A new implantable tool for repeated assessment of supraventricular electrophysiology and atrial fibrillation susceptibility in freely moving rats

Abstract

The complex pathophysiology of atrial fibrillation (AF) is governed by multiple risk factors in ways that are still elusive. Basic electrophysiological properties including atrial effective refractory period (AERP) and conduction velocity are major factors determining the susceptibility of the atrial myocardium to AF. Although there is a great need for affordable animal models in this field of research, in-vivo rodent studies are limited by technical challenges. Recently, we introduced an implantable system for long-term assessment of AF susceptibility in ambulatory rats. However, technical considerations did not allow us to perform concomitant supraventricular electrophysiology measurements. Here, we designed a novel quadripolar-electrode specifically adapted for comprehensive atrial studies in ambulatory rats. Electrodes were fabricated from medical-grade silicone, four platinum-iridium poles and stainless steel fixating pins. Initial quality validation was performed ex-vivo, followed by implantation in adult rats and repeated electrophysiological studies 1, 4 and 8 weeks post implantation. Capture threshold was stable. Baseline AERP values (38.1±2.3 and 39.5±2.0 using 70ms and 120ms S1-S1 cycle lengths, respectively) confirmed the expected absence of rate-adaptation in the unanesthetized state and validated our prediction that markedly higher values reported under anesthesia are non-physiological. Evaluation of AF substrate in parallel with electrophysiological parameters validated our recent finding of a gradual increase in AF susceptibility over-time and demonstrated that this phenomenon is associated with an electrical remodeling process characterized by AERP shortening. Our findings indicate that the miniature quadripolar-electrode is a potent new tool, which opens a window of opportunities for better utilization of rats in AF research.

Cannabinoid Receptor Agonist Inhibits Atrial Electrical Remodeling in a Tachypaced Ex Vivo Rat Model

“…Further experiments will be crucial to elucidate the underlying mechanisms, and to delineate relevant ionic mechanisms. Of note, we recently introduced a methodology enabling comprehensive EP measurements and AF susceptibility testing in ambulatory rats over time (Murninkas et al, 2021). Thus, based on the current findings it will be interesting to explore the effects of CB13 on longer periods of tachypacing in unanesthetized rats in the near future.…”

“…For atrial electrophysiology experiments, hearts were perfused as described above but a balloon was not inserted to the LV cavity and both atria remained intact. A custom-designed quadripolarelectrode was inserted on the RA for simultaneous pacing and recording (Murninkas et al, 2021). The electrode contained two pairs of platinum-iridium poles (one for pacing and one for recordings) with an inter-pair interval of 4 mm.…”

“…The protocol consisted of 10 S1-S1 intervals of 150 ms followed by an S1-S2 interval that was reduced by 1 ms each time until atrial capture failed three consecutive times (Figure 1B). Conduction time was measured during constant atrial pacing at 150-ms CL as the interval between the end of the stimulus applied to one side of the electrode and the first peak of the atrial signal that was recorded in the other side (Murninkas et al, 2021). In addition to AERP and CT measurements, burst pacing was applied to the RA to evaluate for possible arrythmia induction.…”

Guidelines for assessment of cardiac electrophysiology and arrhythmias in small animals

“…Around 16% of investigations used pharmacological modulation ( 24 , 43 , 49 , 50 , 52 ). A small number of studies investigated environmental effects [including herbicide ( 36 ), vaping ( 27 ), and alcohol ( 51 )], aging and development ( 25 , 28 , 41 ), nonischemic heart failure ( 39 ), and the remaining studies performed electrophysiological assessments in nondiseased hearts ( 37 , 46 , 48 ). The most commonly used techniques to evaluate electrophysiological parameters and arrhythmia susceptibility were in vivo electrocardiogram (ECG) or electrode recordings in conscious or anesthetized animals (∼56% of studies) ( 23 – 28 , 30 , 32 , 36 , 38 , 40 – 42 , 46 – 48 , 52 ) or optical mapping in excised hearts or tissues (∼47% of studies) ( 27 , 30 , 31 , 33 – 35 , 39 , 41 , 43 – 45 , 49 – 51 ).…”

“…The most commonly used techniques to evaluate electrophysiological parameters and arrhythmia susceptibility were in vivo electrocardiogram (ECG) or electrode recordings in conscious or anesthetized animals (∼56% of studies) ( 23 – 28 , 30 , 32 , 36 , 38 , 40 – 42 , 46 – 48 , 52 ) or optical mapping in excised hearts or tissues (∼47% of studies) ( 27 , 30 , 31 , 33 – 35 , 39 , 41 , 43 – 45 , 49 – 51 ). The remaining studies used electrode-based or ECG recordings in excised hearts and tissues ( 24 , 25 , 29 , 31 , 32 , 35 , 40 , 41 , 50 ) or in vivo ECG telemetry ( 27 , 29 , 33 , 37 ), and often, a combination of multiple approaches were used to rigorously evaluate electrophysiological properties (including experiments in isolated cardiomyocytes, which are not covered in detail in these guidelines).…”