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Cardiac Ablation Mania

Course Authors

Gerald V. Naccarelli, M.D.

Dr. Naccarelli reports no commercial conflict of interest.

Estimated course time: 1 hour(s).

Albert Einstein College of Medicine – Montefiore Medical Center designates this enduring material activity for a maximum of 1.0 AMA PRA Category 1 Credit(s)™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

In support of improving patient care, this activity has been planned and implemented by Albert Einstein College of Medicine-Montefiore Medical Center and InterMDnet. Albert Einstein College of Medicine – Montefiore Medical Center is jointly accredited by the Accreditation Council for Continuing Medical Education (ACCME), the Accreditation Council for Pharmacy Education (ACPE), and the American Nurses Credentialing Center (ANCC), to provide continuing education for the healthcare team.

 
Learning Objectives

Upon completion of this Cyberounds®, you should be able to:

  • List which supraventricular tachyarrhythmias have greater than a 90% cure rate utilizing radiofrequency catheter ablation techniques

  • List the risks associated with radiofrequency catheter ablation

  • List which ventricular tachyarrhythmias currently have a high cure rate utilizing radiofrequency catheter ablation techniques.

 

Irregular heart rhythms are a common, potentially debilitating and occasionally fatal cardiovascular problem. Over the past few years, tremendous strides have been made in developing non-surgical, catheter based accessory pathway ablation techniques to treat or, hopefully, cure serious cardiac arrhythmias. As with any new technology, there has been a surge of enthusiasm for this less invasive technique. Despite its substantial promise, significant reservations remain for many observers. I have asked an internationally renowned cardiac electrophysiologist, Dr. Gerald Naccarelli, a good friend and former colleague, to try to put "Catheter Ablation Mania" into perspective.

Dr. Naccarelli is currently Professor of Medicine, Chief of the Section of Cardiology and Director of the Cardiovascular Center at The Pennsylvania State University College of Medicine, The Milton S. Hershey Medical Center, where he received his M.D. degree. Dr. Naccarelli serves on the editorial boards of the Journal of Cardiovascular Electrophysiology, Clinical Cardiology and the Journal of Interventional Electrophysiology. Previously he was an associate editor and consulting editor for Circulation and on the editorial board of the American Journal of Cardiology. Dr. Naccarelli has published more than 200 articles and is the author of Clinical Cardiovascular Therapeutics: Cardiac Arrhythmias, a Practical Approach and Implantable Cardioverters/Defibrillators. For his many contributions to cardiovascular disease research and teaching, Dr. Naccarelli was awarded the American Heart Association's Paul Dudley White Award in 1993.

I'm sure you will agree that Dr. Naccarelli has done a superb job and has translated this difficult topic into an understandable and usable guide for non-cardiovascular clinicians.

-- Richard W. Smalling, M.D., Ph.D., Cardiovascular Moderator

Background

Catheter ablation is a technique used to intentionally destroy portions of the conducting system to ameliorate cardiac tachyarrhythmias associated with symptoms such as palpitations, pre-syncope, syncope or, occasionally, sudden death. Electrosurgical units producing radiofrequency energy (an alternating current with a frequency range of 150 KHz to 1200 KHz) are connected to steerable electrode catheters. These catheters are inserted percutaneously through the femoral artery or vein or subclavian vein and advanced into the patient's heart to deliver destructive energy to the endocardial site of interest. Using this technique, energy is passed through the electrical resistance of the tissue, desiccating the tissue and resulting in coagulation necrosis. An increase in temperature of greater than 50 degrees centigrade causes permanent injury to the tissues. Temperature can be monitored during the ablation using special catheters with thermistors. Radiofrequency catheter ablation has become a curative or palliative procedure for various supraventricular and ventricular tachyarrhythmias.

Catheter Ablation of the AV Junction

Patients with atrial-origin arrhythmias, such as atrial fibrillation with a persistent, rapid ventricular response despite maximal medical therapy, present a therapeutic dilemma. Catheter ablation of the AV junction (success rates in >95%) can induce complete AV block, thus controlling the rapid ventricular response. Since there is a resultant junctional escape rhythm, a permanent rate-responsive pacemaker is inserted following the procedure. Although palliative, several studies(1) have demonstrated an improvement in left ventricular function post-ablation by reducing a tachycardia-induced tachycardia.

