HRS Board Review 2025 New Courses (Reviewers Copy)-Workshop 1_Tomaselli_2025

Video Transcription

The correct answer is C, cells in panel A have been exposed to dofetilide. What are the observations here? That is the observations are  the action potentials in the cells in panel A, are not only longer, but they exhibit greater lengthening at longer pacing cycle lengths than cells in panel B.  There's a tendency for working myocardial action potentials to lengthen at slower cycle lengths under basal conditions. Ranolazine by blocking the late sodium current,  dildiazine by blocking the calcium current, would tend to shorten the action potential duration and not exaggerate rate-dependent lengthening. Acutely administered amiodarone has  no consistent effect on the action potential duration and really minimal frequency dependence. Dofetilide on the other hand, would lengthen the action potential duration and has  a reverse use-dependent effect with more IKR rapid component of the delayed rectifier block at longer cycle lengths and  hence longer action potential prolongation at slow pacing rates.

Video Summary

The key observation is that cells in panel A, exposed to dofetilide, have longer action potentials that lengthen more at longer pacing cycle lengths compared to cells in panel B. This is because dofetilide lengthens action potential duration and exhibits reverse use-dependency, meaning it causes greater prolongation at slower pacing rates. In contrast, ranolazine and diltiazem shorten action potential duration by blocking specific currents, and amiodarone has minimal impact on action potential duration and frequency dependence.

Keywords

dofetilide

action potential

reverse use-dependency

ranolazine

diltiazem