A new strategy for direct measurement of sinus atrial conduction time by sinus node threshold determination in a rat-isolated atrium

In this work we have searched for experimental evidence that would corroborate the idea that nodal threshold (NT) is the minimum electric field strength able to promote direct sinus node reset that, in turn, can be verified by a decrease in corrected sinus node recovery time (CSNRT). We have performed direct measurements of sinus node conduction time (SACT) and estimation of atrium sinus conduction time (ASCT). Stimulating pulses (pulse and train methods) generated a uniform electric field, with strength ranging from 1.5-fold to 5-fold the atrial threshold (AT), in the center of the perfusion chamber where isolated right atria were placed. The AT and NT were 67.4 and 192.7 mV cm(-1), respectively. The CSNRT values, obtained with stimulation strength below or above NT, were, respectively (ms; mean +/- standard error of mean) 38.1 +/- 0.42 and 25.2 +/- 0.30. In addition, we verified that NT corresponds to approximately 3-fold the AT; SACT was 1.34-fold ASCT and the overdrive suppression decreases with the increment of stimulation pulse strength. Therefore, by using a new and accurate approach for SNRT determination, we have provided additional experimental evidence for the development of alternative sinus node evaluation methods.