*2.5.2 Dual-chamber pacing*

Later, in the mid-1970s, a dual-chamber pacing—one pacing electrode in the ventricular apex and another in the atrium of heart's right side—has been introduced in medical practice [6]. The dual-chamber pacing most closely resembles the normal physiology of cardiac initiation, compared to other pacemaker modes. Therefore, this device is also called as a physiological pacemaker, which ensures atrium-ventricle timing (synchronization) and suppresses atrial fibrillation (AF), that is, reduces the risk of pacemaker syndrome, which represents the clinical consequences of atrioventricular dyssynchrony after pacemaker implantation. Dual-chamber implantable cardioverter defibrillators (ICDs) provide dual-chamber pacing to prevent both atrial fibrillation and supraventricular tachycardia not available in single-chamber ICDs [16]. Nowadays, most of the currently implanted ICD devices provide overdrive pacing to convert ventricular tachycardia (VT) or deliver electrical shocks to restore normal rhythm in the case of sustained ventricular tachycardia or ventricular fibrillation.

#### *2.5.3 Biventricular pacing*

Biventricular pacing, also called as cardiac resynchronization therapy (CRT), is for people with heart failure due to abnormal work of electrical systems in the heart. The CRT system consists of two components—the pulse generator, or device, and thin, insulated wires called leads. A CRT device delivers tiny amounts of electrical energy to the heart through these leads to restore the normal timing of heartbeats, causing both the ventricles to pump more efficiently. There are two types of CRT devices. One is a special kind of pacemaker called as a cardiac resynchronization therapy pacemaker (CRT-P) or "biventricular pacemaker" [17]. The other is one includes additionally a built-in implantable cardioverter defibrillator (ICD). This device is called a cardiac resynchronization therapy defibrillator (CRT-D), which is used to treat ventricular tachycardia and ventricular fibrillation and avoid sudden cardiac arrest.

The CRT-P device functions like a normal pacemaker to treat slow heart rhythms, as well as delivers small electrical impulses indirectly, however, to the left ventricle to help the both the ventricles contract at the same time.

The CRT-D device combines a dual-chamber pacemaker and a defibrillator. It has the same three leads as a CRT-P, but it can also deliver a high-energy shock to treat fast ventricular arrhythmias (VAs) such as ventricular tachycardia or ventricular fibrillation, which can cause sudden cardiac arrest.

#### *2.5.4 Alternative pacing sites (septum pacing)*

It expected that the right ventricular septal pacing is a valid alternative to apical pacing, which most mimics normal physiology. Whether the pacing of right ventricular outflow tract septum (RVOTS) is superior to right ventricular apex (RVA) pacing with respect to cardiac function is still not fully clear. Placing the pacing electrode on the mid-septum may be more challenging than the RVOTS case. Anyway, the septal pacing is of great interest [18]. There is no need to pass the tricuspid valve, but the outcome is similar to right ventricle pacing.

His bundle pacing in humans was first reported in 2000 [19]. Permanent His bundle pacing is an emerging technique to deliver a more physiological pattern of ventricular pacing and has the potential to mitigate the adverse consequences of chronic right ventricular pacing and promote atrioventricular and intraventricular synchrony. His bundle pacing is a technique that uses the native His-Purkinje system to maintain a physiological pattern of ventricular activation. It is a good alternative to RV and biventricular pacing. However, it is currently undergoing clinical trials to verify whether it has any clinical advantages over RVP or biventricular pacing.

### **3. Radiofrequency ablation to avoid arrhythmias**

#### **3.1 The role of ablation in suppressing arrhythmias**

Though the electrical pacing enables the suppressing of suddenly appearing arrhythmic phenomena, the most effective outcome can be achieved by using ablation techniques and, sometimes, both ablation and pacing methods together.

Radiofrequency ablation (RFA) has revolutionized the treatment of both supraventricular and ventricular arrhythmias. However, conventional, X-ray-guided mapping techniques have a limited utility in the ablation of more complex arrhythmias, such as in atrial tachycardia, atrial fibrillation (AF), and ventricular tachycardia (VT). By using 3D technologies and catheters permitting faster acquisitions, in

association with high-performance imaging techniques, the development of novel mapping systems has led to the overcoming of these limitations [4].
