Regional Myocardial Contractility
The Elusive Phantom of Cardiology
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The characterization of myocardial function, both on the global but even more so on the regional level, remains an elusive art in cardiology—the holy grail for clinicians and researchers alike. Left ventricular (LV) ejection fraction (EF) is being widely used to define global function but has several drawbacks. As a ratio between stroke volume (SV) and end-diastolic volume (EDV), the interpretation of abnormal values or of changes in EF can be difficult or even misleading. Because the function of the ventricle is the delivery of blood to the circulation/organs at an adequate arterial pressure, SV is the more relevant parameter for ventricular function, certainly if measured at rest and during stress/exercise. But both a low and a high EF can deliver such an adequate SV wholly depending on the size of the ventricle, that is, EDV: a large ventricle does not require a high EF to deliver an adequate SV; similarly in normal ventricles as witnessed by the athlete’s heart. On the contrary, a small ventricle (low EDV) will require a high EF to deliver an adequate SV, with possible diastolic problems in consequence. The dependence of EF on loading conditions is another major issue in its interpretation, and the inclination to equate EF with intrinsic contractility is thus completely flawed.1
See Article by Espe et al
When the ventricle is damaged by a myocardial infarction (MI), the interpretation of myocardial function becomes even more difficult because variable compliance of tissue, bulging, and electric and mechanical dyssynchrony create internal shifts in blood, which, much as in mitral insufficiency, change the relationship between myocardial deformation and forward SV. Here, the evaluation of regional function becomes even more important.
In this issue of the journal, Espe et al2 report on a study of regional function after an MI in 62 …