A. Bertaso

The role of cardiac magnetic resonance imaging following acute myocardial infarction

BackgroundAdvances in the management of myocardial infarction have resulted in substantial reductions in morbidity and mortality.MethodsHowever, after acute treatment a number of diagnostic and prognostic questions often remain to be answered, whereby cardiac imaging plays an essential role.ResultsFor example, some patients will sustain early mechanical complications after infarction, while others may develop significant ventricular dysfunction. Furthermore, many individuals harbour a significant burden of residual coronary disease for which clarification of functional ischaemic status and/or viability of the suspected myocardial territory is required.ConclusionCardiac magnetic resonance (CMR) imaging is well positioned to fulfil these requirements given its unparalleled capability in evaluating cardiac function, stress ischaemia testing and myocardial tissue characterisation. This review will focus on the utility of CMR in resolving diagnostic uncertainty, evaluating early complications following myocardial infarction, assessing inducible ischaemia, myocardial viability, ventricular remodelling and the emerging role of CMR-derived measures as endpoints in clinical trials.Key Points• Cardiac magnetic resonance (CMR) imaging identifies early complications after myocardial infarction.• Adenosine stress CMR can reliably assess co-existing disease in non-culprit arteries.• Assessment of infarct size and microvascular obstruction a robust prognostic indicator.• Assessment of myocardial viability is important to guide revascularisation decision-making.

Prognostic value of adenosine stress perfusion cardiac MRI with late gadolinium enhancement in an intermediate cardiovascular risk population

BACKGROUND The high diagnostic accuracy of adenosine stress cardiac magnetic resonance (AS-CMR) for detecting coronary artery stenoses, with high sensitivity and specificity, is well documented. Prognostic data, particularly in non-low risk study populations and for greater than 12 months of follow up, is however lacking or variable in its findings. We present prognostic data, in an intermediate cardiovascular risk cohort undergoing adenosine stress perfusion CMR, over approximately 2 years of follow up. METHODS The study population comprised 362 patients referred for a clinically indicated stress CMR and included patients with proven coronary artery disease (CAD; n=157) or unknown CAD status, yet an intermediate cardiovascular risk profile (n=205). Perfusion imaging was performed at stress (adenosine 140 μg/kg/min) and rest on a 1.5 T system. Patient records and state-wide hospital databases were reviewed. Major adverse cardiac events--death, myocardial infarction, revascularisation or ischaemic hospitalisation--were evaluated over a median follow up of 22 months. RESULTS Of the 362 cases, 90 had a stress perfusion CMR positive for ischaemia and experienced a MACE rate of 24%. Of the 272 negative CMR scans, 225 were also negative for late gadolinium enhancement, and in this group MACE was encountered in only 6 (2.7%) patients. Accordingly a negative stress CMR afforded a freedom from MACE of 97.3%. Freedom from death/myocardial infarction was 99.6%. CONCLUSIONS In patients with confirmed coronary artery disease or at intermediate risk for cardiovascular events, a negative stress perfusion CMR is associated with an excellent prognosis over nearly 2 years of follow up.

Cardiac magnetic resonance, transthoracic and transoesophageal echocardiography: a comparison of in vivo assessment of ventricular function in rats

In vivo assessment of ventricular function in rodents has largely been restricted to transthoracic echocardiography (TTE). However 1.5 T cardiac magnetic resonance (CMR) and transoesophageal echocardiography (TOE) have emerged as possible alternatives. Yet, to date, no study has systematically assessed these three imaging modalities in determining ejection fraction (EF) in rats. Twenty rats underwent imaging four weeks after surgically-induced myocardial infarction. CMR was performed on a 1.5 T scanner, TTE was conducted using a 9.2 MHz transducer and TOE was performed with a 10 MHz intracardiac echo catheter. Correlation between the three techniques for EF determination and analysis reproducibility was assessed. Moderate-strong correlation was observed between the three modalities; the greatest between CMR and TOE (intraclass correlation coefficient (ICC) = 0.89), followed by TOE and TTE (ICC = 0.70) and CMR and TTE (ICC = 0.63). Intra- and inter-observer variations were excellent with CMR (ICC = 0.99 and 0.98 respectively), very good with TTE (0.90 and 0.89) and TOE (0.87 and 0.84). Each modality is a viable option for evaluating ventricular function in rats, however the high image quality and excellent reproducibility of CMR offers distinct advantages even at 1.5 T with conventional coils and software.

