Exercise hemodynamics during long-term implantation of a left ventricular assist device in patients awaiting heart transplantation.

OBJECTIVES: The goal of this study was to assess patients with end-stage heart disease after implantation of a left ventricular assist device at rest and during exercise compatible with activities of daily life. BACKGROUND: Mechanical circulatory assistance with a left ventricular assist device is an accepted therapy for bridging patients with end-stage heart disease to heart transplantation and has been proposed for long-term implantation. METHODS: Three patients (aged 37, 42 and 57 years) with end-stage heart failure required implantation of a pneumatically driven, asynchronous Thermedics left ventricular assist device while awaiting heart transplantation. All were assessed 1 month later during graded supine bicycle exercise (maximal work load 100 to 150 W). Detailed central hemodynamics, including continuous pulmonary artery oxygen saturation and oxygen consumption measurements, were obtained. Two of the patients also underwent upright treadmill exercise with oxygen consumption measurements. RESULTS: During supine bicycle exercise, the heart rate increased from 93 +/- 37 beats/min (95% confidence interval: mean +/- t0.025 x SE) at rest to 119 +/- 54 beats/min and left ventricular assist device rate increased from 82 +/- 47 to 109 +/- 55 beats/min. Oxygen consumption increased from 3.0 +/- 0.9 to 8.7 +/- 2.9 ml oxygen/min per kg body weight. Cardiac output increased from 6.0 +/- 4.4 to 9.6 +/- 7.1 liters/min, yielding an average exercise factor of 8.5 +/- 7.7 and an exercise index of 0.83 +/- 0.61. The patients assessed during treadmill exercise achieved a maximal oxygen consumption of 14.3 and 16.7 ml of oxygen/min per kg. No thromboembolic or other complications attributable to left ventricular assist device implantation occurred during the duration of support. All patients survived orthotopic heart transplantation and are doing well. CONCLUSIONS: Significant work loads compatible with activities of daily life and adequate exercise hemodynamics were demonstrated by these patients while awaiting heart transplantation. Definitive conclusions regarding the use of this device must be viewed as preliminary because only three patients were involved in this study and the failure rate may be as high as 71% (95% confidence interval of left ventricular assist device success as a bridge to transplantation 29.3% to 100%). Final conclusions regarding the safety and efficacy of the left ventricular assist device as a possible long-term circulatory support device must await results of larger multicenter trials in progress.

Modifications of techniques and early results of pulmonary thromboendarterectomy for chronic pulmonary embolism.

In 1980 we described bilateral pulmonary thromboendarterectomy with median sternotomy, cardiopulmonary bypass, deep hypothermia, and circulatory arrest for the relief of pulmonary hypertension caused by chronic pulmonary embolism. In our subsequent experience, which totals 41 patients, we have identified three groups of patients characterized by differences of intraoperative management. In Group A (N = 16) myocardial protection consisted of single-dose crystalloid cardioplegia followed by pericardial irrigation with cold saline. Extrapericardial dissection of the pulmonary arteries was performed. Group B (N = 7) was treated the same as Group A except for the substitution of saline slush contained in a laparotomy pad for iced saline. In Group C (N = 18) myocardial protection was single-dose blood cardioplegia followed by the application of a specially designed cooling jacket to the right and left ventricles. Another modification was that of intrapericardial dissection of the pulmonary arteries with extension of the dissection into the hilar tissues without entrance into the pleural spaces. The hospital mortalities of Groups A, B, and C were 18.7%, 14.3%, and 5.5%, respectively (not statistically significant differences). However, other statistically significant differences (p less than 0.05) among the groups were observed: Phrenic nerve paresis occurred in five of seven (71%) Group B patients but in no Group A or C patients; Group B patients required ventilatory support for 32.2 days compared with 8.4 days for Group A and 6.2 days for Group C; time in the intensive care unit was 36 days for Group B patients versus 13 for Group A and 10.3 for Group C; pulmonary vascular resistance decreased 59% (649 versus 259) intraoperatively in 13 patients in Group C. We believe simultaneous bilateral pulmonary thromboendarterectomy with median sternotomy, cardiopulmonary bypass, deep hypothermia with circulatory arrest, and the modified methods of myocardial preservation and dissection represent current optimal surgical management of this problem.

