"Where is the Heart?" When Cardiac Magnetic Resonance Imaging Helps if Echocardiography is Inconclusive.

Cardiovascular magnetic resonance (CMR) is the gold standard technique to comprehensively assess cardiac structure and function. A 64-year-old male, planned for surgical coronary revascularization, underwent transthoracic and transesophageal echocardiography for a mitral regurgitation, with an eccentric jet of unclear mechanism; these examinations were inconclusive because of the lack of adequate visualization of the cardiac structures. A CMR was then performed to quantify mitral regurgitation and, additionally, it documented a giant hiatus hernia with gastric sliding into the thorax. In this case, CMR helped to better define the severity of a valvular disease and provided ancillary information from the extracardiac findings.

INTRODUCTION

Nowadays, cardiovascular magnetic resonance (CMR) is the gold standard technique to comprehensively assess cardiac structure and function. In some situations, CMR could help to better quantify a valve dysfunction, especially when the echocardiographic evaluation is difficult or inconclusive.[1]

Initial axial and coronal images of the thorax and upper abdomen are acquired to plan the study and, consequently, this often reveals extracardiac findings.[2]

We present a case in which CMR played a pivotal role in the diagnostic valve disease workup and helped to determine the most appropriate therapeutic path.

CASE REPORT

A 64-year-old male with multiple cardiovascular risk factors (arterial hypertension, dyslipidemia, former smoking habit and obesity, with a body mass index of 33 kg/m2) was admitted to our center for an elective coronary angiography after the onset of typical angina with a positive stress test.

Coronary angiography revealed a significant multivessel disease (critical stenosis of the proximal left anterior descending artery and chronic total occlusion of the left circumflex artery, with collateral circulation from the right coronary artery), for which a surgical revascularization was planned [Figure 1].

Figure 1

Coronary angiography. (a) Critical stenosis of the proximal left anterior descending artery (white arrow). (b) Chronic total occlusion of the left circumflex artery (white arrow). (c) Collateral circulation from the right coronary artery (white arrows)

As preoperative workup, the patient underwent transthoracic echocardiography (TTE), with poor acoustic window, that showed a normal biventricular systolic function and a significant mitral regurgitation with an eccentric jet of unclear mechanism [Figure 2].

Figure 2

Transthoracic echocardiography. (a) Mitral regurgitation with eccentric jet in transthoracic echocardiography (apical two-chamber view, a – apical three-chambers view, b)

For a better morphological definition and quantification of mitral regurgitation, in a patient candidate for a cardiac surgery, we performed a transesophageal echocardiography (TEE). This examination was inconclusive because of the lack of adequate visualization of the cardiac structures (only the descending thoracic aorta could be well seen).

Thus, to better quantify the degree of mitral regurgitation and for a further diagnostic investigation in order to clarify the inadequate TEE window, we decided to perform a CMR. Using phase-contrast flow sequences [Figure 3], we documented a severe functional mitral regurgitation (effective regurgitant orifice [ERO] 0.36 cm2, regurgitant volume 32 ml), as a result of tethering of the valve leaflets in the presence of a scar in the basal part of the posterior wall [Figure 4]. In addition, in HASTE and VIBES sequence images, we documented a giant hiatus hernia with gastric sliding into the thorax [Figure 5]. Other additional findings were an azygos lobe in the right lung and multiple renal cysts (in particular a voluminous one in the upper pole of the right kidney) [Figure 6].

Figure 3

Cardiac magnetic resonance phase contrast. (a) Phase-contrast flow sequences in cardiac magnetic resonance across pulmonary. (b) and aortic valve to calculate stroke volume

Figure 4

Mitral valve tethering and posterior wall scar, cardiac magnetic resonance. (a) Tethering of mitral valve leaflets in cine steady-state free precession apical long-axis view (arrow) (b) and an ischemic scar in the basal part of the posterior wall with late gadolinium enhancement (arrow)

Figure 5

Hiatus hernia, cardiac magnetic resonance. (a) Giant hiatus hernia with gastric sliding into the thorax in HASTE transversal section (star) (b) and in VIBES coronal section (white arrows)

Figure 6

Other extracardiac findings, cardiac magnetic resonance. (a) Azygos lobe (arrow) (b) and voluminous cyst in the upper pole of the right kidney (star)

After the results of CMR, the initial surgical strategy changed and the patient underwent a combined intervention of coronary artery bypass grafting and mitral valve annuloplasty. Therefore, these results helped the surgeon to plan the ideal cardiac intervention and the echocardiographer to explain the difficult visualization of cardiac structures during TEE.

