Progress in Cardiac Transplantation

Exercise responses following heart transplantation: 5 year follow-up

Heart transplantation is an established treatment for end stage heart failure. In addition to increased life expectancy, heart transplant recipients report a remarkable improvement in symptoms and functional capacity. Exercise performance following heart transplantation, however, remains impaired even in the absence of exertional symptoms. We have assessed the response to exercise in 47 patients with cardiac failure prior to and then at yearly intervals to five years post transplantation. All patients performed incremental symptom limited exercise tests during which minute ventilation (V'E), oxygen consumption (V'O2) and carbon dioxide production (V'CO2) and heart rate (HR) were measured. Ventilatory response (V'E/V'CO2), anaerobic threshold (V'O2 AT %predicted) and heart rate response (HR/VO2) were calculated. The dead space to tidal volume ratio (VD/VT) and alveolar-arterial oxygen gradient (A-aO2) were computed from transcutaneous monitoring. Despite substantial improvement in subjective functional capacity, heart transplant recipients continue to have limited exercise performance [Maximal V'O2% predicted pre-transplant 41.3 (2.2); 1 year 48.6 (1.7), p <0.001: V'O2 AT% 31.5 (1.1); 1 year 35.6 (1.0); respectively p<0.05]. The maximal oxygen uptake continued to improve at two years post-transplant but, thereafter, there was no further significant change at up to 5 years post transplant [50.9 (1.5)]. At one year post-transplantation peak HR [65.2 (0.9) vs 79.1(1.4)] and the HR/VO2 response [24.0(1.8) vs 79.6(4.2)] were significantly reduced compared to pre-transplant values. The heart rate response remained lower compared to predicted at 5 years post-transplant although there was a significant increase compared to one year post-transplant (32.9 vs 24.0mls/bt). There was a weak but significant relationship between maximal VO2 and peak HR (0.39, p<0.05) and HR/VO2 (r= 0.37, p<0.05) at one year post-transplant. Prior to transplantation the ventilatory response to exercise was elevated [V'E/V'CO2 45.6 (2.5)] and decreased significantly following transplantation [1 yr 34.1 (1.3), respectively p<0.001]. In addition, despite significant improvement in VD/VT after transplantation, it remained higher than normal [Pre VD/VT at maximum exercise 0.35 (0.02); 1 yr 0.31 (0.02); p<0.05]. There was a further fall in the VE/VCO2 and VD/VT at two years post-transplantation with no further change at up to 5 years post transplantation [VE/VCO2 32.0 (1.0); VD/VT 0.29 (0.01)]. Although cardiac output is markedly improved after transplantation, due to chronotropic incompetence associated with denervation, its response remains subnormal and this may explain the residual abnormalities of ventilatory and gas exchange responses to exercise following transplantation.

Induction of Indefinite Survival of Fully Mismatched Cardiac Allografts and Generation of Regulatory Cells by Sarpogrelate Hydrochloride

BACKGROUND

At initiation of the immunologic response, platelets rapidly release chemical mediators such as serotonin (5-hydroxytryptamine, [5-HT]) and cytokines. Sarpogrelate hydrochloride (SH), a selective 5-HT2-receptor antagonist, is used to treat patients with peripheral arterial disease. We investigated the effect of SH on the alloimmune response in a murine cardiac transplantation model.

METHODS

CBA mice underwent transplantation of a C57BL/10 heart and received a short course of SH treatment. Survival of the allograft was recorded. An adoptive transfer study was performed to determine whether regulatory cells were generated. Immunohistochemistry studies of intercellular adhesion molecule 1 (ICAM-1), histological, cell-proliferation, and cytokine assessments were performed.

RESULTS

Untreated CBA mice rejected C57BL/10 cardiac grafts acutely (median survival time [MST], 8 days). In mice given 10 mg/kg of SH, all allografts survived indefinitely (MST, >100 days); these mice also had significantly prolonged survival of donor-specific skin grafts but acute rejection of third-party skin grafts. Secondary CBA recipients given not only whole but also CD4 splenocytes from primary SH-treated CBA recipients with C57BL/10 cardiac allograft had indefinite survival of C57BL/10 hearts (MST, >100 days). SH inhibited upregulation of ICAM-1 on endothelial cells in the allografts. Graft acceptance and hyporesponsiveness were confirmed by the histological and cell-proliferation studies, respectively. Production of interleukin-4 and interleukin-10 from splenocytes of SH-treated transplant recipients increased compared to that from splenocytes of untreated recipients.

