Hybrid quantification of absolute perfusion requires accurate measurement of myocardial mass

Subendocardial and transmural perfusion improve after aortic valve replacement in aortic stenosis. Accordingly, in this issue of EuroIntervention, the publication by Gallinoro et al1 on longitudinal coronary physiology before and after transcatheter aortic valve implantation (TAVI) raises a critical point regarding the quantification of absolute myocardial perfusion. As summarised in Figure 1, we argue that the algorithm for determining absolute myocardial mass from computed tomography (CT) imaging needs validation and currently appears to be inaccurate.

As clearly stated by the developers of invasive continuous thermodilution: “Absolute flow, expressed in mL/min is meaningless because the myocardial distribution to be perfused is unknown and varies widely between different arteries and different subjects”2. Two possible normalisations exist. First, flow during stress conditions can be expressed as a unitless multiple of resting conditions, i.e., coronary flow reserve (CFR). Second, absolute flow (mL/min) can be divided by the amount of distal myocardial mass (g) to calculate perfusion (mL/min/g).

Cardiac positron emission tomography (PET) or magnetic resonance imaging (CMR) intrinsically quantify myocardial perfusion due to their data acquisition and flow models. Other techniques, such...