Coronary spasm, steal, and stenosis: implications for management of ischemic heart disease

Electrophysiologic effects of intravenous dipyridamole

We evaluated the electrophysiologic effects of dipyridamole given intravenously to 24 patients during intracardiac electrophysiologic study. Electrophysiologic parameters were measured before and 5 minutes following infusion of 0.5 mg/kg of dipyridamole. The drug significantly shortened the sinus cycle length by 26 per cent (P less than 0.001), sinuatrial conduction time by 15 per cent (P less than 0.01), maximal sinus node recovery time by 21 per cent (P less than 0.001), atrial and atrioventricular nodal effective refractory period by 8 and by 11 per cent, respectively (both P less than 0.01), ventricular effective refractory period by 4 per cent (P less than 0.001), paced cycle length to atrioventricular nodal Mobitz type II block by 5 per cent (P = 0.046), and QT interval during sinus rhythm by 10 per cent (P less than 0.01). After dipyridamole, the PA interval increased by 16 per cent (P less than 0.001), the AH interval by 11 per cent (P less than 0.01), and the corrected QT interval by 5 per cent (P less than 0.01). During retrograde conduction we observed a shortening of the ventriculoatrial interval by 6 per cent (P = 0.036), retrograde atrioventricular nodal effective refractory period by 5 per cent (P less than 0.001), paced cycle length to atrioventricular nodal Wenckebach and atrioventricular nodal Mobitz type II block both by 8 per cent (P less than 0.01). We conclude that intravenous dipyridamole increases sinus node automaticity and reduces atrial, atrioventricular nodal and ventricular refractory periods, prolongs intra-atrial and atrioventricular nodal conduction, but does not produce any changes in His-Purkinje system conduction times.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium metabolism, calcium-channel blocking agents, and hypertension management

Increasing evidence has suggested that a disturbance of cellular calcium metabolism may have a role in initiating and maintaining elevated systemic vascular resistance in essential hypertension. Controversy exists over whether calcium can alleviate or exacerbate the hypertensive process, and diversity of calcium metabolism in hypertensive patients has been proposed. Calcium-channel blocking agents are potent vasodilators capable of correcting the elevated systemic vascular resistance. Clinical studies have shown that these drugs have antihypertensive efficacy comparable to established agents. The elderly, blacks, and patients with low renin activity respond well to calcium-channel blockers. These drugs may also offer potential advantages over established antihypertensive agents in patients with other coexisting diseases. Sustained release formulations have been developed, and initial experience with long-term efficacy and tolerability is encouraging. The calcium-channel blockers may become first-line therapy for treatment of hypertension in selected patients.

Postinfarction angina

In conclusion, the PIA patient is at high risk, with higher early as well as late mortality. The pathophysiology of PIA is complex and may vary from patient to patient. The concepts of ischemia at a distance and ischemia in the infarct zone have led to a better understanding of early PIA. Coronary spasm may play an important role in most PIA patients as in the general population of patients with angina pectoris. Medical therapy is efficacious in many, although it may on rare occasion aggravate myocardial ischemia. Urgent coronary arteriography is generally safe and should be performed as soon as possible for medically refractory PIA. CABG appears to be safe in experienced hands, but its timing must be individualized. The IABP should be reserved for more unstable patients for fear of vascular complications. Randomized controlled trials such as the BARI Trial will further compare PTCA with CABG.