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Models of coronary artery disease: "critical" versus "functional" coronary artery stenosis
H Schad1, W Heimisch, N Mendler
1Department of Cardiac and Vascular Surgery, German Heart Center Munich.
Insights
Functional stenosis, a 50% reduction in coronary blood flow, is a more sensitive indicator of myocardial ischemia than critical stenosis. This model is preferred for evaluating interventions affecting ischemic heart muscle energy balance.
Area of Science:
- Cardiovascular Physiology
- Myocardial Ischemia Research
- Hemodynamic Monitoring
Background:
- Critical coronary stenosis is defined by abolished reactive hyperemia post-occlusion.
- Functional stenosis is defined by a 50% reduction in myocardial systolic shortening.
- Understanding the functional impact of coronary stenosis is crucial for ischemia research.
Purpose of the Study:
- To compare critical and functional coronary stenosis.
- To evaluate their effects on regional myocardial and global ventricular function.
- To determine the optimal model for studying interventions in myocardial ischemia.
Main Methods:
- Coronary blood flow (Q) was progressively reduced in anesthetized dogs.
- Myocardial segment length and ventricular function were monitored using sonomicrometry and pressure transducers.
- Critical and functional stenosis thresholds were identified based on specific physiological responses.
Main Results:
- Critical stenosis (25% Q reduction) did not impair function but delayed recovery.
- Functional stenosis (approx. 50% Q reduction) caused a 50% decrease in systolic shortening with discrete hemodynamic changes.
- Systolic shortening changes in functional stenosis are sensitive indicators of altered myocardial energy balance.
Conclusions:
- Functional stenosis is a more sensitive indicator of myocardial dysfunction than critical stenosis.
- The functional stenosis model is preferred for evaluating interventions impacting ischemic myocardium.
- Critical stenosis may mask beneficial effects of interventions on myocardial function.
Abstract:
"Critical coronary stenosis" (reduction of coronary blood flow [Q] until reactive hyperaemia following 15s coronary occlusion is just abolished) and "functional stenosis" (reduction of Q until systolic shortening (dL) of post-stenotic myocardium is curtailed by 50%) were compared with respect to the reduction in Q necessary and the effect on regional myocardial and global ventricular function. In 9 anaesthetized (piritramide) dogs, enddiastolic length (edL) and dL of a myocardial area supplied by the left descending coronary artery (LAD) were measured by sonomicrometry. Left-ventricular end-diastolic pressure (LVEDP) and dP/dt, aortic pressure (AoP), stroke volume (SV), and heart rate (HR) were monitored. QLAD was stepwise reduced by a snare. Critical stenosis, present at a 25% reduction of QLAD, had no effect on regional and global ventricular function, but recovery of dL after release of 15s LAD occlusion was significantly delayed. Further obstruction of QLAD progressively impaired dL, reaching 50% dL (functional stenosis) by a flow reduction of about 50%. The decrease in dL was accompanied by an increase in edL. The haemodynamic effects of the functional stenosis were rather discrete (LVEDP + 5%, SV-12%, dP/dtmax-8%). Models of myocardial ischaemia used to study the effect of drugs or other haemodynamically effective interventions should be able to show functional impairment as well as improvement of the ischaemic myocardium. The critical stenosis does not impair myocardial function and, consequently, a favourable influence on the function and, consequently, a favourable influence on the function of ischaemic myocardium by any intervention may not become evident. However, in the presence of a functional stenosis the change in systolic shortening of the ischaemic myocardium is a very sensitive response to any intervention which affects the energy balance of the ischaemic myocardium. Therefore, this model should be preferred.