cardiac imaging

Subepicardial Aneurysm That Was Diagnosed by Cardiac Imaging and Underwent Successful Surgery

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A 63-year-old man was admitted because of current chest pain with perspiration for 6 hours. Electrocardiography showed complete right bundle-branch block and ST-segment elevation on leads II, III, aVF, and V2 through V6 (Figure 1); we therefore suspected an anterior and inferior wall acute myocardial infarction. Coronary angiography revealed total occlusion of the proximal left anterior descending artery (Figure 2 and Movie I in the online-only Data Supplement); the left circumflex and right coronary arteries showed no abnormalities. The left anterior descending artery was recanalized by percutaneous catheter intervention. The patient complained of chest pain the next afternoon after percutaneous catheter intervention, and the ECG was not changed. A transthoracic echocardiogram was performed, which demonstrated that the apical segments of the left ventricular walls were akinetic with normal thickness in the 4-chamber view (Movie II in the online-only Data Supplement), but the apex myocardium was dyskinetic with a perforation (2 mm in diameter) connected to a small apical aneurysm (10×5 mm) covered by intact epicardium that communicated with the left ventricular cavity as demonstrated by color Doppler (Figure 3A and 3B and Movie III in the online-only Data Supplement) from the apical 2-chamber view. This was consistent with a subepicardial aneurysm (SEA). On the follow-up echocardiography performed 8 days after infarction, there was a small thrombus at the apex, and the false aneurysm could not be seen (Figure 3C and Movie IV in the online-only Data Supplement).

Figure 1.

Figure 1.

Electrocardiography showed complete right bundle-branch block and ST-segment elevation on leads II, III, aVF, and V2 through V6.

Figure 2.

Figure 2.

Coronary angiography revealed total occlusion (arrow) of the proximal left anterior descending artery.

Figure 3.

Figure 3.

Apical 2-chamber view showed an apical myocardial perforation (2 mm in diameter) connected to a small apical aneurysm (10×5 mm) covered by intact epicardium (A), which communicated with the left ventricular cavity as demonstrated by color Doppler (B). Follow-up echocardiography performed 8 days after infarction showed a small thrombus at the apex, and the false aneurysm could not be seen (C).

To confirm the diagnosis, cardiac magnetic resonance imaging (MRI) was performed. Axial (Figure 4A) and short-axis (Figure 4B) first-pass perfusion steady-state free-precession MRIs demonstrated an area of microvascular obstruction in the apical wall (solid arrows) with an small aneurysm (open arrow) compatible with a left ventricular rupture. The magnified view (Figure 4C) of the steady-state free-precession MRI confirmed an apical thrombus (arrow) at the area of the ruptured orifice (open arrow) covered by intact epicardium. The 2-chamber-view (Figure 4D) delayed-enhancement inversion-recovery MRI (steady-state free-precession–gradient recalled echocardiography) after intravenous gadolinium injection showed apical acute myocardial infarction with a persistent area of microvascular obstruction (arrowheads), small apical thrombus, and a small aneurysm with clot covered by epicardium (arrow).

Figure 4.

Figure 4.

A, Cine (steady-state free-precession) cardiac magnetic resonance imaging of the 2-chamber view in the diastolic phase clearly showing a diverticulum-like cavity (arrowhead) with thrombus (white arrow) inside. B, In cine imaging of the 2-chamber view in the systolic phase, the diverticulum-like cavity disappeared, which indicated the formation of an aneurysm. The intact epicardium could be seen in this phase (white solid arrow), which was consistent with a subepicardial aneurysm. The thrombus (black arrow) still could be seen in the left ventricular apex. C, Late gadolinium enhancement (LGE) imaging of the short axis. The scar (arrowheads) was demonstrated by enhanced myocardium, whereas significant microvascular obstruction was detected as the hypoenhancement (white arrow) within the necrotic area. D, LGE imaging of the 2-chamber view. Enhanced myocardium was detached in the apex, and thromboses (open arrow) can be seen in the left ventricle and inside the diverticulum.

To prevent epicardial rupture or sudden death, an aneurysmectomy was performed 28 days after infarction. During surgery, a small ruptured orifice filled with thrombus in the left ventricular apex was evident. A ventricular aneurysm resection and coronary artery bypass saphenous vein to left anterior descending artery side anastomosis operation were performed.

Pathological examination showed that the endocardial layer and muscle layer structure ruptured, but the epicardial layer was intact with fibrous tissue and a small number of myocardial cells (Figure 5). The patient was discharged from hospital 10 days after surgery in good condition.

Figure 5.

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Gross pathological examination showed that the epicardial layer of the apical surface was intact (1*), but the endocardial layer and muscle layer structure ruptured (2, arrow), covered by thrombus (3 and 4). Histological examination showed that the epicardial layer was integrity (arrow) with fibrous tissue and a small number of myocardial cells (5).

