Comparison of Heart Rate Variability in Patients after Acute myocardial Infarction and healthy individuals Shemaila saleem et al. Ann. Pak. Inst. Med. Sci. 2011; 7(4): 191-195 190 Original Article Comparison of Heart Rate Variability in Patients after Acute Myocardial Infarction and Healthy Individuals Objective: To compare heart rate variability in patients of acute myocardial with that of healthy individuals and to establish correlation between time and frequency domain indices of heart rate variability in patients with AMI and healthy individuals. Study Design: Non-interventional descriptive study. Place and Duration: Armed Forces Institute of Cardiology (AFIC)/National Institute of Heart Diseases(NIHD), Rawalpindi over six months. Materials and Methods: We studied 45 patients of AMI and same number of age and sex matched normal healthy volunteers. Their 24-hour holter recordings within 48h of acute myocardial infarction were analyzed for HRV in time and frequency domains. Results: The time domain indices; SDNN (healthy volunteers=133±35ms vs. AMI=75±29ms), SDANN (healthy volunteers=118±34ms vs. AMI=65±28ms), SDNNi (healthy volunteers=59±18ms vs. AMI=35±14ms), rMSSD (healthy volunteers=40±17ms vs. AMI=28±13ms) and pNN50 (healthy volunteers=13±9% vs. AMI=6±11%) were significantly decreased (P less than 0.001) in patients with AMI when compared with healthy volunteers. Comparison of frequency domain indices; TP (healthy volunteers=3525±2671ms 2 vs. AMI=1296±1178ms 2 ), VLF (healthy volunteers=2485±2201ms 2 vs. AMI=902±928ms 2 ), LF (healthy volunteers=695±391ms 2 vs. AMI=246±251ms 2 ), HF (healthy volunteers=315±259ms 2 vs. AMI=100±96ms 2 ) between healthy volunteers and patients after myocardial infarction revealed a significant decline (P less than 0.001) in the parameters of patients. SDNNi was significantly correlated with power and VLF in normal healthy volunteers (power; r=0.92, VLF; r= 0.89) as well as in patients with AMI (power; r=0.85, VLF; r= 0.78). Conclusion: Time domain and frequency domain indices of HRV are significantly affected by early phase of AMI. This indicates HRV assessment after AMI may be useful in noninvasive risk stratification. It is suggested that mortality should be verified after follow- up studies of AMI. Time and frequency domain indices are significantly correlated. Key words: Ambulatory electrocardiography, autonomic nervous system, myocardial infarction. Shemaila Saleem * Qazi Waheed Ullah** Syed Muhammad Imran Majeed *** *Assistant Professor, Department of Physiology, Federal Medical and Dental College, Islamabad. **Lecturer, Department of Anatomy, Kohat University of Science and Technology, Institute of Medical Sciences (KIMS), Kohat. ***Head of the Department, Department of Clinical Cardiac Electrophysiology, Armed Forces Institute of Cardiology/ National Institute of Heart Diseases, Rawalpindi. Address for Correspondence Dr. Shemaila Saleem Assistant Professor, Department of Physiology, Federal Medical and Dental College, Islamabad Email drshemailasaleem@gmail.com Introduction HRV reflects beat to beat oscillations in cardiac autonomic modulation. Interactions between the sympathetic and parasympathetic nervous system are fundamental for maintaining homeostasis of the cardiovascular system. Malfunction of these interactions may lead to augmented sympathetic nerve traffic, triggering the occurrence of life-threatening ventricular tachyarrhythmias, whereas amplification in parasympathetic activity may exert a protective and antifibrillatory effect. 1 Autonomic imbalance in MI reflects the changes in the geometry of the viable heart as a result of necrotic and non-contracting segments that cause aggravated sympathetic activity by mechanically distorting the sensory nerve endings. This sympathetic hyperactivity decreases parasympathetic activity directed to the sinus node. 2