Catheter ablation, particularly radiofrequency ablation has revolutionized treatment for tachyarrhythmia. It has evolved rapidly over the years and has proven to be first-line therapy for many tachycardias in most of the patients having recurrent symptoms, which limit their productivity and hinder their lifestyle. the use of catheter ablation was first introduced in the late 1960s; it was designed first for recording, where the surgical treatment of cardiac arrhythmia was the main concept. In 1967, the concept of induction of cardiac arrhythmia was first introduced through programmed electrical stimulation. in the late 1970s, Wellen was able to perform programmed electrical stimulation. and record the activation sequences from more than one recording catheter, followed by the development of both the surgical ablation and the intracardiac recordings. Previously the arrhythmia was terminated by surgical maneuvers, for example, surgical excision of the triggered arrhythmogenic focus for atrial tachycardia and cryo excision of the AV junction in case of resistant supraventricular tachycardia. The maze procedure is one of the well-known procedures, particularly during mitral valve surgery complicated with atrial fibrillation (AF), for AF termination.In 1981, the concept of the transvenous catheter was first defined when a patient that was undergoing an electrophysiological recording following defibrillation, where a high-voltage discharge was emitted when the defibrillator electrode hit the catheter electrode at His. This energy caused damage to underlying tissue.. Direct current cardioversion was first used in atrial fibrillation ablation. The direct current was delivered to the distal electrode and a surface electrode; this led to uncontrollable tissue damage. In the 1990s, radiofrequency ablation replaced the direct current. RF energy is an alternating current generated with a frequency of 350 kHz to 700 kHz (usually 500 kHz on commercially available RF generators) delivered in a continuous, unmodulated sinusoidal manner to create thermal injury. The current is delivered in a unipolar fashion from the tip of the catheter electrode to a large surface (100 cm2 to 250 cm2). A patch is placed against the skin where the electric energy is delivered and converted to thermal injury when it passes through the tissue (resistive heating). Large patches are placed on the patient's back as a ground to avoid skin burns. The tissue in direct contact with the catheter is damaged by resistive heating while deeper and surrounding tissues are heated and damaged by conductive heating. Acute lesions show inflammation and hemorrhage around a central area of coagulative necrosis. Areas with inflammation at the border of central necrosis explain the recurrence of arrhythmias later, as the area may contain viable arrhythmogenic tissue that is acutely non-conductive at the time of ablation but can conduct later after the healing process takes place. .
Current ablation equipment allows temperature monitoring and temperature control, which is a valuable tool during radiofrequency ablation procedures as it provides important information regarding the adequacy of tissue heating, minimizes the development of coagulum and lesion size. Newer technical modifications, including a larger distal electrode and saline cooling, have helped to minimize impedance rise and allow the creation of larger and deeper lesions..In this review article, we will discuss the role of catheter ablation in the management of cardiac arrhythmias, summarize the technical aspects of the procedures, highlight the indications for ablation and discuss complications associated with catheter ablation.
The venous system approached mostly are right and left femoral veins. In the case of difficult coronary sinus cannulation, the internal jugular or subclavian vein approach may be used. Diagnostic catheters are inserted to allow pacing, stimulation, and signal recording at the high right atrium, right ventricle (apex or RVOT), His bundle, and the coronary sinus. The left side can be accessed through an antegrade transeptal puncture from the right atrium into the left atrium or a retrograde aortic approach.
However, for VT in the setting of structural heart disease, catheter ablation is generally reserved for failure of drug-therapy or as adjunctive therapy in the setting of frequent implantable cardioverter-defibrillator (ICD) discharges
There are no absolute contraindications for catheter ablation, relative contraindications may include; 
The contraindications are limited to vascular access contraindication as DVT for femoral vein access and PAD and aortic dissection in case of retrograde aortic approach.
Also, the presence of intracardiac thrombi, to prevent the risk of embolization.
Bleeding diatheses and coagulopathy are the main contraindication for catheter ablation. Usually, the electrophysiologist can interfere with the patient's safety with the INR up to 3.
A variety of catheters is available with at least two ring electrodes that can be used for bipolar stimulation and recording. The catheter may be made of woven Dacron or newer synthetic materials such as polyurethane. Woven Dacron catheters are preferred because of their greater durability and physical properties. These catheters have a variable number of electrodes, electrode spacing, and curves to provide a range of options for different purposes. Although they have superior torque characteristics, their greatest advantage is that they are stiff enough to maintain a shape and yet they soften at body temperature so that they are not too stiff for forming loops and bends in the vascular system to adopt a variety of uses.
