In the heart, action potentials travel through the tissue to orchestrate muscle contraction and make the organ an efficient pump. Scar tissues caused by myocardial infarction impairs electrical conduction. In the rabbit heart, action potentials propagate from the endocardium to the epicardium with a conduction velocity of 30 cm/s. Therefore, a rapid vertical scan is necessary to observe this transmural cardiac conduction at cellular resolution. Here we present an implementation of a versatile remote focusing module, compatible with retrofitting to commercial two-photon microscopes and capable of 0.3 kHz rate axial scanning over the range of 100 μm in cardiac tissue without disturbing the sample or the sample objective. We discuss the necessary optimization to compensate for pulse broadening, power losses and optical aberrations. We demonstrate fast imaging of cardiac cell structure in functionally viable rabbit ventricular slice model. We will apply this system to resolve cardiac electrical signal propagation transmurally in healthy and infarcted hearts.
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