Transmembrane potentials during high voltage shocks in ischemic cardiac tissue

Area of Science:

• Cardiology
• Electrophysiology
• Biomedical Engineering

Background:

• High voltage shocks (HVS) used in defibrillation alter transmembrane potential (TMP) in normal cardiac tissue (NT).
• These alterations, hyperpolarization or depolarization during the refractory period, may contribute to electrical defibrillation mechanisms.
• The effect of HVS on ischemic cardiac tissue (IT) remains less understood.

Purpose of the Study:

• To investigate whether HVS modify TMP in ischemic cardiac tissue (IT) similarly to normal cardiac tissue (NT).
• To compare the electrophysiological responses of NT and IT to HVS delivered during the action potential refractory period.

Main Methods:

• Utilized transmembrane, voltage-sensitive fluorescent dye (TMF) recording techniques with di-4-ANEPPS in Langendorff rabbit hearts.
• Induced local ischemia by occluding the left anterior descending artery (LAD).
• Delivered HVS (biphasic or monophasic) at varying times during the paced action potential (AP) and recorded TMP.

Main Results:

• Ischemic tissue (IT) exhibited a triangular AP shape, reduced amplitude, and shortened duration compared to NT.
• In IT, 100-Volt HVS during the refractory period elicited a significant depolarization of TMP, up to three times the paced AP amplitude.
• In contrast, HVS in NT primarily caused hyperpolarization, with only a slight depolarization in one instance.

Conclusions:

• High voltage shocks (HVS) significantly alter transmembrane potential (TMP) in ischemic cardiac tissue differently than in normal cardiac tissue.
• The pronounced depolarization response in IT suggests a distinct electrophysiological mechanism compared to NT.
• These differential effects of HVS on ischemic versus normal tissue may have critical implications for the success of electrical defibrillation.