Inhomogeneity of myocardial perfusion in heart transplant recipients: evaluation with dobutamine thallium-201 SPECT

Negative Predictive Value and Prognostic Associations of Rb-82 PET/CT with Myocardial Blood Flow in CAV

BACKGROUND

Invasive coronary angiography (ICA) is the traditional screening modality for cardiac allograft vasculopathy (CAV). Positron emission tomography/computed tomography (PET/CT) scan with myocardial blood flow (MBF) quantification has emerged as a potential noninvasive alternative.

OBJECTIVES

The aim of the study was to validate the diagnostic and prognostic value of a previously published algorithm for diagnosing CAV via PET/CT scans with MBF in a larger population. The study also sought to assess the downstream use of ICA when using PET/CT scanning as a screening modality.

METHODS

Patients with heart transplantation without prior revascularization who underwent PET/CT scans with MBF were identified retrospectively. The accuracy of the algorithm was assessed in patients who underwent PET/CT scanning within 1 year of ICA. The prognostic value was assessed via a composite outcome of heart failure hospitalization, myocardial infarction, retransplantation, and all-cause mortality.

RESULTS

A total of 88 patients for the diagnostic portion and 401 patients for the prognostic portion were included. PET CAV 0 had high negative predictive value for moderate to severe CAV (97%) and PET CAV 2/3 had a high positive predictive value for moderate to severe CAV (68%) by ICA. The cohort was followed for a median of 1.2 (IQR: 1.0-1.8) years with 46 patients having an adverse event. The annualized event rates were 6.9%, 9.3%, and 30.8% for PET CAV 0, 1, and 2/3, respectively (P < 0.001).

CONCLUSIONS

An algorithm using PET/CT scanning with MBF demonstrates high a negative predictive value for CAV. PET CAV 2/3 is associated with a higher risk of adverse events and need for revascularization. PET/CT scanning with MBF is a reasonable alternative to ICA for screening for CAV.

Noninvasive monitoring of acute and chronic rejection in heart transplantation

PURPOSE OF REVIEW

Recent years have seen advances in the early detection of cardiac graft rejection.

RECENT FINDINGS

We review the possibilities offered by tissue Doppler imaging and speckle tracking echocardiography, cardiac magnetic resonance, cardiac computed tomography, single positron emission tomography, gene expression profiling, and quantitation of donor-derived cell-free DNA, and microRNAs.

SUMMARY

Noninvasive monitoring of acute and chronic rejection after cardiac transplantation is an unmet need and remains a challenge. Imaging techniques and peripheral blood biomarkers are the most commonly used approaches, and in recent years there has been great progress. Gene expression profiling seems to be useful for ruling out the presence of a moderate to severe acute cellular rejection in stable, low-risk patients. Newer monitoring tools, like donor-derived cell-free DNA or microRNA, seem to be promising for individualizing immunosuppressive therapies and better understanding the mechanisms of rejection.

Inhomogeneous myocardial stress perfusion in SPECT studies predicts future allograft dysfunction in heart transplant recipients

BACKGROUND

Myocardial perfusion gated single photon emission computed tomography (SPECT) can be used for non-invasive detection of coronary artery stenosis and cardiac allograft vasculopathy (CAV), which is a crucial factor for the long-term survival of heart transplant (HTx) recipients. A frequently observed finding in myocardial perfusion imaging of patients after HTx is inhomogeneous myocardial perfusion. This finding is not associated with epicardial CAV, but its prognostic relevance is unclear so far. We therefore evaluated the prognosis of patients with homogeneous versus inhomogeneous myocardial stress perfusion.

METHODS

One hundred four HTx patients (mean 3.6 ± 2.9 years after HTx) without significant stress-induced ischemia (summed stress score ≤3) in gated SPECT and without CAV were included. Myocardial stress perfusion was visually assessed as homogeneous, moderately, or severely inhomogeneous. The mean follow-up period after SPECT was 9.4 ± 3.1 years. End points were the diagnosis of CAV, major cardiac events (MACE) or death, and the development of allograft dysfunction (left ventricular ejection fraction, LVEF <45 %).

RESULTS

Of all HTx patients, 24 % enrolled in this study (n = 25) presented with inhomogeneous myocardial perfusion. Compared to the patients with homogeneous perfusion, these patients were at higher risk for developing allograft dysfunction (multivariate hazard ratio, HR = 5.59). As to the development of CAV, the occurrence of MACE, or death, no statistical differences were observed between patients with homogenous and inhomogeneous perfusion. There was no correlation between myocardial perfusion pattern and prior cardiac allograft rejections.

CONCLUSIONS

Inhomogeneous myocardial stress perfusion in SPECT studies predicts a higher risk for future development of allograft dysfunction in HTx patients (LVEF <45 %) but is not associated with future CAV, MACE, or overall survival.

PET assessment of myocardial perfusion reserve inversely correlates with intravascular ultrasound findings in angiographically normal cardiac transplant recipients

Cardiac allograft vasculopathy (CAV) is the major determinant of long-term survival after heart transplantation. We aimed to evaluate the efficacy of PET as a noninvasive way to assess the early stages of CAV.

