What are the contracting elements of the heart and why are they important? In order to function the heart needs to beat in a controlled rhythmic fashion; this process of contraction and relaxation involves numerous, biochemical, physiological and structural elements. In this chapter, we focus on the cellular components involved in the contractile part of this process, what happens following injury, current treatment options and their limitations, and new cellular strategies aimed at improving cardiac contractility by replacing damaged contractile cells, focusing primarily on replacement of the main contractile cells of the heart, the cardiomyocytes.

Background —Trends in risk-severity and operative mortality (OM) were examined in 3330 consecutive patients aged 70 years and older who underwent isolated coronary artery bypass graft surgery (CABG) between 1982 and 1996. Methods and Results —The proportion of elderly patients rose significantly over time ( P <.001). Crude OM among the elderly was 7.2% in 1982 to 1986, fell to 4.4% in 1987 to 1991, but did not improve thereafter. Logistic regression analysis of OM was used to construct relative risk groups (low, medium, or high). The prevalence of high-risk elderly patients rose significantly over time ( P =.001) from 16.2% in 1982 to 1986 to 19.5% in 1987 to 1991 and 26.9% in 1992 to 1996. OM in high-risk patients fell significantly ( P =.044) from 17.2% in 1982 to 1986 to 9.1% in 1987 to 1991 and was 8.9% in 1992 to 1996. Contemporary independent predictors of OM among elderly patients were poor ventricular function (LV grade 2 to 3, odds ratio [OR], 2.6; 95% confidence interval [CI], 1.3 to 5.2; and LV grade 4, OR, 10.7; 95% CI, 4.4 to 26); previous CABG (OR, 3.7; 95% CI, 2.0 to 7.0), female sex (OR, 1.8; 95% CI, 1.1 to 2.8), peripheral vascular disease (OR, 1.8; 95% CI, 1.1 to 2.8), and diabetes (OR, 1.7; 95% CI, 1.1 to 2.7). Previous angioplasty was protective (OR, 0.3; 95% CI, 0.1 to 0.9). Conclusions —OM in elderly patients has declined significantly in recent years despite an increase in the prevalence and severity of their risk factors. A careful weighing of risk, rather than advanced age alone, should determine who is offered surgical revascularization. In this regard, poor ventricular function and repeat CABG continue to have the greatest impact on OM in elderly patients.

Major advances in the composition and delivery of cardioplegia have helped to reduce the morbidity and mortality associated with coronary bypass surgery. The discovery of the preconditioning response should facilitate the development of more powerful myocardial protective agents. These new agents may act to directly stimulate the preconditioning response or may act in a supplementary fashion to either augment the response or provide protection from alternate pathways. As new techniques of myocardial protection continue to be developed, the risk-to-benefit ratio of coronary bypass surgery will continue to improve. As a result of these improvements, surgeons will be able to offer surgery to an increasingly high risk patient population without increasing the morbidity or mortality currently associated with coronary bypass.

Improvements in surgical technique and advances in myocardial protection have resulted in low rates of morbidity and mortality despite a greater incidence of high-risk patients. Noncardiac morbidity prolongs hospital stays and increases the costs of cardiac surgery. This study examines the preoperative predictors of stroke following isolated coronary bypass surgery. The clinical records of 3910 consecutive patients who underwent isolated coronary bypass surgery at the University of Toronto were reviewed. Stepwise logistic regression identified six independent predictors of stroke following CABG (percent in parentheses) and calculated factor adjusted odds ratios (OR) for each risk factor. Triple vessel coronary artery disease was the most important predictor (1.9%, OR 5.71), followed by normothermic systemic perfusion (3.8%, OR 4.85), age > 70 years (3.2%, OR 3.88), a previous history of transient ischemic attacks or stroke prior to surgery (6.1%, OR 3.7), peripheral vascular disease (4.7%, OR 2.77), and diabetes mellitus (2.6%, OR 2.01). The mechanism of stroke is likely different between these high-risk groups and strategies to prevent postoperative stroke should focus on the mechanisms responsible in high-risk patients.

