Catheter ablation General consideration

1. Catheter ablationGeneral consideration El-Sayed M.Farag (Msc.Cardiology)

2. For most cardiac arrhythmias, medical therapy with antiarrhythmic drugs is not completely effective. In addition to poor or sporadic efficacy, such drugs can be associated with many bothersome and rarely fatal side effects, proarrhythmia, cost, and inconvenience. For this reason, nonpharmacologic interventions, initially using a surgical approach and more recently with catheter ablation, have played an increasingly important role in the management of cardiac arrhythmias. Catheter ablation involves the use of an electrode catheter to destroy small areas of myocardial tissue or conduction system, or both, that are crucial to the initiation or maintenance of cardiac arrhythmias. Arrhythmias most likely to be amenable to cure with catheter ablation are those that have a focal origin or involve a narrow, anatomically defined isthmus.

3. Before 1989, catheter ablation was performed primarily with high-energy direct-current shocks. Typically a multipolar electrode catheter was positioned in the heart and attached to a standard defibrillator. Under general anesthesia, 360 J of direct-current energy was delivered between the distal electrode and a patch placed on the patient's chest. This energy produced an explosive flash, heat, and increased pressure. Myocardial injury resulted from heat, barotrauma, and direct electric injury. More recently, direct-current energy has been replaced with radiofrequency energy as the preferred energy source during catheter ablation procedures.

4. RADIOFREQUENCY CATHETER ABLATION • Catheter ablation procedures are performed in a specially equipped catheterization laboratory, on either an inpatient or outpatient basis. Patients receive conscious sedation before and during the procedure. Two to five multipolar electrode catheters are inserted percutaneously under local anesthesia into a femoral, brachial, subclavian, or internal jugular vein and positioned in the heart under fluoroscopic guidance. Each electrode catheter has four or more electrodes. Typically the most distal electrode pair is used for pacing and the delivery of critically timed extra stimuli, whereas the proximal electrodes are used to record electrograms from localized regions within the heart.

5. EP Diagnostic catheters Boston Scientific2003

6. Decapolar diagnostic catheter Boston Scientific 2003

7. EP Diagnostic Catheters Placement Boston Scientfic2003

8. Sites of electrical recording Quated from Hurst2001

9. The depolarization of the atria starts from the RA and then to the proximal CS and lastly to the distal CS .Also note the ventricular potentials seen on the CS tracings

10. Cardiac Mapping • Flurosopic Mapping Right anterior obligue reveal the ablation catheter located at the base of Koch triangle for ablation of AVNRT. There are also catheters at high right atrium, HIS bundle region, Coronary Sinus, and right ventricular apex. 

11. AVNRT with RBBB was only induced in one patient with cycle length of 340 milliseconds. There are 4 surface EKG (I, II, V1, and V5). The intracardia electrogram revealed high right atrium, His Bundle electrogram proximal (HBE p) and distal (HBE d), Coronary Sinus (CS) from proximal to distal (P,2,3,4,and D), right ventricular apex (RVA), and ablation/mapping catheter proximal and distal (ABL P/D).

12. Non contact mapping • Endocardial Solutions Mapping showing the earliest activation (in red color) in a case of focal atrial tachycardia. The upper right hand panel displays AP projection on the left and LAO projection on the right side. The lower half of the picture shows intracardiac tracings. TV= Tricuspid annulus; IVC= Inferior vena cava; HIS= His bundle; APP= Anteroposterior projection. Quated from indian journal of pacing and electrophysiology2003

13. Contact Mapping • Electroanatomic mapping on CARTO system of focal right atrial tachycardia showing  earliest activation (red color) below cristaterminalis. Indian journal of paing and electrophysiology 2003

14. Basket mapping of normal sinus rhythm. The right upper panel shows the potential map, the earliest activation (red color) at the site of sinus node. In addition, the splines of basket catheters are aligned with the endocardial wall. The right lower panel shows isochronal map of the sinus rhythm. The left panel shows the electrogram from the different splines. SN= Sinus node; TV= tricuspid valve; AVN= Atrioventricular node. Indian journal of pacing and electrophysiology 2003

15. Mapping on Real Position Management System, showing the reference catheter position in coronary sinus and right atrium; and, ablation / mapping catheter in left atrium (AP projection). CS= Coronary Sinus; RV= Right ventricle; ABL= ablation catheter; RSPV= Right superior pulmonary vein; LSPV= left superior pulmonary vein; LIPV= left inferior pulmonary vein. Indian Journal of pacing and electrophysiology 2003

16. Catheter ablation now is performed primarily using radiofrequency energy. Radiofrequency energy, 50 W, is delivered for 30 to 60 seconds as a continuous, unmodulated, sinusoidal waveform with a frequency of approximately 500,000 cycles/s between the 4-mm tip of a deflectable ablation catheter and a ground plate positioned on the patient's back or chest. Most catheter ablation systems in use today monitor the temperature of the ablation electrode and adjust power output automatically to achieve a targeted electrode temperature of 60°C to 70°C.