METHODS

Twenty-seven consecutive patients (20 men and 7 women; mean age +/- SD, 46 +/- 12 y) who had normal results on coronary angiography and normal left ventricular systolic function (ejection fraction >or= 60%) were enrolled at 2.5 +/- 2.1 y after transplantation. Myocardial blood flow (MBF) was assessed using dynamic (13)N-ammonia PET at rest and during adenosine-induced hyperemia, and myocardial perfusion reserve (MPR) was calculated as the ratio of hyperemic MBF to resting MBF. Regional (13)N-ammonia PET was assessed using a 5-point scoring system. The intravascular ultrasound (IVUS) measurements for the extent of intimal hyperplasia, including plaque volume index (calculated as [total plaque volume/total vessel volume] x 100%) and maximum area of stenosis, were compared with MPR by linear regression analysis.

RESULTS

In 27 angiographically normal cardiac transplant recipients, MBF at rest and during adenosine stress and MPR of the left anterior descending artery distribution correlated strongly with the other 2 coronary artery distribution territories (r >or= 0.97, P < 0.0001). Summed stress score and summed difference score showed a moderate inverse correlation with MPR (r = -0.41 and -0.49, respectively; P < 0.05) but not with IVUS measurements. MPR correlated inversely with plaque volume index (r = -0.40, P < 0.05) but not with maximal luminal stenosis as assessed by IVUS. In addition, MPR and IVUS measurements gradually inversely changed after heart transplantation (all P < 0.05).

CONCLUSION

This study confirms that CAV is a progressive process, diffusely involving the epicardial and microvascular coronary system. Plaque burden as determined by IVUS agrees well with MPR as assessed by PET in recipients with normal coronary angiography results. This finding suggests that dynamic (13)N-ammonia PET is clinically feasible for the early detection of CAV and can be used as a reliable marker of disease progression.

Dobutamine myocardial scintigraphy for the prediction of cardiac events after heart transplantation

BACKGROUND

The long-term outcome after heart transplantation (HTx) is essentially influenced by the occurrence and extent of cardiac allograft vasculopathy (CAV). Single photon emission computed tomography-myocardial perfusion imaging (SPECT-MPI) has been shown to be a useful and cost-effective non-invasive method in patients with known or suspected coronary artery disease, but its role in detecting CAV remains unclear.

AIM

To evaluate the accuracy and predictive value of dobutamine MPI in patients after HTx during a 12-month follow-up.

METHODS

Seventy-seven patients (60 males, 17 females) underwent a total of 216 dobutamine MPI examinations over a period of 5 years. Examinations were obtained an average of 89+/-42 months after orthotopic HTx according to a 1-day protocol using 99mTc-methoxyisobutylisonitrile (99mTc-MIBI) with and without attenuation correction. For the present study, findings from 77 MPI examinations (one MPI examination per patient) were analysed visually and semiquantitatively using a 20-segment model. Summed stress scores (SSS) and summed rest scores (SRS) were calculated and receiver operating characteristic (ROC) analysis was performed to detect optimum threshold values. Patients were followed up for 12 months and cardiac events were registered.

RESULTS

Cardiac events were observed in 10 of the 77 patients. Good interobserver agreement was found for global visual and SRS-/SSS-based analysis (kappa=0.74 and 0.66, respectively). SSS was superior to SRS in the detection of cardiac events. ROC analysis showed an optimized SSS threshold value of three. For predicting a cardiac event during the 12-month follow-up, global visual and semiquantitative analysis reached sensitivities of 90% and 90%, specificities of 72% and 88%, accuracies of 74% and 87%, positive predictive values of 32% and 53% and negative predictive values of 98% and 98%, respectively. The sensitivity, specificity, accuracy and positive and negative predictive values for MPI to detect clinically relevant coronary artery stenoses (> or =50%) at conventional coronary angiography were 83%, 87%, 86%, 56% and 96%, respectively.

CONCLUSIONS

Non-invasive dobutamine MPI reliably identifies patients at risk for subsequent cardiac events in cases of CAV, with a high negative predictive value of 98% and an accuracy of 87%.

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.

Tl-201 myocardial SPECT in differentiation of ischemic from nonischemic dilated cardiomyopathy in patients with left ventricular dysfunction

BACKGROUND

The differentiation between ischemic and nonischemic cardiomyopathy by noninvasive modalities is of clinical importance. Whether thallium 201 single photon emission computed tomography (SPECT) could accurately distinguish the two groups remains unclear.

METHODS AND RESULTS

Twenty-nine patients with chronic heart failure (left ventricular ejection fraction < or =40%), including fourteen patients with ischemic cardiomyopathy and fifteen patients with nonischemic dilated cardiomyopathy, underwent Tl-201 SPECT. The stress protocols included treadmill exercise in 8 patients, dipyridamole in 6 patients, and dobutamine infusion in 15 patients. Myocardial SPECT was interpreted with the use of a 17-segment model and 0- to 4-point scale system. Patients with ischemic cardiomyopathy had higher summed stress defect scores (27.9 +/- 9.4 vs 20.6 +/- 8.9, P =.04), more fixed defect segments (5.9 +/- 2.9 vs 3.8 +/- 2.9, P =.05), and more moderate or severe perfusion defect segments on stress scan (7.2 +/- 2.0 vs 4.5 +/- 2.6, P =.004) than did those with nonischemic dilated cardiomyopathy. However, considerable overlap of the scan patterns between the two groups existed. Moderate or severe perfusion defects on stress scan in at least 7 segments were noted in 71% of patients (10/14) with ischemic cardiomyopathy, as compared with 20% of patients (3/15) with nonischemic cardiomyopathy (P =.016).

CONCLUSIONS

Assessment of Tl-201 myocardial SPECT yields only modest value to distinguish nonischemic dilated cardiomyopathy from ischemic cardiomyopathy in patients with chronic heart failure. This technique cannot clearly differentiate individual patients.