Root Mean Square Of Successive RR Interval Differences Research Articles

Heart Rate Variability in Patients with Mitral Stenosis: A Study of 20 Cases from King Abdulaziz University Hospital

Left atrial enlargement in mitral stenosis predisposes to atrial fibrillation (AF). Analysis of heart rate variability (HRV) prior to the onset of an arrhythmia may show alterations in autonomic balance that are known to predispose to the development of AF. The aim of this study was to determine whether HRV in patients with rheumatic mitral stenosis (MS) is abnormal in comparison to normal controls, and to find the relationship between left atrial size and HRV in patients with MS in sinus rhythm and in AF. A series of 24-hour ambulatory Holter electrocardiogram recordings were obtained for 10 consecutive, newly diagnosed untreated subjects with pure mitral stenosis in sinus rhythm, 10 with mitral stenosis complicated by atrial fibrillation and 10 age-matched normal controls. Digitized records were processed using time domain and power spectral analysis. In patients with mitral stenosis in sinus rhythm, we observed significant decrease of the standard deviation of the RR intervals (SDRR), as well as of the root mean square of successive RR interval differences (RMSSD) and Edinburgh index (sNN50), while in patients with AF, the RMSSD and sNN50 were much larger than those in normal. The areas under all spectral bands were markedly increased in patients with AF compared with normal. Furthermore, the high low frequency/high frequency (HLF/HF ratio) ratio was very small compared to normal. HRV measures were independent of atrial size in both groups. Decreased HRV in mitral stenosis patients with sinus rhythm suggests increased sympathetic activity in patients prone to atrial fibrillation, while marked increased of HRV in patients with AF may indicate that parasympathetic activity modulates the intrinsic behavior of the atrioventricular node during atrial fibrillation. The evaluation of HRV may be a useful tool for the identification of patients predisposed to AF.

Nitric oxide and cardiac parasympathetic control in human heart failure

Cardiac parasympathetic control has prognostic significance in heart failure, but the control mechanisms of this system remain poorly defined. We have demonstrated previously a facilitatory role for nitric oxide (NO) in the parasympathetic control of heart rate in young healthy human subjects. In view of the complex abnormalities of regional NO activity observed in chronic heart failure, we now aim to establish if this mechanism is active in subjects with this condition. Groups of 12 heart failure patients [NYHA class II-III; mean age 52 years (range 38-67 years)] and 12 age/sex-matched healthy control subjects [mean age 50 years (range 36-62 years)] were studied. Heart rate variability and baroreflex sensitivity were measured during inhibition of endogenous NO production with N(G)-monomethyl-l-arginine (l-NMMA; 3 mg.h(-1).kg(-1)) and during administration of an equipressor dose of the control vasoconstrictor phenylephrine (12-36 microg.h(-1).kg(-1)). Basal levels of nitrate+nitrite were measured in the plasma as an indication of systemic NO production. In the heart failure patients, despite an equal rise in blood pressure with both drugs, high-frequency indices of heart rate variability increased less with l-NMMA than with phenylephrine: RMSSD (root mean square of successive RR-interval differences) increased by 4+/-2 compared with 26+/-8 ms (P<0.001) and high-frequency power increased by 97+/-62 compared with 1372+/-861 ms(2) (P<0.001). The increases in cross-spectral baroreflex sensitivity were also lower with l-NMMA than with phenylephrine [high-frequency alpha-index, 2.2+/-1.3 and 12.6+/-3.8 ms/mmHg respectively (P<0.001); low-frequency alpha-index, 1.3+/-0.9 and 4.3+/-1.7 ms/mmHg respectively (P<0.05)]. Healthy subjects showed a similar discrepancy in the response of high-frequency indices of heart rate variability to the two drugs, although baroreflex sensitivity responses were significantly different only for the high-frequency alpha-index. Levels of plasma nitrate+nitrite were significantly higher in the heart failure patients compared with controls. These data demonstrate that baroreflex-mediated cardiac parasympathetic activation in human heart failure, as in health, is dependent upon endogenous NO synthesis.