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AF Rate Variability and Symptoms — EECC MCQ

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ModerateArrhythmia & ElectrophysiologyAF Rate Variability and SymptomsEECC

A 70-year-old man with permanent AF on metoprolol 50 mg bd has persistent symptoms of fatigue and exercise intolerance. His resting HR is 78 bpm. 24-hour Holter shows heart rates ranging from 55 to 145 bpm with an average of 88 bpm. What is the likely cause of his symptoms?

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Correct answer: E — Irregular ventricular response with wide rate variability in AF — even with acceptable average and resting rates, the beat-to-beat variability and intermittent fast rates reduce cardiac efficiency; optimising rate control with better rate smoothing may improve symptoms

In AF, the irregularity of ventricular response causes haemodynamic inefficiency beyond simply the average heart rate. Beat-to-beat variability in RR intervals leads to: (1) variable stroke volumes (preload-dependent filling variation); (2) suboptimal diastolic filling during short RR intervals; (3) wasted cardiac energy during long pauses followed by high stroke volume beats. The RACE II trial used resting HR <110 bpm as a 'lenient' target, but individual patients may benefit from tighter control or rhythm control if symptomatic. Options include: (1) optimise rate control (adjust beta-blocker dose, add digoxin); (2) consider rhythm control (ablation or AAD) given persistent symptoms — the EAST-AFNET 4 data support early rhythm control; (3) assess for other causes of fatigue (anaemia, thyroid, sleep apnoea).

Reference: ESC (2024): AF Guidelines