Age-dependent changes in electrophysiology and calcium handling: implications for pediatric cardiac research

Abstract

Rodent models are frequently employed in cardiovascular research, yet our understanding of pediatric cardiac physiology has largely been deduced from more simplified two-dimensional cell studies. Previous studies have shown that postnatal development includes an alteration in the expression of genes and proteins involved in cell coupling, ion channels, and intracellular calcium handling. Accordingly, we hypothesized that postnatal cell maturation is likely to lead to dynamic alterations in whole heart electrophysiology and calcium handling. To test this hypothesis, we employed multiparametric imaging and electrophysiological techniques to quantify developmental changes from neonate to adult. In vivo electrocardiograms were collected to assess changes in heart rate, variability, and atrioventricular conduction (Sprague-Dawley rats). Intact, whole hearts were transferred to a Langendorff-perfusion system for multiparametric imaging (voltage, calcium). Optical mapping was performed in conjunction with an electrophysiology study to assess cardiac dynamics throughout development. Postnatal age was associated with an increase in the heart rate (181 ± 34 vs. 429 ± 13 beats/min), faster atrioventricular conduction (94 ± 13 vs. 46 ± 3 ms), shortened action potentials (APD80: 113 ± 18 vs. 60 ± 17 ms), and decreased ventricular refractoriness (VERP: 157 ± 45 vs. 57 ± 14 ms; neonatal vs. adults, means ± SD, P < 0.05). Calcium handling matured with development, resulting in shortened calcium transient durations (168 ± 18 vs. 117 ± 14 ms) and decreased propensity for calcium transient alternans (160 ± 18- vs. 99 ± 11-ms cycle length threshold; neonatal vs. adults, mean ± SD, P < 0.05). Results of this study can serve as a comprehensive baseline for future studies focused on pediatric disease modeling and/or preclinical testing. NEW & NOTEWORTHY This is the first study to assess cardiac electrophysiology and calcium handling throughout postnatal development, using both in vivo and whole heart models.

Chronic perinatal hypoxia delays cardiac maturation in a mouse model for cyanotic congenital heart disease

“…Awake measurements indicated that P8 hypoxic animals had a slightly longer P-wave duration (13.9 ± 0.5 vs. 12.4 ± 0.3 ms, q = 0.09) and PR interval (46.9 ± 2 vs. 37.3 ± 0.9 ms, q < 0.01). Heart rate variability was also decreased in hypoxic animals (RMSSD: 3.9 ± 0.5 vs. 7.1 ± 1.4, q < 0.005), a parameter that normally increases with postnatal development (29). In vivo ECG parameters were also altered under isoflurane sedation (Fig.…”

“…ECG segments were quantified using ecgAuto software (emka Technologies) for heart rate, heart rate variability, atrial depolarization time (Pwave duration), atrioventricular (AV) conduction time (PR interval), ventricular depolarization time (QRS duration), and ventricular repolarization time [QT interval; uncorrected as heart rate does not significantly alter QT interval in mice (28)]. Heart rate variability was measured as a root mean square of the successive differences (RMSSD) (28,29). Due to motion artifact, only clearly discernable ECG parameters were included in the analysis for each animal.…”

“…The heart was transferred to a temperature-controlled (37 C) constant-pressure (70 mmHg) Langendorff perfusion system. Excised hearts were perfused with Krebs-Henseleit buffer bubbled with carbogen, as previously described (29,30). A stimulation electrode was placed externally on the right atrium, and an atrial pacing protocol was used to determine Wenckebach cycle length (WBCL) and atrioventricular nodal effective refractory period (AVNERP).…”

Stop the beat to see the rhythm: excitation-contraction uncoupling in cardiac research

“…As shown in Figure 1, since its first use for optical mapping in 2007, blebbistatin has all but replaced the other available EC uncouplers. In fact, in the last three years alone, blebbistatin was used twice as often (1,29,36,41,51,56,59,69,74,76,78,83,85,87) as any other uncoupler for imaging applications (25,27,33,46,54,55,80). The use of BDM/DAM and CytoD for optical mapping has essentially ceased, yet due to its lower cost, BDM/DAM may still be a reasonable choice for larger animal (i.e., non-rodent) studies (10,23,25,35,52,70,77), which require larger amounts of an EC uncoupler (72).…”

“…In contrast, the development of optical mapping offered a new mapping approach with superior spatial resolution (53) that is determined by the image sensor specifications (sensor size, number of pixels, and quantum efficiency) and the optical field of view (9). Additionally, the use of calciumsensitive probes enabled simultaneous measurements of electrical activity and intracellular calcium cycling, as demonstrated by Choi and Salama at the turn of the century (15), and now provides unprecedented insight into ECC parameters in normal and diseased hearts (31,42,56,74,76,83).…”