Computer Analysis of the RR Interval-Contractility Relationship during Random Stimulation of the Isolated Heart

Abstract

Hemodynamic variability in patients with atrial fibrillation may originate from a direct influence of the variations in RR intervals on myocardial contractility. With the aid of a computer the serial autocorrelation function and the histogram of the RR intervals of patients with atrial fibrillation receiving no medication were produced. The RR intervals were randomly distributed and the histograms rather skew. Next, random rhythms with histograms matching those of the patients were produced with a radioactive source and a GeigerMiiller counter. These rhythms were used to stimulate isolated perfused rat hearts to study the relationship between the RR interval and a number of contractile parameters. The ECG and the isotonic contractions were digitized and processed by the computer. Serial crosscorrelation coefficients were computed between the RR interval on the one hand, and contraction height, contraction area, and maximum of the first derivative of the contraction on the other hand. The zero order crosscorrelation coefficient between the RR interval and contraction height was 0.6, between the RR interval and contraction area 0.8, and between the RR interval and maximum of first derivative 0.5. Although small, the first and second to approximately the tenth order coefficients were definitely negative. It is concluded that during a random rhythm the contractile parameters of an isolated heart are strongly related to the preceding RR interval. It is conceivable that this relation contributes to the variability of hemodynamic parameters during atrial fibrillation in man. • Atrial fibrillation is a common rhythm disturbance of the heart in man. During this type of arrhythmia the ventricles beat very irregularly and, in general, each contraction differs from the preceding one and from the next. ADDITIONAL KEY WORDS

A Mathematical Model of Human Atrioventricular Nodal Function Incorporating Concealed Conduction

“…The autocorrelation function of the atrial activation times shows linear correlation for small lags, whereas the autocorrelation function of the ventricular interbeat intervals shows no linear correlation (Fig. 3) (Goldstein and Barnett, 1967;Meijler et al, 1968;Bootsma et al, 1970;Stackee et al, 1971;Hashida et al, 1978;Cohen et al, 1983).…”

Autocorrelation Patterns in the Left-Ventricular Pressure Course of Isolated Working Hearts at Sinus Rhythm

“…It was used to analyse electrical fluctuations in acute atrial fibrillation [13], to auto-recognise tachycardia and fibrillation [14], and to access ventricular performance at random RR intervals [15] or in chronic atrial fibrillation [16]. Some standard heart rate variability indices are mathematically related to the autocorrelation within RR-interval time series [7].…”

“…Consequently, randomness is better assessed by a stochastic approach, viz., by declaring an arbitrary portion (10%, presently) of beats, following a randomly selected one, as "very similar" to the referenced one, and by observing the occurrence of such beats in the course of time. If the probability to encounter a "very similar" beat within some time converges to a fixed value as that time is reduced toward zero, and if there is no mutual relation or "memory" [5,15], a Poisson process is expected [9]. An artificial Poisson generator has been used to stimulate isolated hearts, perceiving the arrival of ventricular excitation in case of right atrial fibrillation as a Poisson process [15].…”

Clinical implications of frequency-force relation

“…Postextrasystolic potentiation can also be recognized under certain clinical conditions (Brockenbrough, Braunwald, and Morrow, 1961 ; Durrer, Schuilen burg, and Meijler, 1968), but the compensatory pause, which often follows a premature beat, may confuse the issue, so th at the relative contribution of the potentiating mechanism cannot be differentiated from haemodynamic factors. In order to avoid haemodynamic pitfalls, we have attempted a statistical approach, for the study of the frequencyforce relation in the intact organism, making use of patients with atrial fibrillation.In previous studies we have demonstrated that the ventricular rhythm of patients with atrial fibrillation is random (Meijler, Strackee, van Capelle, and du Perron, 1968;Bootsma, Hoelen, Strackee, and Meijler, 1970). This randomness of the ventricular rhythm indicat es the absence of any relation between successive RR intervals and th us allows one to draw conclusions from relationships found between RR intervals and haemodynamic or contractiIe parameters during atrial fibrillation.…”

“…In previous studies we have demonstrated that the ventricular rhythm of patients with atrial fibrillation is random (Meijler, Strackee, van Capelle, and du Perron, 1968;Bootsma, Hoelen, Strackee, and Meijler, 1970). This randomness of the ventricular rhythm indicat es the absence of any relation between successive RR intervals and th us allows one to draw conclusions from relationships found between RR intervals and haemodynamic or contractiIe parameters during atrial fibrillation.…”