17. Ablation Catheter Boston Scientific 2003

18. Ablator Boston Scientific 2003

19. Thermal injury is the principal mechanism of tissue destruction during radiofrequency catheter ablation procedures.Temperature-dependent depolarization of myocardial tissue and loss of excitability occur at temperatures greater than 43°C. Reversible loss of excitability occurs at tissue temperatures between 43°C and 50°C. Irreversible tissue injury occurs at temperatures greater than 50°C.When the temperature at the electrode tissue interface exceeds 100°C, tissue immediately adjacent to the electrode desiccates, and plasma proteins denature to form a coagulum.

20. The Coagulum Boston Scientific 2003

21. The development of a coagulum results in a rapid increase in impedance, which leads to a dramatic decrease in current density, limiting further lesion growth. The lesions created during radiofrequency catheter ablation procedures are small (<5 mm) and have well-demarcated borders . Methods for improved cooling of the electrode have been developed to allow delivery of higher radiofrequency power. These include the use of larger (8 mm) electrodes, which receive greater convective cooling by the blood, and saline-irrigated electrode tips, in which the electrode is cooled actively.Most ablation catheters are designed specifically for the delivery of radiofrequency current, although ultrasonic,microwave, laser,and cryoablative techniques also have been investigated.

22. Catheter Ablation for Supraventricular Arrhythmias • The therapeutic options for patients with supraventricular arrhythmias include pharmacologic therapy, arrhythmia surgery, and catheter ablation. The optimal management of an individual patient depends on many factors, including the type of arrhythmia, associated symptoms, frequency and duration of episodes, concomitant disease, and patient preference. With the exception of Wolff-Parkinson-White syndrome, supraventricular arrhythmias generally are not life-threatening.

23. From the perspective of catheter ablation, supraventricular arrhythmias can be classified into atrial tachycardia, atrial flutter, atrial fibrillation, accessory pathways or Wolff-Parkinson-White syndrome, and atrioventricular nodal reentrant tachycardia. Catheter ablation of the atrioventricular junction also is used to control the ventricular response in some patients with supraventricular arrhythmias (mainly atrial fibrillation) that cannot be cured with catheter ablation and that are associated with a rapid ventricular response despite the use of pharmacologic therapy. The technique, results, and complications associated with ablation of each of these arrhythmias is discussed.

24. Atrial Tachycardia • The term atrial tachycardia refers to a group of arrhythmias confined to the atrium that have a rate less than 240 beats/min. Atrial tachycardias, which have a focal site of origin or result from macroreentry involving a crucial isthmus of atrial tissue, are amenable to cure with radiofrequency catheter ablation. From an ablation perspective, two major types of atrial tachycardia can be considered: focal (or ectopic) atrial tachycardia and scar-mediated (or incisional) atrial tachycardia.

25. Focal atrial tachycardia may present as a paroxysmal or a sustained arrhythmia. The mechanism of the tachycardia may be elucidated by pharmacologic and pacing maneuvers and may be classified as automatic, triggered, or reentrant. The origin of these arrhythmias may be in the right or left atrium, usually near the pulmonary vein orifices, right atrial appendage, or crista terminalis. In the automatic and triggered tachycardias, catheter ablation is performed by manipulating one or more steerable electrode catheters in the right or left atrium to identify the site of earliest atrial activation, usually at least 30 ms before onset of the P wave.

26. Earliest atrial activation before ablation of atrial tachycardia. Quated from Hurst 2001

27. Once the site is identified, 25 to 50 W of radiofrequency energy is delivered for 30 to 60 seconds. Results of radiofrequency catheter ablation of focal atrial tachycardias have been published in several series. The success rate for ablation among a collective total of 252 patients reported in 16 relevant publications included in their review was 93%. The collective recurrence rate was 7%. The Biosense Carto system has been shown to facilitate mapping of sustained focal atrial tachycardia.

28. Incisional atrial tachycardia is mediated by macroreentry around the scar of a prior surgical atriotomy. These tachycardias frequently are seen as late sequelae after surgical repair of congenital heart disease[.Optimal ablation sites are those that occur within a protected isthmus of slow conduction that typically develops between one end of an atriotomy scar and a nearby anatomic barrier, such as the inferior vena cava, superior vena cava, or tricuspid annulus.The extent of the atriotomy scar may be mapped by identifying sites with distinct double potentials. The two deflections are separated widely near the middle of the scar and coalesce at the ends.

