Due in part, to reduced transplant volume and enrollment has been difficult.

1. Early initiation of sirolimus will prevent or delay the development of intimal thickening and subsequent graft failure.
2. Treatment guided by the development of cardiac allograft vasculopathy (CAV) on intravascular ultrasound (IVUS) will be more effective in delaying progression of CAV compared to treatment guided by angiography.
3. Prevention of the development and progression of intimal thickness on IVUS will prevent the development of heart failure, graft dysfunction, and cardiovascular death related to CAV.
4. Small artery elasticity predicts progression of cardiac allograft vasculopathy and is modified by sirolimus
5. Patients who have no progression of CAV will have favorable improvement in biomarkers and endothelial cells compared to patients who have progression of CAV

Proliferation signal inhibitors (PSIs), sirolimus and everolimus, have been demonstrated to be effective immunosuppressants and delay the progression of cardiac allograft vasculopathy. To date, there are no prospective studies designed to evaluate the potential use of PSIs as a primary immunosuppressant in the prevention of cardiac allograft vasculopathy. The goals of our study are to compare primary vs. secondary preventive strategies and to evaluate the role of intravascular ultrasound compared to coronary angiogram in diagnosing CAV and preventing CAV-related events. The specific aims of the study are:

1. To evaluate the effect of primary vs. secondary initiation of sirolimus on the development of significant coronary artery (> 70% angiographic stenosis, Mean intimal thickness (MIT) 0.5mm or greater, IVUS calculated coronary cross sectional area of < 4mm2 / <6mm2 for mid LAD/Left Maim (LM), < 0.75 fractional flow reserve (FFR) lesion associated with a positive stress test), change in global left ventricle (LV) function, incidence of rejection episodes, and hospitalizations at 1, 2, 3, and 4 years.
2. To determine the effect of IVUS-guided initiation of sirolimus on short-term and long-term outcomes vs. angiogram-guided initiation of sirolimus
3. To determine whether prevention of progression of CAV diagnosed by IVUS prevents graft dysfunction or death related to CAV or heart failure.
4. To assess the correlation between peripheral small artery elasticity, peripheral biomarkers, and endothelial cells, and development of cardiac allograft vasculopathy in order to develop a strategy for determining risk of progression and monitoring treatment.

The study has a prospective and a retrospective arm

Prospective Arm Design: This is a prospective, randomized, partially-blinded pilot study. Randomization for the study will be done in 2 stages.

The first stage of randomization will randomize subjects to either the early or late initiation of sirolimus. At this stage of the randomization, subject will have a 30% chance of being in group 1 (early-initiation of sirolimus), and a 70% chance of being in group 2 (diagnostic-guided sirolimus group).

The second stage randomization will be done only on subjects in group 2 (diagnostic-guided sirolimus group) at the time of their first annual heart transplant review. At the time of their annual heart transplant review, subjects in group 2 will have a 50% chance of being in group 2A (CAV diagnosed by angiogram), and a 50% chance of being in group 2B (CAV diagnosed by intravascular ultrasound).

Group 1: Initiate sirolimus at 6 months after transplant

Group 2A: Initiate sirolimus after development of angiographic stenosis of >70% in a major epicardial vessel or >50% in the left main artery

Group 2B: Initiate sirolimus after development of maximal intimal thickness of 0.5 mm on intravascular ultrasound

Retrospective Arm

The main objective of this retrospective study is to compare a treatment strategy based on the diagnosis of CAV by intravascular ultrasound to a strategy guided by angiogram.

Design: This is a randomized, partially-blinded pilot study. Subjects will be randomized 1:1 to one of two groups. At the time of the randomization, the subject will have a 50% chance of being in group 1 (initiation of sirolimus when CAV is diagnosed by angiogram) and a 50% chance of being in group 2. (Initiation of sirolimus when CAV is diagnosed by IVUS)

Primary Endpoints for Prospective and Retrospective Arms

1. Change in maximal intimal thickness at 1, 2, 3 and 4 years
2. Combination of significant coronary artery disease (as described above), death, major rejection episodes, and decrease in global ejection function of more than 10% from baseline at 3 and 4years.

Secondary endpoints for Prospective and Retrospective Arms

1. Mean MIT at 1, 2, 3, and 4 years
2. Percent atheroma volume at 1,2,3 and 4 years
3. Death from CAV, death from any cause, myocardial infarction, need for PCI, number of hospitalizations, infection rates, evidence of restrictive physiology, arrhythmic event related to CAV or pulmonary hypertension at 4 years.
4. Change in small artery elasticity at 1, 2, 3, and 4 years
5. Change in endothelial progenitor cell count at 1 and 2 years
6. Change in biomarkers (see table) at 1 and 2 years

Inclusion Criteria

For Prospective Arm:

• 18 years or older
• Successful orthotropic heart transplant within 6 months of enrollment

Inclusion Criteria

For Retrospective Arm:

• 18 years or older
• Successful orthotropic heart transplant within 6 months to 3 years of enrolment
• Less than moderate CAV by angiogram or IVUS

Exclusion Criteria

For Prospective Arm:

• Greater than minimal baseline coronary disease
• Chronic kidney disease with creatinine >2mg/dl
• Baseline (1 month) ejection fraction < 50%
• IV contrast allergy
• Rejection within 3 months of enrollment
• Sensitivity to sirolimus or its derivatives
• Prior sirolimus use

Exclusion Criteria

For Retrospective Arm:

• Significant baseline (one month) coronary artery disease (>50% in one or more vessels by angiogram or MIT >0.5 by IVUS)
• Chronic kidney disease with creatinine >2mg/dl
• Baseline (1 month) ejection fraction < 50%
• IV contrast allergy
• Rejection within 3 months prior to enrollment
• Sensitivity to sirolimus or its derivatives
• Prior sirolimus use