Utility of cardiac magnetic resonance imaging for the diagnosis of heart transplant rejection

Role of Radiology in Assessment of Postoperative Complications of Heart Transplantation

Heart transplantation is a pivotal treatment of end-stage heart failure, and recent advancements have extended median posttransplant life expectancy. However, despite the progress in surgical techniques and medical treatment, heart transplant patients still face complications such as rejection, infections, and drug toxicity. CT is a reliable tool for detecting most of these complications, whereas MR imaging is particularly adept at identifying pericardial pathologies and signs of rejection. Awareness of these nuances by radiologists, cardiologists, and surgeons is desired to optimize care, reduce morbidities, and enhance survival.

Appropriate use criteria for cardiovascular magnetic resonance imaging (CMR): SIC-SIRM position paper part 1 (ischemic and congenital heart diseases, cardio-oncology, cardiac masses and heart transplant)

Cardiac magnetic resonance (CMR) has emerged as new mainstream technique for the evaluation of patients with cardiac diseases, providing unique information to support clinical decision-making. This document has been developed by a joined group of experts of the Italian Society of Cardiology and Italian society of Radiology and aims to produce an updated consensus statement about the current state of technology and clinical applications of CMR. The writing committee consisted of members and experts of both societies who worked jointly to develop a more integrated approach in the field of cardiac radiology. Part 1 of the document will cover ischemic heart disease, congenital heart disease, cardio-oncology, cardiac masses and heart transplant.

Cardiac MRI Assessment of Mouse Myocardial Infarction and Regeneration

Small animal models are indispensable for cardiac regeneration research. Studies in mouse and rat models have provided important insights into the etiology and mechanisms of cardiovascular diseases and accelerated the development of therapeutic strategies. It is vitally important to be able to evaluate the therapeutic efficacy and have reliable surrogate markers for therapeutic development for cardiac regeneration research. Magnetic resonance imaging (MRI), a versatile and noninvasive imaging modality with excellent penetration depth, tissue coverage, and soft-tissue contrast, is becoming a more important tool in both clinical settings and research arenas. Cardiac MRI (CMR) is versatile, noninvasive, and capable of measuring many different aspects of cardiac functions, and, thus, is ideally suited to evaluate therapeutic efficacy for cardiac regeneration. CMR applications include assessment of cardiac anatomy, regional wall motion, myocardial perfusion, myocardial viability, cardiac function assessment, assessment of myocardial infarction, and myocardial injury. Myocardial infarction models in mice are commonly used model systems for cardiac regeneration research. In this chapter, we discuss various CMR applications to evaluate cardiac functions and inflammation after myocardial infarction.

Cardiovascular magnetic resonance in heart transplant patients: diagnostic value of quantitative tissue markers: T2 mapping and extracellular volume fraction, for acute rejection diagnosis

BACKGROUND

The diagnosis of acute rejection in cardiac transplant recipients requires invasive technique with endomyocardial biopsy (EMB) which has risks and limitations. Cardiovascular magnetic resonance imaging (CMR) with T2 and T1 mapping is a promising technique for characterizing myocardial tissue. The purpose of the study was to evaluate T2, T1 and extracellular volume fraction (ECV) quantification as novel tissue markers to diagnose acute rejection.

METHODS

CMR was prospectively performed in 20 heart transplant patients providing 31 comparisons EMB-CMR. CMR was performed close to EMB. Images were acquired on a 1.5 Tesla scanner including T2 mapping (T2 prepared balanced steady state free precession) and T1 mapping (modified Look-Locker inversion recovery sequences: MOLLI) at basal, mid and apical level in short axis view. Global and segmental T2 and T1 values were measured before and 15 min (for T1 mapping) after contrast administration.

RESULTS

Acute rejection was diagnosed in seven patients: six cellular rejections (4 grade IR, 2 grade 2R) and one antibody mediated rejection. Patients with acute rejection had significantly higher global T2 values at 3 levels: 58.5 ms [55.0-60.3] vs 51.3 ms [49.5-55.2] (p = 0.007) at basal; 55.7 ms [54.0-59.7] vs 51.8 ms [50.1-53.6] (p = 0.002) at median and 58.2 ms [54.0-63.7] vs 53.6 ms [50.8-57.4] (p = 0.026) at apical level. The area under the curve (AUC) for each level was 0.83, 0.79 and 0.78 respectively. Patients with acute rejection had significantly higher ECV at basal level: 34.2% [32.8-37.4] vs 27.4% [24.6-30.6] (p = 0.006). The AUC for basal level was 0.84. The sensitivity, specificity and diagnosis accuracy for basal T2 (cut off: 57.7 ms) were 71, 96 and 90% respectively; and for basal ECV: (cut off 32%) were 86, 85 and 85% respectively. Combining basal T2 and basal ECV allowed diagnosing all acute rejection and avoiding 63% of EMB.

