Russell Carrington

A stable ovine congestive heart failure model. A suitable substrate for left ventricular assist device assessment.

Similarities in coronary circulation and heart size of sheep to that of humans are specific advantages of a sheep model of congestive heart failure (CHF). CHF was created in 11 sheep (51 ± 4 kg) by selective sequential intracoronary injection of 90 μ microspheres under 1.5% isoflurane anesthesia. Hemodynamic characteristies were assessed at baseline, 4 weeks after establishment of CHF (ejection fraction [EF] < 35%, n = 11), and 26 weeks (n = 7) later. Baseline echocardiographic EF was 59 ± 5% and fell to 26 ± 5% after 5 ± 2 embolizations. The left ventricular (LV) pressure-volume relationship showed stable decreases in LV end-systolic elastance (Ees) and preload recruitable stroke work. Intravenous infusion of dobutamine increased Ees from 2.8 ± 1.7 to 4.3 ± 2.2 and 4.5 ± 1.4 mmHg/ml at heart rates of 140 and 160/min, respectively, at baseline. Increases of Ees (from 1.3. ± 0.5 to 2.3 ± 0.7 and 1.9 ± 0.5 mmHg/ml at heart rates of 140 and 160/min, respectively) with dobutamine under CHF conditions did not exceed Ees values at baseline without dobutamine. This response to dobutamine infusion did not change 26 weeks after establishment of CHF. This stable ovine CHF model is proposed for studies on the long-term effects of cardiac assist devices. ASAIO Journal 1997; 43:M408-M413.

Ventricular remodeling after cardiomyoplasty in heart failure sheep: passive and dynamic effects

BACKGROUND Recent reports claim that cardiomyoplasty (CMP) has a girdling effect on the left ventricle, to prevent dilatation and functional deterioration, but the mechanism of its long-term effects on the native heart is not known. We compared the relative role of CMPs active squeezing and passive girdling in chronically failing hearts. METHODS After induction of stable heart failure (left ventricular ejection fraction = 27% +/- 7%) by staged coronary microembolization, CMP was performed in 11 of 18 sheep. After 8 weeks pacing training of the latissimus dorsi muscle (LDM), cardiac assist was begun with 1:2 synchronous bursts in 6 sheep (d-CMP, n = 6), and the LDM in the passive group (p-CMP, n = 5) remained unstimulated. Four (base line) and 30 weeks after induction of heart failure, the pressure-volume relationship was derived. RESULTS After 30 weeks in d-CMP the slope (Emax) of the end-systolic pressure-volume relationship increased by 66% +/- 55% (p < 0.05) and external work efficiency by 48% +/- 41% (p < 0.01). In the passive CMP and control groups, slope and external work efficiency were unchanged. Conversely, left ventricular end-diastolic volume decreased (-14% +/- 12%, p < 0.05) in the dynamic CMP group compared with a static course in the passive CMP group (3% +/- 10%, p > 0.05) and an increase (18% +/- 15%, p < 0.05) in controls. CONCLUSIONS Dynamic CMP improved native hearts contractility and external work efficiency. In addition, whereas passive CMP has simply a girdling effect, dynamic CMP also induces reverse left ventricular chamber remodeling.

Cardiomyoplasty reduces myocardial oxygen consumption: implications for direct mechanical compression

BACKGROUND This study investigates the possibility of reducing myocardial oxygen consumption by dynamic cardiomyoplasty in chronic heart failure. The sheep model used is relevant for cardiac assist using direct mechanical cardiac compression. METHODS In 7 sheep, heart failure was induced by staged intracoronary microembolization followed by dynamic cardiomyoplasty. Six months later, the effect of latissimus dorsi muscle stimulation in the 2:1 mode (on, cardiomyoplasty; off, control) was studied. Left ventricular pressure-volume loops were obtained by conductance, micromanometer, and inferior vena cava occlusion catheter. Myocardial oxygen consumption was derived from left main coronary artery blood flow and oxygen content of arterial and coronary sinus blood. RESULTS Cardiomyoplasty had no significant effect on left ventricular hemodynamic variables such as end-systolic pressure. However, cardiomyoplasty increased stroke volume and ejection fraction significantly by 11% +/- 12% and 11% +/- 10%, respectively. Although pressure-volume area and external work did not increase with cardiomyoplasty, myocardial oxygen consumption decreased by 21% +/- 11%. Therefore, cardiomyoplasty increased myocardial efficiency (external work/myocardial oxygen consumption) by 16% +/- 13%. CONCLUSIONS Despite limited hemodynamic improvement from dynamic cardiac compression by cardiomyoplasty in sheep with chronic heart failure, myocardial oxygen consumption was significantly reduced. These findings provide a rationale for reverse remodeling of the failing heart using direct mechanical compression.

Thoracoscopic approach for biopsy of the latissimus dorsi cardiomyoplasty wrap

J Thorac Cardiovasc Surg Carrington, Christopher Horam, Peter Brady and Stephen N. Hunyor Melissa A. Bochner, Regina Crameri, Yi Fei Huang, Osamu Kawaguchi, Russell Thoracoscopic approach for biopsy of the latissimus dorsi cardiomyoplasty wrap http://jtcs.ctsnetjournals.org/cgi/content/full/115/4/958 the World Wide Web at: The online version of this article, along with updated information and services, is located on

In situ measurements of skeletal muscle power output using new capacitive strain gauge

Experiments are described in which a fatigue index is determined for the latissimus dorsi muscle of sheep in situ, using capacitive strain gauges. Parallel experiments for invasive and non-invasive measurements are conducted, measuring global contraction and relaxation rates and shortening duration for paced muscle. The results show that, above one pulse per burst (5V, 100 μs pulsewidth), contraction rates (62±11 mm s−1) and relaxation rates (50±7 mm s−1) are constant for unloaded muscle. For one animal, fatigue testing with a 2.5 kg load at six pulses per burst shows shortening rates increasing to a maximum (80 mm s−1) after 30 s and reducing to 5 mm s−1 after 150 s. The decrease in shortening amplitude is used as a fatigue index, log displacement against time. Power output is load dependent, measuring 4.7 Wkg−1 with a 2.5 kg load. There is good agreement between the invasive and non-invasive measurements, thus providing a method for monitoring changes in muscle parameters non-invasively during future pacing transformation.