# Impaired coronary blood flow at higher heart rates during atrial fibrillation: investigation via multiscale modelling

## TL;DR

This study uses multiscale computational modeling to investigate how increased heart rates during atrial fibrillation impair coronary blood flow, revealing that higher rates and variability significantly disrupt myocardial perfusion beyond 90 bpm.

## Contribution

It provides novel insights into the hemodynamic effects of atrial fibrillation at different heart rates using a validated multiscale model, highlighting the limitations of coronary perfusion pressure as a measure at high rates.

## Key findings

- Coronary blood flow impairment increases with higher heart rates during AF.
- Beat-to-beat variability amplifies coronary flow disturbances at elevated HR.
- Coronary perfusion pressure is unreliable for HR above 90 bpm.

## Abstract

Background. Different mechanisms have been proposed to relate atrial fibrillation (AF) and coronary flow impairment, even in absence of relevant coronary artery disease (CAD). However, the underlying hemodynamics remains unclear. Aim of the present work is to computationally explore whether and to what extent ventricular rate during AF affects the coronary perfusion. Methods. AF is simulated at different ventricular rates (50, 70, 90, 110, 130 bpm) through a 0D-1D multiscale validated model, which combines the left heart-arterial tree together with the coronary circulation. Artificially-built RR stochastic extraction mimics the \emph{in vivo} beating features. All the hemodynamic parameters computed are based on the left anterior descending (LAD) artery and account for the waveform, amplitude and perfusion of the coronary blood flow. Results. Alterations of the coronary hemodynamics are found to be associated either to the heart rate increase, which strongly modifies waveform and amplitude of the LAD flow rate, and to the beat-to-beat variability. The latter is overall amplified in the coronary circulation as HR grows, even though the input RR variability is kept constant at all HRs. Conclusions. Higher ventricular rate during AF exerts an overall coronary blood flow impairment and imbalance of the myocardial oxygen supply-demand ratio. The combined increase of heart rate and higher AF-induced hemodynamic variability lead to a coronary perfusion impairment exceeding 90-110 bpm in AF. Moreover, it is found that coronary perfusion pressure (CPP) is no longer a good measure of the myocardial perfusion for HR higher than 90 bpm.