CONCLUSIONS

In heart transplant patients, a combined CMR approach using T2 mapping and ECV quantification provides a high diagnostic accuracy for acute rejection diagnosis and could potentially decrease the number of routine EMB.

Decision making about healthcare-related tests and diagnostic test strategies. Paper 2: a review of methodological and practical challenges

OBJECTIVES

In this first of a series of five articles, we provide an overview of how and why healthcare-related tests and diagnostic strategies are currently applied. We also describe how our findings can be integrated with existing frameworks for making decisions that guide the use of healthcare-related tests and diagnostic strategies.

STUDY DESIGN AND SETTING

We searched MEDLINE, references of identified articles, chapters in relevant textbooks, and identified articles citing classic literature on this topic.

RESULTS

We provide updated frameworks for the potential roles and applications of tests with suggested definitions and practical examples. We also discuss study designs that are commonly used to assess tests' performance and the effects of tests on people's health. These designs include diagnostic randomized controlled trials and retrospective validation. We describe the utility of these and other currently suggested designs, which questions they can answer and which ones they cannot. In addition, we summarize the challenges unique to decision-making resulting from the use of tests.

CONCLUSION

This overview highlights current challenges in the application of tests in decision-making in healthcare, provides clarifications, and informs the proposed solutions.

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.

Magnetic resonance imaging of the transplanted pediatric heart as a potential predictor of rejection

AIM

To evaluate cardiac magnetic resonance imaging (CMR) as a non-invasive tool to detect acute cellular rejection (ACR) in children after heart transplant (HT).

METHODS

Thirty pediatric HT recipients underwent CMR at the time of surveillance endomyocardial biopsy (EMB) and results were compared to 14 non-transplant controls. Biventricular volumes, ejection fractions (EFs), T2-weighted signal intensities, native T1 times, extracellular volumes (ECVs) and presence of late gadolinium enhancement (LGE) were compared between patients and controls and between patients with International Society of Heart and Lung Transplantation (ISHLT) grade ≥ 2R rejection and those with grade 0/1R. Heart rate (HR) and brain natriuretic peptide (BNP) were assessed as potential biomarkers.

RESULTS

Significant ACR (ISHLT grade ≥ 2R) was an infrequent event in our population (5/30, 17%). Ventricular volumes, EFs, LGE prevalence, ECVs, native T1 times, T2 signal intensity ratios, HR and BNP were not associated with the presence of ≥ 2R ACR.

CONCLUSION

In this pilot study CMR did not reliably identify ACR-related changes in pediatric HT patients.

Diagnostic performance of cardiac magnetic resonance for the detection of acute cardiac allograft rejection: a systematic review and meta-analysis

BACKGROUND

Several studies have addressed the diagnostic accuracy of cardiac magnetic resonance (CMR) to assess acute cardiac allograft rejection (ACAR) compared with endomyocardial biopsy (EMB). But the methodological heterogeneity limited the clinical application of CMR. Accordingly, we have sought a comprehensive, systematic literature review and meta-analysis for the purpose.

METHODS

Studies prior to September 1, 2014 identified by Medline/PubMed, EMBASE and Cochrance search and citation tracking were examined by two independent reviewers. A study was included if a CMR was used as a diagnostic test for the detection of ACAR.

RESULTS

Of the seven articles met the inclusion criteria. Only four studies using T2 relaxation time as a CMR parameter could be pooled results, because the number of studies using other parameters was less than three. By using DerSimonian-Laird random effects model, meta-analysis demonstrated a pooled sensitivity of 90% [95% confidence interval (CI), 79% to 97%], a pooled specificity of 83% (95% CI, 78% to 88%), and a pooled diagnostic odds ratio (DOR) of 61.66 (95% CI, 18.09 to 210.10).