Quantitative evaluation of the myocardial preservative characteristics of nifedipine during hypothermic myocardial ischemia.

Nifedipine, a slow calcium-channel blocker, has been used to preserve myocardial function in the ischemic heart. To quantitatively evaluate the effectiveness of nifedipine as a cardioplegic agent during moderate hypothermia (28 degrees C), 15 pigs were evaluated on total and right heart bypass with measurement at normothermia and after 1 hour of hypothermic ischemia of stroke volume, coronary blood flow, myocardial oxygen consumption, and lactate extraction. Myocardial tissue gases (oxygen and carbon dioxide) were continuously monitored. Animals were divided into three groups: hypothermic ischemia, hypothermic ischemia with infusion of nifedipine carrier without nifedipine, and hypothermic ischemia with nifedipine and its carrier. A significant decrease in stroke volume was seen in all three groups; however, the depression was significantly greater following hypothermic ischemia than following cardioplegia with either nifedipine or its carrier. The mean recovery value of stroke volume was highest in the nifedipine group, but this difference between nifedipine and its carrier alone did not reach statistical significance. Coronary blood flow, myocardial oxygen consumption, lactate extraction, and tissue gases failed to substantiate a significant benefit when nifedipine was compared with its carrier alone. We conclude that under these hypothermic conditions, no proven statistically significant advantage was noted in the nifedipine group when compared with the nifedipine carrier group in swine. However, both nifedipine and the carrier were superior as a myocardial preservative when compared with hypothermic ischemic arrest alone.

Risk factors for pulmonary thromboendarterectomy.

Pulmonary thromboendarterectomy is being performed with increasing frequency for incapacitating pulmonary hypertension caused by chronic large-vessel pulmonary embolism. However, patient-related risk factors and procedural complications associated with morbidity and mortality have not been fully defined. From Oct. 1, 1984, to April 10, 1989, we performed pulmonary thromboendarterectomy using deep hypothermia and circulatory arrest in 127 consecutive patients (62.2% male, mean age 50 +/- 16 [standard deviation], range 20 to 82 years) in whom the exposure and dissection of the pulmonary arteries and methods for myocardial protection have been standardized. End points for univariate and multivariate analyses of risk factors were reperfusion pulmonary edema leading to respiratory insufficiency as defined by ventilator dependency (greater than or equal to 5 days) (31.5%, 39/124) and hospital mortality (12.6%, 16/127). Multivariate analyses showed that ascites and need for 4 units of blood or more predicted ventilator dependency (p less than 0.03). Increased cardiopulmonary bypass times predicted both end points (p less than 0.03 to less than 0.0001), and failure to achieve at least a 50% reduction in pulmonary vascular resistance strongly predicted hospital death (p less than 0.0001). However, other factors that exhibited trends for association with one of the end points may prove important with a larger sample size. A hospital mortality rate of 12.6% for pulmonary thromboendarterectomy is acceptable when compared with approximately 25% for heart-lung transplantation, which is the only therapeutic alternative. Increased ventilator dependency and hospital mortality can be anticipated with longer cardiopulmonary bypass times and inadequate reduction of pulmonary vascular resistance.

Accurate localization of ruptured sinus of Valsalva aneurysm by real-time two-dimensional Doppler flow imaging.

The surgical approach to the repair of a ruptured sinus of Valsalva aneurysm can depend on the cardiac chamber into which rupture occurs. This report details the color flow Doppler images in two patients who developed a right sinus of Valsalva aneurysm to right atrial fistula owing to bacterial endocarditis. In both cases, the color flow Doppler image was superior to contrast aortography in identifying the chamber into which rupture had occurred. The early experience with real-time two-dimensional Doppler flow imaging suggests that this noninvasive technique is valuable in the management of ruptured sinus of Valsalva aneurysms.