Discussion

There are several potentially life-threatening complications: arrhythmias, cardiogenic shock, and ventricular wall rupture with the formation of aneurysm. In left ventricular complete free wall ruptures account for almost 4% of patient deaths after acute myocardial infarction (33% occur within the first 24 hours, 85% within the first week),1 complete septal ruptures (accounting for 1%–5% of all infarct-related deaths),2 and the formation of false aneurysms. Although true aneurysms typically do not require emergency treatment, false aneurysms, or pseudoaneurysms, are the result of a complete rupture of the ventricular wall with containment of the resulting hematoma by adherent pericardium and thus have a high mortality rate. SEA is rare; of 1814 hearts examined after postmortem arteriography from autopsy subjects at the Johns Hopkins Hospital, 704 had 1140 infarcts, and only 3 SEAs were found (0.2% of infarcts).3 Because SEAs are precursors to pseudoaneurysms with a high propensity to rupture, immediate treatment is often lifesaving. Although conservative management has been reported to be successful in asymptomatic chronic SEAs,4 surgical treatment is still considered the standard of care, especially for symptomatic acute SEAs, as in our case. The options include aneurysmectomy (resection) or aneurysmorrhaphy (patch repair). In addition to an elevated risk of death, patients with SEAs are initially difficult to diagnose owing to a lack of specific symptoms. Although the transthoracic echocardiography demonstrated the abnormality, sometimes the features are not distinct enough to differentiate aneurysm subtypes, and MRI or computed tomography may be helpful for accurate diagnosis. Because SEAs have a high risk of rupture, if patients have a history of acute myocardial infarction or signs of coronary artery disease, the cardiac surgery therapy should be performed as soon as the diagnosis confirmed.

In a patient with continued chest pain after acute myocardial infarction, subendocardial left ventricular aneurysm/impending rupture should be considered as an uncommon life-threatening differential diagnosis. In our case, the SEA was found by transthoracic echocardiography and was confirmed on a dedicated cardiac MRI. Emergency surgery guided by these imaging findings most likely saved the patient’s life.

2014 Top Stories in Cardiology: Cardiac Imaging.

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In assembling the top stories of 2014 in the field of cardiac imaging, we have focused on the major modalities of noninvasive imaging—echocardiography, nuclear cardiology, cardiac magnetic resonance imaging (CMR), and cardiac computed tomographic (CCT) imaging.

Echocardiography

The management of patients with severe mitral regurgitation due to myxomatous degeneration of the valve, particularly if asymptomatic, remains vexing. Naji and colleagues1 reported on exercise echocardiographic and clinical data in almost 900 patients with myxomatous mitral regurgitation, the majority of whom were asymptomatic. Patients were followed for a composite outcome for an average of over 6 years. Significant predictors of adverse outcomes included percent of age-/sex-predicted metabolic equivalents, heart rate recovery, resting right ventricular systolic pressure, atrial fibrillation, and LV ejection fraction. The importance of this paper lies not only in the large population with long-term follow-up, but also with the incorporation of exercise parameters into the usual clinical data, which had not been done before in such a large population. In the absence of randomized trials addressing timing of mitral valve surgery for asymptomatic severe mitral regurgitation, which are unlikely to be performed, this type of observational data set will inform guidelines and practice patterns.

Nuclear Cardiology

Almost 10 years ago, the American College of Cardiology published the first of a series of papers on the appropriate use of medical testing, originally called “Appropriateness Criteria,” now referred to as “Appropriate Use Criteria” (AUC). The goal of these recommendations is to optimize the efficiency and value of cardiac testing, based as much as possible on the published literature but also incorporating critical expert opinion. Recommendations are grouped by common clinical indications, and are categorized as “appropriate,” “may be appropriate” (formerly “uncertain”), or “rarely appropriate” (formerly “inappropriate”). Studies categorized as rarely appropriate are generally thought to be low-yield, in low-risk populations as an example. While AUC documents have been published for all common cardiac imaging tests and also for disease states such as stable ischemic heart disease or heart failure, there exists almost no literature validating the AUC categories in a prospective way against clinical outcomes. In this important paper, Doukky and colleagues2 report on over 1500 outpatients who were clinically referred for SPECT myocardial perfusion imaging. The studies were classified based on the 2009 AUC for SPECT myocardial perfusion imaging into two categories as appropriate/uncertain or as inappropriate. Patients were followed for an average of over 2 years for adverse events. Among the studies categorized as being of appropriate/uncertain indication, the SPECT results showed the usual prognostic value, in that an abnormal study was associated with a higher risk for adverse events compared with a normal study. However, among the SPECT studies characterized as inappropriate, there was not demonstrable prognostic association. To some degree, this was a result of the very low event rate among those with inappropriate studies, in turn related to the very low prevalence of abnormal studies. Nonetheless, these data are the first to examine the AUC recommendations in terms of association with outcomes, and validate the recommendations of the AUC documents. The importance of this paper lies in the fact that, within the next few years, payors including CMS will be mandating incorporation of AUC into the stream of test-ordering behavior. Having well-validated criteria is a critical element in the widespread acceptance of this approach.