CONCLUSIONS

CMR seems to have a high sensitivity and moderate specificity in the diagnosis of ACAR. However, as a result of CMR for diagnostic ACAR should be comprehensively considered by physicians and imaging experts in the context of clinical presentations and imaging feature. Further investigations are still required to test different parameters and study condition.

Correlation of cardiovascular magnetic resonance imaging findings and endomyocardial biopsy results in patients undergoing screening for heart transplant rejection

BACKGROUND

Endomyocardial biopsy (EMB) is the current gold standard to screen for heart transplant rejection but has important risks and limitations. Cardiovascular magnetic resonance imaging (CMRI) is increasingly used to characterize cardiac function and myocardial tissue. We evaluated the diagnostic accuracy of CMRI compared with EMB and clinically diagnosed heart transplant rejection.

METHODS

Comprehensive CMRI scans were performed on adult heart transplant recipients within 24 hours of EMB (routine or clinically indicated), before initiation of any anti-rejection therapy, and blinded to EMB results. Multivariable analysis was used to create CMRI diagnostic criteria for comparison with a positive EMB (Grade ≥ 2R or antibody-mediated rejection) and clinical rejection (change in medical therapy to treat rejection).

RESULTS

Sixty participants (75% male; mean age, 51 ± 14 years) were recruited, providing 73 comparisons between CMRI and EMB for the diagnosis of rejection. Multivariable logistic regression identified myocardial edema (T2 relaxation time) and right ventricular end-diastolic volume index as independent predictors of a positive EMB. Combining threshold right ventricular end-diastolic volume index and edema values predicted a positive EMB with very good accuracy: sensitivity, 93%; specificity, 78%; positive predictive value, 52%; and negative predictive valve, 98%. CMRI was more sensitive than EMB at predicting clinical rejection (sensitivity of 67% vs 58%).

CONCLUSIONS

CMRI has high sensitivity and high negative predictive value in predicting biopsy-positive heart transplant rejection and may be useful as a screening test before routine EMB. CMRI also has better sensitivity for clinically diagnosed heart transplant rejection and could be helpful in cases of negative rejection on the biopsy specimen.

Prevalence of different forms of infarct-atypical late gadolinium enhancement in patients early and late after heart transplantation

BACKGROUND

Late gadolinium enhancement cardiac magnetic resonance (LGE-CMR) enables high-resolution myocardial tissue characterization, showing the results of different injuries, especially in the early period after heart transplantation (HTX).

OBJECTIVES

We sought to apply LGE-CMR to investigate the prevalence and patterns of infarct-atypical myocardial involvement and associated mechanisms in patients early and late after HTX.

METHODS

LGE-CMR was performed on a 1.5-T MRI scanner (Philips, Best, the Netherlands) in 89 patients: group 1 (48 patients) less than 2.5 years after operation (1.2 ± 0.5 years) and group 2 (41 patients) later this period (8.2 ± 4.2 years). Following LGE-CMR, the presence, distribution, patterns of infarct-atypical LGE and possible associated mechanisms were assessed.

RESULTS

71 % of group 1 patients (34/48) showed infarctatypical LGE whereas 57 % of group 2 patients (22/41) were affected (p = 0.25). Fewer segments/patients were involved later after HTX (1.6 ± 2.0 vs. 2.9 ± 3.1 segments/ patient; p = 0.03), but only diffuse LGE-CMR pattern decreased significantly (11.5 % of affected segments in group 1 vs. 6.5 % in group 2; p\0.001). Group 2 had lower ischemic time (181 ± 53 vs. 208 ± 61 min; p = 0.03), the donors were younger (33 ± 13 vs. 41 ± 13 years; p = 0.01) and fewer donors were Toxoplasma gondii seropositive (4 vs. 22pts; p\0.001).

CONCLUSION

Infarct-atypical LGE was found in a significant number of patients early post-HTX, however, fewer patients and myocardial segments per patient were affected later after HTX. Many potential factors seem to be involved, but the exact mechanisms are still unclear. Future studies are necessary to test prognostic implications associated with LGE-CMR patterns.

