Beat-to-beat variability in atrial fibrillation: averaging mitral inflow
A 71-year-old woman with permanent atrial fibrillation and HFpEF is studied for worsening dyspnea. Heart rate is 110 bpm and irregular. LVEF is 55%, LA volume index 42 mL/m². Over 10 consecutive cardiac cycles, mitral inflow E velocity varies from 0.6 to 1.4 m/s and deceleration time from 120 to 260 ms. Septal e' is 6 cm/s and lateral e' is 8 cm/s. TR peak velocity is 3.0 m/s. The sonographer measures the single beat with the highest E velocity (1.4 m/s) and reports E/e' of 20, concluding that filling pressures are elevated. The referring clinician asks whether this is reliable.
1. How should mitral inflow and tissue Doppler measurements be averaged in AF, and why? Which beats are acceptable?
Read the worked answer
In AF, filling varies with the preceding RR interval, so a single beat can mislead. Average 3-5 consecutive cardiac cycles (some laboratories use 5-10) for E velocity, deceleration time, and e'. Do not choose the highest or longest beat; select consecutive beats and, if possible, beats whose RR intervals are within about 10-20% of the mean. Avoid post-pause beats and very short cycles, which produce nonrepresentative extremes. Measure at end-expiration with a sweep speed of 50-100 mm/s, sample volume at the mitral leaflet tips, and align the cursor with flow. For E/e', average E and average e' from the same set of beats, or calculate E/e' beat by beat and average.
2. Given the variability, how would you interpret E/e', TR velocity, and other findings? What additional measurements would improve confidence?
Read the worked answer
The reported E/e' of 20 is based on the single highest E (1.4 m/s), which is likely to overestimate filling pressure. If the averaged E is about 1.0 m/s and averaged e' is 6-8 cm/s, E/e' is roughly 13-17, which is less definitive. E/e' is also less reliable in AF because e' is affected by irregular annular motion and the ratio assumes a steady state. The TR peak of 3.0 m/s is above the 2.8 m/s threshold and, together with LA volume index 42 mL/m² and symptoms, supports elevated filling pressures. Additional useful measurements: IVC size and collapsibility, hepatic vein Doppler, pulmonary vein S/D and Ar, mitral deceleration time, and left atrial strain. Invasive hemodynamics may be needed if the decision depends on it.
3. What technical factors can cause beat-to-beat variation, and how would you control them?
Read the worked answer
Beat-to-beat variation can come from true irregular RR intervals, respiratory variation, sample-volume position (annulus vs leaflet tips), angle, gain, wall filter, sweep speed, and patient movement. Control these by using a stable apical four-chamber view, placing the sample volume at the leaflet tips, aligning the cursor with inflow, recording at end-expiration, setting a sweep speed of 50-100 mm/s, and using ECG timing to identify cycles. Do not measure during a movement artifact. If the patient is tachycardic, average more beats; if the rhythm is very irregular, consider repeating after rate control if clinically appropriate.