Coronary Vasoconstriction
1) Coronary flow limiting stenoses are caused by concentric or eccentric artherosclerotic plaques, with or without potential for local vasomotor changes. Fixed flow limiting stenoses present smooth muscle cell atrophy and/or plaque rigidity and are associated with the predictable ischaemic threshold and a stable pattern of effort related myocardial ischaemia.
Dynamic stenoses are usually eccentric, with compliant segments of the wall and preserved muscular media, and are associated with a variable ishaemic threshold.
2) Vasoconstriction at the site of stenoses may result from (1) neural vasoconstrictor stimuli, (2) impairment of vasodilator mechanisms, (3) increased response of dysfunctional vascular smooth muscle cells to vasoconstrictor stimuli, or (4) variable combination of these mechanisms.
3) In animal models, and possibly in unstable patients, the severity of stenosis may also be modulated by platelet aggregates.