Effect of prophylactic epsilon-aminocaproic acid on blood loss and transfusion requirements in patients undergoing first-time coronary artery bypass grafting. A randomized, prospective, double-blind study.

The prophylactic use of aprotinin has recently been reported to be associated with a significant decrease in blood loss in patients undergoing cardiopulmonary bypass procedures. One of the primary effects of aprotinin is prevention of plasmin degradation of platelet function. Because aprotinin is commercially unavailable in the United States at this time, we evaluated epsilon-aminocaproic acid with respect to decreased perioperative blood loss. We prospectively randomized 40 patients undergoing first-time coronary artery bypass grafting without prior sternotomy into two groups: one group (n = 21) received prophylactic and preincision epsilon-aminocaproic acid and the other (n = 19) received a placebo. No significant differences existed between patient groups with respect to age, body surface area, cardiopulmonary bypass time, and aortic crossclamp time. Cumulative blood loss at 4, 8, 12, and 24 hours after chest closure was significantly less in the epsilon-aminocaproic acid group (426 +/- 242 ml versus 634 +/- 224 ml, p = 0.002, at 12 hours). Only one patient receiving epsilon-aminocaproic acid was given blood or blood components compared to five patients in the placebo group (p < 0.02). D-dimers and fibrin split products were significantly less prevalent in the epsilon-aminocaproic acid group (at 4 hours: 0/20 versus 7/16, p < 0.002 and 5/20 versus 12/19, p < 0.05, respectively). None of the patients had a perioperative myocardial infarction or cerebrovascular accident. The prophylactic administration of epsilon-aminocaproic acid results in a significant decrease in blood loss in patients undergoing first-time coronary artery bypass grafting, and blood transfusion requirements are significantly less. It may be important to administer epsilon-aminocaproic acid before skin incision to be optimally effective.

Temporary extracorporeal support of the right ventricle.

Six patients having severe right ventricular failure after cardiac surgical procedures were treated temporarily with an extracorporeal pump to bypass the right ventricle. The initial operative procedures included coronary artery bypass procedures with and without concomitant valvular and aortic replacement. A Biomedicus centrifugal pump was used as the right ventricular assist device in most cases. The assist period ranged from 3 to 96 hours, and an intra-aortic balloon pump was used in five of the six patients. All patients initially responded to the right ventricular assist device, four were successfully weaned, and one patient is a long-term survivor. The use of a right ventricular assist device is not difficult or complicated and can be lifesaving for those patients having potentially reversible profound right ventricular failure.

Chronic thromboembolic occlusion in the adult can mimic pulmonary artery agenesis.

In the first 100 patients operated on for C T-E PH, three were referred with the diagnosis of UPAA having been made elsewhere. We found that many features of these two conditions are so similar that differential diagnosis is very difficult. Shared features may include findings on chest x-ray film, pulmonary angiography, CT scan and MRI studies. Since the two conditions vary substantially with respect to the methods of potential surgical correction, recognition of this possible differential diagnostic dilemma is important.

Mechanical support: assist or nemesis?

Our 6-year experience with ventricular assist devices was reviewed to determine variables associated with improved survival. Forty-three patients (mean age 62 +/- 14 years) were supported after balloon pumping and pressors proved inadequate. Twenty-eight patients could not be weaned from cardiopulmonary bypass, 12 patients deteriorated in the intensive care unit after cardiac surgery, and three had a bridged to transplantation. Overall, 47% (20/43) of patients could not be weaned from the ventricular assist devices, and 26% (11/43) were weaned but died before discharge, resulting in a hospital mortality rate of 72% (31/43). The remaining 28% (12/43) of patients were discharged and have survived 9 to 62 months. Early institution of ventricular assist devices (p less than 0.01), use of biventricular support (p less than 0.01), use of ventricular assist devices as a bridge to transplantation (p less than 0.05), and increased operator experience (p less than 0.05) were associated with improved survival. When patient and disease-related variables were analyzed, only age less than 60 years (p less than 0.01) and unexpectedly preoperative myocardial infarction associated with shock (p less than 0.05) were related to improved survival. Death was caused by insufficient ventricular recovery, stroke, multiple organ system failure, sepsis, or a combination of these complications. During long-term follow-up, two patients have died of congestive heart failure, and one is significantly impaired from a stroke. Two other patients are functional class III and seven patients are class I. Although hospital mortality was high (72%), the use of ventricular assist device support resulted in overall "long-term" survival of a significant percentage (28%) of patients, 47% (8/17), in the past 12 months, all of whom would have died without it. Therefore we currently recommend a trial of ventricular assist devices support for most patients who fail to be weaned from cardiopulmonary bypass, deteriorate in the perioperative period, and as a bridge to transplantation. Long-term survival is determined by the complications from ventricular assist devices support and functional status of the remaining myocardium.