CONCLUSION

SH induced indefinite survival of fully allogeneic cardiac allografts, generated CD4 regulatory cells, inhibited ICAM-1 expression in the allografts, and upregulated IL-4 and IL-10 production.

[Incidence and dynamic behavior of spontaneous echocardiographic contrast and atrial thrombi in the transplanted heart]

BACKGROUND

Standard orthotopic heart transplantation produces important anatomic and functional atrial alterations with subsequent thrombotic risk. Therefore the aim of this study was to analyze the prevalence and evolution of spontaneous echocardiography, atrial thrombi and embolic events.

PATIENTS AND METHOD

52 consecutive transplanted patients were analyzed with transesophageal echocardiography and hemodynamic studies performed at 15 days and one year after transplantation.

RESULTS

Spontaneous echocardiography contrast was present in 27 patients (52%). Ten atrial thrombi were observed (19.2%), 9 with spontaneous echocardiography contrast. Six atrial thrombi appeared on day 15 and 4 after one year (with spontaneous echocardiography contrast on the previous study). Using multiple logistic regression analysis left atrial size was the only independent predictor factor for spontaneous echocardiography contrast (OR = 1.27; 95% CI, 1.09-1.54) and was an important predictor factor of atrial thrombi formation (OR = 1.19; 95% CI, 1.04-1.42). Likewise, the main predictor of atrial thrombi was the presence of spontaneous echocardiography contrast (OR = 116; 95% CI, 8.4-999). The hemodynamic pattern did not predict either the presence of spontaneous echocardiography contrast or atrial thrombi. The global incidence of embolic events was 4% less than previously described.

CONCLUSIONS

The incidence of atrial thrombi and spontaneous echocardiographic contrast after standard orthotopic heart transplantation was 19.2% and 52%, respectively. An enlarged atrium and/or spontaneous echocardiography contrast was found to increase the risk of atrial thrombi. Considering the dynamic nature of atrial thrombi formation, periodical transesophageal echocardiography studies are recommended after heart transplantation.

Sudden death and tailored medical therapy in elective candidates for heart transplantation

BACKGROUND

Due to the shortage of donor organs there is a long waiting time for heart transplantation. As a consequence, a high mortality rate on the waiting list diminishes the potential benefit of the procedure. Tailored medical therapy optimized according to the individual patients demands was introduced to select responding HTx candidates for continued management without transplantation. The development of modes of death over time (heart failure, sudden arrhythmic) in this population is unknown.

METHODS

In 434 elective candidates for heart transplantation, submitted to our institution in the years 1984-1997 (50% coronary artery disease, mean age 51.6 +/- 12 years, 86% males) medical therapy was adjusted according to the results of repeated right heart catherizations. Adjuncts to conventional therapy with ACE inhibitors, digitalis and diuretics were amiodarone, beta-blockers, spironolactone, oral anticogulants, molsidomine or nitrates. Only patients not responding to these measures were processed to HTx. Clinical events (death, mode of death, HTx, resuscitation) were noted and analyzed by the Kaplan-Meier method and related to patients characteristics by multivariance analysis.

RESULTS

During the mean follow-up of 2.36 +/- 2.4 years only 113 patients (25%) received a donor heart. One hundred-sixteen patients (26%) died without transplantation. Eighty-three (72%) of the deaths were sudden, 24 (20%) due to progression of heart failure and 9 (8%) due to other reasons. A shift from heart failure to sudden death was observed. Including 8 successful resuscitations due to documented VT/VF, there is a 20% risk of having a major arrhythmic event during the first two years of observation. Long-term (>1 year) medical responders had better hemodynamics at entry. Patients who died suddenly had similar clinical and hemodynamic data at entry than patients who needed an early transplant, but were in a comparable NYHA stage before death than long-term medical responders (2.15 +/- 0.8 vs 1.82 +/- 0.6, NS). Patients dying suddenly had significant more ventricular premature beats (1.6 +/- 2.9%/24 hours vs 1.06 +/- 2.8%/24 hours, p < .01) and complex ventricular arrhythmias (7.3 +/- 2.7/24 hours vs 1.98 +/- 5.6/24 hours, p < .01) than long-term responders. Seventy-five percent of all sudden death occurred during the first 2 observation years.

CONCLUSIONS

The rate of heart failure death in elective candidates for heart transplantation under optimized medical therapy is low when patients are followed closely and transplant can be done rapidly after deterioration is recognized. Sudden death represents the highest risk for most patients. This event occurred predominantly in stable patients under tailored medical therapy without indication for HTx at that time. Our results strongly demand strategies for risk stratification and the investigation of prophylactic measures in this population.

