Initial clinical trial of substernal epicardial echocardiography: SEEing a new window to the postoperative heart.

BACKGROUND: Postoperative echocardiography windows are often of poor quality because of intervening air spaces around the heart and great vessels. We assessed the utility of a new commercially available adult chest drainage tube that has been modified with the addition of a sterile sleeve to accommodate the introduction of a nonsterile pediatric transesophageal echocardiography (TEE) probe. The TEE probe lies in a substernal epicardial position on the postoperative heart allowing one to perform substernal epicardial echocardiography (SEE). METHODS: Informed consent was obtained from 21 consecutive adult cardiac operation patients. At the completion of the operation the SEE drainage tube was inserted through the rectus muscle and into the pericardium. After chest closure, all patients underwent a full echo examination using an Acuson pediatric biplane probe in the SEE position. Views obtained and ease of insertion were judged on a 1 to 10 (worst to best) scale. RESULTS: Full SEE examinations were completed in an average of 12 minutes. Ease of probe entry and manipulation was excellent (ratings of 9.3 and 9.6, respectively). The quality of the anatomic images was also excellent. Substernal epicardial echocardiography tube positioning was integral to the orientation of the images obtained. There were no complications related to the placement of the SEE tubes or TEE probes. In 4 of 21 patients (19%) the SEE methodology was used serially in the intensive care unit to accurately assess ventricular function and filling during weaning of an intraaortic balloon and inotropic agents. CONCLUSIONS: Substernal epicardial echocardiography is a safe and highly effective methodology for the serial echocardiographic assessment of the postoperative heart.

Effects of potassium channel opener aprikalim on the receptor-mediated vasoconstriction in the human internal mammary artery.

BACKGROUND: Arterial grafts for coronary artery bypass grafting such as the internal mammary artery (IMA) may develop spasm perioperatively. The purpose of this study was to investigate the effects of the potassium channel opener, aprikalim, on the receptor-mediated vasoconstriction in the human IMA in vitro. METHODS: We studied 160 IMA rings taken from coronary artery surgery in organ baths. The interaction between aprikalim and four vasoconstrictors 5-hydroxytryptamine (5-HT), norepinephrine (NE), endothelin-1 (ET-1), and angiotensin II (AII) was investigated in two ways. RESULTS: Aprikalim relaxed IMA rings precontracted by the vasoconstrictors to 66.40 +/- 5.9% for 5-HT (EC50: -6.78 +/- 0.26 LogM), 57.40 +/- 5.5% for NE (-6.54 +/- 0.39 LogM), 81.00 +/- 6.7% for ET-1 (-6.58 +/- 0.26 LogM), and 93.90 +/- 2.5% for AII (-7.80 +/- 0.23 LogM). The relaxation in endothelium-denuded rings contracted by AII was similar to that in the endothelium-intact rings. The relaxation was attenuated by glibenclamide (3 microM) in 5-HT or NE-precontracted IMA. Pretreatment with aprikalim at 1 microM depressed AII-induced contraction (33.20 +/- 7.5% versus 59.70 +/- 7.3%, p < 0.01) but only shifted the curves rightward for 5-HT or NE (EC50 3.1 or 4.3-folds higher, p < 0.05), whereas at 30 microM it also significantly depressed the maximal contraction for 5-HT (35.70 +/- 4.9% versus 103.30 +/- 9.8%, p < 0.001) and NE (90.60 +/- 15.6% versus 125.60 +/- 7.9%, p < 0.05). In contrast, aprikalim did not significantly depress the contraction induced by ET-1 (p > 0.05). CONCLUSIONS: We conclude that aprikalim has vasorelaxant effects on IMA and the effect is vasoconstrictor-selective and endothelium-independent. Aprikalim may provide clinically useful vasorelaxant effects in coronary bypass surgery.

ATP-sensitive potassium channel openers may mimic the effects of hypoxic preconditioning on the coronary artery.