Interstitial hydrostatic pressures in patients undergoing CABG and valve replacement.

Using the Scholander-Hargens wick technique to measure interstitial fluid hydrostatic pressure (IFP) in thigh muscle (MIP) and subcutaneous tissue (SQIP), we have studied 12 patients undergoing cardiopulmonary bypass (CPB). Simultaneous measurements were made of serum total proteins (TP) and colloid osmotic pressure (COP). Bypass was carried out with a nonblood, noncolloid prime. In the postoperative period, colloid and blood were given which raised COP above prebypass levels (see Table II). MIP rises more with hemodilution than does SQIP and is less negative throughout. MIP rises faster when COP drops than does SQIP. These findings suggest that subcutaneous tissue interstitial space is loose and has a high compliance, whereas muscular tissue interstitial space is tight and has a low compliance. The increased pressure represents increase in fluid which is then removed promptly as COP is restored in the postoperative period. Experimental studies in animals show a response similar to MIP in the myocardium.

Operative predictors of delirium after pulmonary thromboendarterectomy. A model for postcardiotomy delirium?

Pulmonary thromboendarterectomy is an innovative surgical technique for treating pulmonary hypertension caused by chronic thromboembolism. The procedure uses cardiopulmonary bypass but necessitates dramatically longer bypass times than coronary artery bypass grafting or valve operations. We prospectively evaluated 22 patients undergoing pulmonary thromboendarterectomy to determine the incidence of delirium and its relationship to certain preoperative and postoperative medical variables as well as to duration of cardiopulmonary bypass, deep hypothermia, and circulatory arrest. Delirium occurred in 77% of patients with a peak incidence around 72 hours postoperatively. No preoperative or postoperative medical variable distinguished delirious from nondelirious patients. Total bypass time was not associated with delirium, but deep hypothermia time and total circulatory arrest time were both strongly associated. Overall prediction of delirium was 81% when total circulatory arrest time was considered. Further analysis suggested that a total circulatory arrest time greater than 55 minutes was both sensitive to (82%) and specific for (80%) delirium. Implications for the mechanism of postcardiotomy delirium and future research directions are discussed.

Clinical comparisons of methods of myocardial protection.

Currently, numerous methods are in use for myocardial hypothermia as a myocardial preservation modality for cardiac operations. During cardiac ischemia we have compared myocardial surface cooling with topical cold saline (Group I, N = 9), crystalloid cardioplegia plus topical cold saline (Group II, N = 8) and cardioplegia with a specially designed cooling jacket (Group III, N = 8) in patients undergoing aortic or mitral valve replacement, or both. Temperatures were assessed and recorded continuously in standardized locations for the right and left ventricular epicardium and endocardium. In Group I the rate of cooling was significantly slower than in the other two groups. Also, excessive gradients were developed across the left and right ventricular walls. In Group II the rate and depth of cooling were adequate and initial temperature gradients were eliminated. However, over the period of ischemia, significant rewarming occurred. In Group III temperatures were reduced rapidly and uniformly and maintained at or below 10 degrees C for the duration of the ischemic period. These differences are statistically significant (p less than 0.05). For optimal myocardial hypothermia, we recommend the following: separate cannulation of the superior and inferior venae cavae with caval snares; venting of the pulmonary artery (if inadequate, pulmonary vein occlusion or direct left atrial venting); induction of myocardial hypothermia with crystalloid or cold blood cardioplegia; and maintenance of hypothermia by the cooling jacket described herein. It is also desirable to continuously monitor temperatures of the right and left ventricular endocardial and epicardial surfaces.

