Discussion

Dyssynchrony-associated left ventricular dysfunction secondary to ventricular pre-excitation in patients with asymptomatic Wolff–Parkinson–White syndrome has been reported in several recent studies.Reference Tomaske, Janousek and Razek ^{1 –} Reference Peach, Flosdorff and Gebauer ⁵ In these studies, right-sided septal accessory pathway was recognised as the main cause of left ventricular dyssynchrony.Reference Tomaske, Janousek and Razek ^{1 ,} Reference Kwon, Bae and Kim ² In our patient, the vector of the delta wave on 12-lead electrocardiogram suggested involvement of a right anteroseptal pathway. To our knowledge, similar cases have rarely been diagnosed in infants, and only eight cases have been reported previously (Table 1).Reference Kwon, Bae and Kim ^{2 –} Reference Peach, Flosdorff and Gebauer ^{5 ,} Reference Suzuki, Suzuki and Inuzuka ^{7 ,} Reference Kim, Jeong and Huh ⁸ In these patients, a long time elapsed between the diagnosis of left ventricular dyssynchrony and the initiation of resynchronisation therapy, such as catheter ablation and pharmacologic treatment. Some of the patients received anti-failure therapy with diuretics, beta-blockers, angiotensin-converting enzyme inhibitors, and digoxin before resynchronisation therapy began, but all patients poorly responded to treatment. Moreover, left ventricular function worsened or arrhythmias such as supraventricular tachycardia developed in some patients before the initiation of resynchronisation therapy. As previously hypothesised, the cause of left ventricular dysfunction is not only the movement of dyskinetic segments associated with a functional aneurysm but also pathological ventricular remodelling secondary to myocardial perfusion defects, changes in coronary blood flow, and regional molecular abnormalities.Reference Fazio, Mongiovi and Sutera ⁹ Moreover, a causal relation between dyssynchrony-associated left ventricular dysfunction and dilated cardiomyopathy has been reported.Reference Kwon, Carter and Carter ^{3 ,} Reference Kim, Jeong and Huh ^{8 –} Reference Bosser, Marcon and Lethor ¹⁰ Because we considered early resynchronisation therapy essential, we wanted to start resynchronisation therapy at the same time that anti-failure medication was begun.

Table 1 Summary of reports on patients in whom asymptomatic Wolff–Parkinson–White syndrome with severe left ventricular dyssynchrony and dysfunction was diagnosed before 2 years of age.

CA=catheter ablation; HTx=heart transplantations; LV=left ventricle; LVDd=left ventricle end-diastole dimension; SVT=supraventricular tachycardia

Previous studies have reported the effectiveness of catheter ablation for accessory pathway in older children and adults.Reference Tomaske, Janousek and Razek ^{1 ,} Reference Kwon, Bae and Kim ² In contrast, reports on catheter ablation in infants are rare, and low body weight and an age of several months are associated with increased procedural and ablation risks. Pharmacologic therapy is a suitable treatment for infants, but only five cases in which pharmacologic therapy was tried have been reported. Amiodarone (five cases) Reference Kwon, Carter and Carter ^{3 ,} Reference Cadrin-Tourigny, Fournier and Andelfinger ^{4 ,} Reference Suzuki, Suzuki and Inuzuka ^{7 ,} Reference Kim, Jeong and Huh ⁸ and propafenone (one case) Reference Peach, Flosdorff and Gebauer ⁵ have been used, and treatment was successful in four patients given amiodarone and the patient given propafenone. We report the first case to our knowledge to successfully respond to flecainide. Similar to our case, three previously reported patients were given only pharmacologic therapy – without catheter ablation. All of these patients responded to treatment, and normal left ventricular function was completely restored within several months or several years.Reference Cadrin-Tourigny, Fournier and Andelfinger ^{4 ,} Reference Peach, Flosdorff and Gebauer ^{5 ,} Reference Suzuki, Suzuki and Inuzuka ⁷

Flecainide has stronger negative inotropic activity, but is more effective than other sodium-channel blockers for conduction block of accessory pathway associated with Wolff–Parkinson–White syndrome in children. When we treat supraventricular tachycardia with poor responses to pharmacologic treatment with ATP or Ca channel blocker, which suppress atrio-ventricular conduction, we often use Na channel blocker such as flecainide in order to suppress accessory pathway directly. We recognise that we can use flecainide safety in a carefully monitored setting. Because of such experience that flecainide suppresses accessory pathway conduction promptly and absolutely, we considered to use it first in our case. In fact, we could safely use flecainide by performing continuous electrocardiogram monitoring and frequent echocardiographic assessment to detect exacerbations of congestive heart failure. We did not use amiodarone despite previous successful reports because of its adverse effects associated with long-term administration, such as interstitial lung disease, abnormal thyroid function, and corneal pigmentation.Reference Bosser, Marcon and Lethor ¹⁰ In our patient, flecainide was the most suitable treatment not only in terms of efficacy but also safety.