BACKGROUND: This study was designed to investigate the effects of the potassium channel opener KRN4884 in mimicking hypoxic preconditioning on coronary arteries and to explore the possible mechanisms. METHODS: In the organ chamber, porcine coronary artery rings (n = 96) were studied in 6 groups (n = 16 in each group): I. CONTROL: normoxia (pO2 > 200 mmHg); II. Hypoxia-reoxygenation: 60-minute hypoxia (pO2 < 15 mmHg) followed by 30-minute reoxygenation; III. Preconditioning: 5-minute hypoxia followed by 10-minute reoxygenation prior to hypoxia-reoxygenation; IV. KRN4884-pretreatment: KRN4884 (30 microM) was added into the chamber 20 minutes before hypoxia-reoxygenation; V. 5-HD-pretreatment: sodium 5-hydroxydecanoate (5-HD, 10 microM) was given 20 minutes prior to KRN4884-pretreatment; and VI. GBC-pretreatment: glibenclamide (GBC, 3 microM) was added 20 minutes prior to KRN4884-pretreatment. Concentration-contraction curves for U46619 (n = 8 in each group) were constructed. Concentration-relaxation curves for bradykinin (n = 8 in each group) related to endothelium-derived hyperpolarizing factor (EDHF) were established in the rings precontracted with U46619 (30 microM) in the presence of Nomega-nitro-L-arginine (L-NNA, 300 microM) and indomethacin (7 microM). RESULTS: The maximal relaxation induced by bradykinin was reduced in hypoxia-reoxygenation (54.6 +/- 4.3% versus 85.2 +/- 5.7% in control, p = 0.001). This reduced relaxation was recovered in KRN4884-pretreatment (78.9 +/- 3.7%, p = 0.014) or preconditioning (79.9 +/- 3.7%, p = 0.009). 5-HD- but not GBC-pretreatment abolished the effect of KRN4884-pretreatment (78.9 +/- 3.7% versus 53.5 +/- 4.7%, p = 0.009). CONCLUSIONS: Hypoxia-reoxygenation reduces the relaxation mediated by EDHF in the coronary artery. This function can be restored by either hypoxic preconditioning or the potassium channel opener KRN4884. The mechanism of such effect is mainly related to the mitochondrial ATP-sensitive K+ channels.

Inhibition of vasoconstriction by angiotensin receptor antagonist GR117289C in arterial grafts.

BACKGROUND: Angiotensin II (AII) has been suggested to be one of the important factors for genesis of graft spasm in coronary artery bypass surgery. The aim of this work was to investigate the effects of the nonpeptide angiotensin receptor AT1 antagonist GR117289C on the contraction induced by AII and other vasoconstrictors in isolated human internal mammary artery (IMA) preparations. METHODS: Two hundred eight IMA rings taken from 64 patients undergoing coronary artery bypass grafting were studied in organ baths. The interaction between GR117289C and AII or the other vasoconstrictors (U46619, norepinephrine, endothelin-1, and potassium chloride) was investigated in two ways. RESULTS: GR117289C induced near-maximal relaxation (94.5% +/- 2.9%) in IMA rings precontracted by AII. In IMA rings incubated with 1 or 10 nmol/L GR117289C, contractile responses to AII were attenuated in a concentration-related manner, whereas the dose-response curve did not shift to the right when higher doses of AII were administered, suggesting that the AT1 receptor blockade was noncompetitive in nature. Moreover, GR117289C also induced significant relaxation (82.9% +/- 8.1%) in IMA rings precontracted by U46619, but no inhibitory responses to U46619 could be observed when IMA rings were incubated with GR117289C. GR117289C did not alter responses to potassium chloride, norepinephrine, and endothelin-1. CONCLUSIONS: These results indicate that GR117289C is a potent, selective, noncompetitive AT1 receptor antagonist that may have a possible antagonistic effect on the thromboxane A2 receptor. Because AII and thromboxane A2 are important vasoconstrictors in the genesis of graft spasm, GR117289C may become an alternative treatment to relieve graft spasm.

Continuous intravenous insulin infusion reduces the incidence of deep sternal wound infection in diabetic patients after cardiac surgical procedures.

