Renal artery stenosis: Extracting quantitative parameters with a mathematical model fitted to magnetic resonance blood flow data

Acceleration time of systolic coronary flow velocity to diagnose coronary stenosis in patients with microvascular dysfunction

BACKGROUND

The aim of this study was to test whether acceleration time of systolic coronary flow velocity could contribute to the diagnosis of coronary stenosis in patients with microvascular dysfunction, on the basis of the hypothesis that systolic coronary flow is less influenced by microvascular function because of compressed myocardium.

METHODS

Coronary flow velocity was assessed in the left anterior descending coronary artery during hyperemia with intravenous adenosine by echocardiography in 502 patients who were scheduled for coronary angiography because of coronary artery disease and significant valvular disease. Coronary flow velocity reserve (CFVR) and the percentage acceleration time (%AT), as the percentage of the time from the beginning to the peak of systolic coronary flow over systolic time during hyperemia, were calculated. The diagnostic ability of CFVR and %AT for angiographic coronary artery stenosis was then analyzed. As invasive substudies, fractional flow reserve and %AT by a dual-sensor (pressure and Doppler velocity) guidewire were measured simultaneously with %AT on transthoracic echocardiography (n = 14).

RESULTS

Patients with coronary stenosis had significantly lower CFVR (1.7 ± 0.4) and greater %AT (65 ± 9%) compared with those without stenosis (2.6 ± 0.6 and 50 ± 13%, respectively). Percentage acceleration time by Doppler echocardiography was in good agreement with %AT (r = 0.98) and fractional flow reserve (r = 0.74) invasively measured by dual-sensor guidewire. Cutoff values of CFVR and %AT were determined as 2.0 and 60% in receiver operating characteristic curve analysis. The sensitivity, specificity, and accuracy of CFVR to detect coronary stenosis were 71.1%, 77.3%, and 75.4%, while those of %AT were 83.4%, 71.8%, and 75.4%, respectively. In addition, %AT provided high accuracy to detect coronary stenosis, especially in patients with previous myocardial infarctions, valvular disease, and left ventricular hypertrophy (81.1%, 84.1%, and 73.4%, respectively).

CONCLUSIONS

The %AT of systolic coronary flow velocity is a promising marker to diagnose coronary stenosis in patients with microvascular dysfunction.

Characterization of the time course of the superior mesenteric, abdominal aorta, internal carotid and vertebral arteries blood flow response to the oral glucose challenge test using magnetic resonance imaging

Blood flow to the splanchnic circulation increases postprandially which may cause a reduction in systemic and cerebral perfusion leading to postprandial syncope in the elderly who lack adequate cardiovascular reserve. We used multi-station 2D phase contrast cine magnetic resonance imaging (PC-MRI) with the aim of characterizing the time course of the haemodynamic response to an oral glucose challenge test (OGCT) in the large arteries perfusing the splanchnic, systemic and cerebral circulations (superior mesenteric artery SMA, abdominal aorta AA, internal carotid arteries, ICA and vertebral arteries VA). In this study nine fasted healthy volunteers were studied. Separate cine PC-MRI scans were acquired in the neck and in the abdomen every 88 s, these two measurements being interleaved for ten baseline scans at each station with the scanner automatically moving the subject between the two stations. After ingestion of the OGCT, a further 30 cine PC-MRI scans were acquired at each station. Using this technique we were able to characterize with frequent sampling of volumetric blood flow the time course of blood flow response to the OGCT of the SMA, AA and both VA and ICA. We found a substantial variation between individuals in the amplitude and the time to the peak of the SMA blood flow response to the OGCT which correlated positively with body mass index. MRI provides a robust, non-invasive method of studying normal physiology that could be valuable in studies of diseases such as postprandial hypotension.