Cardiomyopathy
In patients with hypertrophic CMP CFVR is markedly lower compared with healthy controls. Abnormal CFVR values were more common in symptomatic compared with asymptomatic subjects and in those with left ventricular outflow tract obstruction. Impaired CFVR was a strong and independent predictor of outcome in hypertrophic CMP patients.43
In 132 patients with idiopathic dilated CMP with angiographically normal coronary arteries and left ventricular ejection fraction <40 % CFVR values were abnormal (<2) in nearly two-thirds of the participants and were associated with a worse prognosis during 2-year follow-up.44
Prognostic Value
Recently, low CFVR values have been shown to have prognostic significance in different clinical situations. In octogenarians (369 subjects) a reduced CFVR in LAD in the setting of a stress echo negative for wall motion abnormalities helps to risk stratify the subset at higher risk of mortality and major adverse cardiac events (MACE). The best CFVR cut-off predicting untoward cardiac events in this population was 1.93.45
In nearly 400 patients with angiographically normal coronary arteries, normal wall motion during stress and chest pain (microvascular angina), those with CFVR value >2 showed significantly better outcome during almost 5-year follow-up compared with the group with impaired CFVR.46 In more than 300 subjects with known or suspected coronary artery disease but with negative stress echocardiography (by wall motion criteria), CFVR ≤1.92 with dipyridamole is an independent predictor of worse prognosis.47 The 3-year event-free survival is 68 % versus 98 % in groups with reduced and preserved CFVR, respectively. In the setting of intermediate coronary stenosis (50–70 %) a CFVR value >2 predicts good prognosis during a mean follow-up of 15 months.48
Reduced CFVR (<2 with dipyridamole) is an independent predictor of unfavourable outcome in patients with non-ischaemic dilated cardiomyopathy during 22 months of follow-up.23 After heart transplantation CFVR <2.6, using adenosine, is the main independent predictor of MACE for a period of almost 2 years49.
In the largest study so far on CFVR assessment – 4,313 patients with known or suspected coronary artery disease – 4-year mortality was markedly higher in subjects with CFVR ≤2 than in those with CFR >2, both considering the group with ischaemia and the group without ischaemia at stress echocardiography. CFVR was also an independent predictor of mortality along with inducible ischaemia during stress echocardiography, resting wall motion score, left bundle branch block, age, male gender and diabetes mellitus.50
Clinical Utilisation
Considering the multiple areas of clinical application of CFVR measurement, the reasonable question arises why CFVR has not become a routine diagnostic test and a standard part of non- invasive echocardiographic assessment in patients suspected of or at increased risk of epicardial or microvascular coronary artery disease? A meaningful explanation for the lack of more widespread utilisation of CFVR measurement is that this method requires considerable anatomical and technological knowledge. A specific setting of the echo scanner is a prerequisite in order to be able to assess coronary flow. Also, there is a learning curve and initially a lot of time has to be dedicated to technical aspects and to acquiring necessary skills.