BACKGROUND: Diabetes mellitus is a risk factor for deep sternal wound infection after open heart surgical procedures. We previously showed that elevated postoperative blood glucose levels are a predictor of deep sternal wound infection in diabetic patients. Therefore, we hypothesized that aggressive intravenous pharmacologic control of postoperative blood glucose levels would reduce the incidence of deep sternal wound infection. METHODS: In a prospective study of 2,467 consecutive diabetic patients who underwent open heart surgical procedures between 1987 and 1997, perioperative blood glucose levels were recorded every 1 to 2 hours. Patients were classified into two sequential groups: the control group included 968 patients treated with sliding-scale-guided intermittent subcutaneous insulin injections (SQI); the study group included 1,499 patients treated with a continuous intravenous insulin infusion in an attempt to maintain a blood glucose level of less than 200 mg/dL. There were no differences between these groups with respect to age, sex, procedure, bypass time, antibiotic prophylaxis, or skin preparation methods. RESULTS: Compared with subcutaneous insulin injections, continuous intravenous insulin infusion induced a significant reduction in perioperative blood glucose levels, which led to a significant reduction in the incidence of deep sternal wound infection in the continuous intravenous insulin infusion group (0.8% [12 of 1,499]) versus the intermittent subcutaneous insulin injection group (2.0% [19 of 968], p = 0.01 by the chi2 test). Multivariate logistic regression revealed that continuous intravenous insulin infusion induced a significant decrease in the risk of deep sternal wound infection (p = 0.005; relative risk, 0.34), whereas obesity (p < 0.03; relative risk, 1.06) and use of an internal thoracic artery pedicle (p = 0.1; relative risk, 2.0) increased the risk of deep sternal wound infection. CONCLUSIONS: Use of perioperative continuous intravenous insulin infusion in diabetic patients undergoing open heart surgical procedures significantly reduces major infectious morbidity and its associated socioeconomic costs.

Coincidence of true and false left ventricular aneurysm.

Coincidence of true and false left ventricular aneurysm is very rare. To date 6 cases have been reported in the world literature. We present a case of false aneurysm emanating from a posterior true aneurysm of the left ventricle. These findings were demonstrated preoperatively by transesophageal echocardiography and were confirmed at operation. The aneurysms were successfully resected and the ventricle repaired.

Glucose control lowers the risk of wound infection in diabetics after open heart operations.

BACKGROUND: Elevated blood glucose levels in the postoperative period are associated with an increased risk of deep wound infection in diabetic individuals undergoing open heart operations at Providence St. Vincent Hospital. METHODS: Of 8,910 patients who underwent cardiac operations between 1987 and 1993, 1,585 (18%) were diabetic. The rate of deep sternal wound infections in diabetic patients was 1.7%, versus 0.4% for nondiabetics. Nine hundred ninety patients had their operation before implementation of the protocol and 595 after implementation. Charts of all diabetic patients were reviewed. Mean blood glucose levels were calculated from documented results of finger-stick glucometer testing. RESULTS: Thirty-three diabetic patients suffered 35 deep wound infections: 27 sternal (1.7%) and eight at the donor site (0.5%). Infected diabetic patients had a higher mean blood glucose level through the first 2 postoperative days than noninfected patients (208 +/- 7.1 versus 190 +/- 0.8 mg/dL; p < 0.003) and had a greater body mass index (31.5 +/- 1.4 versus 28.6 +/- 0.1 kg/m2; p < 0.05). Multivariable logistic regression showed that mean blood glucose level for the first 2 days (p = 0.002), obesity (p < 0.002), and use of the internal mammary artery (p < 0.02) were all independent predictors of deep wound infection. Institution of a protocol of postoperative continuous intravenous insulin to maintain blood glucose level less than 200 mg/dL was begun in September 1991. This protocol resulted in a decrease in blood glucose levels for the first 2 postoperative days and a concomitant decrease in the proportion of patients with deep wound infections, from 2.4% (24/990) to 1.5% (9/595) (p < 0.02). CONCLUSIONS: The incidence of deep wound infection in diabetic patients was reduced after implementation of a protocol to maintain mean blood glucose level less than 200 mg/dL in the immediate postoperative period.

Long-term outcome, survival analysis, and risk stratification of dynamic cardiomyoplasty.