Assessment of sub-clinical acute cellular rejection after heart transplantation: comparison of cardiac magnetic resonance imaging and endomyocardial biopsy

OBJECTIVE

Comparing the diagnostic value of multi-sequential cardiac magnetic resonance imaging (CMR) with endomyocardial biopsy (EMB) for sub-clinical cardiac allograft rejection.

METHODS

One hundred and forty-six examinations in 73 patients (mean age 53 ± 12 years, 58 men) were performed using a 1.5 Tesla system and compared to EMB. Examinations included a STIR (short tau inversion recovery) sequence for calculation of edema ratio (ER), a T1-weighted spin-echo sequence for assessment of global relative enhancement (gRE), and inversion-recovery sequences to visualize late gadolinium enhancement (LGE). Histological grade ≥1B was considered relevant rejection.

RESULTS

One hundred and twenty-seven (127/146 = 87 %) EMBs demonstrated no or mild signs of rejection (grades ≤1A) and 19/146 (13 %) a relevant rejection (grade ≥1B). Sensitivity, specificity, positive predictive, and negative predictive values were as follows: ER: 63 %, 78 %, 30 %, and 93 %; gRE: 63 %, 70 %, 24 %, and 93 %; LGE: 68 %, 36 %, 13 %, and 87 %; with the combination of ER and gRE with at least one out of two positive: 84 %, 57 %, 23 %, and 96 %. ROC analysis revealed an area under the curve of 0.724 for ER and 0.659 for gRE.

CONCLUSION

CMR parameters for myocarditis are useful to detect sub-clinical acute cellular rejection after heart transplantation. Comparable results to myocarditis can be achieved with a combination of parameters.

KEY POINTS

• Magnetic resonance imaging is useful for the assessment of cardiac allograft rejection. • CMR has a high negative predictive value for exclusion of allograft rejection. • Diagnostic performance is not yet good enough to replace endomyocardial biopsy.

Cardiac magnetic resonance T2 mapping in the monitoring and follow-up of acute cardiac transplant rejection: a pilot study

BACKGROUND

Acute rejection is a major factor impacting survival in the first 12 months after cardiac transplantation. Transplant monitoring requires invasive techniques. Cardiac magnetic resonance (CMR), noninvasive testing, has been used in monitoring heart transplants. Prolonged T2 relaxation has been related to transplant edema and possibly rejection. We hypothesize that prolonged T2 reflects transplant rejection and that quantitative T2 mapping will concur with the pathological and clinical findings of acute rejection.

METHODS AND RESULTS

Patients were recruited within the first year after transplantation. Biopsies were graded according to the International Society for Heart Lung Transplant system for cellular rejection with immunohistochemistry for humoral rejection. Rejection was also considered if patients presented with signs and symptoms of hemodynamic compromise without biopsy evidence of rejection who subsequently improved with treatment. Patients underwent a novel single-shot T2-prepared steady-state free precession 4-chamber and 3 short axis sequences and regions of interest were drawn overlying T2 maps by 2 independent blinded reviewers. A total of 74 (68 analyzable) CMRs T2 maps in 53 patients were performed. There were 4 cellular, 2 humoral, and 2 hemodynamic rejection cases. The average T2 relaxation time for grade 0R (n=46) and grade 1R (n=17) was 52.5±2.2 and 53.1±3.3 ms (mean±SD), respectively. The average T2 relaxation for grade 2R (n=3) was 59.6±3.1 ms and 3R (n=1) was 60.3 ms (all P value <0.05 compared with controls). The T2 average in humoral rejection cases (n=2) was 59.2±3.3 ms and the hemodynamic rejection (n=2) was 61.1±1.8 ms (P<0.05 versus controls). The average T2 relaxation time for all-cause rejection versus no rejection is 60.1±2.1 versus 52.8±2.7 ms (P<0.05). All rejection cases were rescanned 2.5 months after treatment and demonstrated T2 normalization with average of 51.4±1.6 ms. No difference was found in ventricular function between nonrejection and rejection patients, except in ventricular mass 107.8±10.3 versus 127.5±10.4 g (P < 0.05).

CONCLUSIONS

Quantitative T2 mapping offers a novel noninvasive tool for transplant monitoring, and these initial findings suggest potential use in characterizing rejections. Given the limited numbers, a larger multi-institution study may help elucidate the benefits of T2 mapping as an adjunctive tool in routine monitoring of cardiac transplants.