29. In isthmus-dependent flutter, activation proceeds along the atrial side of the tricuspid annulus in either clockwise or counterclockwise direction , and the subeustachian isthmus serves as a crucial zone of slow conduction, enabling reentry to sustain. Counterclockwise isthmus-dependant flutter,also called common atrial flutter,is characterized by biphasic flutter waves in II,III,and aVF .Clockwise isthmus- dependant flutter characterized by upright fluter waves in II,III,and aVF.

30. Non-isthmus-dependent flutter refers to any fixed reentrant atrial circuit that does not involve the subeustachian isthmus. The circuit often develops in the setting of scar tissue. This scar tissue may represent microreentry within diseased tissue or macroreentry around a surgical scar. The latter differs from scar-mediated atrial tachycardia (described earlier) only in rate. Atypical atrial flutter involves an activation sequence that varies from one atrial beat to another. In this case, the reentrant pathway is not fixed, and the arrhythmia is mechanistically indistinguishable from coarse atrial fibrillation.

31. Atrial Flutter • Atrial flutter is an atrial arrhythmia characterized by a regular rate, a uniform morphology, and a rate greater than 240 beats/min. Atrial flutter is usually accompanied by a fixed 2:1 ventricular response, and it is this rapid ventricular response that results in most symptoms. Atrial flutter may be observed transiently after cardiac surgery or may persist for months to years. Many different forms of atrial flutter exist, which has led to multiple classification schemes. A simple but useful way to categorize atrial flutter is as (1) isthmus dependent, (2) non-isthmus dependent, and (3) atypical forms. Isthmus-dependent atrial flutter is named as such because the reentrant circuit involves the subeustachian isthmus in the inferior aspect of the right atrium between the tricuspid annulus and the eustachian valve.The complete circuit has been shown also to involve atrial septal tissue, the anterior roof of the right atrium, and the lateral wall of the atrium anterior to the crista terminalis.

32. Isthmus-dependent and non-isthmus-dependent atrial flutters can be cured withcatheterablation In isthmus-dependent flutter, the subeustachian isthmus represents an ablation target. Lesions are placed in one or more lines across the isthmus from tricuspid annulus to the inferior vena cava. In non-isthmus-dependent flutter, the slow conduction zone is identified with entrainment mapping, then becomes the ablation target. In contrast, atypical atrial flutter does not rely on an anatomically defined circuit and cannot be cured by ablation of a single target.

33. Catheterablation of typical atrial flutter is performed using a deflectable ablation catheter positioned in the inferior right atrium, usually by the right femoral vein. In early series of these procedures, lesions were placed at putative exit sites of the slow conduction isthmus until atrial flutter terminated.Recurrence rates were relatively high with this approach. In subsequent work, the importance of achieving bidirectional conduction block in the subeustachian isthmus was established. Use of this strategy has led to an acute success rate of 100% and recurrence rates of 7% in four published series.

34. Site of atrial flutter ablation َQuated from Indian Journal of pacing and electrophysiology 2003

35. Ablation of atrial flutter

36. An unresolved issue in atrial flutter ablation is whether anticoagulation is required before or after the ablation procedure. Because thromboembolic events can be associated with cardioversion of atrial flutter. It seems appropriate to manage patients for ablation as if they are undergoing cardioversion. In practice, patients are given warfarin (Coumadin) for at least 4 weeks before ablation, and warfarin is discontinued 3 days before the procedure, then restarted the night after. Anticoagulation is continued for at least 1 month after the procedure.

37. Atrial Fibrillation • Swartz et alare credited with being the first to show that chronic atrial fibrillation can be cured usingcatheterablation techniques. In this landmark report, presented at the American Heart Association Meeting in 1994, these authors reported that creation of linear lesions in the right and left atrium results in a progressive increase in the organization of atrial activity until sinus rhythm is restored. The placement of the lesion lines was designed to emulate those placed surgically in the Maze procedure developed by Cox et al.

38. An initial series of three patients who underwent successful ablation of atrial fibrillation was published in 1994. Later that year, Haissaguerre et al reported the successful ablation of paroxysmal atrial fibrillation in a patient with the creation of three linear lesions in the right atrium, two longitudinal and one transverse, using a specially designed 14-pole ablation catheter.

39. Haissaguerre et al found that a purely right-sided ablation approach was successful in 33% of patients and that a higher success rate (60%) could be achieved with the addition of ablative lesions placed in the left atriumThese investigators also found that linear lesions often were arrhythmogenic because of gaps in the ablative lines, yet many patients ultimately were cured with ablation of a single rapidly firing ectopic focus. These ectopic foci were found at the orifices of the left or right superior pulmonary veins or near the superior vena cava.

