Is index of microvascular resistance of Sisyphean utility in Takotsubo syndrome?

Abstract

Figure 1 A man in his fifties with angina, diabetes, hypertension and a normal heart on echocardiogram is admitted for a functional coronary angiogram. He has a long segment of atherosclerotic disease in the proximal and mid LAD (upper panel with bolus thermodilution). The Pd/Pa, FFR, CFR, *MRR, IMR and IMR Corr are 0.81, 0.67, 2.5, *3.7, 33, and 28 consecutively. Post-stenting (lower panel with repeat bolus thermodilution), the corresponding values are 0.95, 0.87, 5.7, *7.1, 19, and 19; the raised IMR normalized and CFR doubled. This demonstrates that epicardial coronary artery disease and flow rheology influence IMR. IMR can be recalculated with coronary wedge pressure (Pw) to account for collateral circulation. However, since there are no visible collaterals and the lesion is non-critical, it is unlikely that Pw is higher than 30 mmHg, but the **IMR is still elevated at 26 using this upper value. Alternatively, IMR can be repeated in a non-culprit vessel, although this complicates the procedure. Nevertheless, given that pre-stenting CFR ≥ 2, the discordant IMR should be disregarded in practice. Bolus thermodilution indices are systematically overestimated. After all, a *seven-fold reserve range of coronary microvascular resistance is biologically implausible.