Heart rate turbulence

Heart rate turbulence (HRT) is a physiological phenomenon characterized by a short-term fluctuation in the heart rate following a naturally occurring premature ventricular contraction (PVC). It reflects the heart’s ability to regulate and return to its baseline rhythm after a disruption in normal electrical activity.

Overview

After a PVC, the heart momentarily speeds up, followed by a gradual slowing down back to the baseline heart rate. This biphasic pattern—first an acceleration, then a deceleration—is what defines heart rate turbulence. Unlike many cardiac diagnostic tests that require external stimuli or stress, HRT can be measured noninvasively during routine ambulatory electrocardiographic monitoring (such as a Holter monitor) since PVCs are commonly observed in the general population.

Physiology

HRT is thought to be mediated by the baroreflex, a homeostatic mechanism that helps maintain blood pressure stability. A PVC temporarily reduces cardiac output, triggering a reflex response that accelerates the heart rate. This is quickly followed by a baroreceptor-mediated slowing as the heart adjusts to the transient change in hemodynamics.

Parameters

HRT is typically quantified using two main parameters:

• Turbulence onset (TO): The initial acceleration in heart rate after the PVC.
• Turbulence slope (TS): The rate at which the heart rate slows down and returns to baseline.

Lower or absent HRT responses (blunted TO and TS) are associated with impaired autonomic function and reduced vagal tone.

Clinical Significance

HRT has emerged as a valuable noninvasive marker in risk stratification for patients with various cardiovascular conditions:

• After a myocardial infarction (heart attack), abnormal HRT has been shown to be a significant predictor of cardiac mortality.
• In patients with congestive heart failure, abnormal HRT may indicate a higher risk of sudden cardiac death due to malignant ventricular arrhythmias.
• HRT, when used in conjunction with other cardiac risk markers such as left ventricular ejection fraction and heart rate variability, enhances the predictive power of identifying high-risk individuals.

Advantages

• Noninvasive and cost-effective
• Can be measured from long-term ECG recordings
• Reflects both autonomic nervous system and baroreflex activity

Limitations

• Requires a sufficient number of PVCs for accurate analysis
• Affected by beta-blockers and other autonomic-modulating drugs
• Not applicable in individuals with atrial fibrillation or frequent arrhythmias that mask normal sinus responses

See Also

• Heart rate variability
• Baroreflex
• Sudden cardiac death
• Myocardial infarction
• Ventricular arrhythmia
• Holter monitor