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A β-Blocker may be Effective on Ventricular Contractile Mechanisms in Atrial Fibrillation Patients with Heart Failure with Preserved, but not Reduced, Ejection Fraction

Shinichi Ushiroda

Background: Ventricular contractile responses to β-blockers remain largely unknown in patients with AtrialFibrillation (AF) and Heart Failure (HF), despite the recommended use of β-blockers as first-line pharmacotherapyfor these patients. This study investigated β-blocker effects on ventricular contractile mechanisms, namely theFrank-Starling Mechanism (FSM), Mechanical Restitution (MR), and Postextrasystolic Potentiation (PESP), whichare closely associated with ventricular contractile function, in AF patients with HF with preserved (HFpEF) versusreduced Ejection Fraction (HFrEF).

Methods: Twenty AF patients were divided into two groups based on EF: the HFpEF group (EF ≥ 50%, n=14)and the HFrEF group (EF<40%, n=6). Using impedance cardiography, an FSM-MR graph and a PESP graph werecreated by applying (dZ/dt) min values representing the peak velocity of aortic blood flow on the y-axis againstpreceding RR interval (RR1) or RR1/pre-preceding RR interval (RR2) ratio values on the x-axis at baseline and afteradministration of a β-blocker in AF patients with HFpEF versus HFrEF.

Results: With the β-blocker administration, rates of increase in median (dZ/dt) min values showed a significantpositive correlation with the rates of increase in median RR1 values as the functions of the FSM-MR in AF patientswith HFpEF (ρ=0.88, P<0.001), in contrast to those with HFrEF (ρ=−0.43, P=0.40). PESP index values representingthe extent of the effect of PESP were similarly and significantly decreased after administration of the β-blocker inboth groups: AF patients with HFpEF (baseline: median 5.9 [Interquartile Range (IQR) 2.0-16.9] vs. after β-blocker:median 1.6 [IQR 0.62-7.2]; P=0.023), and AF patients with HFrEF (baseline: median 6.6 [IQR 0.66-22.6] vs. after β-blocker: median 1.2 [IQR 0.06-15.1]; P=0.028).

Conclusions: From the perspective of ventricular contractile mechanisms in AF, the β-blocker may be effectiveon the Frank-Starling mechanism and mechanical restitution in AF patients with HFpEF, but not HFrEF