METHODS: To analyze the long-term outcome of dynamic cardiomyoplasty, we retrospectively studied 127 consecutive patients who underwent this procedure in Paris, France (n = 76), São Paulo, Brazil (n = 37), and Portland, Oregon (n = 14). Preoperative data were collected for patients operated on between January 1985 and June 1994 and examined with respect to effect on long-term survival. Patients had a mean age of 50 +/- 13 years and were predominantly male (82%). In 46% the cause of disease was ischemic. Concomitant operations were performed in 22 patients. RESULTS: Operative mortality was 12% (15/127). Kaplan-Meier survival +/- standard error at 1 through 5 years was 73% +/- 4%, 57% +/- 5%, 49% +/- 6%, 44% +/- 6%, and 40% +/- 7%, respectively. There was a distinct improvement at 6 months in New York Heart Association functional class (3.2 +/- 0.05 vs 1.7 +/- 0.07, p < 0.0001) and a small but significant increase in left ventricular ejection fraction (20% +/- 0.8% vs 23% +/- 1.5%, p = 0.04). Ninety-day mortality was associated with low right ventricular ejection fraction, a blunted hemodynamic response to exercise testing, and requirement for an intraaortic balloon pump at the time of the operation. Using a stepwise Cox regression method of multivariable survival analysis (n = 101), we determined that atrial fibrillation, New York Heart Association class IV, high pulmonary capillary wedge pressure, and balloon pump use were independent variables simultaneously associated with poor overall survival. When metabolic testing variables were added to this model, peak oxygen consumption eliminated both pulmonary capillary wedge pressure and functional class from the model, albeit with fewer (n = 74) patients. CONCLUSION: Dynamic cardiomyoplasty is an evolving therapy for symptomatic congestive heart failure, the results of which may be enhanced by intelligent, risk-sensitive patient selection.

Multicenter trial of dynamic cardiomyoplasty for chronic heart failure. The American Cardiomyoplasty Group.

OBJECTIVES: The purpose of this study was to prospectively assess the effect of dynamic cardiomyoplasty in patients with symptomatic chronic heart failure. BACKGROUND: Since the first procedure was performed in 1985, dynamic cardiomyoplasty has been developed for use in patients with chronic heart failure. The aging population in developed countries has made heart failure a growing public health concern. Heart transplantation is appropriate or available for only a small proportion of these patients because of limited donor supply. Effective alternatives to transplantation are needed. METHODS: Eight centers in North and South America performed 68 cardiomyoplasty procedures between May 1991 and September 1993. Data were prospectively collected every 6 months and compared with preoperative values using paired t tests, chi-square tests and actuarial survival analyses. RESULTS: Patients had a mean (+/- SD) age of 57 +/- 1 years and were predominantly male (53 [78%] of 68). Heart failure etiology was classified as idiopathic in 47 (69%) of 68 patients and ischemic in 21 (31%). The in-hospital mortality rate was 12% (8 of 68), and the survival rate at 6 and 12 months was 75 +/- 5% and 68 +/- 6%, respectively. Objective improvements were seen at 6 months (n = 49) in left ventricular ejection fraction (23 +/- 1% vs. 25 +/- 1%, p = 0.05), stroke volume (50 +/- 2 vs. 56 +/- 3 ml/beat, p = 0.02) and left ventricular stroke work index (26 +/- 1 vs 30 +/- 2 g/m2 per beat, p = 0.01). Improvements in mean New York Heart Association functional class (3 +/- 0.04 vs. 1.8 +/- 0.1, p = 0.0001) and activity of daily living score (59 +/- 3 vs. 80 +/- 2, p = 0.0001) were also observed. There were no significant changes at 6 months in peak oxygen consumption (15 +/- 1 vs. 16 +/- 1 ml/kg per min), cardiac index (2.26 +/- 0.08 vs. 2.33 +/- 0.08 liters/min per m2), pulmonary capillary wedge pressure (19 +/- 2 vs. 18 +/- 1 mm Hg) or heart rate (87 +/- 2 vs. 82 +/- 3 beats/min). CONCLUSIONS: These data suggest that dynamic cardiomyoplasty improves ventricular systolic function, reduces symptoms of heart failure and improves objective measures of quality of life in patients with congestive heart failure. This improvement occurred without changes in peak exercise capacity, ventricular filling pressure or actuarial survival.

