Optical Mapping in Rat Models of Atrial Dilation

Abstract

Atrial fibrillation (AF) is commonly associated with atrial dilatation caused by pressure or volume overload. Acute atrial stretch may create a myocardial substrate to promote AF via stretch-activated channels and mechano-electrical feedback mechanisms. However, enhanced AF vulnerability in chronic dilated atria occurs as a result of complex remodeling that includes changes of myocyte membrane currents, altered intracellular Ca2+ homeostasis and alterations of the extracellular matrix (e.g. interstitial fibrosis). Here, we dissect the role of acute stretch-related changes versus those occurring as part of the long-term remodeling process. Spontaneous hypertensive rats (SHR) with chronic atrial dilation were compared to normotensive Wistar-Kyoto rats (WKY) and to WKY rats with acute biatrial dilation (dil-WKY) obtained with atrial balloons (inserted into both atria and inflated with controlled pressure after baseline recording). Briefly, the hearts were perfused on a Langendorff's apparatus and then the ventricles were excised just below the atrio-ventricular junction. To maximize atrial perfusion and staining main coronary ventricular branches were cauterized. Atria were stained with a bolus injection of a red-shifted voltage-sensitive dye (di-4-ANBDQPQ). An ultrafast wide-field macroscope operating at 2 KHz (100 x 100 pixel) was developed to optically map action potential propagation of Langendorff's perfused-atria and to test AF vulnerability. AF was induced through burst pacing and occurred in 5.8% of WKY, 10.6% of dil-WKY and 17.4% of SHR atria. Action potential duration at 90% repolarization (APD90) was prolonged in SHR as compared to WKY and dil-WKY. APD90 variability between contiguous regions was increased in both dil-WKY and SHR compared to WKY, potentially contributing to the increased AF vulnerability. Next, we analyzed activation maps during AF episodes. Occasionally, they exhibited a stable reentry pattern characterized by similar origin and propagation on a beat-to-beat basis. Alternatevely, the origins of successive reentrant waves varied randomly and the arrhythmia was perpetuated by coexisting reentrant circuits, maintained through the continuous annihilation and creation of multiple wavelets. Voltage oscillations during AF were analyzed in time and frequency domains, and the spectrogram (Fourier transform) revealed coexisting reentrant circuits at different frequencies. Analysis of the dispersion of the action potential durations and conduction velocity maps will clarify the mechanism of AF in chronic and acute models of atrial dilation.