Catheter Ablation of Accessory Pathways

Radiofrequency catheter ablation has been successful in curing patients with supraventricular achyarrhythmias secondary to the Wolff-Parkinson-White syndrome. Treatment begins with an electrophysiology study to verify the diagnosis and map the location of the accessory pathway. In patients with left free-wall accessory pathways, a catheter is inserted into the femoral artery and advanced retrograde across the aortic valve and positioned underneath or on top of the mitral valve with careful mapping prior to an ablation attempt. Using fluoroscopy with LAO and RAO views, anatomic sites of pathways can be located. Transeptal catheterization (left atrial catheterization by puncture of the inter-atrial septum using a long needle inserted through the femoral vein) can also be performed and delivery of radiofrequency energy over the valve can be performed at the atrial insertion site. A catheter within the coronary sinus helps in mapping of left-sided accessory pathways and anatomically marks the AV groove separating atrial from ventricular tissue.

In patients with right-sided accessory pathways, the procedure can be performed by advancing the ablation catheter underneath the tricuspid valve or over the tricuspid valve annulus at the ventricular or atrial insertion site of the accessory pathway. Posteroseptal accessory pathways can be mapped in the posteroseptal space around the coronary artery sinus ostium.

The Effectiveness of Catheter Ablation of Accessory Pathways

Radiofrequency catheter ablation is successful in destroying accessory AV connections in 90 to 99% of patients.(2),(3) Location of the pathway may have an effect on the overall success rate. Left free wall accessory pathway ablations are successful in 90-99% of cases. Posteroseptal and right free wall accessory pathway ablations may be less effective (90-93%).(2) The success rate for anteroseptal pathways is high, approaching that of left free wall accessory pathways. Given the pathway's proximity to the AV node, the risk of AV block may limit the overall success rate in this anatomic area. The success rate for the Mahaim form (a right sided atriofascicular fiber) of AV connection is in excess of 90%.(4) Some accessory pathways are difficult to ablate, regardless of anatomic location. At the time of surgery, these pathways often have epicardial anatomic locations or broad branches.

The high success rate of radiofrequency catheter ablation for patients with accessory pathways has made this a front-line therapy. In addition, the cost savings of this therapy have been verified.(5) Although antiarrhythmic drugs, such as flecainide, are extremely effective in treating patients with re-entrant arrhythmias in the Wolff-Parkinson-White syndrome, these drugs are now being used less frequently, due to the advantages of curing patients with this technique.

Complications from Accessory AV Connection Ablations

The insertion of multiple catheters with prolonged procedure times of several hours(6) have resulted in complications (1-3%) including right and left-sided thrombus formation, cardiac perforation and tamponade, complete AV block, stroke, peripheral thrombotic events and, rarely, death. The risk of AV block is higher in patients who have pathways in the anteroseptal region. Because of the complex nature of the catheter manipulations, prolonged radiation exposure may occur. Radiation safety is of concern and serious short-term effects of extended radiation have been reported but, fortunately, are very rare.

Catheter Ablation of AV Node Reentrant Tachycardia

The use of radiofrequency catheter ablation has been highly successful in curing patients with AV node reentrant tachycardia (a common cause of paroxysmal supraventricular tachycardia (PAT or PSVT)). Initial attempts to modify the AV node used the anterior approach with modification of atrial tissue proximal to the Bundle of His. This ablation of the so-called "fast pathway" was effective; however, the risk of AV block was as high as 5-10%. An alternative approach was developed to deliver energy to modify the slow pathway, either anatomically or through mapping of "slow" pathway potentials." Jackman et al(7) identified discrete, high frequency, low amplitude signals in the posterior septal area near the ostium of coronary sinus. The delivery of radiofrequency energy over the tricuspid annulus in this area was successful in preventing the induction of AV nodal reentrant tachycardia in the majority of patients. This result suggested that the slow pathway component of the circuit was extranodal and, anatomically, was within the triangle of Koch. Using similar techniques, other laboratories(8) have reported slow pathway ablation guided by anatomic considerations.

Successful ablation of slow pathway conduction is usually associated with the development of an accelerated junctional rhythm. With slow pathway ablation, very little change will be noted in electrophysiologic characteristics of the AV node, except that the supraventricular tachycardia will no longer be inducible. In patients who have a fast pathway junction ablation, a prolongation of the PR and AH interval will be noted. "Noninducibility" represents the best predictor of success for AVNRT ablation, although echo beats can still be noted without loss of long-term efficacy.

Short-term success rates for multiple laboratories have demonstrated that AV node reentrant tachycardia can be eliminated in from 90-99% of patients. A small percentage of patients will have recurrence and may need a second procedure. The risk of AV block, using the slow pathway technique is low, ranging from one to three percent. The risk of AV block, using the anterior approach, is five to ten percent, thus limiting the use of this approach. Although venous thrombosis or other mechanical problems can occur using this technique, the risk of the procedure is low since no arterial cannulation is performed.

