Myocardial Mechanisms Causing Heart Failure Early After Cardiac Transplantation

Subnormothermic preservation in somah: a novel approach for enhanced functional resuscitation of donor hearts for transplant

Organ preservation at 4°C results in temporally irreversible injury to cellular structure and function. This study was designed to evaluate the possibility of storing hearts at ambient temperatures in novel organ preservation solution Somah to prevent damage and preserve optimum function by maintaining cellular energy over the temperature range of storage. Porcine hearts were stored in Celsior at 4°C and Somah at 4°C, 13°C and 21°C for 5 h thereafter reperfused and reanimated in vitro for 3 h. Heart weights, histopathology, ultrastructure and 2-dimensional echocardiography (2D-Echo) assessments showed preservation of structure in Somah groups. Tissue high-energy phosphate levels in Somah groups after storage were significantly greater than the Celsior hearts (p < 0.05) and highest in the 21°C Somah hearts. Upon reperfusion, myocardial O2 consumption and lactate levels quickly achieved steady state in 21°C hearts, but were delayed in Somah 4/13°C groups and severely depressed in the Celsior group. Inotrope and electroconversion requirements were inversely related to storage temperature. In vitro 2D Echo demonstrated a discordantly attenuated function in the Celsior group, moderate functionality in 4°C Somah group and superior reestablishment of performance in the Somah higher temperature groups. Hearts stored in Somah at 21°C were metabolically and functionally superior to any other groups.

Sub-normothermic preservation of donor hearts for transplantation using a novel solution, Somah: a comparative pre-clinical study

BACKGROUND

Hearts preserved ex vivo at extreme hypothermia (4°C) undergo time-dependent irreversible injury. Our studies using a novel solution, Somah, suggest that hearts are viably preserved at 21°C. In this study we evaluate the relative efficacy of Somah for preservation of hearts at 21°C when compared with the clinically used Celsior and University of Wisconsin (UWS) solutions.

METHODS

Porcine hearts arrested by cardioplegia at 21°C using Somah, Celsior or UWS solution were stored in the respective solutions at 21°C (n = 5) for 5 hours and then reperfused ex vivo for functional assessment. We assessed development of edema, cardiac tissue high-energy phosphate (HEP; ATP + creatine phosphate) levels and release of cardiac enzymes. Alterations in left ventricular wall thicknesses and functional parameters were examined by 2-dimensional (2D) echocardiography. Changes in myocardial oxygen consumption (MVO2) and lactate utilization were assessed at reperfusion.

RESULTS

Heart weights were unaltered during 5-hour storage in all groups. After storage, HEP levels were 28.33 ± 5.51, 10.20 ± 2.78 and 5.92 ± 1.46 nmol/liter per milligram protein (p < 0.001) in the Somah, Celsior and UWS group hearts, respectively. Upon reanimation, 2D echocardiography showed edema in the Celsior and UWS hearts; prompt attainment of physiologic function was associated with rapid establishment of aerobic metabolism not requiring stimulatory interventions in the Somah hearts, but not in the Celsior/UWS hearts. Percent fractional area change, ejection fraction and stroke volume were significantly higher (p < 0.001) in Somah hearts than in Celsior and UWS group hearts.

CONCLUSIONS

Increased synthesis of HEP, rapid metabolic switch and optimal function together provide evidence that hearts procured for transplantation are preserved in a superior viable condition at 21°C with Somah, but not with other commonly used clinical preservation solutions.

High prevalence of exercise-induced heart failure with normal ejection fraction in post-heart transplant patients

AIM

Post-heart transplant patients are at increased risk of diastolic dysfunction. The aim of this study was to assess the prevalence of isolated only exercise-induced heart failure with normal ejection fraction (HFNEF) in heart transplant recipients.

METHODS AND RESULTS

To determine pulmonary capillary wedge pressure (PCWP) at rest and during exercise, 81 patients after orthotopic heart transplantation with normal left ventricular ejection fraction (LVEF) underwent exercise right heart catheterization with simultaneous exercise echocardiography. Based on PCWP values, the patients were divided into three groups. Twenty-one patients had no evidence of HFNEF (PCWP at rest < 15 mmHg, maximal PCWP during exercise < 25 mmHg, prevalence 26%). Forty-seven subjects were found to have only exercise-induced HFNEF (PCWP at rest < 15 mmHg, maximal PCWP during exercise ≥ 25 mmHg, prevalence 58%). Thirteen patients had HFNEF already at rest (PCWP ≥ 15 mmHg at rest, prevalence 16%). Of the noninvasive parameters obtained at rest, multivariate regression analysis identified LV mass index adjusted for allograft age to be an independent predictor of exercise-induced HFNEF.

