Page 64 - Coronary hemodynamics in acute myocardial infarction - Matthijs Bax

Chapter 4
Figure 1. A typical Doppler-tipped guide wire used for instantaneous measurement of intravascular flow velocity.
Coronary flow reserve in acute myocardial infarction
In 1996, Kern et al were the first to study coronary blood flow directly in patients in the setting of acute myocardial infarction (MI) by using a Doppler- tipped guidewire. In 41 patients with an acute MI, coronary blood flow velocity measured in the culprit artery during primary angioplasty by Doppler guidewire was compared with TIMI flow grade.16 In these patients, TIMI flow grades <3 were consistently associated with low baseline coronary blood flow velocity. However, among the 35 patients with post-interventional TIMI flow grade 3, 13 had a low baseline coronary blood flow velocity of <20 cm/s. In the total cohort of 42 patients, 11 patients had a clinical event during a median follow-up period of 18 months; of these events, nine occurred in patients with angiographic TIMI flow grade 3 but a low baseline blood flow velocity in the infarct-related arteries. This study shows that patients with TIMI flow grade 3 after primary percutaneous coronary intervention (PCI) have a wide range of flow velocity patterns and suggests that Doppler flow velocity measurement can further distinguish patients at increased risk for clinical events.
Ishihara et al measured relative CFVR in infarct-related arteries (IRAs) in a series of 14 patients with a first anterior wall acute MI directly after primary angioplasty and at 14 days and 6 months’ follow-up.17 Absolute CFVR is calculated as the ratio of hyperemic to baseline average peak flow velocity. A CFVR of <2.0 is generally considered to be abnormal. Relative CFVR is calculated as the ratio of the absolute CFVR in the IRA to the absolute CFVR in the reference artery. The CFVR measures the functional status of the distal microvascular bed and
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