Synthetic catheters cannot be manipulated or change shapes within the body, so they are less desirable. The synthetic catheters are cheaper and offer smaller sizes (2 to 3 French). Currently, most electrode catheters are size 3 to size 8 French. The smaller sizes are used in children. In adult patients, sizes 5 to 7 French catheters are routinely used. Other diagnostic catheters have a deflectable tip. These are used to reach and record from specific sites (e.g., coronary sinus, crista terminal is, tricuspid valve). In most instances, the standard woven Dacron catheters suffice, and they are significantly cheaper. Mapping catheters fall into two general categories:
Some ablation catheters have a cooled tip, one through which saline is infused to allow for enhanced tissue heating without superficial charring or internal cooling.
Ablation catheters deliver RF energy through tips that are typically 3.5 to 5 mm in length but may be as long as 10 mm. Catheters delivering microwave, laser, cryothermal, or pulsed-ultrasound energy to destroy tissue are currently under active investigation.
In the second category, standard catheters with up to 24 poles that can be deflected to map large and/or specific areas of the atrium (e.g., coronary sinus, tricuspid annulus). Shaped catheters as “halo” record from around the tricuspid ring or a lasso catheter on a deflectable shaft to record from 10 to 20 electrodes in the pulmonary vein ostia, and basket catheters which have up to 64 poles or prongs that spring open and which are used to acquire simultaneous data from within a given cardiac chamber.
A catheter is available from which has five flexible splines with four electrodes on each spline allowing one to acquire 20 sites of activation. The 2-mm interelectrode distance allows for high-density mapping. The floppiness of the splines sometimes makes for variable contact in misinterpretation of data.
More recently a new catheter was has been developed a 64-pole roving catheter. This mapping (mini basket) catheter has an 8 F bidirectional deflectable shaft and a basket electrode array (usual mapping diameter 18 mm) with eight splines, each spline containing eight small (0.4 mm2), low-impedance electrodes (total 64 electrodes). The interelectrode spacing along the spline is 2.5 mm (center-to-center). Mapping can be performed with the basket in variable degrees of deployment (diameter ranging 3 mm to 22 mm). The location of each of the 64 electrodes is identified by a combination of a magnetic sensor in the distal region of the catheter and impedance sensing on each of the 64 basket electrodes. The location of each basket electrode is obtained whether the basket is fully or only partially deployed.
The junction box is a rectangular box that receives the intracardiac signals from the catheters and provides the interface to the physiologic recorder. Multiple switches within the junction box are designated to a recording and stimulation channel which can be selected through the recording apparatus. To minimize noise on the channels, the junction box is mounted close to the patient foot.
The physiologic recorder records, displays, and stores intracardiac and surface recordings. It consists of filters, amplifiers, display screens, and recording software. From the junction box, the physiologic signals are introduced into the recorder. These signals are typically low in amplitude and are amplified before displaying and recording. The recording system amplifies and filters each input channel separately, with most current systems supporting up to 64 or more channels. The amplifiers can automatically or manually adjust gain control. The amplifiers should be mounted as close to the patient table as possible, to reduce the cable length of the intracardiac connections and surface ECGs, which minimizes the signal noise. The amplifier is then connected to the main physiologic recorder through a channel, which, ideally, should run separately from electric power cables. Filters are used to eliminate unnecessary signals that distort electrograms (EGMs).
High pass filters eliminate signals below a given frequency while low pass filters eliminate signals above a given frequency. Most intracardiac electrograms are clearly identified when the signal is filtered between a high pass of 40 Hz and a low pass of 500 Hz.
A programmable stimulator is necessary to obtain electrophysiologic data beyond measurements of conduction intervals. Stimulators are capable of various modes of pacing, including rapid pacing, delivery of single or multiple extra stimuli following a paced drivetrain, and delivery of timed, extra stimuli following sensed beats. Stimulators are capable of delivering variable currents, from 0.1 mA to 10 mA. With the satisfactory positioning of catheters, current thresholds under 2 mA (with 2 ms pulse width) can usually be achieved in both the atrium and ventricle. Higher outputs are seen in the diseased myocardium, within the coronary sinus, and with the use of anti-arrhythmic medications. The output is usually set at twice the diastolic threshold. Pacing at higher outputs is discouraged because may led to the far-field capture and altered the QRS and EGM configuration and may mislead diagnosis, the recommendation is either to start at low amplitude until capture, or start at high output and go low until failure of capture then increase a step.
