A 7-year-old boy was admitted to our emergency department after losing consciousness for an hour. The boy suffered a sudden cardiac and respiratory arrest 1 h ago while exercising at school. He was immediately given external chest compression and defibrillation used AED equipped in the school. As a result, his heartbeat and respiration recovered. When the boy was sent to our hospital, he was conscious and agitated which was alleviated by sedation and intracranial pressure reduction. His vital signs were measured: heart rate 124/min; respiratory rate 25/min; blood pressure 102/55 mmHg. On his physical examination, the liver and spleen were not touched under the ribs and there was no edema in the lower limbs. The boy and his parents were in generally good health and other family members denied a history of syncope, sudden death or cardiomyopathy.
There were no obvious abnormalities in the brain MRI and video electroencephalogram (VEEG). The electrocardiogram (ECG) revealed Ptf-V1 < -0.04 mm s and biphasic P waves, indicating left atrial enlargement and the chest X-ray revealed an enlarged heart shadow. The echocardiogram showed biatrial enlargement, especially in the left atrium (LA: 32 mm, RA: 30 mm), decreased diastolic function (E/A = 2.6; E Peak deceleration time 130 ms; Constant volume diastolic time 49 ms), moderate mitral valve regurgitation and left ventricular ejection fraction of 51.8%. Except for bilateral enlargement, cardiac magnetic resonance (CMR) indicated no abnormalities (see Figure 1). The ECG at the time of the AED discharge indicated ventricular fibrillation (see Figure 2). Troponin T and brain natriuretic peptide (BNP) levels were normal.
Genetic analysis revealed the boy had a heterozygous missense mutation [c.611(exon8)G>A,p.R204H] of TNNI3 which was not detected in his biological parents and de novo (see Figure 3). This mutation located in exon 19 of TNNI3 which was conserved. We analyzed the mutation using bioinformatics protein function prediction software PolyPhen_2 and Mutation Taster and found the variant is possibly detrimental. Common genetic mutations in arrhythmias such as SCN5A, KCNH2, KCNQ1, CACNA1C, RYR2, and LMNA were not found in the family members.
According to the results above, we concluded that the boy was a patient of primary RCM. At present, the vital signs of the boy are stable. We communicated with the parents and suggested installing an implantable cardioverter defibrillator (ICD) for the boy, but the parents refused. We have informed his parents that a heart transplant may be required if the disease progresses further. At present, the boy is being treated with oral diuretics and metoprolol tartrate tablets and he is in outpatient follow-up.