Comparison of myocardial temperatures with multidose cardioplegia versus single-dose cardioplegia and myocardial surface cooling during coronary artery bypass grafting.

Myocardial hypothermia with multidose cardioplegia has not been compared with single-dose cardioplegia and myocardial surface cooling with a cooling jacket in patients having coronary artery bypass grafting. In this study, 20 patients with three-vessel disease undergoing coronary bypass at 28 degrees C with bicaval cannulation, caval tapes, and pulmonary artery venting (4.9 +/- 0.7 grafts per patient) were prospectively randomized equally into group I (multidose cardioplegia) and group II (single-dose cardioplegia with a cooling jacket). The initial dose of cardioplegic solution was 1000 ml. Group I then received 500 ml of cardioplegic solution every 20 minutes, delivered into the aortic root and available grafts. In group II, after the cardioplegic solution had been administered, a cooling jacket covering the right and left ventricles was applied. In both groups temperatures were recorded every 30 seconds at five ventricular sites: (1) right ventricular epicardium; (2) right ventricular myocardium or cavity, 7 mm; (3) left ventricular epicardium; (4) left ventricular myocardium or cavity, 15 mm; and (5) septum, 20 mm. Group mean temperatures at each site at various times were compared within each group and between the two groups by analysis of variance. Aortic crossclamp time was 60.3 +/- 12.1 minutes in group I and 52.8 +/- 7.3 minutes in group II (p = 0.12); cardiopulmonary bypass time was 103.7 +/- 11.1 minutes in group I versus 87.7 +/- 12.7 minutes in group II (p less than 0.01). One minute after the cardioplegic solution was initially given, temperatures between groups at each site were not statistically different, but left ventricular epicardial temperatures within both groups were significantly higher than in the other four sites. Nineteen minutes after administration of the cardioplegic solution, temperatures in group I at all sites were higher than in group II. Similarly, throughout the entire period of aortic crossclamping, mean temperatures (except left ventricular myocardial site), maximum temperatures, and percentage of time all temperatures were 15 degrees C or higher were greater in group I than in group II. The following conclusions can be reached: 1. Initial myocardial cooling with 1000 ml of cardioplegic solution is not significantly limited by coronary artery disease but is suboptimal (16 degrees or 17 degrees C) in the inferior left ventricular epicardium because of continual warming from the aorta and subdiaphragmatic viscera. 2. Without myocardial surface cooling, excessive external myocardial rewarming to 18 degrees to 22 degrees C occurs within 20 minutes at all sites after delivery of the cardioplegic solution.(ABSTRACT TRUNCATED AT 400 WORDS)

Cost reduction by combined carotid endarterectomy and coronary artery bypass grafting.

A significant cost reduction is likely if patients who require coronary artery bypass grafting with significant carotid stenosis have simultaneous carotid endarterectomy and bypass grafting, provided risk is not increased. To investigate this issue, we retrospectively identified cases from February 1977 to May 1994 with first-time isolated carotid endarterectomy, coronary bypass, or combined procedures. In the isolated carotid endarterectomy population, median age was 69 years and 58% (85/146) were male, as compared with 68 years and 68% (68/100) male in the combined group; median age of the coronary bypass cohort was 65 years and 76% (381/500) male. A significantly higher percentage of patients in the coronary bypass versus combined group were in New York Heart Association functional class IV. In the combined group there was a significantly higher incidence of older age, diabetes, hypertension, hyperlipidemia, renal failure, and congestive heart failure. There was no difference among the three groups with respect to hospital mortality (0%, 3.4%, and 4.0%, respectively) and permanent stroke (0.7%, 1.2%, and 0%, respectively). Hospital costs were $4,896, $10,959 and $11,089, respectively, with a savings of $4,766 (30%), and Medicare hospital reimbursement was $8,575, $23,071, and $23,071, respectively, with a savings of $10,077 (25.3%). Thus, in appropriate patients, a combined procedure is cost effective, eliminating a second surgical procedure and the cost of the postoperative stay (3.7 +/- 2.4 days) associated with isolated carotid endarterectomy. Risk of permanent stroke or death is not increased.

