Amplitude Changes during Ventricular Fibrillation: A Mechanistic Insight.

Area of Science:

• Cardiovascular Physiology
• Electrophysiology
• Cardiac Arrhythmias

Background:

• Clinical observation shows decreasing electrocardiogram (ECG) amplitude and frequency during ventricular fibrillation (VF) correlate with ischemia progression and predict defibrillation success.
• In vitro studies indicate ECG amplitude decline during VF occurs independently of ischemia and VF frequency.
• This study aimed to elucidate the roles of cellular electrical activity and global electrical organization in ECG amplitude changes during VF.

Purpose of the Study:

• To investigate the cellular and global electrical contributions to ECG amplitude changes during ventricular fibrillation (VF).
• To differentiate the effects of ischemia and altered extracellular potassium on VF dynamics and ECG amplitude.

Main Methods:

• Rabbit hearts were Langendorff-perfused and subjected to VF, with ECG and epicardial optical action potentials recorded simultaneously.
• Experimental conditions included maintained perfusion (control), global ischemia (low-flow), and elevated extracellular potassium (8 mM [K+](o)).
• Analysis involved measuring signal amplitudes and evaluating electrical coordination using cross-correlation of optical signals.

Main Results:

• During VF, control conditions showed a steady-state decrease in ECG amplitude (∼57% baseline). Low-flow ischemia led to a continuous decline (to 33% by 600s).
• Optical recordings revealed greater amplitude reduction in the left ventricle (LV) compared to the right ventricle (RV) in control conditions.
• Elevated [K+](o) resulted in complex changes: ECG amplitude increased (105% baseline), while LV optical amplitude decreased (60% baseline), with increased electrical coordination.

Conclusions:

• The decline in ECG amplitude during VF is attributed to both reduced systolic activation at the cellular level and increased desynchronization of inter-cellular electrical activity.
• Ischemia exacerbates ECG amplitude reduction, while elevated extracellular potassium influences cellular and global electrical dynamics differently, impacting ECG amplitude and coordination.