Page 111 - Coronary hemodynamics in acute myocardial infarction - Matthijs Bax

Coronary autoregulation and fatal events in stable CAD
Limitations
There are some limitations to this study that deserve mention. First, the present study represents a relatively small study population. Consequently, although all-cause mortality, as well as cardiac mortality, is strikingly different between patients with normal or abnormal reference vessel CFVR, these results should be considered hypothesis generating.
Second, measurement of intracoronary blood flow velocity is considered technically challenging, and accurate evaluation of CFVR is dependent on the experience of the cardiologist. However, in this study, all coronary flow velocity measurements were performed by operators with ample experience in intracoronary flow velocity measurements.
Finally, no intracoronary pressure measurements were performed in
the reference coronary artery. Thereby, although reference vessels with
significant epicardial narrowing were not selected for coronary flow velocity 6 measurements, a potential role of subclinical atherosclerosis of the conduit
artery in the absence of focal narrowing in the impairment of reference vessel
CFVR cannot be excluded. However, (subclinical) narrowing of the reference
vessel in patients with abnormal reference vessel CFVR would have resulted
in a decreased hyperemic flow velocity.4,28 Furthermore, in the absence of
disturbed autoregulation, the normal physiological compensatory vasodilation
by means of autoregulation in response to a decreased perfusion pressure
induced by coronary narrowing is not associated with an increase in basal flow velocity.18,19 Therefore, these findings locate the cause for an impaired reference
CFVR to the coronary microvasculature, and the combination of finding implies
disturbed autoregulation as the key impediment to CFVR.
Conclusions
An impaired reference vessel CFVR is associated with an increased hazard for fatal events at long-term follow-up in patients with stable CAD. Impairment of reference vessel CFVR results from disturbed coronary autoregulation, leading to an increased coronary flow velocity under baseline conditions. Further studies are warranted to elucidate the origin of dysfunction of the coronary autoregulatory mechanism, as well as its role in the unfavorable outcome of patients with stable CAD.
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