Step E for EKG-Based Heart Rate Reserve in Stress Echocardiography

Abstract

Cardiac autonomic unbalance is a major determinant of vulnerability to arrhythmias and a risk factor for sudden death. The clinical assessment with baroreflex sensitivity or heart rate variability remains complex, time-consuming, and inaccurate. The sympathetic reserve can be easily assessed with zero training and 100% reproducibility during stress echocardiography through heart rate reserve, calculated from 1-lead ECG present in the echo monitor as the peak-to-rest ratio of heart rate. The normal cutoff values are higher (≥1.80) for stronger chronotropic stresses such as exercise or dobutamine and lower (>1.22) for milder chronotropic stresses such as dipyridamole or adenosine, which stimulate cardiac afferent neurons through A2A adenosine receptors, independently of inducible ischemia and arterial hypotension. A reduced heart rate reserve is a sign of abnormal cardiac sympathetic reserve, an important prognostic factor, and a potential therapeutic target. A reduced heart rate reserve and inducible regional wall motion abnormalities have incremental value in predicting outcomes. Heart rate reserve is imaging-independent and useful to assess the arrhythmic vulnerability and cardiac autonomic unbalance during stress echocardiography.