CONCLUSIONS

In heart transplant recipients with normal LVEF, there is a high prevalence of exercise-induced HFNEF. LV mass index adjusted for allograft age is predictive of exercise-induced HFNEF.

Cardiac magnetic resonance T2 mapping in the monitoring and follow-up of acute cardiac transplant rejection: a pilot study

BACKGROUND

Acute rejection is a major factor impacting survival in the first 12 months after cardiac transplantation. Transplant monitoring requires invasive techniques. Cardiac magnetic resonance (CMR), noninvasive testing, has been used in monitoring heart transplants. Prolonged T2 relaxation has been related to transplant edema and possibly rejection. We hypothesize that prolonged T2 reflects transplant rejection and that quantitative T2 mapping will concur with the pathological and clinical findings of acute rejection.

METHODS AND RESULTS

Patients were recruited within the first year after transplantation. Biopsies were graded according to the International Society for Heart Lung Transplant system for cellular rejection with immunohistochemistry for humoral rejection. Rejection was also considered if patients presented with signs and symptoms of hemodynamic compromise without biopsy evidence of rejection who subsequently improved with treatment. Patients underwent a novel single-shot T2-prepared steady-state free precession 4-chamber and 3 short axis sequences and regions of interest were drawn overlying T2 maps by 2 independent blinded reviewers. A total of 74 (68 analyzable) CMRs T2 maps in 53 patients were performed. There were 4 cellular, 2 humoral, and 2 hemodynamic rejection cases. The average T2 relaxation time for grade 0R (n=46) and grade 1R (n=17) was 52.5±2.2 and 53.1±3.3 ms (mean±SD), respectively. The average T2 relaxation for grade 2R (n=3) was 59.6±3.1 ms and 3R (n=1) was 60.3 ms (all P value <0.05 compared with controls). The T2 average in humoral rejection cases (n=2) was 59.2±3.3 ms and the hemodynamic rejection (n=2) was 61.1±1.8 ms (P<0.05 versus controls). The average T2 relaxation time for all-cause rejection versus no rejection is 60.1±2.1 versus 52.8±2.7 ms (P<0.05). All rejection cases were rescanned 2.5 months after treatment and demonstrated T2 normalization with average of 51.4±1.6 ms. No difference was found in ventricular function between nonrejection and rejection patients, except in ventricular mass 107.8±10.3 versus 127.5±10.4 g (P < 0.05).

CONCLUSIONS

Quantitative T2 mapping offers a novel noninvasive tool for transplant monitoring, and these initial findings suggest potential use in characterizing rejections. Given the limited numbers, a larger multi-institution study may help elucidate the benefits of T2 mapping as an adjunctive tool in routine monitoring of cardiac transplants.

Cardiovascular magnetic resonance in the diagnosis of acute heart transplant rejection: a review

BACKGROUND

Screening for organ rejection is a critical component of care for patients who have undergone heart transplantation. Endomyocardial biopsy is the gold standard screening tool, but non-invasive alternatives are needed. Cardiovascular magnetic resonance (CMR) is well suited to provide an alternative to biopsy because of its ability to quantify ventricular function, morphology, and characterize myocardial tissue. CMR is not widely used to screen for heart transplant rejection, despite many trials supporting its use for this indication. This review summarizes the different CMR sequences that can detect heart transplant rejection as well as the strengths and weaknesses of their application.

RESULTS

T2 quantification by spin echo techniques has been criticized for poor reproducibility, but multiple studies show its utility in screening for rejection. Human and animal data estimate that T2 quantification can diagnose rejection with sensitivities and specificities near 90%. There is also a suggestion that T2 quantification can predict rejection episodes in patients with normal endomyocardial biopsies.T1 quantification has also shown association with biopsy proven rejection in a small number of trials. T1 weighted gadolinium early enhancement appeared promising in animal data, but has had conflicting results in human trials. Late gadolinium enhancement in the diagnosis of rejection has not been evaluated.CMR derived measures of ventricular morphology and systolic function have insufficient sensitivity to diagnose mild to moderate rejection. CMR derived diastolic function can demonstrate abnormalities in allografts compared to native human hearts, but its ability to diagnose rejection has not yet been tested.There is promising animal data on the ability of iron oxide contrast agents to illustrate the changes in vascular permeability and macrophage accumulation seen in rejection. Despite good safety data, these contrast agents have not been tested in the human heart transplant population.

