Systematic assessment of intracoronary pressure-flow relationships in patients with severe aortic stenosis and coronary artery disease before and after transcatheter aortic valve implantation

Abstract

Patients with severe aortic stenosis undergoing transcatheter aortic valve implantation (TAVI) commonly have coronary artery disease, and the optimal treatment of this coexistent coronary disease has not been defined. For patients without severe aortic stenosis, the use of intracoronary physiology has been shown to improve outcomes when compared to an angiographic-guided approach.

The use of intracoronary physiology to guide revascularisation decisions for patients with severe aortic stenosis is contingent on understanding how aortic valvular stenosis affects coronary flow velocity. TAVI permits a unique opportunity to assess the impact of aortic stenosis on the coronary circulation because physiological assessments can be made in the presence of severe aortic stenosis (pre-TAVI) and then in the absence of severe aortic stenosis (post-TAVI) in the same patient.

In the series of mechanistic studies that comprise this thesis, I will utilise such an approach in order to isolate the effect of the stenosed aortic valve on the coronary circulation, minimising the potential effect of any confounding factors. I will utilise combined coronary pressure and flow velocity measurements, both at resting conditions and during hyperaemia, before and after TAVI. I will perform phasic analyses to examine the differential effects of TAVI on coronary flow velocity in different phases of the cardiac cycle, when the valve is either open or closed.

My first set of experiments will determine the acute effects of TAVI on coronary flow velocity over different phases of the cardiac cycle, and its effect on the most common clinically-used indices of coronary stenosis severity (FFR and iFR).

Secondly, I will quantify the effect of severe aortic stenosis on microcirculatory function and determine if this is influenced by coexistent coronary stenoses.

Finally, I will examine the longer-term effects of relieving aortic stenosis on coronary haemodynamics by repeating invasive pressure and flow velocity studies in patients 6-months following TAVI. This will allow me to determine whether acute changes in coronary flow velocity seen immediately after TAVI are sustained, or whether they change at longer-term follow-up, and how this impacts indices of coronary stenosis severity.