Prognostic Value of Ultra-Short Heart Rate Variability Measures Obtained from Electrocardiogram Recordings of Hospitalized Patients Diagnosed with Non-ST-Elevation Myocardial Infarction

<b>Background:</b> Myocardial infarction (MI) is a common emergency with high rates of morbidity and mortality. Current risk stratification scores for non-ST-elevation MI (NSTEMI) use subjective or delayed information. Heart rate variability was shown to correlate with prognosis following MI. This study aimed to evaluate ultra-short heart rate variability (usHRV) as a prognostic factor in NSTEMI patients. <b>Methods</b>: A retrospective analysis was performed on 183 NSTEMI patients admitted to Rambam Health Care Campus in 2014. usHRV measures, including the standard deviation of normal-to-normal intervals (SDNN) and root mean square of successive differences (RMSSD), were calculated. Logistic regression assessed whether clinical, laboratory, or usHRV parameters predicted severe in-hospital complications like heart failure (HF), atrial flutter/fibrillation (AFL/AF), ventricular tachycardia/fibrillation (VT/VF), and atrioventricular block (AVB). Both Cox and logistic regression were used for survival analysis. <b>Results</b>: Of 183 patients (71.6% male, mean age 67.1), 35 (19%) died within 2 years. In-hospital complications included 39 cases (21.3%) of HF, 3 cases (1.6%) of VT/VF, and 9 cases (4.9%) of AVB. Lower usHRV was significantly associated with higher mortality at 2 years and showed marginal significance at 90 days and 1 year. Increased usHRV was linked to a higher risk of in-hospital ventricular arrhythmia (VT/VF). <b>Conclusions</b>: Overall, this study is in agreement with previous research, showing a correlation between low usHRV and a higher mortality risk. However, the association between usHRV and the risk of VT/VF demands further investigation. More expansive prospective studies are needed to strengthen the observed associations.