Cardiac MR Imaging

Several relatively small studies have suggested that the presence and/or extent of late gadolinium hyperenhancement (LGE) on CMR imaging in patients with hypertrophic cardiomyopathy is associated with the risk for adverse events or with markers of adverse events. In this largest study to date,3 the authors assembled almost 1300 patients with hypertrophic cardiomyopathy from several centers around the world who had CMR imaging and were followed for a median of over 3 years. There was a significant association between the extent of LGE and risk for sudden death events. Among patients without established risk factors for sudden death, the extent of LGE was associated with sudden death risk, and, among those without LGE, risk was very low. The importance of this data set is that it more clearly establishes the role of CMR imaging in the prediction of sudden death risk in patients with hypertrophic cardiomyopathy. For those in whom the ICD decision may be uncertain on the basis of the usual clinical risk factors, the presence or absence of a certain mass of LGE on CMR imaging can tip the scales one way or the other on that critical decision point. For patients without any of the established risk factors, the presence and extent of LGE may drive consideration for an ICD that might not otherwise have been entertained. This study population is much larger with longer follow-up than all previous studies, allowing much more statistical power in analysis.

Cardiac CT Imaging

The technology of cardiac CT angiography has evolved substantially over the last decade, and, while the focus of much of the literature has been to recapitulate and expand the application of this modality in the same way as invasive angiography has been done, more recently, increasing attention has been on the evaluation of “non-obstructive” coronary artery disease (CAD). This can be imaged more routinely with contemporary CT techniques. In this paper, Bittencourt and colleagues4 report on over 3000 patients who had CT angiography whose scans were evaluated for the presence and extent of obstructive as well as non-obstructive CAD, and who were followed for a median of over 3 years for the occurrence of cardiovascular death or nonfatal myocardial infarction. The expected relation of obstructive CAD to events was seen, but, of great interest, those patients with extensive non-obstructive CAD had a risk for events that was similar to that in patents with less extensive obstructive CAD. Non-obstructive plaque extent added incremental information to risk stratification. These data are important for advancing the possibility of incorporating information on extent of imaged plaque into risk assessments, which may, in the future, help guide treatment decisions, or decisions regarding intensity of risk-factor management.

Conclusions

While the mature imaging modalities of echocardiography and nuclear cardiology have long had published data sets involving thousands of patients with sophisticated statistical analyses, the studies cited above suggest that the more recently evolved modalities of cardiac MR and cardiac CT have also reached a similar point regarding the rigor of prognostic data sets and publications. As always, finer gradations of risk assessment and stratification do not necessarily translate into enhanced management for patients, and must be tested separately and not simply be assumed.

Radiation Exposure from Cardiac Imaging Procedures

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Annual exposure that exceeded background levels by >3 millisieverts was not uncommon among insured adults.

How does radiation exposure from typical use of medical imaging compare with background radiation or accepted occupational exposures? In this analysis, authors used administrative data from a large insurer to evaluate cardiac imaging use in almost one million adults (age, <65) and estimated the effective dose of radiation from such procedures.

From 2005 to 2007, 90,121 patients (9.5%) underwent at least one cardiac imaging procedure, with a mean cumulative effective dose of 16.4 millisieverts (range, 1.5–189.5 mSv). Most of the effective dose (74%) came from myocardial perfusion imaging (MPI). About half of all cardiac imaging procedures — and three quarters of MPIs and cardiac computed tomography scans — were performed in physicians’ offices. Effective radiation doses that exceeded the background level from natural sources by >3 mSv annually occurred in 92.3 per 1000 enrollees, and doses exceeding annual limits for occupational exposure (>20 mSv) occurred in 3.3 per 1000.

Comment: The questions, of course, are whether these imaging procedures were appropriate and whether risks from radiation exposure were offset by sufficient benefit. Editorialists point to ongoing efforts to minimize radiation exposure and contend that the estimates used here are too high. They also remind us that the morbidity and mortality associated with coronary heart disease can be mitigated by accurate diagnostic testing. However, as cumulative radiation doses become a bigger issue, alternative forms of testing that do not employ ionizing radiation will be needed and preferable.


Published in Journal Watch General Medicine August 5, 2010