**4. Clinical findings**

SQTS is characterized by a short QT interval in the ECG, with an asymmetric and sharp T wave, especially in precordial leads. Short or absent ST segments and paroxysmal episodes of atrial or ventricular fibrillation (**Figures 1** and **2**). The most common symptoms are palpitations (30%), syncope (25%) and cardiac arrest (40%) [17]. Ventricular and atrial fibrillation is present in most patients [18]. Cardiac events usually occur in adrenergic situations (noise or exercise), although occasionally it can also occur at rest [19]. Despite no studies focused on diet, any food modifying significantly the potassium levels may affect the QT interval. Symptoms occur in all age groups, with an increasing rate of SCD between 14 and 40 years of age. The probability of presenting with SCD as the first symptom increases with age, reaching 41% at 40 years of age [5]. A slightly male predominance was suggested, but recent analysis showed that although males present syncope more frequently than females, they show a lower risk of arrhythmic events and/or SCD [20]. In addition,

*Short QT Syndrome: Update on Genetic Basis DOI: http://dx.doi.org/10.5772/intechopen.106808*

#### **Figure 1.**

*ECG taken from a 39-year-old patient with SQTS; QT interval: 310 ms, QTc: 355 ms (corrected by using Bazett's formula).*

#### **Figure 2.**

*ECG diagram and cellular ionic currents under normal conditions (A) and SQTS (B). Voltage-gated Na+ and K+ currents define the ventricular action potential and the QT interval of the ECG. The functional effect of IKs, IKr or IK1 gain-of-function or INa or CaL loss-of-function on the ventricular action potential results in the shortening of the action potential associated with SQTS.*

some studies suggest that genes located on the X chromosome may be involved in the regulation of the QTc interval [21].
