Hemodynamic observations after orthotopic transplantation of the canine heart

Modulation of catecholamine responsiveness and beta-adrenergic receptor/adenylyl cyclase pathway during cardiac allograft rejection1 2

BACKGROUND

This study investigated the changes of catecholamine responsiveness and beta-adrenergic receptor/adenylyl cyclase pathway during acute cardiac transplant rejection.

METHODS

Isogeneic Lewis to Lewis and allogeneic Dark Agouti (DA) to Lewis rat cardiac transplants were studied 3 and 5 days after heterotopic intraabdominal transplantation (n=6/group). Myocardial blood flow (MBF), left ventricular systolic pressure (LVSP), maximum pressure development (+dP/dt), and end-diastolic pressure (LVEDP) were measured using an intraventricular balloon. Contractile response to dobutamine (5 microg/kg/min) was also assessed. In separate groups beta-adrenergic receptor density and adenylyl cyclase activity were measured in the grafts, in the recipients' native hearts and in native hearts of sham-operated controls.

RESULTS

During mild to moderate rejection cardiac function indices remained unchanged, although MBF and contractile response to dobutamine decreased significantly (P<0.05) in the allogeneic group. The beta-adrenergic receptor density was significantly (P<0.05) increased in both isografts and allografts and in the native hearts of allografted recipients in comparison to native hearts of controls. Adenylyl cyclase activity showed a significant decrease (P<0.05) only in allografts. During severe rejection, LVSP and +dP/dt decreased and LVEDP increased in allografts in comparison to isografts (P<0.05). This was accompanied by a significant decrease in MBF, contractile response to dobutamine, beta-adrenergic receptor density, and adenylyl cyclase activity (P<0.05).

CONCLUSIONS

Both microcirculatory disturbances and primary alteration in adenylyl cyclase activity may contribute to decreased contractile reserve in mild to moderate cardiac allograft rejection, whereas beta-adrenergic receptor density seems to be also influenced by cardiac denervation. Severe rejection leads to systolic and diastolic heart failure with complex dysregulation of the beta-adrenergic receptor/adenylyl cyclase pathway and impaired microcirculation.

Cardiac function of transplanted rat hearts using a working heart model assessed by magnetic resonance imaging

BACKGROUND

A direct correlation between graft rejection and cardiac contractile function in small-animal models has been difficult to establish because (i) the conventional non-working heart model is greatly different from the orthotopic heart in terms of left ventricular work and (ii) it is difficult to obtain hemodynamic data in situ. We have used magnetic resonance imaging (MRI) techniques to obtain noninvasive, in-situ quantitation of ventricular volume after heterotopic cardiac transplantation.

METHODS

Infra-renal heterotopic cardiac transplantation was performed on rats using syngeneic and allogeneic untreated donors in both working and non-working left heart models. An occluding balloon catheter in the inferior vena cava was used to vary the pre-load to the graft. An arteriovenous fistula was created to raise inferior caval oxygen saturation. Magnetic resonance imaging measurements were carried out at day 3, 4, and 5 post-transplantation. Left ventricle end-diastolic and end-systolic volumes were calculated using a biplanar ellipsoid model.

RESULTS

Stroke volume was significantly increased in the working heart model as compared to the non-working model. At day 4 post-transplant, the diastolic pressure-volume relationship in the allograft group was significantly shifted, indicative of decreased myocardial distensibility, whereas the indices of systolic function were preserved.

CONCLUSIONS

We have developed a heterotopic transplant working rat heart model and have used it to assess in-situ cardiac function by MRI. Sensitive indices of diastolic contractile function can be obtained in this rodent transplant model that correlate well with histologic evidence of early rejection.

Myocardial lactate dehydrogenase and its isoenzyme activities in transplanted human hearts

Lactate dehydrogenase and its heart (H) and muscle (M) subunit activities were studied in right ventricular endomyocardial biopsies from eight transplanted human hearts and compared with five chronically failing hearts and six normal human hearts from brain-dead liver/kidney donors. Of the 17 transplant biopsies (taken 5-95 weeks postoperatively), only two showed histologic signs of chronic rejection: They were excluded from the group analysis. A higher proportion of the M subunit of lactate dehydrogenase (M%) was found in the transplanted and the chronically failing hearts than in the normal hearts, presumably reflecting increased myocardial anaerobic glycolytic stress. In the early post-transplantation period, M% was higher in the transplanted than in the chronically failing hearts. Thereafter M% gradually fell, but had not reached normal levels 1-2 years after transplantation. During that time it was similar to the values in the chronic-failure hearts. In the two biopsies with chronic rejection, M% was nearly twice as high as in contemporaneous biopsies showing mild or no rejection. Monitoring of enzymatic adaptation from endomyocardial biopsies may be of clinical interest.