Lessons learned before and after cardiomyoplasty: risk sensitive patient selection and post procedure quality of life.

BACKGROUND: This paper unveils some of the clinical lessons we have learned from caring for cardiomyoplasty patients over the past 7 years. We examine both the clinical and scientific rationale for expanding the time frame of "procedural mortality" from 30 days to 90 days. METHODS: Utilizing this definition of procedural mortality, preoperative patient variables were applied to postoperative patient outcomes in order to develop a risk sensitive method of patient selection. Preoperative atrial fibrillation, elevated pulmonary capillary wedge pressure, decreased peak oxygen consumption, and the requirement of intra-aortic balloon pump at the time of cardiomyoplasty, were all found to be independent risk factors for early death following cardiomyoplasty. RESULTS: This analysis, which has been previously published, is reviewed and enhanced with the mathematical equations for duplicating these relative risk calculations. The mathematical model presented herein allows a method of risk stratification, which obviates the need for randomized congestive heart failure controls in the future. In the absence of a statistically regulated control population, we also examine the 1-year clinical outcomes of the nonrandomizd control group of patients, who were followed during the North American FDA Phase II Cardiomyoplasty Trial. CONCLUSIONS: This quality of life comparison with cardiomyoplasty patients at 1 year revealed a significant decrease in intensive care unit patient-days, a significant increase in activity of daily living score, and a significant improvement in New York Heart Association functional class as compared to control.

Is referral source a risk factor for coronary surgery? Health maintenance organization versus fee-for-service system.

We began performing coronary artery bypass grafting for a large health maintenance organization (HMO) in 1974, as the sole provider of their cardiac surgery. The outcomes of our HMO group of patients were compared with those of our patients treated on a fee-for-service (FFS) basis. The HMO system entails preintervention and multidisciplinary screening conferences and is devoid of self-referral and personal financial incentives. Since 1985, the operative mortality for HMO patients has been consistently lower than for FFS patients. There were 8483 operations during this study period: 3168 (37%) were in the HMO group, with an overall operative mortality of 2.7%, and 5315 (63%) were in the FFS group, with an operative mortality of 4.6% (p=0.00002). This difference was investigated with univariate and multivariable analyses. Sixteen factors were found to univariately affect the risk of operative mortality; for five of these risk correlates there was a significant maldistribution between the HMO and FFS patients. Logistic regression was used to explore the influence of this imbalance in risk factors. The model found seven independent risk factors (left ventricular failure, emergency coronary bypass, redo bypass, nonuse of the internal thoracic artery, unstable angina, age, and diabetes) that significantly affected operative mortality. The FFS group variable closely approached independent risk significance at p=0.059. This multivariable model explained only one third of the observed differences in actual mortality between the HMO and FFS groups. The system-wide angioplasty/coronary bypass ratio, which could not be used in a patient-specific model, was 0.6 in the HMO system and 1.5 in the FFS group. Other factors related to the operating structure of a mature, large HMO may account for the remainder of the difference. The HMO referral system, through a powerful selection process, resulted in fewer emergencies, redo bypass operations, and catheterization complications that, in turn, yielded lower operative mortality than a noncoordinated FFS system of cardiovascular management.

Reversed bevel technique for anastomosis at the aortic arch.

We describe a method for performing the distal anastomosis in replacement of the ascending and the proximal arch of the aorta with specific attention to obtaining accurate length and orientation of the graft. This method reduces the incidence of both anastomotic dehiscence due to tension and obstruction caused by redundant graft.

Up to thirty-year survival after aortic valve replacement in the small aortic root.

