ABC | Volume 115, Nº1, July 2020

Original Article Benchimol-Barbosa et al. Dynamic AV-conduction to RR-interval Coupling Arq Bras Cardiol. 2020; 115(1):71-77 Discussion Atrial ventricular conduction is themost important determinant of the PR-interval duration, which undergoes dynamic fluctuations depending on autonomic and health statuses, age, instantaneous HR, medications, stance and respiratory frequency. 17 The evaluation of the PR-interval by using either P wave-onset or P wave-peak approaches as fiducial points has been shown to provide accurate and precise results, and, thus, are both appropriate to assess AVCT inter-beat variations. 14,17 In the present study, highly trained longdistance runners and healthy sedentary subjects had their maximal aerobic power assessed, and AVCT coupled to the preceding RR- Figure 1 – Scatterplot and regression line of beat-by-beat RR-interval as a function of respective PR-peak interval of a 30 y.o. Control subject (a) and a 19 y.o. Athlete (b). Two hundred heartbeat sequences of respective RR- and PR-peak intervals series are shown in (c) and (d). In (a), PR-peak interval increases as RR interval increases (positive slope: 0.0227; r = 0.50; p < 0.01), clearly observed in (c) (spontaneous concordant condition). Conversely, in (b), PR-peak interval decreases as RR interval increases (negative slope: -0.0316; r = -0.68; p < 0.01). In (d), note periods of reciprocal variation in RR- and PR-peak intervals (spontaneous discordant conduction): PR-peak interval shortens as RR-interval increases (dotted arrow) and PR-peak interval increases as RR-interval shortens (decremental conduction, solid arrow) (see text for details). Athlete RR-interval Figure 2 – (a) Regression line slope values of pooled AVCT vs. mean RR-intervals (RR-AVCTslope) as a function of VO2 consumption expressed as maximal metabolic equivalent (MET) achieved during stress test and respective boxplot. Note that RR-AVCTslope tends to be more negative as physical conditioning status increases (grey dots), when compared to sedentary individuals (white dots). Box-plots showing median, interquartile range and 95% confidence intervals are shown in the vicinity of the respective group points. Specificity, sensitivity and accuracy values were computed utilizing RR-AVCTslope = 0.0044 as a cut-off criterion. (b) Illustration of 19 y.o. Athlete’s ECG segment depicting a sequence of normal sinus beats showing AVCT lengthening as RR-interval decreases, indicating AV decremental conduction. Note P-wave and R wave peaks taken as the fiducial points for assessment of the PR-peak interval. AVCT was assessed as PR peak interval. AVCT – atrioventricular conduction time (see text for details). R-pico P-pico P-pico 73