LETTERS TO THE EDITOR Angina Caused by Reduced Vasodilator Reserve of the Small Coronary Arteries. I: Spasm of Resistance Vessel Concept

Study of Cannon et aI. Cannon and colleagues (2) demonstrated inappropriate arteriolar constriction in patients with atyp ical chest pain and msignificant coronary artery disease. These cases . which may represent a distin ct syndrome. offer a number of lines of evidence. First. Cannon et al. demon strated for the first time that . 'v asoconstrictor stimuli act ing at the arter iolar level can actually cause myocardial ischemia by overriding the powerful autore gulatory mechan isms that are 'designed' to prevent ischerrua.' and the ability to override vasodilation has been a basic premise of the spasm of resistance vessel concept. When the concept was first proposed in 1973. it was unqu estioned conventional WIsdom that resistance vesse ls were mvariably widely dilated in ischemic heart disease because of the physiologic vaso dilating reactive hyperemi c response to ischemi a. and symptoms were thought to occur only when the dilatory or cardiac reserve was exhausted . While usually not clearly verbalized. it seemed to be understood that spasm of resistance vessels could not occur. as this spasm would Itself mduce ischemia and this ischemia would activate reactive hyperemia and reverse spasm. Second . Cannon' s group demonstrated vasoconstriction of resistance vessels in the absence of spasm of epicardial arter ies. and this occurrence is another basic tenet of the concept. As the hypothesis considers spasm in epic ardi al arteries to be concomitant with or reflex to primary spasm in mural arteries. it follows that mild primary spasm of resistance vessels might not be accompanied by significant changes in epicardial arteries. Third . evid ence was presented that ergonovine can act on resistance vessels . and as ergon ovme potent iates preexistmg tendenci es for spasm. this has important implications for the concept. It IS sugges ted that serious consideration be grven to the possibil ity that all ergonov meinduced angina IS due to spasm of resistance vesse ls and not to prim ary spasm of epicardia l arteries. and that spas m evident in ep icardi al arteries IS reflex. If this is so . a major step has been taken toward localizing spasm to resistance vesse ls m ischemic heart disease. Fourth . nearly a quarter of the patients had histories of previous myocardial infarction. and the association of vasoconstnction of resistance vesse ls with myocardial infarction is of critical importance to the concept. The hypothesis states that myocardial infarction is due to spasm of resistance vesse ls. and Cannon et al. provided direct ev idence that at least some patients with infarcn on have coro nary artenolar constriction. Th is evidence supports the information that factors associated with infarction. such as cold exposure and smoking. cause vasoconstnc tion of resistance vessels. and it is known that ischemi c heart disease is linked with disorder s involving vasoconstriction of resistance vessels. such as 1237