40. The foci generally were found in the superior veins, most of which were well inside the veins (9 to 40 mm from the orifice). In a separate report, the same group described their experience in locating and ablating right atrial foci in eight patients with paroxysmal atrial fibrillation. These foci were found along the crista terminalis or near the coronary sinus ostium.

41. Mapping the ectopic foci requires the presence of frequent bursts of fibrillatory activity or at least of premature atrial beats. The site of earliest activity associated with these initiating beats then must be identified. Ideally a site is found with local activity preceding the ectopic P wave by 40 to 160.Provocative maneuvers, including isoproterenol and adenosine infusions and burst pacing, may be required to elicit atrial ectopy. It is unclear, however, whether provoked ectopy matches that which occurs clinically. Because ectopic beats are fleeting, it is difficult to map their origin systematically.

42. Conversion of atrial fibrillation to sinus rhythm on achievement of conduction block from the right superior pulmonary vein (RSPV) to the left atrium during energy delivery. Note the continuation of fibrillatory activity in the ostium of the RSPV. From top to bottom, Surface ECG lead V1 is displayed followed by bipolar intracardiac recordings from the high right atrium (HRA), poles 4,5 and 5,6 of the Lasso catheter positioned in the ostium of the RSPV (PV 4,5 and PV 5,6), and the ostium of the coronary sinus .

43. Spontaneous termination of fibrillatory activity in the RSPV 20 minutes after ablation.

44. Ablation systems now are being developed using balloon-tipped ablation catheters that allow for the rapid creation of circumferential lesions at the junction between the pulmonary veins and left atrium. If these systems are proved safe and effective, catheterablation of focally initiated atrial fibrillation may become a routine procedure based only on anatomic considerations.

45. Lasso Catheter Biosense Webster 2002

46. Preexcitation Syndromes (Atrioventricular Reciprocating Tachycardia), Wolff-Parkinson-White Syndrome, and Concealed Pathways • Accessory pathways are anomalous extranodal connections that connect the epicardial surface of the atrium and ventricle along the atrioventricular groove. Accessory pathways can be classified based on their location along the mitral or tricuspid annulus; and whether they are capable of antegrade conduction, retrograde conduction, or both. Accessory pathways that are capable only of retrograde conduction are concealed, whereas those capable of antegrade conduction are manifest, showing preexcitation on a standard electrocardiogram (ECG).

47. The termWolff-Parkinson-White syndrome is reserved for patients who have preexcitation and symptomatic tachyarrhythmias. Among patients with Wolff-Parkinson-White syndrome, atrioventricular reciprocating tachycardia (AVRT) is the most common arrhythmia, occurring in 75% of patients. AVRT is subclassified further into orthodromic and antidromic AVRT. During orthodromic AVRT, the reentrant impulse uses the atrioventricular node and specialized conduction system for conduction from the atrium to the ventricle and uses the accessory pathway for conduction from the ventricle to the atrium. During antidromic AVRT, the reentrant impulse travels in the reverse direction with conduction from the atrium to the ventricle occurring through the accessory pathway.

48. Mapping of concealed accessory pathways and more accurate localization of manifest accessory pathways require analysis of the retrograde atrial activation sequence or antegrade ventricular activation sequence. Right-sided and posteroseptal accessory pathways typically are localized and ablated using a steerable electrode catheter with a 4-mm distal electrode positioned along the tricuspid annulus or in the coronary sinus os from the inferior vena cava. The location of left-sided accessory pathways can be determined using a multipolar electrode catheter positioned in the coronary sinus, which runs parallel to the left atrioventricular groove, or with a steerable catheter positioned in the left atrium or ventricle. Once localized to a region of the heart, precise mapping and ablation are performed using a steerable 4-mm tipped electrode catheter positioned along the mitral annulus using the transseptal or retrograde aortic approach.

49. Locations of accessory pathyways Quated from Hurst 2001

50. Appropriate sites for radiofrequency energy delivery during ablation of manifest accessory pathways are characterized by early ventricular activation, the presence of an accessory pathway potential, and stability of the local electrogram. Appropriate sites for energy delivery in patients with retrogradely conduction accessory pathways mapped during ventricular pacing or orthodromic AVRT are characterized by continuous electric activity, the presence of accessory pathway potential, and electrogram stability. Once an appropriate target site is identified, radiofrequency energy is delivered for 30 to 60 seconds with a target electrode temperature of 60°C to 70°C. At successful ablation sites, interruption of conduction through the accessory pathway usually occurs within 10 seconds and often within 2 seconds of the onset of radiofrequency energy delivery.