DISCUSSION

CMR and echocardiography are noninvasive imaging modalities that are of paramount importance in daily clinical practice for diagnosis, prognosis and treatment planning in patients with left-sided valvular heart disease (VHD).[1]

Current clinical guidelines recommend TTE or TEE as the first-line diagnostic modality for the evaluation of left-sided VHD.[3] Echo is relatively cheap, fast, noninvasive and can be performed in real time at the bedside or in the ambulatory setting.

CMR is an established diagnostic modality for assessment of left-sided VHD and is progressively gaining ground in modern-day clinical practice.[1] CMR provides accurate information on functional and morphological valvular abnormalities, VHD severity and left ventricular function. Recent clinical guidelines recommend CMR as an alternative to inconclusive TTE examinations, caused by poor acoustic windows, for instance.[4]

In patients with mitral valve regurgitation (MVR), echocardiography is useful to discriminate organic from functional MVR. Assessment of MVR severity is based on a range of qualitative and semiquantitative measures (including valve morphology and movement, left ventricular dilatation and function, left atrial dilatation, ERO area, vena contracta width, flow reversal in the pulmonary veins and pulmonary artery pressure).[5]

One of the main limitations of routine echocardiography for hemodynamic assessment is that, due to the assumption of a circular geometry of the flow pattern, the complex dynamic nature of the blood flow tends to be overlooked. As a result, the quantification of transvalvular flow is challenging and possibly inaccurate. Furthermore, echocardiography can only measure velocities in line with the transducer beam, making it susceptible to errors caused by misalignment of the transducer beam to the direction of the blood flow, especially for eccentric and dynamic flow jets.

Considering this particular case, accurate quantification of regurgitant volume is a central component to the management of mitral regurgitation. CMR helps to accurately quantify mitral regurgitation as the difference between total left ventricular stroke volume and forward stroke volume, using steady-state free precession and phase-contrast imaging. The CMR measurement of mitral regurgitant volume is reproducible and can quantify mitral regurgitation regardless of regurgitant jet morphology.[6]

CMR scan could also reveal extracardiac findings such as hiatus hernia, azygous lobe fissure and renal cyst. In CMR, the hiatus hernia can be described as a structure contiguous to the alimentary tract, on axial and/or coronal images, and may contain a gas/fluid level. This condition can often alter the normal mediastinal anatomy and lead to difficult interpretation of echocardiographic images. The azygous lobe fissure, a common anatomical variant that should not be confused with pathology, occurs as the displaced azygous vein makes a deep invagination into the apical segment of the right upper lobe, carrying with it both pleural layers. As it lacks its own bronchus, it is not a true anatomical accessory lobe. The most common focal renal pathology identified at CMR is a renal cyst. Most of these lesions will be simple benign cysts of no clinical relevance; however, a proportion of cystic renal lesions have malignant potential, and these findings need a careful interpretation. In some cases, only the upper poles of the kidneys are visualized, due to the constraints of the field of view at the time of CMR. This can make accurate localization and characterization of potential renal abnormalities challengings and lead to overinvestigation, potential misinterpretation and incorrect diagnosis.[27]

CONCLUSION

We described an interesting case, in which CMR helped to better define the severity of a left-sided VHD and provided ancillary information from extracardiac findings.

Therefore, CMR is an advisable and well-established imaging technique to support clinical management in patients with cardiovascular disease, especially when the first-level examinations are incomplete or inconclusive. Moreover, in axial and coronal images of the thorax and upper abdomen, the field of view is larger than the target organ of interest, which may reveal extracardiac anatomical variants or pathology.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.