Cellular and Functional Imaging of Cardiac Transplant Rejection

Heart transplantation is now an established treatment for patients suffering from end-stage heart diseases. With the advances in immunosuppressive treatment, the survival rate for transplant patients has improved greatly. However, allograft rejection, both acute and chronic, after heart transplantation is still a limitation leading to morbidity and mortality. The current clinical gold standard for screening rejection is endomyocardial biopsy (EMB), which is not only invasive, but also error-prone, due to the limited sample size and the site location of sampling. It would be highly desirable to have reliable and noninvasive alternatives for EMB in monitoring cardiac allograft rejection. The objective of this review is to highlight how cardiovascular imaging can contribute to noninvasively detecting and to evaluating both acute and chronic allograft rejection after heart transplantation, in particular, cardiovascular MRI (CMRI); and how CMRI can assess both immune cell infiltration at the rejecting organ, and the cardiac dysfunctions resulting from allograft rejection.

Diagnostic performance of multisequential cardiac magnetic resonance imaging in acute cardiac allograft rejection

AIMS

We evaluated cardiac magnetic resonance imaging (CMR) as a non-invasive test for cardiac allograft rejection.

METHODS AND RESULTS

We performed CMR on 50 heart-transplant recipients. Acute rejection was confirmed in 11 cases by endomyocardial biopsy (EMB) and presumed in 8 cases with a recent fall in left-ventricular ejection fraction (LVEF) not attributable to coronary allograft vasculopathy. Control patients had both normal LVEF and no significant rejection on EMB. Cardiac magnetic resonance imaging evaluated myocardial function, oedema, and early and late post-Gadolinium-DTPA contrast enhancement. Patients with confirmed rejection demonstrated elevated early relative myocardial contrast enhancement (4.1 +/- 0.3 vs. 2.8 +/- 0.2, P < 0.001) and a trend to higher oedema suggested by higher relative myocardial intensity on T(2)-weighted imaging compared to controls (2.1 +/- 0.1 vs. 1.7 +/- 0.1, P = 0.1). With rejection defined as increased early contrast enhancement or myocardial oedema, the sensitivity and specificity of CMR compared with EMB were 100 and 73%, respectively. Eight patients with presumed rejection also had elevated early myocardial contrast enhancement compared with controls, (8.7 +/- 1.9 vs. 2.8 +/- 0.2, P < 0.05), which reduced following increased immunosuppression (8.7 +/- 1.9 vs. 4.6 +/- 1.2, P < 0.05). In these patients LVEF improved following increased immunosuppression (32 +/- 5 vs. 46 +/- 5%, P < 0.05).

CONCLUSION

Cardiac magnetic resonance imaging is a promising modality for non-invasive detection of cardiac allograft rejection.

The role of multimodality cardiac imaging in the transplanted heart

Heart transplantation (HT) is an established life-saving treatment option for patients with end-stage heart failure. Despite many advances in the field, the development of acute cellular rejection (ACR) and cardiac allograft vasculopathy (CAV) represent significant causes of 1- and 5-year morbidity and mortality, respectively. The search for noninvasive techniques to assess cardiac allograft function and detect treatable ACR and CAV remains a priority objective for heart transplant professionals. In this review we will: 1) highlight the clinical significance of ACR and CAV in adult cardiac transplant recipients and 2) discuss how different noninvasive imaging modalities (echocardiography, cardiac computed tomography, myocardial perfusion imaging, and cardiac magnetic resonance) have been used in the evaluation of these clinical challenges after HT.

Cardiovascular magnetic resonance in the diagnosis of acute heart transplant rejection: a review

BACKGROUND

Screening for organ rejection is a critical component of care for patients who have undergone heart transplantation. Endomyocardial biopsy is the gold standard screening tool, but non-invasive alternatives are needed. Cardiovascular magnetic resonance (CMR) is well suited to provide an alternative to biopsy because of its ability to quantify ventricular function, morphology, and characterize myocardial tissue. CMR is not widely used to screen for heart transplant rejection, despite many trials supporting its use for this indication. This review summarizes the different CMR sequences that can detect heart transplant rejection as well as the strengths and weaknesses of their application.

