Accelerated phase 4 Na leakage into cardiac cells is associated with which mechanism?

Accelerated phase 4 Na leakage into cardiac cells is associated with which mechanism?

• A. Automaticity
• B. Triggered Activity
• C. Reentry
• D. Afterdepolarization

Answer: (A)

Accelerated phase 4 Na leakage points to automaticity. When sodium leaks into a cell during the diastolic interval, the slope of phase 4 depolarization becomes positive, causing the membrane potential to drift toward the threshold spontaneously. Once threshold is reached, an action potential fires without an external stimulus, creating ectopic Pacemaker activity. This is the hallmark of automaticity, where cells that normally don’t pace the heart begin generating impulses on their own. This differs from triggered activity, where afterdepolarizations occur after an action potential due to calcium handling or other factors, and from reentry, which requires a circuit of tissue and a wavefront that re-enters the tissue.

Accelerated phase 4 Na leakage points to automaticity. When sodium leaks into a cell during the diastolic interval, the slope of phase 4 depolarization becomes positive, causing the membrane potential to drift toward the threshold spontaneously. Once threshold is reached, an action potential fires without an external stimulus, creating ectopic Pacemaker activity. This is the hallmark of automaticity, where cells that normally don’t pace the heart begin generating impulses on their own.

This differs from triggered activity, where afterdepolarizations occur after an action potential due to calcium handling or other factors, and from reentry, which requires a circuit of tissue and a wavefront that re-enters the tissue.