Heart transplantation: a review

This article explores current developments and continuing dilemmas in heart transplantation. Statistical trends such as the increased number of candidates and the increased waiting time are described. Recent developments in implantable ventricular assist device technology and the perioperative use of nitric oxide are also highlighted. In addition, advances in patient management from pretransplant care to long-term follow-up are presented, and alternatives to heart transplantation in current use and for the future are explored.

Maximal exercise testing for the selection of heart transplantation candidates: limitation of peak oxygen consumption

BACKGROUND

Peak exercise oxygen consumption (peak VO2), which is considered an indicator of prognosis in advanced heart failure, is currently being used as a major criterion in many centers for the selection of candidates for heart transplantation. Available studies suggest that patients with peak VO2 < 14 mL/min/kg have improved survival and significant functional benefit with transplantation. Since patients may terminate symptom-limited exercise tests for a variety of reasons, peak VO2 does not necessarily reflect maximal VO2, leading to the possibility of inappropriate selection for transplantation. Therefore, we investigated the proportion of transplant candidates referred for exercise testing considered to have achieved maximal results from studies.

METHODS

Fifty-five patients with heart failure, aged 51+/-9 years, (mean +/- SD) underwent maximum symptom-limited exercise tests on a cycle ergometer utilizing a Jones stage 1 incremental protocol. Tests were considered maximal if subjects achieved peak heart rate (HR) > 85% predicted ("cardiocirculatory limitation") or peak minute ventilation (VE) > 85% predicted ("ventilatory limitation"), and achieved an anaerobic threshold (AT) by noninvasive measures.

RESULTS

Seven tests were terminated because of chest pain, ST-segment abnormalities, or ventricular arrhythmias. Of the remaining 48 studies, the reasons for stopping exercise were leg fatigue in 52%, dyspnea in 16%, and both symptoms in 23%. Sixteen of the 48 patients (33%) had peak VO2 < 14 mL/min/kg. In 8 of these 16 patients, both peak HR and VE were < 85% predicted. Of these eight without apparent HR or ventilatory limitation, none had oxygen desaturation below 90% or fall in BP, two were in atrial fibrillation, and only three had evidence that an AT was achieved.

CONCLUSIONS

Among the patients with peak VO2 < 14 mL/min/kg, there were no objective signs of a cardiocirculatory or a respiratory limitation to exercise in half of them, and 31% did not achieve an AT either, thus not meeting any criteria to support evidence of maximal exercise. Exercise tests without objective evidence of cardiocirculatory or ventilatory limitation may not represent maximal performance. Consequently, peak VO2 may misclassify an appreciable proportion of candidates if the test results are submaximal.

CLINICAL IMPLICATIONS

Clinical exercise studies indicating low peak VO2 must be interpreted in the context of whether a defined objective exercise limitation is evident to avoid biasing the selection of heart transplant candidates.

Long-term cardiopulmonary exercise performance after heart transplantation

Functional capacity is an important outcome variable for heart transplantation, but there are few data that examine the temporal relation and duration of improvement in cardiopulmonary exercise performance after cardiac transplantation. Cardiopulmonary exercise performance was measured in 140 patients who underwent 426 treadmill exercise tests up to 9 years after cardiac transplantation. Univariate and multivariate analyses were used to predict postoperative improvement in functional capacity. Peak oxygen consumption (VO2) significantly improved from 14.2 +/- 3.7 ml/min/kg before to 21.4 +/- 5.6 ml/min/kg at a mean of 11.2 +/- 3.0 months after the transplant procedure (p < 0.001). When peak aerobic capacity was compared with a normal population, peak VO2 was < 50% of predicted in only 9 patients (12%), from 50% to 70% in 34 patients (44%), from 70% to 90% of predicted in 24 patients (31%); 10 patients (13%) were able to achieve > 90% of peak predicted VO2. The improvement seen at 6 months did not significantly change over 9 years of follow-up. Significant preoperative univariate predictors of.1-year postoperative improvement in peak VO2 were preoperative peak VO2 (p = 0.004), age (p < 0.001), ischemic cardiomyopathy (p = 0.007), and preoperative left ventricular ejection fraction (p < 0.001). Peak VO2 at 1 year in patients able to perform the test was not significantly influenced by acute rejection episodes, donor body surface area, or donor/recipient size ratio. In conclusion, exercise capacity is significantly improved within 6 months after cardiac transplantation, and maintained as long as 9 years after procedure. The magnitude of postoperative improvement is inversely related to preoperative peak VO2 and age.