Variabilidad de la frecuencia cardíaca: sus fundamentos fisiopatológicos y su utilidad como índice pronóstico post-infarto agudo del miocardio / Variability of cardiac frequency: it physiopathological basis and it utility as pronostic index on post myocardial acute infarction

ABSTRACT

The analysis of heart rate variability studies the normal oscillatory changes of the cardiac cycle. These changes are periodicals or incidental and are controlled by humoral, sympathetic and parasympathetic stimuli. Time domain analysis variations of cardiac cycle using the standard deviation of RR intervals in 24 hours (SDRR) and the percentage of difference between adjacent normal RR intervals of more than 50 ms (pNN50). Frequency domain, converts beat to beat fluctuation of heart rate into different components of frequency by a fast Fourier transformation. They are classified, according to their magnitude, in high frequency (>0.15 Hz), low frequency (0.04-0.15 Hz), very low frequency (0.003-0.04 Hz) and extremely low frequency (<0.003 Hz). The high frequency fluctuations are predominantly related to parasympathetic activity. The physiology of very low and extremely loe frequency fluctuations remain unclear. Many reports have shown that a decrease in heart rate variability after myocardial infarction may independently identify patients at risk for sudden death. However, the physiopathological basis of these findings is not yet elucidated