Page 52 - Coronary hemodynamics in acute myocardial infarction - Matthijs Bax

Chapter 3
Data extraction
The ratio of mean distal coronary pressure to average peak blood flow velocity was used as an index of microvascular resistance.13, 14 The ratio of transvascular pressure gradient (mean aortic pressure minus right atrial pressure) to baseline average peak blood flow velocity was used as an index of baseline microvascular resistance index. Because right atrial pressure was not routinely measured, it was estimated to be 10 mm Hg in all patients. Minimal microvascular resistance index was defined as microvascular resistance during hyperemia. The variable arteriolar resistance index, which represented autoregulatory function, was expressed as baseline microvascular resistance minus minimal microvascular resistance. Baseline average peak blood flow velocity, CFVR, and baseline microvascular resistance values were also noted after correction for the rate– pressure product (parameter for global cardiac workload, defined as a product of systolic blood pressure and heart rate).
Clinical events
Two patients who died at follow-up showed higher baseline and minimal microvascular resistances in IRAs compared with the study group (7.8 ± 2.5 mm Hg/s/cm, p = 0.03, and 5.8 ± 1.5 mm Hg/s/cm, p = 0.009, respectively). Other values of physiologic data (Table 1) did not differ significantly from those in the study group. One patient underwent coronary artery bypass graft surgery. Eight patients underwent repeat angioplasty (4 patients showed target lesion restenosis, 1 had a subacute stent closure, and 3 underwent non-IRA angioplasty). Six patients with asymptomatic significant restenosis at 6-month follow-up (angiographic restenosis >50% at visual assessment without angina) were excluded from analysis because of possible influences on flow velocities. Ten patients with an uncomplicated clinical course at follow-up refused repeat angiography. (Microvascular resistance values in the acute phase of MI in all excluded patients, other than those who died, did not differ from those in the study group.) The remaining 73 of the initial 100 patients constituted the study cohort and were analyzed in the present study.
Statistical analysis
Variables are presented as numbers and percentages of patients. Continuous variables are expressed as mean ± SD. Normal distributed variables were tested by 2-tailed Student’s t test for paired or unpaired data, as appropriate.
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