Physiology of the native heart and Thermo Cardiosystems left ventricular assist device complex at rest and during exercise: implications for chronic support.

Studies of patients supported with a left ventricular assist device have considered determinants of acute survival emphasizing the role of right heart function. In patients with refractory heart failure awaiting heart transplantation, chronic left ventricular assist device implantation may provide an opportunity for rehabilitation before surgery if hemodynamics are adequate at rest and during activities of daily life. For the assessment of the efficacy of the left ventricular assist device in this setting, four patients in whom the HeartMate pneumatic left ventricular assist device had been implanted were tested during graded supine bicycle exercise with Doppler echocardiography interrogation and central hemodynamic measurements. Patients with left ventricular assist device increased total left ventricular-left ventricular assist device complex output with exercise as Fick cardiac output increased from 5.7 +/- 1.5 to 8.6 +/- 3.1 L/min (mean +/- standard deviation). In two patients, peak left ventricular assist device rate and output were either present at the start of exercise or reached at mid-exercise and were associated with abrupt increases in left ventricular filling pressures (pulmonary capillary wedge pressure = 9 to 27 mm Hg and 12 to 24 mm Hg, respectively). During exercise, left ventricular end-diastolic size and pressure increased as right ventricular dimensions decreased or remained the same (patients 1, 3, and 4: 1.7 to 1.8 cm, 4.7 to 3.9 cm, and 2.6 to 1.8 cm, respectively) despite increased right atrial filling pressures, implying a decrease in functional right ventricular diastolic compliance. Although the left ventricular assist device functioned as a series pump at rest, Fick cardiac output exceeded left ventricular assist device output during exercise consistent with parallel ejection of the left ventricle through the native aortic valve. During exercise, residual left ventricular function may contribute to the hemodynamic response by (1) active filling of the left ventricular assist device to reduce filling time and to overcome left ventricular assist device inflow cannula impedance, (2) augmentation of total cardiac output with parallel ejection out of the native aortic valve, or (3) reduction of ventricular interaction-related changes in functional right ventricular diastolic compliance. When residual left ventricular function is sufficient, hemodynamics with exercise may be limited by peak left ventricular assist device rate. Although right ventricular function may affect acute postoperative survival, residual left ventricular function and peak left ventricular assist device rate may be important determinants of exercise performance during chronic implantation. A preliminary model of factors affecting the "left ventricular-left ventricular assist device complex" performance at rest and during exercise is presented.

Successful mechanical circulatory support for noncoronary shock.

Mechanically assisted recovery from shock and long-term survival of nontransplant patients with acute noncoronary myocardial decompensation have not been previously reported. We treated nine patients (aged 8 to 53 years) who were referred with acute nonischemic cardiogenic shock (pulmonary capillary wedge greater than 20, cardiac index less than 1.5 L/min/m2, mean blood pressure less than 60 mm Hg, ejection fraction less than 0.3%). Eight patients had viral prodromes, and one patient was peripartum. All patients' lungs were mechanically ventilated, and pharmacologic support failed in all patients. Two patients received steroids. All received mechanical circulatory support. Seven were initially supported with intraaortic balloon counterpulsation pumps. Two patients recovered with intraaortic balloon counterpulsation pumps alone (3 days and 4 days). Four patients received left ventricular assist devices (3, 7, 10, and 79 days), and two received biventricular support devices (10 days and 14 days). One patient was supported with extracorporeal femoral vein-to-femoral artery bypass for 6 days. Four patients required dialysis (4 days to 5 weeks). Seven patients underwent myocardial biopsies, of which three demonstrated acute myocarditis. All patients recovered ventricular function (ejection fraction greater than 0.55%), and all are New York Heart Association functional class I, 7 months to 4 1/2 years after support. Mechanical circulatory assist devices may be lifesaving for patients with acute nonischemic myocardial decompensation. Patients should be supported for at least 2 weeks before transplantation is considered.