Radiofrequency Catheter Ablation of Atrial Origin Tachycardias

Catheter ablation has been effective in curing atrial origin tachycardias, including ectopic and intraatrial-re-entrant tachycardia, and sinus re-entrant tachycardia. Most atrial tachycardias are along the crista terminalis in the right atrium or near the pulmonic veins in the left atrium. For atrial tachycardias, the sequence of atrial activation is usually recorded by endocardial mapping. At the earliest site of atrial activation, radiofrequency energy is delivered. Pace mapping and concealed entrainment techniques may be used to confirm the ideal ablation site. The success rate for radiofrequency catheter ablation of atrial origin tachycardias, in general, is in excess of 80%. However, most of these cases have been carefully selected and the overall results may be lower than the initial reported results.

Atrial flutter usually occurs secondary to a macroreentrant right atrial arrhythmia. Acute success rates can be achieved in 80-90% of patients by ablating the isthmus of slow conduction in the posteromedial right atrium between the os of the coronary sinus and the tricuspid annulus. Long-term success rates are lower than other forms of SVT due to high recurrence rates.

Catheter Ablation of Ventricular Tachycardia

Catheter ablation has been very successful in curing patients with ventricular tachycardia and no discernible heart disease. Successful ablation of right ventricular outflow tract (left bundle branch block, inferior axis morphology) and idiopathic left ventricular (right bundle branch block, superior axis morphology) VT have exceeded 80%. Catheter ablation is less effective in curing reentrant ventricular tachycardias associated with coronary artery disease. Partial cure of the arrhythmia is achieved in about 50% of patients. For ventricular tachycardia in patients with an otherwise normal heart, catheter ablation is the procedure of choice; in patients with VT and coronary artery disease, palliative attempts to ablate patients should be considered if other pharmacologic or ICD options have not been successful in adequately controlling the VT.

Summary

Radiofrequency catheter ablation has had widespread acceptance as a primary accepted therapy for the treatment of patients with tachyarrhythmias. In patients with the WPW syndrome and AV node re-entry, catheter ablation is a front-line procedure for cure. In patients with rapid atrial tachyarrhythmias, AV junction ablation is an alternative palliative procedure. Patients with primary atrial tachycardias can be considered for this technique, depending on the location of their atrial focus, the severity of their symptoms and their drug refractoriness. Early results of ablation for atrial flutter are encouraging. Further studies may make this a front-line therapy for such patients. In patients with ventricular tachycardia and no structural heart disease, radiofrequency catheter ablation should be considered as a front-line curative therapy and as an alternative to anti-arrhythmic drugs. In patients with VT associated with structural heart disease, catheter ablation should be considered as palliative therapy in patients who are not easily controlled with pharmacologic or device therapy.

Dr. Naccarelli can be reached for questions at the sites listed below: Gerald V. Naccarelli M.D., Cardiology Section, H047, M.S. Hershey Medical Center; Pennsylvania State University College of Medicine; 500 University Drive; Hershey, PA 17033

e-mail: gnaccare@med.hmc.psu.edu
Phone: (717) 531-390
Fax: (717) 531-4077


Footnotes

1Heinz G, Siostroznek P, Kreiner G, et al: Improvement in left ventricular systolic function after successful radiofrequency His bundle ablation for drug refractory, chronic atrial fibrillation and recurrent atrial flutter. Am J Cardiol 69:489, 1992.
2Jackman WM, Wang W, Friday KJ, et al. Catheter ablation of accessory atrioventricular pathways (Wolff-Parkinson-White syndrome) by radiofrequency current. N Engl J Med 1991:324:1605.
3Kuck KH, Schluter M, Geoger M, et al. Radiofrequency current ablation of accessory atrioventricular pathways. Lancet 1991;337:1557.
4McClelland JH, Wang X, Beckman KJ, et al. Radiofrequency catheter ablation of right atriofascicular (Mahaim) accessory pathways guided by accessory pathway activation potentials. Circulation 1994;89:2655.
5deBuitleir M, Sousa J, Bolling SF, et al. Reduction in medical care cost associated with radiofrequency catheter ablation of accessory pathways. Am J Cardiol 1991;68:1656.
6Hindricks G, MERFS. the European radiofrequency survey (MERFS): Complications of radiofrequency catheter ablation of arrhythmias. Eur Heart J 1993;14:1644.
7Jackman WM, Beckman KJ, McClelland JH, et al. Treatment of supraventricular tachycardia due to atrioventricular nodal reentry by radiofrequency catheter ablation of slow-pathway conduction. N Engl J Med 1992;327:313.
8Jazayeri MR, Hempe SL, Sra JS, et al. Selective transcatheter ablation for the fast and slow pathways using radiofrequency energy in patients with atrioventricular nodal reentrant tachycardia. Circulation 1992;85:1318.