A primary and backup cardioverter/defibrillator should be available throughout all EP studies, defibrillators deliver energy in a biphasic waveform which offers enhanced defibrillation success. Defibrillation pads are attached to the patient and electrically grounded.
Following personnel are required for an electrophysiology study/ablation.
Counseling of patients and explanation of the procedure is the main step of preparation.
Complete blood count, renal function, and liver functions should be checked, especially in patients who are on antiarrhythmic drugs.
Coagulation profile is checked, especially for patients on anticoagulation.
The patient is draped and the site of vascular access is cleaned with antiseptic agents similar to other cardiac catheterization procedures.
The electrophysiologic study consists of a systematic analysis of dysrhythmias by recording and measuring a variety of electrophysiologic events with the patient in the basal state and by evaluating the patient's response to programmed electrical stimulation. To perform and interpret the study correctly, we have to understand certain concepts and methods, including the different types of electrogram recordings, measurement of atrioventricular (A-V) conduction intervals, activation mapping, and response to programmed electrical stimulation. Knowledge of the significance of the various responses, particularly to aggressive stimulation protocols, is mandatory before employing such responses to make clinical judgments.
This depends on the type of ablation procedure.
Electrograms can be recorded as unfiltered or filtered unipolar signals or bipolar signals.
Cardiac mapping is the process by which arrhythmias are characterized and localized. Conventional mapping involves acquiring electrogram data from fixed and moving catheters and creating mental activation maps with two-dimensional fluoroscopic images.
Three-dimensional anatomic localization of the catheter assists in mapping and ablation. These technologies involve the acquisition of multiple electrogram locations to provide a high-resolution activation, voltage, or propagation map. In addition to correlating local electrograms to three-dimensional cardiac structures, these newer mapping techniques reduce radiation exposure to the patient and physician. The most widely used electroanatomic mapping system localizes the mapping and ablation catheter through a magnetic field. Three coils located beneath the patient generate ultra-low magnetic fields that temporally and spatially code the area within the patient. With a magnetic field sensor in its tip that is referenced to an externally located patch on the patient, the catheter can be displayed and recorded in three dimensions with intracardiac electrograms.
Another technology offers electroanatomic mapping by creating electrical fields between opposing pairs of patch electrodes located on the patient’s chest. Six patches are placed on the body to create three orthogonal axes with the heart located centrally. A transthoracic electrical field is created through each pair of opposing patch electrodes, and the mapping catheter delivers this signal for processing.
Magnetic navigational systems are more frequently being utilized for mapping and ablation of various arrhythmias as well as for guidance in the placement of left ventricular leads. This system uses large external magnets that sit closely on each side of the patient allowing for magnetic navigation of percutaneous devices. The catheters or guide-wires have small magnetic tips that respond to changes in magnetic field vectors that are programmed by the physician remotely. Advantages of this approach include a softer catheter tip which likely reduces the trauma that can occur with stiffer ablation catheters as well as decreasing physician exposure to radiation. Other robotic navigation systems are also in development.
Measurements of the Basic Intervals 
Complications associated with catheter ablation depends on the type of arrhythmia and the site of ablation.
Catheter ablation is now the mainstay treatment of most arrhythmia, it can offer a better choice for those suffering recurrent arrhythmias, and is a permanent treatment with a greater than 90% success rate of AVRT and AVNRT ablation. The best choice for the symptomatic accessory pathway, atrial flutter and atrial fibrillation, and ultimately the best choice for those suffering drug-refractory VT or PVC-induced cardiomyopathy.
Catheter ablation is now the mainstay treatment of most arrhythmia, it can offer a better choice for those suffering recurrent arrhythmias, and is a permanent treatment with a greater than 90% success rate of AVRT and AVNRT ablation. While catheter ablation is usually done by a cardiologist, the monitoring and follow-up of the patients are done by the primary care provider, internist, and nurse practitioner. Even though the success of catheter ablation is high for many atrial arrhythmias, the procedure is also associated with a fair number of serious complications that include death, pulmonary vein stenosis, esophageal perforation, heart block requiring a pacemaker, stroke, phrenic nerve injury, and vascular access complications. It is important to educate the patient on the potential complications before the procedure. 
