Cardiac contractility modulation by electric currents applied during the refractory period.
Inotropic effects of electric currents applied during the refractory period have been reported in cardiac muscle in vitro using voltage-clamp techniques. We investigated how electric currents modulate cardiac contractility in normal canine hearts in vivo. Six dogs were instrumented to measure regional segment length, ventricular volume (sonomicrometry), and ventricular pressure. Cardiac contractility modulating (CCM) electric currents (biphasic square pulses, amplitude +/-20 mA, total duration 30 ms) were delivered during the refractory period between pairs of electrodes placed on anterior and posterior walls. CCM significantly increased index of global contractility (E(es)) from 5.9 +/- 2.9 to 8.3 +/- 4.6 mmHg/ml with anterior CCM, from 5.3 +/- 1.8 to 8.9 +/- 4.0 mmHg/ml with posterior CCM, and from 6.1 +/- 2.6 to 11.0 +/- 7.0 mmHg/ml with combined CCM (P < 0.01, no significant change in volume axis intercept). End-systolic pressure-segment length relations showed contractility enhancement near CCM delivery sites, but not remotely. Relaxation was not influenced. CCM increased mean aortic pressure, but did not change peripheral resistance. Locally applied electrical currents enhanced global cardiac contractility via regional changes in myocardial contractility without impairing relaxation in situ.
Mohri
Satoshi
S
Department of Medicine, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA.
He
Kun-Lun
KL
Dickstein
Marc
M
Mika
Yuval
Y
Shimizu
Juichiro
J
Shemer
Itzhak
I
Yi
Geng-Hua
GH
Wang
Jie
J
Ben-Haim
Shlomo
S
Burkhoff
Daniel
D
D000818:Animals; D001011:Aorta / Q000502:physiology; D001794:Blood Pressure; D004285:Dogs; D004553:Electric Conductivity; D004558:Electric Stimulation; D004566:Electrodes; D005260:Female; D006352:Heart Ventricles / Q000033:anatomy & histology; D008297:Male; D009200:Myocardial Contraction; D018408:Patch-Clamp Techniques; D011312:Pressure; D013599:Systole; D014655:Vascular Resistance; D016276:Ventricular Function; D016277:Ventricular Function, Left