The GRAFT Study: Evaluation of Graft Function, Rejection and Cardiac Allograft Vasculopathy in First Heart Transplant Recipients.

Objective

1. To assess the relationship between myocardial perfusion, coronary anatomy and longitudinal myocardial function in heart transplanted (HTX) patients with and without coronary allograft vasculopathy (CAV).
2. Evaluation of systolic and diastolic capacity during exercise in HTX patients with and without CAV.
3. Evaluation of non-invasive methods for CAV diagnosis.
4. To assess left ventricular (LV) and right ventricular (RV) function in the acute phase and during follow-up (5 times) the first year after transplantation and furthermore to compare advanced echocardiographic evaluation of graft function with cardiac magnetic resonance imaging (CMRI), right heart catheterization, and positron emission tomography (PET).
5. Finally, to evaluate the impact of acute and repetitive rejection on myocardial graft function measured by standard 2D echocardiography and advanced echocardiography with analysis of longitudinal myocardial function.

Hypothesis

1. Timing of development and degree of CAV can be measured non-invasively combining myocardial longitudinal deformation measurement by advanced echocardiography and coronary flow velocity reserve (CFVR) by echocardiography and PET. This combination of methods can detect CAV before it is angiographic visual and gives supplementary information of the impact on myocardial graft function. This setup might be more appropriate in evaluation of the myocardial graft function and CAV than standard echocardiography and coronary angiography (CAG). Optical coherence tomography (OCT) can detect CAV in early phases and gives supplementary characterization of the plaque.
2. Modern non-invasive methods (longitudinal deformation, 3D echocardiography, CMRI and PET) can be used in RV and LV myocardial function assessment and represents more valid markers of the function than standard echocardiography in HTX patients.
3. During exercise patients with CAV will show impaired longitudinal myocardial deformation and restrictive filling with significant increasing LV and RV filling pressures.
4. Myocardial longitudinal deformation is a better marker of acute rejections than conventional ejection fraction (EF). After an episode of severe acute rejection the graft function will improve, but instances of repetitive rejections will lead to impaired longitudinal systolic function with preserved LV EF.

Background Mean survival after HTX at our center is 15.6 years. Complications remain frequent and serious. In the first postoperative year the main causes of death are graft failure, rejections and infection. At long term follow up main causes of death are CAV and malignancies.

CAV is characterized by diffuse concentric intima thickening involving both epicardial vessels and the coronary microvascular system. After 10 years more than 50% of patients shows angiographic signs of CAV.

In our clinical approach HTX-patients are followed with annual CAG and standard echocardiography with estimation of LV systolic function by EF. EF is often within normal range even though CAV lesions are evident by CAG, suggesting that LV EF is an inappropriate parameter for detecting impaired myocardial function in CAV. Symptoms of graft dysfunction first present themself with severe CAV. Studies have shown that CAG often misses CAV in early phases. OCT is a novel intravascular imaging modality with excellent spatial resolution. It has been used in a few small cross sectional studies with HTX patients and seems like a promising tool for detecting CAV and gives supplementary characterization of the plaque.

In various cardiac diseases it is well known that ischemia and fibrosis often affect the endocardial longitudinal oriented layers leading to abnormal systolic function of both LV and RV. Longitudinal deformation by tissue Doppler and strain analysis has shown to be better markers for systolic function in HTX patients compared to standard measurements such as LV EF. Longitudinal LV systolic function is dependent of endocardial perfusion. CFVR represents the capacity of the coronary circulation to dilate, due to increased myocardial metabolic demands and is expressed by the difference between the hyperaemic and resting flow. CFVR has been shown to correlate with the degree of decreased longitudinal deformation in myocardial infarction. CFVR measurements in HTX patients with color Doppler echocardiography and PET scan have shown a significant correlation to CAV.

RV failure is an early, potentially fatal, complication to HTX. Standard echocardiographic measurement does not seem to reflect the overall RV systolic performance and clinical status of the patient. Prior studies have found impaired RV function after HTX, but most studies of RV function were not performed with simultaneous right heart catheterization or assessment of RV EF by CMRI (golden standard). Overall the function and change over time of RV have not been fully studied using modern echocardiographic techniques or assessment by CMRI.

Acute rejection is an inflammatory response most frequently in the first 6 months after HTX. Two thirds experience rejection episodes within first year.

Rejections are often asymptomatic and associated with poor outcome, including development of CAV. Patients are followed with routine biopsies (gold standard), but these are expensive, time consuming and inconvenient for the patient. The role of conventional echocardiography has not yet found a significant role in the diagnostics of acute rejections and furthermore how repeated rejections influence on graft function is not well described.

Study objective, design and methods Study 1 Design: A cross sectional study consisting of 50 stabile HTX patients. These will be selected with 25 patients with no or light CAV and 25 patients with moderate or severe CAV. 25 matched controls.

Methods:

Severity of CAV will be evaluated by:

• CAG supplied with OCT.
• CFVR measurement by echocardiography with adenosine induced hyperemia.
• CFVR measurement with H215O-PET.

Graft function will be evaluated by:

• 2D and 3D echocardiography (including longitudinal deformation and tissue Doppler)
• Diastolic (and systolic) stress test: Bicycle exercise with simultaneously echocardiography and right heart catheterization.

Blood samples are taken for analysis of myocardial fibrosis markers, CRP, TNT and NT-proBNP.

Study 2 Design: A prospective cohort study with 20 newly transplanted patients over a period of 12 months.

Methods: LV and RV function shall be measured by:

• 2D and 3D echocardiography (including longitudinal deformation, tissue Doppler, CFVR, LV and RV EF),
• CMRI for LV and RV EF, strain and mass
• Right heart catheterization
• H215O-PET at baseline and after 3 month in the assessment of RV function
• Coronary angiography after 3 and 12 month will be supplied with OCT for early signs of CAV development.

Biopsies are performed according to routine protocol after transplantation. Blood samples for analysis of myocardial fibrosis markers, CRP, TNT and NT-proBNP.

Study 3 Design: Prospective examination of correlation between graft function, CAV and rejection. Information of former episodes of acute rejection is collected retrospective. Study objectives are all living HTX patients (approx. 200) in the period of 2011-2013.

Methods: Advanced echocardiography (including longitudinal deformation and tissue Doppler), biopsies (rejection evaluation) and CAG (CAV evaluation).

Publication Plan:

Positive as well as negative result from study 1-3 will be published. We aim at publishing study 1-3 in peer review international, scientific journals. Study 3 is expected to be published in 2014 and study 1 and 2 in 2016. MD, PhD student Tor Skibsted Clemmensen will draft the manuscripts and be 1st author hereof.

Ethical considerations Adenosine, used for CFVR measurement and PET, often causes mild facial flushing, chest discomfort and dyspnoea. After suspended infusion symptoms last less than one minute since half time is below 10 seconds.

Right heart catheterisation is part of the standard protocol after HTX. Only patients in study 1 might be subjected to more catheterisations than normally. Complications are rare with experienced operators.

The radiation dose of H215O-PET is 2-2,5 mSv, approximately the same as one year background radiation. Patients in study 1 will be subjected to one examination, patients in study 2 two examinations.

No additional CAG are made in the studies. OCT examination is considered very safe with a risk of complication <0,5%.

The investigators are convinced that the possible risks are outweighed by the expected benefits from this study and no study-related examinations will be conducted until informed consent form has been signed.

Regional Scientific Ethical Committee of Central Denmark has approve the studies.