|||Guidelines for Clinical Intracardiac Electrophysiological and Catheter Ablation Procedures. A report of the American College of Cardiology/American Heart Association Task Force on practice guidelines. (Committee on Clinical Intracardiac Electrophysiologic and Catheter Ablation Procedures). Developed in collaboration with the North American Society of Pacing and Electrophysiology. Circulation. 1995 Aug 1; [PubMed PMID: 7634483]|
|||Durrer D,Schoo L,Schuilenburg RM,Wellens HJ, The role of premature beats in the initiation and the termination of supraventricular tachycardia in the Wolff-Parkinson-White syndrome. Circulation. 1967 Nov [PubMed PMID: 6050923]|
|||Wellens HJ, Value and limitations of programmed electrical stimulation of the heart in the study and treatment of tachycardias. Circulation. 1978 May [PubMed PMID: 346253]|
|||Coumel P,Aigueperse J,Perrault MA,Fantoni A,Slama R,Bouvrain Y, [Detection and attempted surgical exeresis of a left auricular ectopic focus with refractory tachycardia. Favorable outcome]. Annales de cardiologie et d'angeiologie. 1973 May-Jun [PubMed PMID: 4731537]|
|||[PubMed PMID: 28357007]|
|||[PubMed PMID: 7270717]|
|||[PubMed PMID: 7097946]|
|||Weber H,Schmitz L, Catheter technique for closed-chest ablation of an accessory atrioventricular pathway. The New England journal of medicine. 1983 Mar 17 [PubMed PMID: 6828100]|
|||Nath S,DiMarco JP,Haines DE, Basic aspects of radiofrequency catheter ablation. Journal of cardiovascular electrophysiology. 1994 Oct [PubMed PMID: 7874332]|
|||Michelucci A,Antonucci E,Conti AA,Alessandrello Liotta A,Fedi S,Padeletti L,Porciani MC,Prisco D,Abbate R,Gensini GF, Electrophysiologic procedures and activation of the hemostatic system. American heart journal. 1999 Jul [PubMed PMID: 10385775]|
|||[PubMed PMID: 10683351]|
|||[PubMed PMID: 19652728]|
|||[PubMed PMID: 31075787]|
|||Dewire J,Calkins H, Catheter Ablation of Atrial Fibrillation to Maintain Sinus Rhythm. Journal of atrial fibrillation. 2013 Feb-Mar [PubMed PMID: 28496812]|
|||Peters NS, Catheter ablation for cardiac arrhythmias. BMJ (Clinical research ed.). 2000 Sep 23 [PubMed PMID: 10999884]|
|||Del Carpio Munoz F,Buescher T,Asirvatham SJ, Teaching points with 3-dimensional mapping of cardiac arrhythmias: taking points: activation mapping. Circulation. Arrhythmia and electrophysiology. 2011 Jun [PubMed PMID: 21673021]|
|||[PubMed PMID: 21156773]|
|||[PubMed PMID: 31855343]|
|||[PubMed PMID: 8540455]|
|||Ren JF,Marchlinski FE,Callans DJ, Left atrial thrombus associated with ablation for atrial fibrillation: identification with intracardiac echocardiography. Journal of the American College of Cardiology. 2004 May 19 [PubMed PMID: 15145112]|
|||Katritsis DG, Catheter Ablation of Atrioventricular Nodal Re-entrant Tachycardia: Facts and Fiction. Arrhythmia & electrophysiology review. 2018 Dec [PubMed PMID: 30588309]|
|||Joseph JP,Rajappan K, Radiofrequency ablation of cardiac arrhythmias: past, present and future. QJM : monthly journal of the Association of Physicians. 2012 Apr [PubMed PMID: 22080101]|
|||[PubMed PMID: 10026355]|
|||[PubMed PMID: 10758931]|
|||Robbins IM,Colvin EV,Doyle TP,Kemp WE,Loyd JE,McMahon WS,Kay GN, Pulmonary vein stenosis after catheter ablation of atrial fibrillation. Circulation. 1998 Oct 27 [PubMed PMID: 9788832]|
|||Eitel C,Ince H,Brachmann J,Kuck KH,Willems S,Gerds-Li JH,Tebbenjohanns J,Richardt G,Hochadel M,Senges J,Tilz RR, Atrial fibrillation ablation strategies and outcome in patients with heart failure: insights from the German ablation registry. Clinical research in cardiology : official journal of the German Cardiac Society. 2019 Feb 20; [PubMed PMID: 30788620]|
|||Yi F,Hou W,Zhou C,Yin Y,Lu S,Duan C,Cao M,Li M,Toft ES,Zhang H, Radiofrequency Ablation Versus Antiarrhythmic Drug Therapy for Atrial Fibrillation: Meta-Analysis of Safety and efficacy1. Journal of cardiovascular pharmacology. 2019 Jan 25; [PubMed PMID: 30688797]|