Aortic valve replacement (AVR) in the small aortic root has been reported to be associated with obstruction of left ventricular output. This study was designed to investigate the determinants of long-term survival after the implantation of small size prostheses. From September 1961 to December 1993, 2,977 patients underwent isolated aortic valve replacement at our institution. Of these patients, 447 who were older than 18 years received small size (21 mm or less) prostheses. Long-term survival was investigated in the 404 patients who survived operation (more than 30 days) with 92% follow-up completeness (mean +/- deviation 7.1 +/- 6.4; maximum, 31 years). The age was younger than 50 years in 62 patients, 50 to 59 years in 60, 60 to 69 years in 99, 70 to 79 years in 138, and 80 to 94 years in 45; 67% were men. Thirty patients (7%) had previous AVR. Prosthesis usage included early Starr-Edwards models in 130 (32%), current Starr-Edwards (model 1260 since 1969) in 50 (12%), Carpentier-Edwards (porcine) in 113 (28%), and other prostheses in 111 patients (27%). One hundred sixteen patients (26%) had concomitant coronary artery bypass grafting (CABG). Eleven variables (age divided as above, sex, preoperative functional class, body surface area [BSA], small BSA [less than 1.6, 1.7, 1.8, or 1.9 m2], period of operation, previous AVR, type of prosthesis, size of prosthesis, concomitant CABG, and re-replacement) were investigated with regard to the long-term survival by the Kaplan-Meier method, and age, concomitant CABG, and type of prosthesis were significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Adventitial inversion technique in repair of aortic dissection.

We describe a new technique for aortic anastomosis in the repair of acute dissection. The aorta is buttressed by inverting the adventitia without the use of Teflon or other synthetic materials. This technique provides a safe and secure anastomosis.

Mitral insufficiency after pericardiectomy for constrictive pericarditis.

We report the case of a 24-year-old man in whom a clinical syndrome developed while he was on active military duty in Saudi Arabia that was subsequently diagnosed as constrictive pericarditis. Phrenic nerve to phrenic nerve pericardiectomy and posterior pericardial release successfully relieved the ventricular constriction with a resultant increase in the cardiac index from 1.9 to 3.8 L.min-1.m-2. Transesophageal echocardiographic monitoring during the operation disclosed trace mitral regurgitation before median sternotomy. The severity of the regurgitation noticeably increased to the moderate level immediately after pericardial resection. This echocardiographic finding had improved 1 week later, but the regurgitation still was greater than baseline. Mitral valve function had returned to baseline by 4 weeks after the operation. Possible mechanisms of this evolving pattern of perioperative mitral valve dysfunction are discussed.

Component analysis of bilateral anterior cardiomyoplasty.

This experiment was designed to analyze the mechanism of ventricular augmentation generated with bilateral anterior cardiomyoplasty by comparing it in an acute setting with its components, the left anterior cardiomyoplasty and the right anterior cardiomyoplasty. Hemodynamic variables were measured in 8 dogs before and after each flap was positioned around the heart. Stimulation was achieved by R-wave synchronous latissimus burst pacing at a ratio of 1:4, an amplitude of 5 V, a frequency of 33 Hz, and a duration of 30% of the R-R interval. Hemodynamic changes were again recorded during latissimus stimulation. Construction of the bilateral anterior wrap (static cardiomyoplasty) caused some depression of baseline hemodynamic function, which was greater than that caused by either the static right or left anterior cardiomyoplasty. With stimulation of the muscles (dynamic cardiomyoplasty), the bilateral wrap caused significant biventricular augmentation. Evaluation of the components of the bilateral wrap demonstrated that dynamic right anterior cardiomyoplasty also provided significant biventricular augmentation, but the dynamic left anterior cardiomyoplasty augmented only right-sided variables. The mechanism of biventricular compression by the bilateral procedure is due mostly to the right wrap. The right anterior cardiomyoplasty may provide significant biventricular compression for treatment of heart failure, without the complexity associated with bilateral anterior cardiomyoplasty.

Clinical cardiomyoplasty: preoperative factors associated with outcome.