RESULTS

T2 quantification by spin echo techniques has been criticized for poor reproducibility, but multiple studies show its utility in screening for rejection. Human and animal data estimate that T2 quantification can diagnose rejection with sensitivities and specificities near 90%. There is also a suggestion that T2 quantification can predict rejection episodes in patients with normal endomyocardial biopsies.T1 quantification has also shown association with biopsy proven rejection in a small number of trials. T1 weighted gadolinium early enhancement appeared promising in animal data, but has had conflicting results in human trials. Late gadolinium enhancement in the diagnosis of rejection has not been evaluated.CMR derived measures of ventricular morphology and systolic function have insufficient sensitivity to diagnose mild to moderate rejection. CMR derived diastolic function can demonstrate abnormalities in allografts compared to native human hearts, but its ability to diagnose rejection has not yet been tested.There is promising animal data on the ability of iron oxide contrast agents to illustrate the changes in vascular permeability and macrophage accumulation seen in rejection. Despite good safety data, these contrast agents have not been tested in the human heart transplant population.

CONCLUSION

T2 quantification has demonstrated the best correlation to biopsy proven heart transplant rejection. Further studies evaluating diastolic function, late gadolinium enhancement, and iron oxide contrast agents to diagnose rejection are needed. Future studies should focus on combining multiple CMR measures into a transplant rejection scoring system which would improve sensitivity and possibly reduce, if not eliminate, the need for endomyocardial biopsy.

Application of cardiac magnetic resonance imaging in cardiomyopathy

Cardiomyopathies account for a significant portion of morbidity and mortality in patients with heart disease. The diagnosis and identification of the underlying disorder are essential for directing appropriate life-saving therapy. Cardiac magnetic resonance imaging (CMR) is an ideal method for the noninvasive evaluation of cardiomyopathies of unknown etiology. In addition, there is increasing prognostic evidence to support the use of this technology in patient risk stratification. CMR is not limited by anatomic barriers and is able to characterize tissue abnormalities that previously could often be identified only through biopsy. This review discusses the utility of CMR in the assessment of cardiomyopathies, including specific imaging techniques and their application in ischemic and nonischemic settings.

Diagnosis of graft coronary artery disease

PURPOSE OF REVIEW

Graft coronary artery disease is the leading cardiac cause of death in patients who have undergone cardiac transplantation. Due to denervation, classic symptoms of angina are not reliable. Many transplant centers have a protocol of routine annual surveillance cardiac angiography because treatment options are limited, especially with advanced disease. Angiography is an assessment of the arterial lumen, however, and can miss nonfocal disease. This paper reviews invasive and noninvasive diagnostic tools for graft coronary artery disease. Intravascular ultrasound is the most sensitive, but the cost and lack of widespread expertise make it unpopular. Noninvasive techniques have been studied. An ideal test would be sufficiently sensitive to detect disease and allow for prognostic information. Dobutamine echocardiography is the most sensitive noninvasive test but can have a high false-positive rate. It is also not universally available. Exercise nuclear imaging is specific and can be used as a confirmatory test in patients with positive dobutamine echocardiograms.

RECENT FINDINGS

Computed tomographic imaging and cardiac magnetic resonance imaging are exciting new modalities but require further study.

SUMMARY

There is no test sensitive and specific enough yet that can be confidently used to replace coronary angiography.

A comparison of myocardial perfusion and rejection in cardiac transplant patients

INTRODUCTION

Although histological evaluation of the cardiac tissue is the current gold standard for evaluation of rejection, we hypothesized that cardiac perfusion MRI is a safe non-invasive method that correlates tissue blood flow changes with biopsy proven rejection in the cardiac transplant patient.

MATERIALS AND METHODS

In a retrospective study from 1984-2001, 83 patients underwent 135 MR Gd-DTPA imaging studies. In 8 patients (9%), biopsies graded 2 or higher (by ISHLT criteria) provided evidence of rejection. Patients were age and sex matched to 11 non-rejected controls for imaging analysis. Time-signal intensity curves generated for a mid-ventricle LV short axis slice during rest and adenosine stress allowed determination of myocardial blood flow (MBF, ml/min/gm). ROC curve analysis by SPSS allowed estimation of sensitivity and specificity.

RESULTS

At rest, there was no difference in MBF between patients with prior rejection vs. those without (1.18 +/- 0.26 vs. 1.16 +/- 0.29). At stress there was a decrease in MBF for patients with prior rejection episodes (3.27 +/- 0.74) compared to no rejection (3.60 +/- 0.72), P = 0.067). The area under the ROC curve was 0.82, with specificity and sensitivity of 75% and 81%, respectively.