CONCLUSION

T2 quantification has demonstrated the best correlation to biopsy proven heart transplant rejection. Further studies evaluating diastolic function, late gadolinium enhancement, and iron oxide contrast agents to diagnose rejection are needed. Future studies should focus on combining multiple CMR measures into a transplant rejection scoring system which would improve sensitivity and possibly reduce, if not eliminate, the need for endomyocardial biopsy.

Cardiac allograft remodeling after heart transplantation is associated with increased graft vasculopathy and mortality

The aim of this study was to assess the patterns, predictors and outcomes of left ventricular remodeling after heart transplantation (HTX). Routine echocardiographic studies were performed and analyzed at 1 week, 1 year and 3-5 years after HTX in 134 recipients. At each study point the total cohort was divided into three subgroups based on determination of left ventricle mass and relative wall thickness: (1) NG-normal geometry (2) CR-concentric remodeling and (3) CH-concentric hypertrophy. Abnormal left ventricular geometry was found as early as 1 week after HTX in 85% of patients. Explosive mode of donor brain death was the most significant determinant of CH (OR 2.9, p = 0.01) at 1 week. CH at 1 week (OR 2.72, p = 0.01), increased body mass index (OR 1.1, p = 0.01) and cytomegalovirus viremia (OR - 4.06, p = 0.02) were predictors of CH at 1 year. CH of the cardiac allograft at 1 year was associated with increased mortality as compared to NG (RR 1.87, p = 0.03). CR (RR 1.73, p = 0.027) and CH (RR 2.04, p = 0.008) of the cardiac allograft at 1 year is associated with increased subsequent graft arteriosclerosis as compared to NG.

Prevalence of different gadolinium enhancement patterns in patients after heart transplantation

OBJECTIVES

Transplant coronary artery disease (TCAD) limits long-term survival after heart transplantation (HTX). We hypothesized that contrast-enhanced magnetic resonance imaging (CE-MRI) detects chronic TCAD-related myocardial infarctions (MIs), even in patients with angiographically classified mild TCAD.

BACKGROUND

Coronary angiography underestimates the TCAD-degree, subsequently missing occluded small coronary arteries and resulting MI. CE-MRI as a noninvasive imaging technique identifies infarct-typical MI and myocardial fibrosis.

METHODS

CE-MRI (gadolinium: 0.2 mmol/kg/bw) was performed in 53 HTX patients on a 1.5-T MRI scanner (Philips, Best, the Netherlands). Infarct-typical CE-MRI areas were classified as: I=<or=25%, II=25% to 50%, III=50% to 75% and IV=>or=75%. Infarct-atypical forms were divided into diffuse, spotted, intramural, and infero-septal. Coronary angiography results were reviewed qualitatively with the TCAD score (TCAD I=mild evidence; II=30% to 75%, III=>or=75% stenosis). Groups were compared with analysis of variance (statistically significant p values<or=0.05).

RESULTS

Infarct-typical CE-MRI was already present in TCAD I+II, increased significantly between groups (I=23%, II=33%, III=84%, p<0.05), and involved only single coronary territories in TCAD I but multiple vessels in TCAD II+III. Infarct-atypical CE-MRI was equally distributed across all TCAD stages (I=50% vs. II=58% vs. III=42%, p=NS) without relation to a coronary territory. Patients with only infarct-atypical CE-MRI were associated with significantly better left ventricular function compared with patients with infarct-typical or combined CE-MRI patterns (ejection fraction=66+/-6% vs. 45+/-16% or 60+/-13%; end-diastolic volume=139+/-32 ml vs. 148+/-27 ml or 164+/-43 ml; end-systolic volume=47+/-15 ml vs. 81+/-27 ml or 69+/-38 ml, p<or=0.05).

CONCLUSIONS

CE-MRI allows identification of silent MI in apparently event-free HTX patients and is able to disclose myocardial fibrosis already in patients with absent or mild angiographic TCAD. CE-MRI might be helpful to establish an earlier TCAD diagnosis and to intensify medical treatment. Future studies are necessary to test prognostic implications associated with CE-MRI patterns.