Comparison of functional capacity in patients with end-stage heart failure following implantation of a left ventricular assist device versus heart transplantation: results of the experience with left ventricular assist device with exercise trial.

BACKGROUND: Use of a permanent left ventricular assist device (LVAD) has been proposed as an alternate treatment of patients with end-stage heart failure. The purpose of this study was to compare the functional capacity of patients following implantation of a LVAD vs heart transplant (HTx). METHODS: Eighteen patients from 6 centers who received an intracorporeal LVAD as a bridge to HTx underwent treadmill testing 1 to 3 months post-LVAD and again post-HTx. Baseline and peak measurements, including oxygen consumption, blood pressures, and respiratory rate were made during each treadmill test. RESULTS: Peak oxygen consumption was 14.5+/-3.9 ml/kg/minute post-LVAD and 17.5+/-5.0 ml/kg/minute post-HTx (p < .005). The percentage of the predicted peak oxygen consumption based on gender, weight, and age was 39.5%+/-5.5% post-LVAD and 47.7%+/-10.9% post-HTx (p < .005). Exercise duration was lower post-LVAD than post-HTx (10.3+/-4.2 minute vs 12.5+/-5.4 minute, p < .05). After LVAD implantation, peak total oxygen consumption correlated with peak LVAD rate and output. Eight patients reached an LVAD rate of 120 beats per minute (bpm) before the conclusion of exercise, the maximum rate for the outpatient electric device. The peak respiratory exchange ratio post-LVAD was 1.15+/-0.22 and post-HTx was 1.15+/-0.18, consistent with a good effort in both groups. CONCLUSIONS: Patients demonstrated a lower functional capacity post-LVAD than post-HTx. For some patients functional capacity post-LVAD may be improved by a higher maximum LVAD rate and output.

Bridging from acute to chronic devices.

Mechanical circulatory support used as a bridge to chronic transplantation is now a firmly established treatment modality. Trials evaluating circulatory assist for permanent circulatory assist device implications are underway. A population of patients is beginning to emerge who are resuscitated using readily available "acute" devices and need long-term supporting "chronic" device to bridge either cardiac transplantation or permanent device implantation. Careful management of this new acute-to-chronic bridge group will maximize the chances of a successful long-term outcome. The best strategies for management may only unfold by later analysis of larger populations. This article summarizes the current utilization of acute and chronic devices, as well as the small but growing population of acute-to-chronic bridge patients, and suggests what seem today to be sound management principles for them.

Spurious identification of critical intercostal arteries by evoked responses during aortic resection.

A patient with an acute dissection of the thoracic aorta is described. Intraoperative evoked-response evaluation suggested the presence of a critical intercostal vessel in the excluded segment, but no major vessel could be identified. Expedient grafting and reestablishment of flow led to prompt recovery of the evoked response, suggesting that mechanical distortion of the aorta by the distal cross-clamp led to a compromised flow through a subadjacent intercostal artery that was an important source of cord perfusion. Recognition of this possibility is important because it may prevent time-consuming attempts to implant small vessels in the excluded segment, which are not major contributors to spinal cord blood flow.

Dissectors for pulmonary thromboendarterectomy.

Even with circulatory arrest during pulmonary thromboendarterectomy, continued back-bleeding obscures the operative field. This necessitates frequent interruptions of dissection to allow aspiration with a second instrument. Therefore, pulmonary thromboendarterectomy dissectors are described that allow simultaneous suction of blood from the operative field. Before the use of these dissectors, circulatory arrest time was 59 +/- 23 minutes in 124 consecutive patients. In the last 10 consecutive patients using these dissectors, the mean circulatory arrest time has been 52 +/- 22 minutes (p = not significant). It is anticipated that with a larger database, the ability to aspirate blood simultaneously during the dissecting process will result in a significant shortening of circulatory arrest time.