Uhl's anomaly

Uhls anomaly is an exceedingly rare congenital abnormality characterised by the almost complete absence of the myocardium in the right ventricle [1]. Consequently the right ventricle develops a parchment like appearance with associated diminution of function. It was first described in 1952, and it is thought that fewer than 50 cases have since been described. During embryonic development the human heart advances through phased embryological processes. It is thought that loss of the right ventricular myocardium must only occur after complete cardiac development. Apoptosis is a routine component of postnatal morphogenesis of the human heart and it has been speculated that unrestrained right ventricular myocardial apoptosis may be responsible [2]. Prior to the advent of echocardiography the majority of cases were diagnosed post mortem. However with advancing imaging capabilities, now exemplified by cardiac magnetic resonance (CMR) imaging, the diagnosis can be made more readily providing an opportunity to intervene surgically. Patients often present in infancy and rarely survive to adulthood without intervention. The typical imaging findings consist of a thinned, akinetic right ventricular wall in association with a paucity of trabeculation with a dilated right ventricular cavity [3].

An unusual cause of cardiac failure.

Left ventricular noncompaction (LVNC) is a rare cardiomyopathy characterized by deep intertrabecular recesses communicating with the main ventricular chamber. Cardiac magnetic resonance offers high spatial resolution, and thereby substantial aptitude for the diagnosis of LVNC. Additional clinically relevant information, including thrombus and myocardial fibrosis evaluation, can be readily acquired. These images demonstrate classical LVNC morphology in conjunction with its potential sequelae.

ADENOSINE STRESS PERFUSION CMR RELIABLY RISK STRATIFIES PATIENTS WITH PRIOR EXERCISE TREADMILL TESTING

Background ETT is an inexpensive and easily accessible non-invasive test. However it affords only modest sensitivity and specificity for ischaemic heart disease (IHD). Accordingly ETT can often provide results that are either equivocal or which run contrary to clinical suspicion. Therefore, clinicians frequently request an additional non-invasive test to clarify matters. Adenosine stress perfusion CMR has been shown to have a high sensitivity and specificity for the detection of IHD. We sought to evaluate a cohort of patients who had a recent ETT followed by stress perfusion CMR to examine the clinical utility of CMR in risk stratifying these patients.

Stress perfusion CMR reliably risk stratifies patients with prior exercise treadmill testing

Seventy patients (50% male, age 58.4 years ±11.2; mean ±SD) were identified. Twelve (17%) had a history of previous MI or revascularisation. Seventeen had an objectively positive ETT, of which 7 (41%) had a positive stress CMR. Thirty one had an equivocal ETT, of which 8 (26%) had a positive stress CMR. Twenty two had a negative ETT, of which 3 (14%) had a positive CMR. All positive CMRs had stenoses ≥50% at angiography, except for two patients (11%), both from the equivocal ETT group. A negative CMR, irrespective of ETT status, resulted in a 0% MACE rate at median 23 months (IQR 20-27) follow up. No positive CMRs were seen in negative or equivocal ETTs where ≥ 10 metabolic equivalents (METS) were attained. Conclusions Adenosine stress perfusion CMR can reliably risk stratify patients independent of previous ETT result. A negative CMR is associated with an excellent prognosis at a median of 23 months follow up.