Hemodynamic profiles at rest and during supine exercise after orthotopic cardiac transplantation

To characterize the spectrum of hemodynamic findings after orthotopic cardiac transplantation, 20 healthy heart transplant recipients with no evidence of cardiac dysfunction by noninvasive testing were studied for 1 to 51 months (mean 15) following surgery. After routine endomyocardial biopsy, right-sided heart pressures and thermodilution cardiac outputs were measured at rest (supine) and during symptom-limited, graded supine exercise. In addition, the effect of respiration on right atrial pressures and waveforms was determined at rest (supine, legs down), and after passive leg raising (volume loading). During exercise, striking increases of pulmonary artery, pulmonary artery wedge and right atrial pressures were seen. The mean pulmonary artery pressure rose 45% during the first stage of exercise (p less than 0.001) and by peak exercise it had increased 87% above resting values. The pulmonary artery wedge pressure increased significantly with passive leg elevation (p less than 0.001) and during the first stage of exercise rose 61% above baseline values. By peak exercise the mean pulmonary artery wedge pressure was more than double the resting value. Similarly, the right atrial mean pressure increased significantly (p less than 0.001) with passive leg elevation and nearly tripled at peak exercise. All values promptly returned to near baseline after exercise. The cardiac output increased 98% during exercise. During early exercise, the rise in cardiac output was mediated primarily by an increase in stroke volume. At rest, there was an abnormal response in right atrial mean pressure during slow deep inspiration in 7 individuals with legs down and in 12 after passive leg elevation (volume loading), including 4 of 10 patients studied beyond 1 year.(ABSTRACT TRUNCATED AT 250 WORDS)

Early and late hemodynamic evaluation after cardiac transplantation: a study of 28 cases

Right heart catheterization was performed in 28 patients 1 week and 6 to 24 months after orthotopic cardiac transplantation. All patients were receiving cyclosporine and methylprednisolone orally. At early catheterization, right heart pressures as well as pulmonary capillary wedge pressure still remained above normal values in the majority of patients. Systemic arterial hypertension was already present in 29% of the patients and cardiac index was usually in the normal range, without any inotropic support. Results of late catheterization showed continuing improvement with return of right heart pressures to normal values in most but not all patients. Systemic arterial hypertension was noted in nearly all patients and is likely to be the result of hypervolemia secondary to cyclosporine-induced sodium retention. The increase in cardiac index, which was above normal values in 39% of the patients, was also consistent with hypervolemia in the setting of cardiac denervation. Thus, cardiac function at rest is satisfactory at short- and long-term assessment after cardiac transplantation, but the development and persistence of systemic arterial hypertension associated with cyclosporine use are a matter of concern in such patients.

Time course of resolution of pulmonary hypertension and right ventricular remodeling after orthotopic cardiac transplantation

Most patients with severe congestive heart failure have secondary pulmonary hypertension (PHT). Elevation of pulmonary vascular resistance (PVR) to greater than 480 dynes.sec.cm-5 (6 Wood units) is currently the principle hemodynamic contraindication to orthotopic cardiac transplantation. We performed serial two-dimensional Doppler echocardiographic examinations and right heart catheterizations in 24 recipients (21 men, 14-58 years old) of orthotopic cardiac transplants to determine the time course of resolution of PHT and the concomitant remodeling of the donor right ventricle. Right and left heart filling pressures declined in parallel and reached the upper normal range at 2 weeks after the transplant procedure and remained unchanged at 1 year follow-up. Mean pulmonary arterial pressure (mm Hg) decreased from 38 +/- 9 preoperatively to 22 +/- 5 at 2 weeks and was 19 +/- 5 at 1 year after the transplantation procedure. At 1 year after surgery, PVR had decreased from 202 +/- 89 dynes.sec.cm-5 preoperatively to 99 +/- 36 dynes.sec.cm-5 (p less than .001), while cardiac output increased from 3.7 +/- 1.2 to 6.3 +/- 1.5 liters/min (p less than .001). Echocardiographic analysis showed that transplant recipients had an enlarged right ventricle on day 1 after surgery, and a volume overload contraction pattern and tricuspid regurgitation was present in the majority. This increase in right ventricular size was maintained at 1 year follow-up while the incidence of tricuspid regurgitation decreased. We conclude that there is rapid resolution of moderately elevated pulmonary arterial pressures after cardiac transplantation.(ABSTRACT TRUNCATED AT 250 WORDS)

Patent foramen ovale complicating heart transplantation. A window on posttransplantation hemodynamics

A patient developed refractory hypoxemia and right-to-left shunt across a patent foramen ovale after orthotopic cardiac transplantation. The right-to-left shunt was produced by volume overload of the donor right ventricle during the period of early postoperative myocardial depression and resolved with preload reduction and diuresis. Increased preload of the right heart needs to be considered in the early postoperative management after cardiac transplantation. The foramen ovale of the donor and recipient should be evaluated at operation by visual and probe examination and securely closed if either is patent, since this pattern of hemodynamic changes is common following cardiac transplantation.

