Prediction of human transplantation arteriopathy and coronary events with lung/heart count ratios during intravenous dipyridamole thallium-201 imaging

Transplant allograft vasculopathy: Role of multimodality imaging in surveillance and diagnosis

Cardiac allograft vasculopathy (CAV) is a challenging long-term complication of cardiac transplantation and remains a leading long-term cause of graft failure, re-transplantation, and death. CAV is an inflammatory vasculopathy distinct from traditional atherosclerotic coronary artery disease. Historically, the surveillance and diagnosis of CAV has been dependent on serial invasive coronary angiography with intravascular imaging. Although commonly practiced, angiography is not without significant limitations. Technological advances have provided sophisticated imaging techniques for CAV assessment. It is now possible to assess the vascular lumen, vessel wall characteristics, absolute blood flow, perfusion reserve, myocardial contractile function, and myocardial metabolism and injury in a noninvasive, expeditious manner with little risk. The current article will review key imaging modalities for the surveillance, diagnosis, and prognosis of CAV and discuss coronary physiology of transplanted hearts with emphasis on the clinical implications for provocative and vasodilator stress testing.

Quantitative left ventricular systolic function: From chamber to myocardium

One of the most common indications for obtaining a Doppler echocardiographic study is to ascertain left ventricular (LV) systolic function. There are many ways in which LV function can be determined, but an important assumption that is often overlooked is that every measure that we commonly use is only a surrogate marker of LV function due to the fact that it is impossible to characterize the complex geometric and volumetric function of the ventricle (or myocyte) in a single number. Stated in another way, there is no one perfect measure of LV function. The ejection fraction has emerged as the preeminent method to express LV performance, but although ejection fraction is universally accepted, there are a number of other techniques that can assess LV function and, when taken together, provide a more comprehensive picture both of global and regional LV function. Each of these measures (including ejection fraction) has variable dependence on loading conditions, heart rate, and geometric position that limits its accuracy. Understanding the limitations of each measure will allow the physician to more intelligently understand the true status of the myocardium.

Diagnostic and prognostic value of dobutamine thallium-201 single-photon emission computed tomography after heart transplantation

BACKGROUND

Cardiac allograft vasculopathy (CAV) is a major cause of mortality in heart transplant recipients. We investigated the diagnostic and prognostic value of dobutamine thallium-201 ((201)Tl) single-photon emission computed tomography (SPECT) in heart transplant recipients.

METHODS

We studied 47 patients (age 51.6 +/- 11.7 years, 37 men), at a mean of 34.0 +/- 21.4 months after heart transplant, who received dobutamine (201)Tl SPECT, echocardiography and coronary angiography within 1 month of each other. SPECT was considered abnormal in the presence of reversible or fixed defects in >/=2 segments. Significant CAV was defined as >/=50% luminal stenosis.

RESULTS

Coronary angiograms were normal in 37 patients. Non-significant CAV was detected in 1 patient and significant CAV in 9 patients. The sensitivity, specificity, positive predictive value and negative predictive value of SPECT for the detection of significant angiographic CAV were 89%, 71%, 42% and 96%, respectively. Large reversible perfusion defects (>/=6 segments) always indicated significant CAV. In patients with normal left ventricular function, a lung/heart ratio (LHR) of >/=0.37 during stress was also an independent predictor of significant CAV (odds ratio 15.5, p = 0.04). A higher stress LHR was associated with greater vessel involvement (r = 0.516, p = 0.0002). Patients with impaired left ventricular function also had higher stress and resting LHR. Over 40.3 +/- 21.9 months after the first SPECT, 1 patient developed significant angiographic CAV and another 4 had cardiac death. Large reversible perfusion defect was a significant predictor of cardiac death (p = 0.002).

CONCLUSIONS

Dobutamine (201)Tl SPECT is a useful method for detecting patients with significant CAV and assessing prognosis. It is reasonable and safe to design individualized surveillance intensity of coronary angiography for post-transplant patients on the basis of non-invasive monitoring of dobutamine (201)Tl testing.

Usefulness of Progressive Inhomogeneity of Myocardial Perfusion and Chronotropic Incompetence in Detecting Cardiac Allograft Vasculopathy: Evaluation with Dobutamine Thallium-201 Myocardial SPECT

BACKGROUND

The aim of the study was to investigate the value of longitudinal follow-up of dobutamine thallium-201 single photon emission tomography ((201)Tl SPECT) in the development of significant cardiac allograft vasculopathy (CAV) after orthotopic heart transplantation.

METHODS

We studied 38 cardiac recipients (mean age 57 +/- 12 years) who underwent at least two follow-up dobutamine (201)Tl SPECT since January 1998. All patients had normal coronary angiography and normal left ventricular function initially.

RESULTS

After 2.3 +/- 1.8 years, 12 patients developed significant CAV and there were 4 cardiac deaths (1 died suddenly). Of the 99 scans retrospectively analyzed, patients with significant CAV had elevated values of inhomogeneity score, lung/heart ratio (LHR) at stress and lower left ventricular ejection fraction (all p < 0.05). The higher values of inhomogeneity were significantly correlated with higher stress LHR (r = 0.301, p = 0.021), and lower ejection fraction (r = -0.379, p < 0.001). Progressive inhomogeneity was noted in all heart recipients, and more rapid, although statistically insignificant, in patients who developed significant CAV. Ten patients had inadequate chronotropic response to dobutamine infusion up to 40 mug/kg/min in the follow-up studies. The late onset of chronotropic incompetence was an independent predictor of CAV development (p = 0.03).

CONCLUSIONS

Progressive inhomogeneity of myocardial perfusion, higher lung uptake at stress and chronotropic incompetence assessed by dobutamine (201)Tl myocardial SPECT provide incremental diagnostic value in detecting significant CAV.

Alphavbeta3-targeted detection of arteriopathy in transplanted human coronary arteries: an autoradiographic study

Graft arteriopathy (GA), characterized by diffuse concentric narrowing of coronary arteries, is the major cause of late graft failure in cardiac transplantation. alphavbeta3 Integrin is up-regulated in proliferating vascular cells and may constitute an appropriate target for imaging GA. We used a human/mouse chimeric model of GA, in which segments of human coronary artery were transplanted to severe combined immunodeficiency mice, followed by reconstitution with allogeneic human peripheral blood mononuclear cells (PBMC). This led to vascular remodeling characterized by neointima formation over a period of 4 wk. alphavbeta3 expression in the graft was minimal in animals without PBMC, considerably increased by 2 wk, and decreased toward baseline by 4 wk after PBMC reconstitution. Cell proliferation was maximal at 2 wk, correlating with peak alphavbeta3 expression. RP748, an 111In-labeled alphavbeta3 (active conformation)-targeted radiotracer was injected into groups of 5 recipients at 0, 2, and 4 wk after PBMC reconstitution. Relative uptakes, defined as autoradiographic intensity in the graft/native aortas closely tracked the proliferative process. Specificity of uptake was demonstrated using excess nonlabeled tracer. In conclusion, alphavbeta3 integrin is transiently up-regulated (and activated) in GA and may be targeted by RP748 for detection of the proliferative process in early GA.