Discussion
The main findings of this study are: 1) granulomatous myocarditis may
present as recurrent atrial arrhythmia including AF. 2) These patients
have a higher risk of stroke (26.7%) and predisposition to
thromboembolism in the absence of traditional risk factors. 3) Isolated
atrial involvement was observed in over 80% of this patient population.
The etiology of granulomatous myocarditis could either be cardiac
sarcoidosis or tuberculosis. 4) They respond well to immunosuppression
(Sarcoidosis) and anti-tuberculosis therapy (TB).
The entity of atrial myocarditis has been described in the past but has
not received much attention. An important study by Frustaci et. al
showed evidence of atria limited myocarditis in 66% of “lone” AF
patients studied by endomyocardial biopsy of atria.13A study has also demonstrated antibodies against myosin in the sera of
AF patients.14 A series of 13 patients with AM has
also shown that atrial giant cell myocarditis (GCM) has a favorable
prognosis when compared to the classic variety of
GCM.4 Our data indicates that “isolated atrial
myocarditis” could be a substrate for atrial arrhythmias, which could
also be life threatening.15
The sensitivity of 18F FDG PET in detecting cardiac
involvement in sarcoidosis has been around 87.5%.16Cardiac MRI also aids in the diagnosis but its value in detecting atrial
pathology is not well established. The sensitivity and predictive value
of 18F FDG PET scan for detecting AF was 54% and 96.1% in a recent
study.17
The possible consequences of AM have been highlighted in the Figure 4.
An autopsy study of young sudden death victims with ventricular
pre-excitation showed evidence of AM in 50%.15 Since
inflammation is a potent pro-thrombotic state, the risk of
thromboembolic complications could be heightened in this population. In
the present study, 26.7% of patients with AM presented with an ischemic
stroke with LA thrombus detected in one patient. Inflammation my alter
the electrical milieu, resulting in multiple atrial arrhythmias that
could be refractory to conventional management. Our study had 33.3% of
the patients presenting with more than one atrial arrhythmia.
Involvement of the sinus node may lead to sinoatrial node disease and
bradycardia. Other possible presentations could be idiopathic atrial
enlargement, atrial tumor mimic, macro re-entrant arrhythmias and
AF.6,18
Corticosteroids have been conventionally used to manage myocarditis. A
customised approach to granulomatous myocarditis has been shown to
improve outcomes in patients presenting with ventricular arrhythmias.
Patients with evidence of myocardial inflammation have been shown to
benefit from immunosuppression and based on 18F FDG
PET uptake.19 All our patient’s received
immunosuppression with corticosteroids and methotrexate. After
establishing an etiological diagnosis of granulomatous or lymphocytic
myocarditis we managed our patients with immunosuppression in addition
to standard rate and rhythm control for AF. At follow up there was
recurrence of AF in 26.7% of patients. This was managed by
intensification of immunosuppression along with standard anti-arrhythmic
medications and cardioversion.
Limitations:
This is a single center study with a limited number of patients. The
prospective cohort of patients is from a region where tuberculosis and
sarcoidosis are prevalent. The etiology of myocarditis may vary in
different parts of the world. Nevertheless, the study provides a
framework for the evaluation of AF patients when no cause is readily
evident. Larger studies from multiple regions may be required to shed
light on the etiology of AM in different geographies.
Serological testing for viruses and anti-myosin cardiac antibodies was
not performed.
Though we could follow up our patients for a significant period, longer
follow up may be needed to observe the consequences of this condition.