A prospective randomized controlled trial was performed to determine optimal flow rates and hemoglobin concentrations for continuous normothermic blood cardioplegia and to compare warm heart surgery with standard intermittent cold blood cardioplegia. Thirty-five patients received intermittent cold blood cardioplegia, low hemoglobin low flow, low hemoglobin high flow, high hemoglobin low flow, or high hemoglobin high flow warm blood cardioplegia (seven patients per group: low hemoglobin, 50 g/l; high hemoglobin, 80 g/l; low flow, < 80 ml/min; high flow, > 80 ml/min). Hypothermia resulted in a significantly greater accumulation of ADP and AMP during cross clamp, consistent with impaired mitochondrial function. Low hemoglobin low flow warm blood cardioplegia increased myocardial oxygen consumption and coronary sinus blood flow after cross clamp release, and also decreased lactate consumption. Postoperative myocardial performance and diastolic compliance were reduced in low hemoglobin low flow warm patients, and diastolic compliance was increased with high hemoglobin high flow warm blood cardioplegia when compared with cold patients. In this study, continuous normothermic cardioplegia was safe when delivered at 80 ml/min or greater, with a hemoglobin concentration of at least 80 g/l, affording myocardial metabolic and functional recovery comparable to that found after intermittent cold blood cardioplegia.

entricular assistance may salvage viable myocardium after a severse ischemic insult. The effects of myocardial ischemia have been studied extensively over the last twenty-five years. The concept of an &dquo;all or none&dquo; phenomena of myocyte necrosis has been replaced by the concept of a gradation of injury. The resultant functional and structural changes are dependent on the duration of the coronary occlusion, the number of collateral vessels, the metabolic and hemodynamic conditions during which the myocardium is made ischemic, and the timing and nature of reperfusion. Early studies established the timing of cell death after coronary ligation in an acute canine model. Jennings and Reimer [1] ligated the circumflex branch of the left coronary artery in dogs for periods ranging from 5 to 60 minutes followed by reperfusion for 3 to 5 days. They examined the posterior papillary muscle for the extent of myocyte necrosis. With prolonged periods of occlusion, greater proportions of the papillary muscle were necrotic. In dogs subjected to less than fifteen minutes of occlusion followed by reperfusion there was no evidence of necrosis. They also examined the effects of collateral blood flow. In dogs subjected

Count-based scintigraphic left ventricular end-diastolic (LVED) volume measurement was optimized using a reproducible method for determining left ventricular counts and an independently measured average apparent tissue attenuation coefficient (0.16 cm-1). Tissue depth was calculated by triangulation. Results were compared to single-plane contrast ventriculographic volumes by an area-length method, performed within one hour, in 18 patients. The overall correlation of measurements of LVED volume by the 2 methods was 0.96 with standard error of the scintigraphic estimate of 15.8 ml. For 6 patients with angiographically normal wall motion, the correlation of volume measurements was 0.99 with standard error of the estimate of 5.1 ml. The mean absolute difference in LVED volume by the 2 methods was 3.8 ml in the group with normal wall motion compared to 19.2 ml in the 12 patients with angiographically abnormal wall motion. Area-length LVED volume calculation assumes that the left ventricle conforms to a standard shape. Discrepancies in volume estimates with abnormal ventricular wall motion suggest that the area-length method is less accurate. Optimized count-based LVED left ventricular volume measurement is accurate and might be preferable to single-plane contrast angiographic volume measurement of abnormal ventricles.

The saphenous vein (SV) remains the conduit of choice for lower limb revascularization. When SV is unavailable, or unsuitable, two alternative conduits have been employed: gluteraldehydestablized human umbilical vein (HUV) and polytetrafluoroethylene (PTFE). In this study of the 218 patients who underwent lower limb revascularization, 3-year patency of 85 SV graft was 75% compared to 34% for the 66 HUV grafts and 33% for the 67 PFTE grafts. Three factors were found to independently influence patency: the indication for surgery, the site of the distal anastomosis, and the angiographic runoff. The SV group had significantly better patency than either HUV or PFTE in each of these subgroups. No consistent difference between HUV and PTFE was found. A risk score was obtained by assigning a value of 1 to 3 for each of the factors influencing patency--indication: 1 = claudication, 2 = rest pain, 3 = ischemic lesions; site: 1 = above knee (AK), 2 = below knee (BK), 3 = tibial; runoff 1 = good (two or three vessels), 2 = fair (one vessel), 3 = poor (no vessel). Patients with the lowest risk scores (3 to 4) had the best 3-year patency: SV, 78%; HUV, 44%; and PTFE, 48%. Patients with the highest risk scores (7 to 9) had the worst 3-year patency: SV, 68%; HUV, 32%; and PTFE, 28%. SVs had better patency under high- and low-risk conditions and remain the conduit of choice for lower limb revascularization. Both HUV and PTFE have equivalent and acceptable patency when SV is unavailable or unstable.