Novel Functions (Work-Rest and Day-Night Regimens) in a New Cardiomyostimulator for Cardiac Bioassist

The LD-PACE II, a new cardiomyostimulator was manufactured by CCC del Uruguay with the support of the Illini Group, Chicago, Illinois. The LD-PACE II was designed for use in cardiomyoplasty, aortomyoplasty, and skeletal muscle ventricle. All parameters specified as programmable can be changed in a noninvasive manner (using a programming interface wand connected to a computer using the Windows 95/98 environment). Most of the functions of the new stimulator are similar to functions of previously used devices (Transform, Medtronic; EKS 445, Russia). In the case of bradycardia or atrio-ventricular blockage, the LD-PACE II will act as a pacemaker with a basic pacing rate between 36 and 120 BPM. In order to prevent the stimulator from inappropriately sensing events, there is a ventricular refractory period (195-480 ms). Hysteresis (0-20%) allows the patient's heart rate to temporarily fall below the lower rate without inducing immediate pacing. Synchronization delay (2-350 ms) obtains the optimal time of muscle contraction. Adaptive delay allows the automatic change in the delay time with a change of heart rate. The cardiosynchronization ratio is programmed from 1:1-1:16. Muscle output is inhibited if the heart rate is higher than the synchronization upper rate (120-226 BPM). The adaptive ratio allows for the automatic change of the cardiosynchronization ratio with an increase in heart rate. Delivery of a muscle pulse train is triggered by paced or sensed ventricular events. Characteristics of the pulse train are changes in pulse amplitude (0.44-0.75 V), pulse width (0.061-0.076 ms), pulses per burst (1-8), and pulse interval (15.6-132.8 ms). The adaptive pulse train duration will automatically decrease the train duration with an increase in heart rate and inhibit muscle contraction during the diastolic phase. The LD-PACE II does however have two new functions which prove to be extremely important for clinical use based on experimental research. 1. Work-rest regimen. In the conventional stimulation regimen, the latissimus dorsi muscle (LDM) works 24 hours daily with no rest except for short periods between contractions. The LD-PACE II is able to deliver alternating periods of muscle contractions and rest. Work and rest periods may be programmed independently between 1 and 120 minutes in increments of one minute. The work-rest regimen may be useful clinically if muscle contractions are needed for cardiac assist postoperatively. Morphological (light microscopy, transmission electron microscopy) and electrophysiological data show that a short period of work followed by a long period of rest does not damage the ischemic muscle. 2. Day-night regimen. This feature is also brand new. It allows for a change in the ratio of muscle contractions according to a patient's activity level. During the day the cardiosynchronization ratio may be set from 1:1 to 1:4 and during the night it may be set for 1:8 to 1:16. This allows the LDM to have a long rest period, prevents overuse, and prolongs batNovel functions (work-rest and day-night regimens) in a new cardiomyostimulator for cardiac bioassist 40 tery life. Data confirmed that there is no depression in hemodynamics when the ratio is slowed or turned off during the night. The first experimental tests of the LD-PACE II (in Milwaukee, Wisconsin, Detroit, Michigan and Paris, France) showed good functional ability of a high caliber. The first clinical cardiomyoplasty with the LD-PACE II was performed on April 2, 2000 at the Bahamas Heart Center.