Prognostic value of adenosine stress perfusion cardiac magnetic resonance with late gadolinium enhancement

Objective To determine the prognostic value of a normal adenosine stress perfusion CMR in combination with late gadolinium enhancement in intermediate risk patients with suspected ischaemic heart disease (IHD). Background Adenosine stress CMR is a non invasive test with high sensitivity for the detection of IHD, and is now frequently combined with late gadolinium enhancement (LGE) imaging. This may augment its prognostic accuracy for predicting cardiovascular events. Previous studies have failed to appraise the combination of adenosine stress perfusion CMR with LGE for this purpose, and generally populations at low risk for cardiovascular events have been assessed. We sought to determine the clinical utility of stress perfusion CMR with LGE in the evaluation of intermediate risk patients. Methods Retrospective study of 362 consecutive patients referred to at ertiary cardiology centre for as tress perfusion CMR. Perfusion imaging was obtained at stress (adenosine 140 µg/kg/min) and rest on a 1.5T machine. Late enhancement was assessed with dual pass gadolinium (0.2mmol/kg total dose). A negative test, assessed qualitatively, was defined as the absence of both reversible ischaemia and LGE. Patient records, hospital databases and national death index were reviewed. MACE - death, myocardial infarction, revascularisation or ischaemic hospitalisation - were evaluated over a median follow up of 22 months (IQR 18-25). Results The cohort of 362 patients had a mean age of 62.6 years ±11.9 (mean ±SD), 152 (53.1%) male and 94 (32.8%) had a history of previous MI or PCI. Of the 362, 96 (27%) had a stress perfusion CMR positive for ischaemia, 266 (73%) were negative. Of the 266 negative CMR, MACE was encountered in only 6 (2%) patients (5 PCI and 1 death due to heart failure). Accordingly a negative stress CMR afforded a freedom from MACE of 98%. Conclusion In patients at intermediate risk for cardiovascular events, a negative stress perfusion CMR is associated with an excellent prognosis. This is consistent with the approximate 1% annualised cardiovascular event rate seen in negative stress imaging with other modalities.

Adenosine stress perfusion CMR accurately identifies the culprit vessel

Background The diagnostic evaluation of patients with suspected ischaemic heart disease (IHD) frequently involves a functional assessment of ischaemia. Adenosine stress perfusion CMR is a non-invasive test with high sensitivity for the detection of IHD, however rarely is its accuracy for culprit vessel identification assessed. We sought to determine the accuracy of stress perfusion CMR for identifying the culprit vessel. Furthermore, we sought to affirm the specificity of a positive CMR against an angiographic gold standard. Methods Retrospective study of patients with a positive stress perfusion CMR and subsequent coronary angiography. Perfusion imaging was obtained at stress (adenosine 140 µg/kg/min) and rest on a 1.5T scanner. Late enhancement was assessed with dual pass gadolinium (0.2mmol/kg total dose). Angiographic stenosis ≥ 50% was defined as significant. The presence or absence of a significant lesion together with the correlation between ischaemic territory on CMR and angiographic culprit vessel was evaluated. Results Thirty seven patients (60% male, age 65.1 years ± 11.3; mean ± SD) had a positive CMR with subsequent angiography, with follow up data for a median 24 months (IQR 21-27 months). Thirtee np atients (35%) had previous myocardial infarction or revascularisation. Of the cohort of 37, six (16%) had normal angiograms and 31 (84%) had a significant epicardial stenosis. Of the six false positives, three had localised septal hypoperfusion, while a further three had circumferential defects. Of the 31 patients correctly identified, CMR accurately established the territory of the culprit vessel in 29 (94%). The vessels confirmed as ischaemic were left anterior descending 12 (39%), circumflex 6 (19%) and right coronary artery 13 (42%). Conclusions Adenosine stress perfusion CMR reliably identifies the territory supplied by the culprit vessel (29 out of 31 94%). Furthermore, we reaffirm the high specificity (84%) of stress perfusion CMR.

Evaluation of the significance of intermediate coronary artery stenoses by stress perfusion CMR

Background A number of patients undergoing assessment for possible ischaemic heart disease proceed straight to coronary angiography without prior non-invasive functional tests. When an intermediate coronary lesion is then encountered, the functional significance of that lesion is often unclear. Invasive assessment with fractional flow reserve can clarify the situation but is not always available and involves significant expense. Non-invasive tests are then frequently requested to guide treatment. Adenosine stress perfusion imaging has been shown to have a high sensitivity and specificity for detecting ischaemic heart disease. We sought to determine the ability of stress perfusion CMR to guide management in these patients.