Cardiac contractility modulation by electric currents applied during the refractory period

Area of Science:

• Cardiovascular Physiology
• Cardiac Electrophysiology
• Biomedical Engineering

Background:

• In vitro studies demonstrated inotropic effects of electric currents during the cardiac refractory period.
• Voltage-clamp techniques have been used to study these effects in isolated cardiac muscle.

Purpose of the Study:

• To investigate the in vivo effects of electric currents on cardiac contractility in normal canine hearts.
• To determine if cardiac contractility modulation (CCM) electric currents can enhance global and regional myocardial contractility.
• To assess the impact of CCM on cardiac relaxation and hemodynamic parameters.

Main Methods:

• Six dogs were instrumented with sonomicrometry and pressure sensors to measure cardiac function.
• Cardiac contractility modulation (CCM) electric currents (biphasic, +/-20 mA, 30 ms) were applied during the refractory period.
• Regional segment length, ventricular volume, and pressure were recorded to calculate contractility indices (e.g., Ees).

Main Results:

• CCM significantly increased the index of global contractility (Ees) with anterior, posterior, and combined electrode placements (P < 0.01).
• Enhanced contractility was observed near CCM delivery sites but not remotely.
• CCM did not significantly alter the volume axis intercept or influence cardiac relaxation.
• Mean aortic pressure increased with CCM, while peripheral resistance remained unchanged.

Conclusions:

• Locally applied electrical currents, specifically CCM, can enhance global cardiac contractility in vivo.
• This enhancement is mediated by regional changes in myocardial contractility.
• CCM effectively improves cardiac contractility without impairing relaxation or significantly altering peripheral hemodynamics.