Dynamic cardiomyoplasty has been used clinically to augment the ventricular function of a failing heart. Fifteen clinical dynamic cardiomyoplasties have been performed at Allegheny General Hospital since 1985. Left ventricular ejection fraction improved in long-term survivors from a preoperative value of 0.23 +/- 0.02 to 0.32 +/- 0.05 with postoperative cardiomyostimulation (p < 0.05). There was an average reduction of 2 +/- 0.3 New York Heart Association classes (3.6 +/- 0.2 before operation versus 1.6 +/- 0.4 after operation; p < 0.001). Postoperative mortality was 27% (4/15), and early mortality (within 6 months after operation) was 20% (3/15). Significant preoperative differences between survivors and nonsurvivors were found in right ventricular ejection fraction (0.53 +/- 0.03 versus 0.30 +/- 0.07; p < 0.05), pulmonary artery mean pressure (19 +/- 2 versus 34 +/- 6 mm Hg; p < 0.05), pulmonary artery diastolic pressure (12 +/- 1 versus 25 +/- 5 mm Hg; p < 0.05), and pulmonary vascular resistance (1.4 +/- 2 versus 2.5 +/- 0.7 Wood units; p < 0.05). Dynamic cardiomyoplasty can be done with low operative mortality in patients with isolated left ventricular failure, but mortality is high in those with biventricular failure or pulmonary hypertension. Improvement in functional class and ventricular function can be expected in long-term survivors. Application of these findings to patient selection will improve the risk/benefit ratio for dynamic cardiomyoplasty.

Correlation of electrophysiological activation patterns to tension generation in stimulated latissimus dorsi muscle.

Skeletal muscle has been used for biomechanical assist in experimental and clinical studies. Central to the success of these procedures is the generation of sufficient muscle force for the lifetime of the subject. Burst (tetanic) stimulation results in summation of individual twitches and generates higher power output. However, the superiority of paraneural versus intramuscular as well as proximal versus middle and distal intramuscular stimulations remains unclear. Electrophysiological mapping and mechanical performance of seven canine latissimus dorsi muscles were analyzed. The mechanism of higher tension generation produced by: (1) increased temporal summation; (2) greater motor units activated; or (3) result of both were determined. The parameters primarily dependent on the number of activated motor units are significantly greater following paraneural and proximal intramuscular stimulations. The parameters mainly related to temporal summation are not different between various electrode configurations. For intramuscular stimulation, it is the location of interelectrode field rather than the location of the cathode per se that determines the mechanical performance of the skeletal muscle. Furthermore, tension development of skeletal muscle is primary nerve activation rather than direct muscle stimulation. The higher tension generation that resulted from different electrode configurations is produced by activating a higher number of muscle fibers through the neuromuscular junctions.

Prolonged open sternotomy and delayed sternal closure after cardiac operations.

Maintenance of an open sternotomy (OS) after a complicated cardiac operation is an adjunct in the treatment of the severely impaired heart. We hypothesized that predictors of the timing, morbidity, and prognosis of delayed sternal closure (DSC) could be determined by intensive case review. Prolonged OS was used in 107 of 6,030 adult open heart patients (1.8%) between 1987 and 1991. Indications for OS were hemodynamic instability (40), myocardial edema (18), intractable bleeding (23), relentless arrhythmias (9), and ventricular assist devices (17). Delayed sternal closure was carried out in 75 of 107 patients at a mean of 3.4 +/- 0.3 days after OS. Fifty of these 75 (67%) survived and were discharged an average of 43 +/- 6 days after closure. Fifty-seven patients died: 32 before DSC at 3.7 +/- 0.8 days after OS and 25 after DSC at 27 +/- 4 days after OS. Baseline cardiac index (1.7 +/- 0.1 L.min-1.m-2) improved an average of 1.0 +/- 0.1 L.min-1.m-2 after OS (p less than or equal to 0.001) and remained stable through DSC (2.5 +/- 0.3 L.min-1.m-2) and late (9 +/- 0.7 days) follow-up (2.8 +/- 0.1 L.min-1.m-2). Delayed sternal closure in patients without ventricular assist devices was significantly more likely to be successful (45/63 versus 9/27; p less than 0.002) when carried out after the onset of a negative daily fluid balance. Sternal infection occurred in 4 of 75 (5%) patients after DSC and was associated with bleeding as an indication for OS (3/15 versus 1/60; p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)