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Pattern of changes over time in myocardial blood flow and microvascular dilator capacity in patients with normally
S S Kushwaha1, J Narula, N Narula
1Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
Insights
Myocardial blood flow is elevated in the first year after heart transplant but coronary microvascular function normalizes between 1-3 years. After 3 years, microvascular dilator capacity is impaired despite normal blood flow.
Area of Science:
- Cardiology
- Transplantation Medicine
- Cardiovascular Physiology
Background:
- Orthotopic heart transplantation is a life-saving procedure.
- Assessing long-term cardiovascular health post-transplant is crucial.
- Coronary microvascular function may be affected by the transplant process.
Purpose of the Study:
- To investigate changes in myocardial blood flow and coronary microvascular dilator capacity over time after heart transplantation.
- To determine if these parameters normalize or become impaired in the long term.
Main Methods:
- Positron emission tomography (PET) was used to measure myocardial blood flow at rest and during adenosine stress.
- 24 patients were studied between 1 and 86 months post-transplant.
- Patients were grouped by time since transplantation: 1-12 months, 13-34 months, and >= 37 months.
Main Results:
- Basal myocardial blood flow was elevated in the 1-12 month group compared to later groups and normal controls.
- Coronary microvascular function was normal in patients 13-34 months post-transplant.
- After 3 years (>= 37 months), maximal dilator capacity was impaired, despite normal basal blood flow.
Conclusions:
- Early after heart transplant (1-12 months), elevated basal myocardial blood flow occurs without impaired microvascular function.
- Coronary microvascular function tends to normalize between 1 and 3 years post-transplant.
- Long-term (>3 years) heart transplant recipients show impaired microvascular dilator capacity, indicating potential long-term cardiovascular changes.
Abstract:
This study tests the hypothesis that myocardial blood flow and coronary microvascular dilator capacity vary as a function of time after orthotopic heart transplantation in humans. Positron emission tomography measurements of myocardial blood flow were obtained at rest and during adenosine in 24 patients between 1 and 86 months after heart transplantation. At the time of the study all patients were clinically well and had angiographically normal epicardial coronary artery vessels. Patients were divided into 3 groups based on time from transplant to positron emission tomography measurement of myocardial blood flow: group 1 to 12 months (n = 9); group 13 to 34 months (n = 8); and group > or = 37 months (n = 7). Basal myocardial blood flow in group 1 to 12 months (1.86+/-1.01 ml/min/g) exceeded (p <0.05) that of group 13 to 34 months (1.17+/-0.73) and group > or = 37 months (0.98+/-0.34). In group 13 to 34 months, basal myocardial blood flow and maximal dilator capacity (minimal coronary vascular resistance with adenosine 36+/-12 mm Hg/ml/min/g) were comparable to that of normal volunteers (1.01+/-0.20 and 37+/-, respectively). In group > or = 37 months, maximal flow response to adenosine was reduced (2.54+/-1.25 vs 3.16+/-0.52, respectively, p = 0.06). Maximal dilator capacity in group > or = 37 months (60+/-34) was impaired versus group 1 to 12 months (36+/-10) and group 13 to 34 months (36+/-12; both p <0.05) as well as normals (37+/-9, p <0.05). During the first year after cardiac transplantation basal myocardial blood flow is elevated out of proportion to external determinants of myocardial oxygen demand, but maximal dilator capacity of the coronary microcirculation is normal. Between 1 and 3 years both basal myocardial blood flow and microvascular function tend to normalize. After 3 years, although basal myocardial blood flow is normal, microvascular dilator capacity is impaired.