Early mechanical function in the heterotopic heart transplant

The characteristics of left ventricular (LV) function in the nonimmunosuppressed heterotopic heart transplant (TX) with less than 3 hr of cold preservation, were studied in 12 awake chronically instrumented dogs prior to TX (control), 1-12 hr post TX (P1), 12-24 hr post TX (P2), and 24-48 hr post TX (P3). Micromanometers measured LV transmural pressure and ultrasonic transducers measured ventricular dimension in order to allow calculations of myocardial mechanical properties. Immediately after transplant (P1) there was significant (P less than 0.05) depression noted in both diastolic function and systolic function (peak LV pressure, 137 +/- 5 vs 80 +/- 10 mm Hg; dp/dtmax, 2642 +/- 170 vs 1038 +/- 98 mm Hg/sec; maximum velocity of minor axis shortening, 4.46 +/- 0.50 vs 2.41 +/- 0.56; and Emax, 6.5 +/- 1.2 vs 2.0 +/- 1.4 mm Hg/ml). However, the contractility reserve (studied in six dogs) as estimated by postextrasystolic potentiation ratio was maintained (1.41 +/- 0.07 vs 1.37 +/- 0.15), suggesting reversibility of the depressed function. Over the next 2 days the diastolic function and the systolic function (at P3: 109 +/- 6 mm Hg, 1842 +/- 450 mm Hg/sec, 5.54 +/- 0.77 cm/sec, and 4.5 +/- 1.3 mm Hg/ml, respectively) gradually improved toward control. Microscopic examination of the autopsied hearts did not show significant evidence of rejection. Thus, the early depression of function in the heart TX appeared to be the result of ischemia from preservation and surgical trauma.(ABSTRACT TRUNCATED AT 250 WORDS)

Results of radionuclide assessment of cardiac function following transplantation of the heart

Radionuclide assessment of ejection fraction was determined early and late postoperatively following cardiac transplantation in 16 patients. In 11 patients, ejection fraction was determined within 48 hours of an endocardial biopsy. There was no relationship between the severity of histologically evident rejection and the ejection fraction (Pearson correlation coefficient [r] = -0.11; p = 0.47). In 2 patients, severe graft fibrosis developed with consequent diminution in ejection fraction. There was no relationship between severity and duration of rejection or the amount of immunosuppression required to treat acute rejection and the development of graft fibrosis. The mean resting ejection fraction in 7 patients in follow-up ranging from 6 to 21 months after transplantation was 0.59 +/- 0.06 (standard deviation), and the mean exercise ejection fraction in 6 of these patients was 0.72 +/- 0.08. Radionuclide-determined ejection fraction is not predictive of rejection early after operation. During short-term late follow-up, systolic left ventricular function at rest and exercise has been retained at normal levels.

Hemodynamic observations one and two years after cardiac transplantation in man

Cardiac catheterization studies were performed in eight patients 1 year after cardiac transplantation and in two of these again at 2 years. Intracardiac pressures at rest were normal in all patients, both 1 and 2 years postoperatively. Average cardiac index at rest at 1 year was 2.3 liters/min/m 2 and average heart rate was 90 beats/min. Responses to amyl nitrite, atropine, and tyramine failed to demonstrate efferent autonomic reinnervation of the donor hearts. Findings associated with a 10-min period of submaximal supine bicycle exercise 1 year after transplantation included: (1) a gradual rise in heart rate throughout most of the exercise period; (2) prompt elevation of left ventricular end-diastolic pressure by an average increment of 10 mm Hg, followed by a decrease during late exercise in some patients; (3) a progressive increase in LV systolic pressure throughout the first half of the exercise period; (4) a continuously positive change in LV rate of pressure change (dp/dt) throughout exercise; (5) an average 44% increase in stroke volume; and (6) an average 92% increase in cardiac output. The slope of the regression of cardiac output on oxygen uptake during exercise was within the range of normal. Cardiac output, however, was lower than normal both at rest and during exercise, and the arteriovenous oxygen diflerence was accordingly widened.

In one patient studied 1 and 2 years after transplantation, hemodynamic findings were comparable on both occasions. In the other, however, the cardiac output response to exercise was distinctly diminished at 2 years as compared to 1 year, due almost entirely to failure of the stroke volume to increase. Coronary arteriography in this recipient revealed evidence of occlusive coronary disease compatible with graft atherosclerosis.

These studies demonstrate the sustained capacity of the transplanted human heart to support normal physical activity late in the postoperative period. Although utilizing atypical adaptive mechanisms characteristic of the denervated heart, the transplanted heart responds in a directionally appropriate manner to the metabolic demands of exercise.