CONCLUSION

This study suggests that perfusion MR imaging can be used in assessing the cardiac transplant patient for rejection related microvascular changes. The high specificity and sensitivity recorded from the ROC curve illustrates the potential utility of this diagnostic test for future studies.

Evaluation of perfusion and viability in hypothermic non-beating isolated porcine hearts using cardiac MRI

The donor heart undergoes degradation during hypothermic storage. An assessment of donor heart preservation is typically done with histological or biochemical methods that are not feasible in the clinical setting. We describe a method to study the donor heart using cardiac perfusion MRI that is potentially feasible for clinical use. Standard cardiectomy was performed in the pig model and the hearts were stored in normal saline at 5 degrees C. Imaging was performed by using a rapid gradient-echo sequence (FLASH) with saturation-recovery preparation for T1-weighting in the short axis and horizontal long axis views. Approximately 80 serial images were acquired at a rate of 1/s during administration of 0.006 mmol/ml Gd-DTPA (500 ml, 1 l/min). Signal intensity vs. time curves were generated for each heart and slice imaged and compared to a 0.006 mmol/ml Gd-DTPA reference. H&E stained biopsies of the LV, RV, and septum were also obtained. The mean duration of heart storage (N=10) was 8.8 h (range 4.2-19.2 h). Histologically, no differences were seen in H&E stained biopsies among hearts at different storage times. However cardiac MRI revealed a decrease in perfusion units in each subsequent heart tested after 4.2 h. (R=0.49). Average peak up-slope was used as a surrogate measure for flow capacity through the microvasculature and peak contrast enhancement was used as a measurement of viable microvasculature. The 4 h heart had 83% peak contrast enhancement of the reference standard, as compared to 44% for the 19.2 h heart. The decrease in peak enhancement is directly related to the duration of storage time. No correlation of peak up-slope of the intensity curve to storage time was found. This new application of cardiac MRI in the donor heart is applicable to: (1) assessing marginal hearts, (2) evaluating donor heart preservation techniques, and (3) correlating pre- to post-transplant viability.

Diagnostic performance of cardiovascular magnetic resonance in patients with suspected acute myocarditis: comparison of different approaches

OBJECTIVES

The aim of this research was to identify the diagnostic performance of gadolinium-enhanced and T2-weighted cardiovascular magnetic resonance (CMR) in suspected acute myocarditis.

BACKGROUND

Acute myocarditis is difficult to diagnose; CMR provides various means to visualize myocardial inflammatory changes. A CMR approach with clear-cut diagnostic criteria would be desirable.

METHODS

We investigated 25 patients with suspected acute myocarditis (18 males, 44 +/- 17 years) and 23 healthy controls (13 males, 29 +/- 10 years). Cardiovascular magnetic resonance studies included the following sequences: 1) T2-weighted triple inversion recovery; 2) T1-weighted spin echo before and over 4 min after gadolinium injection; and 3) inversion recovery-gradient echo 10 min after gadolinium injection. Qualitative and quantitative image analysis was performed for: 1) focal and global T2 signal intensity (SI); 2) myocardial global relative enhancement (gRE); and 3) areas of late gadolinium enhancement (LGE).

RESULTS

Both global T2 SI and gRE were higher in patients than in controls (T2: 2.3 +/- 0.4 vs. 1.7 +/- 0.4; p < 0.0001, gRE: 6.8 +/- 4.0 vs. 3.7 +/- 2.3; p < 0.001). The sensitivity, specificity, and diagnostic accuracy for T2 (cutoff value of 1.9) were 84%, 74%, and 79%, respectively; gRE: (cutoff value of 4.0) 80%, 68%, and 74.5% respectively; LGE: 44%, 100%, and 71%, respectively. The best diagnostic performance was obtained when "any-two" of the three sequences were positive in the same patient yielding a 76% sensitivity, 95.5% specificity, and 85% diagnostic accuracy.

CONCLUSIONS

A combined CMR approach using T2-weighted imaging, early and late gadolinium enhancement, provides a high diagnostic accuracy and is a useful tool in the diagnosis and assessment of patients with suspected acute myocarditis.