Heart rate turbulence

Heart rate turbulence is the short pattern that a healthy heart rhythm shows after a premature ventricular beat: a brief speed-up over the next two beats, then a slower return past the starting rate. It is measured on a 24-hour ECG ECG ECG A recording of the heart's electrical activity, taken with electrodes on the skin. ECG-based RR intervals are the reference standard for measuring HRV. More about ECG and reported as turbulence onset, in percent, and turbulence slope, in milliseconds per beat.

Why this measure exists

A premature ventricular beat is a natural experiment on the baroreflex baroreflex Baroreflex The reflex that steadies blood pressure from beat to beat by changing heart rate. Its built-in delay makes heart rate rise and fall about every 10 seconds, the 0.1 Hz rhythm in LF power. More about Baroreflex . It arrives early and pumps little blood, so blood pressure dips for a beat; the baroreflex answers by briefly withdrawing vagal braking (the heart speeds up) and then, as pressure overshoots, by reapplying it (the heart slows). Bauer and colleagues’ 2008 consensus statement for the International Society for Holter and Noninvasive Electrophysiology describes the pattern as an indirect test of baroreflex function: in people whose baroreflex is weakened, the turbulence is blunted or absent. The statement rates it as appropriate for stratifying risk after a heart attack and in heart failure. Sassi and colleagues’ 2015 position paper left it out of its review because the consensus statement already covered it.

The formula

$$\mathrm{TO} = \frac{(\mathrm{RR}_{+1}+\mathrm{RR}_{+2})-(\mathrm{RR}_{-2}+\mathrm{RR}_{-1})}{\mathrm{RR}_{-2}+\mathrm{RR}_{-1}}\times 100$$

Turbulence onset compares the two normal intervals after the premature beat premature beat Ectopic beat A heartbeat that starts outside the heart's normal pacemaker and usually comes early. Ectopic beats are common, but they distort HRV unless removed or corrected. More about Ectopic beat and its pause with the two before it: a negative value means the heart sped up. Turbulence slope is the steepest regression slope over any five consecutive sinus intervals within the first 15 after the premature beat, in ms per interval, measured on the average pattern of all the premature beats in the recording. An onset below 0 % and a slope above 2.5 ms per interval count as normal; one abnormal value is category 1 and both abnormal is category 2.

Worked example

normalearly beat, pausespeed-upslow-down

A line chart of twelve heartbeat intervals. The first two sit at 880 ms. The third drops to 528 ms, the premature beat, and the fourth rises to 1232 ms, the pause after it. The next two intervals sit just below 880 ms, a brief speed-up, and the following intervals climb to about 915 ms before returning to 880 ms. Turbulence onset for this pattern is -3.5 percent.

For the pattern drawn above, the two intervals after the pause add up to less than the two before the early beat, so turbulence onset is -3.5 %: the heart sped up, as a healthy baroreflex makes it do.

What moves it

Baroreflex strength, so age, heart disease, diabetes and beta-blockers all change it. It needs real premature ventricular beats that pass the method’s filters for prematurity and pause, and a clean 24-hour ECG around each one.

When it misleads

It cannot be measured in anyone who has no premature ventricular beats (studies after heart attacks classed those people with the normal group), or in atrial fibrillation. A wearable’s interval series, with the premature beats removed as artifacts artifacts Artifact An error in a heartbeat recording, such as a missed, extra or mistimed beat, often caused by movement or poor sensor contact. Artifacts can badly distort HRV numbers. More about Artifact , has thrown the measurement away. It is a clinical risk marker, not a wellness number, and this page describes it only so that the term is not a mystery.

Where you will see it

Holter analysis software and the research literature on risk after a heart attack. Kubios HRV does not print it; wearables do not show it. The Task Force does not cover it. What are nonlinear HRV measures and do I need them? puts it in context.