Assessment of prognostic value of heart rate response to single deep breath in cases of acute myocardial infarction involving anterior wall or inferior wall within first 12 hours of admission

Introduction: The sympatho-vagal balance on the SA node produces beat to beat variation in heart rate which is markedly increased in normal subjects on deep breathing cycles. Heart rate variability testing gives an estimation of altered vagal-sympathetic balance and is a marker of low vagal tone on the heart. This study assesses a simple bedside test involving a single cycle of deep breathing to assess heart rate variability response.
Methods: A prospective observational study was done from May 2018 to September 2018 in the department of cardiology in 52 subjects diagnosed as suffering from acute myocardial infarction. For this test, ECG recording in all limb leads was taken while the patient was asked to perform deep breathing for ten seconds. The difference between the maximum and minimum R-R interval was recorded as an index of heart rate variability. The patient was then followed up till discharge for improvement or deterioration in clinical condition.
Results: Forty-one subjects (78.8%) had a heart variability response of less than 10 beats per minute and the rest eleven (20.2%) individuals had a variability response of >10 beats per minute. Patients who had low heart rate variability (n=41) showed higher incidence of acute left ventricular failure (75%), arrhythmia (17.5%) as compared to patients who had normal heart rate variability.
Conclusions: This test can serve as an inexpensive, feasible and bedside alternative to conventional methods and can be correlated with negative prognosis in patients with acute MI.