c,AnOfficial Journalof thecAmerican Heartc/Association, Inc. CURRENTTOPICS

disorders, suchas arrhythmias, myocardial ischemic syndromes andhypertension. Asinthecaseof,Bantagonists, slow-channel inhibitors constitute a heterogeneous groupwitha variable degree ofselectivity forheartmuscle, atrioventricular conduction, peripheral vessels andthecoronarycirculation. Their hemodynamic effect isthenetresult ofa complex interplay ofsimultaneous changes inheart rate, preload, afterload, contractility andcoronarybloodflow. In animals, these agents reduce myocardial ischemic injury andmay enhance collateral perfusion; inman,they havesalutary effects inexertional angina inwhich theyprobably actbyreducing cardiac work, aneffect quantitatively notdissimilar tothatproduced by:antagonists. Thisapproach thusprovides analternative modeof medical therapy forpatients withexertional angina whodonottolerate dblockers orinwhom blockers are contraindicated bythepresenceofbronchospasm or peripheral vascular disease. However, themajoradditional advantage thatslow-channel antagonists unquestionably have over blockers isthefact that theyall are potent coronary vasodilators. In contrast, antagonistsconstrict coronary vessels. For this reason, the adventofslow-channel inhibitors such asverapamil, nifedipine anddiltiazem isaverytimely landmark inrelation tothewealth ofdatathathaveconfirmed thebelief that coronaryvasospasm plays an important rolenot onlyinthepathogenesis ofclassic variant angina, butalsoinmany patients withunprovoked angina,myocardial infarction orsudden death inthesetting ofdiseased aswell asnormal coronaryarteries. Forapatient who hasnormal orrelatively normal coronaryvessels butwhodevelops vasospastic angina, slow-channel inhibitors arelikely tobecometheagents ofchoice andpreliminary clinical experience isinline withthese considerations. Similarly, patients whohaveexertional andvasospastic angina aremore likely toderive greater behefits fromslow-channel inhibitors thanfrom blockade, whichmay aggravate coronaryspasm.Evidence also indicates that certain slow-channel antagonists may beuseful inother cardiocirculatory disorders, such as