Every Q has an A

Myocarditis: Quesions answered by Dr. Vimal Raj

First of all, I would like to thank IACI for giving me this opportunity to be discussing this very important topic and providing insights into this.

In our experience, we have seen patients at different stages of the disease with different clinical severity. Often the patients are seen in an outpatient setting and have atypical chest pain symptoms with some history of viral illness in the recent past. It is unlikely for patients with myocarditis to require Intensive Care support unless the disease is extensive.  In the setting of COVID-19, most patients referred to us are relatively stable and can tolerate the procedure. However, this may vary from one institute to the other and from one city to another city.

The timing of the study can be crucial in making the right diagnosis. It is advised to perform the study within the first five to seven days of clinical presentation to ensure the best results.  With regards to COVID-19 related myocarditis, the timelines for scanning can vary significantly. We have seen patients presenting with symptoms suggestive of myocarditis at the onset of the disease itself while some patients have presented few weeks after being discharged from the hospital. We have also seen a handful of cases of patients presenting with vaccine-related myocarditis.

To summarise, most of these patients are relatively stable and can undergo cardiac MRI.  The patient should ideally undergo the scan within one week of clinical presentation of myocarditis to get the best results.

Imaging diagnosis of myocarditis is based on the Lake Louise criteria. This criterion was modified in 2018 to include parametric mapping and has shown improved sensitivity in the diagnosis of myocarditis. With the modified criteria, we need both T1 and T2 based imaging findings to be positive to make a diagnosis of myocarditis. T2 based imaging include standard myocardial oedema sequences (STIR) and T2 mapping. While T1 imaging includes T1 mapping, ECV or delayed enhancement imaging.

In a comparative study between the original and the modified Lake Louise criteria, the newer criteria had a higher sensitivity (87.5 vs. 72.5%) in diagnosing myocarditis (https://www.jacc.org/doi/10.1016/j.jacc.2021.01.043#: ~:text=Parametric%20mapping%20is%20included%20in,techniques%20 (5%E2%80%937). Therefore having parametric mapping techniques will certainly improve the diagnosis and confidence in our cardiac MRI report.

If you do not have parametric mapping, then you should perform T2 weighted STIR images along with early and late gadolinium enhancement imaging. In our practice, we have certainly come across few cases where the standard T2 weighted STIR imaging is normal while the T2 mapping images are suggestive of oedema.

In summary, if you do not have access to parametric mapping you should continue to perform cardiac MRI scans to assess for myocarditis and use the original Lake Louise criteria for making the diagnosis.

The right ventricular free wall is very thin and can pose problems in the diagnosis of myocarditis. Delayed enhancement and parametric mapping analysis are also challenging when it comes to RV free wall. CMR is certainly better at visualising the RV free wall when compared to echocardiography. It can demonstrate areas of wall motion abnormality and aneurismal outpouching when it comes to arrhythmogenic right ventricular cardiomyopathy. It is also excellent in quantifying ventricular function and volumes.

To achieve the best results in differentiating artefacts from an abnormality on delayed enhancement or parametric mapping sequences you can use two techniques. One is to look at the same area in different imaging planes, for example, 4 chamber in comparison to the short-axis image. Another method is to repeat the particular sequence by swapping the phase encoding direction. If the abnormality persists then it is likely to be real and if it does not persist then it is likely to be artifactual and can be ignored.
Over the last few months, we have seen multiple patients with COVID-19 presenting with symptoms suggestive of myocardial injury/myocarditis. We have performed CMR in these patients and have seen a variety of abnormalities. Most of them have raised T1 and T2 values with involvement of the LV lateral wall with epicardial to mid myocardial late gadolinium enhancement. We have also seen few patients who have had secondary complications related to COVID-19 vasculopathy with small embolic infarcts in CMR.

Patients with COVID-19 related myocardial injury should undergo a follow-up CMR study in 3 to 6 months to assess for progression/resolution. This we have not managed to achieve due to various patient-related and financial factors. We do expect the amount of myocardial injury to reduce and resolve over some time but more evidence is required to confirm this theory. A significant number of our patients presented with persistent tachycardia or exertional symptoms after completely recovering from COVID-19.
Endomyocardial biopsy is certainly the gold standard in diagnosing myocarditis. This is however not easily available or routinely performed in Indian hospitals for diagnosis of myocarditis. The diagnostic performance of endomyocardial biopsy is also significantly variable based on the availability of histopathological and interventional expertise. The ventricular septum on the RV side is the preferred site of biopsy and it may give a false negative report if the disease spares the septum. In our practice, if the clinical picture and/or the CMR parameters suggest myocarditis, the endomyocardial biopsy is avoided.

The specific role of endomyocardial biopsy is in patients where differentiation of Giant Cell myocarditis from sarcoidosis is required or in patients who have an infiltrative disease with uncharacteristic CMR findings. Performing a CMR examination before a myocardial biopsy is also helpful in guiding the interventional cardiologist to decide the site of biopsy.

EXPERT – Dr. Vimal Raj

Contributed by Dr. Ragini sharma
Dr. Ragini Sharma
Head of Department,
Dept of Radiology,
PKR Healthcare Institute, Amb, Haryana
Dr. Vimal Raj
Head of Department,
Cardiothoracic Imaging,
Narayana Health city, Bangalore.