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Low birth weight (LBW) is a risk factor for mortality in neonatal and infant heart surgery. The purpose of this study was to determine the contemporary outcomes and risk factors of cardiac surgery in low weight babies. The records of 75 consecutive infants weighing <2.5 kg having heart surgery were reviewed. The median weight was 2100 g (range 800-2500 g) and median age was 11 days (range 2-86 days). Half (n=38) of the infants were premature. Diagnoses included: arch obstruction (n=14), hypoplastic left heart syndrome (HLHS) (n=12), tetralogy of Fallot (ToF) or pulmonary atresia (PA)/ventricular septal defect (VSD) (n=11), transposition of the great arteries (TGA) (n=7), total anomalous pulmonary venous return (TAPVR) (n=5), and other (n=20). There were two early deaths. Follow-up was available on all infants with a median duration of 1320 days (range 6-3055 days). Cumulative Kaplan-Meier survival at one year was 90% [95% confidence interval (CI), 80-95%] and at five years was 88% (95% CI, 77-94%). Overall mortality amongst patients with genetic/chromosomal abnormalities was higher, 28% vs. 5.4% amongst patients without such abnormalities (P=0.008). Age, prematurity, preoperative mechanical ventilation, prostaglandins, non-cardiac organ dysfunction, extra-cardiac malformations, perioperative extracorporeal membrane oxygenation (ECMO), and type of procedure were not associated with significant differences in mortality. Cardiac surgery in LBW infants can be performed with low early and mid-term mortality. LBW infants with chromosomal/genetic anomalies have a higher risk.

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Application and development of muscle powered cardiac assist devices is limited by the ability to predict the sustainable power output of in situ conditioned muscle under the expected loading conditions and geometrical constraints. Empirical definition of the sustained power limits and representative models of the bounding conditions where continuous power can be obtained are needed for device design and optimization. The latissimus dorsi muscles of four goats were chronically conditioned for 11 weeks with an implanted myostimulator. The ability to sustain power under isotonic conditions was evaluated across a range of contraction durations (100-600 ms) and rates (10-120 contractions/min). Muscles were characterized both biomechanically and myothermically to develop and evaluate three increasingly complex empirically-based models of metabolic utilization per contraction based on (1) the duty cycle, (2) a linear function of activation time, and (3) a multivariate-derived function of contraction duration, muscle load, and shortening distance. A clearly defined boundary for sustainable stimulation conditions was observed and was best represented by the linear metabolic model. These data provide both an empirical measure of chronically sustainable muscle power and predictive metabolic models that may be used to optimize the power harnessed for skeletal muscle actuated devices.