six patients had variable and unpredictable ECG responses to ergonovine. All patients were in an active phase of their disease. The variability of ST segment directional response to ergonovine is considered to be on the basis of disparate sensitivity of the coronary circulation to intravenous ergonovine. Because of this variable response, the ECG response alone should not be considered as the standard indicator for CAS presence but should be utilized with other hemodynamic and angiographic criteria.

Pacemaker-mediated tachycardias: A rapid bedside technique for induction and observation

The DDD pacemaker allows sensing and pacing in both chambers and can, therefore, maintain atrioventricular synchrony. However, this pacemaker creates an additional anterograde conduction system between the atrium and ventricle and, in the presence of ventriculoatrial (VA) conduction, the possibility of pacemaker-mediated tachycardia exists. A simple bedside technique that does not require catheterization or expensive equipment was used to detect VA conduction. Just after DDD pacer implantation, an attempt was made to detect VA conduction in 31 patients. Ambulatory monitoring (Holter) was done for 24 hours after implantation and at 2 to 4 and 6 to 8 weeks after implantation to detect pacemaker-mediated tachycardia. Attempts to induce pacemaker-mediated tachycardia were made using a special programmable external stimulator at follow-up after implantation. It was found that (1) all the 17 patients with detectable VA conduction had pacemaker-mediated tachycardia when the atrial refractory period was less than the VA conduction time, (2) pacemaker-mediated tachycardias were not inducible or detected spontaneously when atrial refractory period was equal to or greater than VA conduction time + 50 ms, (3) VA conduction was not detectable in 9 of the 17 patients at a later visit. Six of these 9 received antiarrhythmic therapy or had developed congestive heart failure. VA conduction has important implications in patients with DDD pacemakers and can be readily evaluated at the bedside.

Acute and Long-Term Outcome After Palmaz-Schatz Stenting: Analysis From the New Approaches To Coronary Intervention (NACI) Registry

The randomized Stent Restenosis Study (STRESS) and Belgium Netherlands Stent (Benestent) trials established that elective use of Palmaz-Schatz stents (PSSs) in native coronary arteries with de novo lesions is associated with increased procedural success and reduced restenosis. However there are other clinical indications for which stents are commonly used (unplanned use, vein grafts, restenosis lesions) that are not addressed in these studies. From 1990-1992, 688 lesions in 628 patients were treated with PSSs in the New Approaches to Coronary Intervention (NACI) registry. Angiographic core laboratory readings were available for 543 patients (595 lesions, of which 106 were stented for unplanned indications, 239 were in saphenous vein bypass grafts, and 296 were previously treated). The cohort of patients in whom stents were placed for unplanned indications had more women, current smokers, and had a higher incidence of recent myocardial infarction (MI). Patients who underwent stenting of saphenous vein grafts were older, had a higher incidence of diabetes mellitus, unstable angina, prior MI, and congestive heart failure. Lesion success was similar in all cohorts (98%), but procedural success was significantly higher for planned stenting (96% vs 87%; p < 0.01). Predictors of adverse events in-hospital were presence of a significant left main stenosis and stenting for unplanned indication. The incidence of target lesion revascularization by 30 days was significantly higher for patients undergoing unplanned stenting due to a higher risk for stent thrombosis. Recent MI, stenting in native lesion, and small postprocedural minimum lumen diameter independently predicted target lesion revascularization at 30 days. Independent predictors of death, Q-wave myocardial infarction, or target lesion revascularization at 1 year included severe concomitant disease, high risk for surgery, left main disease, stenting in the left main coronary artery, and low postprocedure minimum lumen diameter.

PROPRANOLOL THERAPY DURING PREGNANCY IN A PATIENT WITH IDIOPATHIC HYPERTROPHIC SUBAORTIC STENOSIS: IS IT SAFE?

A case is presented of a low birth weight infant born prematurely with depressed respiration, sinus bradycardia, and hypoglycemia associated with maternal propranolol therapy during pregnancy and up until labor and delivery. The need for caution in the casual use of propranolol during pregnancy in an asymptomatic patient with IHSS and the potential fetal complications are emphasized.