We have already talked about the electrical stability of a young heart (e.g., severe hypok alemia could be unnoticed in a newborn while the same plasma level of potassium could be lethal for an adult). VT is infrequent in children and represents less than 1% of clinical arrhythmias, while benign PVCs are much more frequent. Up to 20% of children may present benign PVCs in the first year of life. PVCs in the newborn and in the young should be judged according to morphology and not according to number. Twenty four thousand monomorphic, isolated PVCs are less worrying than 24 polymorphic or repetitive PVCs. The presence of isolated PVCs in infancy is not worrying; on the contrary, usually the sooner they start, the sooner they end. Much more worrying are PVCs starting in a “healthy” teenager, since several causes such as myocarditis or cardiomyopathy need to be ruled out. According to some authors, PVCs originating in the left ventricle with an RBBB morphology may disappear during childhood, while PVCs originating from the right ventricle with an LBBB morphology tend to persist.

Again, a VT with LBBB morphology and thus arising in the right ventricle, once ARVC has been ruled out, is usually more benign than the VT originating in the left ventricle. In fact, the RV is the well-known site of benign arrhythmias, mainly represented by RVOT VT. To differentiate VT from SVT clinically, there is no cutoff for the heart rate before the ECG reading, but in the newborn and the nursling, VT is usually slower than SVT. Moreover, in small children, an accelerated idioventricular rhythm (AIVR) alternating with a regular SR is not a rare event among VTs.

In pediatric age, ventricular tachycardia (VT) is extremely rare. While a cardiologist sees 1000 VTs frequently associated with a myocardial infarction or a previous myocardial infarction, a pediatric cardiologist sees ten VTs all caused by different situations (Table 12.1). In childhood, VT can have a narrow QRS complex. All signs currently used in cardiology to diagnose a VT are valid: AV dissociation, VA retroconduction, and the presence of capture and fusion beats. If the aspect of the QRS complex is similar to a classic bundle branch block, we are usually more likely to be dealing with an SVT conducted with aberrancy; furthermore, the knowledge of the different types of youth VT is mandatory (RVOT VT has an LBBB morphology with vertical axis, while Belhassen’s VT has an RBBB associated with a left anterior fascicular block) (Fig. 12.1). Adenosine can be used as a diagnostic tool, considering that a low rate of VT is responsive to adenosine administration (less than 1%). Furthermore, it is important to establish if there is a structural cardiac disease or if VT appears in the absence of a structural heart disease. The young patient without known cardiac disease normally presents an IVT. The most common is the RVOT VT; moreover, the right ventricle is the site of different types of IVT such as moderator band VT, tricuspid annulus VT, and papillary muscle VT. The left ventricle is the site of the idiopathic left ventricle tachycardia (ILVT) originating from the left posterior hemifascicle (also known as Belhassen’s VT or verapamil-sensitive VT) [1]. There are also other forms of left-sided IVT, such as left ventricular outflow tachycardia (LVOT) with an LBBB morphology like RVOT but with a rapid transition in the precordial leads (R > S in V1 and V2), mitral annulus VT, great cardiac vein VT, left anterior hemifascicle VT, papillary muscle VT, and left ventricular summit VT. Nonidiopathic VT could be the clinical manifestation of myocarditis, which should always be considered either as an acute presentation or a previous undiagnosed myocarditis with fibrosis, cardiomyopathies, or cardiac tumors (hamartomas and cardiac tumors should be considered in young children with incessant VT).

Among CHD, tetralogy of Fallot is the most affected by VT in the late follow-up. Mustard or Senning repairs may be complicated by VT due to a failing systemic right ventricle [2]. The incidence of VT in patients with tetralogy of Fallot is 4%, while the sudden death incidence 20 years after the surgical correction is 2% [3]. Risk factors for sudden death are surgical correction consisting in annular patch, severe pulmonary regurgitation, left ventricular systolic dysfunction, and QRS duration >180 ms. Other congenital heart diseases associated with VT are coronary anomalies, Ebstein or Ebstein-like severe tricuspid valve dysplasia, univentricular heart with severe impairment of systolic function, and patients with Eisenmenger syndrome. Coronary anomalies associated with VT are ALCAPA and ACAOS. The clinical presentation of ALCAPA is left ventricular dysfunction in the nursling, while in late childhood it could be diagnosed following a VT/FV starting after physical exercise or emotional stress; it should be noted that the rest ECG is rarely normal. On the contrary, ACAOS patients have a normal ECG.

The most common cause of VT and sudden death (SD) in young patients is hypertrophic cardiomyopathy [4]. The prevalence of HCM is 1:500; except for the mutation of sarcomeric proteins transmitted in the autosomic dominant way during childhood, the hypertrophic phenotype is shared by several syndromes such as Pompe disease, Danon disease, Noonan syndrome, and Friedreich ataxia and other neuromuscular syndromes such as Anderson-Fabry disease, Kearns-Sayre syndrome, Barth syndrome, etc. In these patients, association with short PR interval and pre-excitation is frequent.

Another cause of VT and SD is ARVC, where VT typically has an LBBB morphology. ARVC could be difficult to diagnose at the beginning of the disease, and differential diagnosis with benign RVOT could be problematic. Typical ECG patterns such as negative T waves in the right precordial leads could be fleeting and transient, while the epsilon wave, a pathognomonic sign, appears when the disease is quite advanced and has a low sensitivity. As said before, the distinction between ARVC and RVOT is crucial; the first is an evolving disease associated with a high risk of SD, while the second is a benign condition with a nonnegligible rate of spontaneous resolution and an RFCA success rate >90%.

Long QT syndrome is the paradigm of channelopathies; nevertheless, the opposite condition of short QT syndrome recently entered the large family of channelopathies [5]. It is important to acknowledge that “electrical” diseases are associated with circadian or longer ECG variation and faced with a borderline ECG it is important to collect a detailed medical and family history. In addition, the cardiologist should (1) perform the ECG recording at different times and body temperatures, (2) analyze the family’s ECGs, and (3) perform an exercise test and a Holter ECG (the last one is important in young children who may not be able to perform an exercise test). Furthermore, long QT syndrome diagnosis is based on a probabilistic evaluation that includes instrumental evaluation, clinical examination, and molecular exams (Schwartz score).

Brugada syndrome is a channelopathy inherited in an autosomal dominant manner, characterized by the presence of ST elevation in the right precordial leads. Up to now, 12 mutations have been described; mutation of the SCN5A gene with a downregulation of the sodium channel is the most frequent mutation found in 15–20% of cases, while the mutation of CACNA1c expressed with the loss of calcium channel function has been described in 7–10% of cases. The resting ECG may present a long PR interval, which is rare in young patients and therefore could be an important clue.

Hence, the right ventricle outflow tract is the focus of most arrhythmias and those purely “electrical” such as RVOT VT and, on the other hand, those associated with a structural alteration such as tetralogy of Fallot or ARVC. The odd vulnerability of RVOT is due to genetic characteristics, embryological development (crista neuralis), and, finally, anatomic features of this area, which is involved in several congenital heart diseases (Fig. 12.2). The left ventricle has its own “Bermuda Triangle” too: the postero-basal aspect. In fact, this is a site involved in different situations with significant arrhythmic expressions such as mitral valve prolapse, Duchenne dystrophy, nonischemic fibrosis, myocarditis, and ARVD extended to the left ventricle (Fig. 12.3).