Pathophysiology of Intracardiac Ablation: How Does Ablation Work?

Radiofrequency catheter ablation (RFA) of cardiac tissue has been well-characterized in animal models. Both unipolar (HUA88) and bipolar (TAN91) radiofrequency ablation cause similar acute and chronic effects, the extent of which is determined by the amount of energy applied to the tissue. It has been shown that the application of microwave (LIE98,WOR02), cryogenic (DUB98,WOR02), laser, (WOR02), and ultrasonic (WOR02) energy result in similar cellular damage as radiofrequency energy.

Radiofrequency energy produces cell damage by heating the tissue and causing coagulative necrosis (cell death). These areas of cell death will eventually be replaced with fibrosis (scar tissue). (WOL94,REM98,LIE00) As one increases the energy applied to tissue, one will see an increase in the coagulation area and an increase in thermal damage. (REM98) Interestingly, this technique has been used to stiffen the palate (roof of the mouth) to prevent snoring. (MAI00) It has been speculated that RFA may cause direct valve tissue injury in patients undergoing ablation of accessory pathways.(MIN92) In fact, Wolfsohn et al (WOL94) found that when they accidentally applied energy to one of the valves of the heart they caused a fibrous scar. Another group (TAN91) found pathologic changes in the tricuspid valve when AV node or His bundle ablation was attempted in dogs. These changes included edema, swelling of the spongiosa, degenerative change of collagen fibers, endocardial thickening, and slight fibrosis and destruction of the valvular tissue. Additionally, collagen is the substance in the body that forms the support structure of tissue. Collagen in heart tissue denatures (breaks down) and contracts when heated to >65° CelciusVIC02. In fact, the chordae tendinae also contract when heated to >65° Celcius (VIC02). This contraction of heart tissue has also been noted by another group.LIE00 Though this technique has not been studied on heart valves one can infer that similar cellular changes may occur when this energy is applied to cardiac valves. RFA has been used to stiffen the palate (roof of the mouth) to prevent snoring. (MAI00) In fact, Wolfsohn et al (WOL94) found that when they accidentally applied energy to one of the valves of the heart they caused a similar fibrous scar.

The acute (1-7 days) effects of RFA (50-300J) include a lesion that is round-oval in shape, centrally-pale with varying amounts of a hemorrhagic rim.(HUA88) Occasionally, there is a mural thrombus over the lesion (~20% occurrence). There is central coagulation necrosis, peripheral contraction band necrosis, and interstitial edema and fibrinous material on the endocardium. (TAN91) During days 3-7, one observes a rim of granulation tissue composed of proliferating capillaries and fibroblasts admixed with acute and mononuclear inflammatory cells. (HUA88) Finally, the chronic effects are usually evident at 4-6 weeks after RFA. Chronic lesions are round-oval to irregular in shape, well-circumscribed, and fibrotic.(HUA88) The acute edema has almost disappeared and there are almost mature collagen fibers and a mild increase in elastic fibers.(TAN91) Much of these pathological observations were made in dog models however, Huang et al (HUA88) found that dog tissue damage was very similar to the tissue damage found in postmortem humans. RFA lesion size is, in part, determined by the amount of energy applied (typically, 50-700Joules). However, energy levels of 100-300J have been shown to cause similar lesion sizes (LxWxDepth, ~4.8×4.6×4.3mm) (HUA91). Earlier work by Huang et al (HUA87), demonstrated the application of unipolar RFA with an energy level of 50J caused an average subacute (7-10d) lesion size of 4x4x2mm.

References:

WOL94 Wolfsohn AL, Green MS, and Walley VM, “Pathology of Radiofrequency Catheter Ablation of the Atrioventricular Node,” Modern Pathology, Vol. 7, No. 4 (1994), pp. 494-496.

REM98 Remorgida V, “Tissue thermal damage caused by bipolar forceps can be reduced with a combination of plastic and metal,” Surgical Endoscopy, Vol. 12 (1998), pp. 936-939.

LIE00 Liem LB, Pomeranz M, et al, “Electrophysiological Correlates of Transmural Linear Ablation,” PACE, Vol. 23 (January 2000), pp. 40-46. MAI00 Mair EA and Day RH, “Cautery-assisted palatal stiffening operation,” Otolaryngol Head Neck Surg, Vol. 122 (April 2000), pp. 547-555.

MIN92 Minich LL, Snider AR, Dick M II, “Doppler Detection of Valvular Regurgitation After Radiofrequency Ablation of Accessory Connections,” Am J Cardiol, V. 70 (July 1, 1992), pp. 116-117.

VIC02 Victal OA, Teerlink JR, et al, “Left Ventricular Volume Reduction by Radiofrequency Heating of Chronic Myocardial Infarction in Patients with Congestive Heart Failure,” Circulation, Vol. 105 (March 19, 2002), pp. 1317-1322.

LIE98 Liem LB and Mead RH, “Microwave Linear Ablation of the Isthmus Between the Inferior Vena Cava and Tricuspid Annulus,” PACE, Vol. 21 (November 1998, Part I), pp. 2079-2086.

WOR02 Liem LB, “Catheter Ablation Using Alternative Energy Sources,” EP Lab Digest, (September/October 2002), pp. 10-12. DUB98 Dubuc M, Talajic M, et al, “Feasibility of Cardiac Cryoablation Using a Transvenous Steerable Electrode Catheter,” J Interventional Cardiac Electrophysiology, Vol. 2 (1998), pp. 285-292.

TAM95 Tamura K, Fukuda Y, Ishizaki M, Masuda Y, Yamanaka N, Ferrans V. “Abnormalities in elastic fibers and other connective-tissue components of floppy mitral valve,” Am Heart J, V. 129, No. 6 (June 1995), pp. 1149-1158.

NAS04 Nasuti JF, Zhang PJ, Feldman MD, Pasha T, Khurana JS, Gorman JH III, Gorman RC, Narula J, and Narula N, “Fibrillin and Other Matrix Proteins in Mitral Valve Prolapse Syndrome,” Ann Thorac Surg, V. 77 (2004), pp. 532-536.

DAV78 Davies MJ, Moore BP, Braimbridge MV, “The floppy mitral valve – Study of incidence, pathology, and complications in surgical, necropsy, and forensic material,” Br Heart J, V. 40 (1978), pp. 468-481.

WHI87 Whittaker P, Boughner DR, Perkins DG, Canham PB, “Quantitative structural analysis of collagen in chordae tendinae and its relation to floppy mitral valves and proteoglycan infiltration,” Br Heart J, V. 57 (1987), pp. 264-269.

BAK88 Baker PB, Bansal G, Boudoulas H, Kolibash AJ, Kilman J, Wooley CF, “Floppy Mitral Valve Chordae Tendinae: Histopathologic Alterations,” Hum Pathol, V. 19 (1988), pp. 507-512.

GRA03 Grande-Allen KJ, Griffin BP, Ratliff NB, Cosgrove DM, Vesely I, “Glycosaminoglycan Profiles of Myxomatous Mitral Leaflets and Chordae Parallel the Severity of Mechanical Alterations,” JACC, V. 42, No. 2 (July 16, 2003), pp. 271-277.

HUA88 Huang SKS, Graham AR, Bharati S, Lee MA, Gorman G, and Lev M, “Short- and Long-Term Effects of Transcatheter Ablation of the Coronary Sinus By Radiofrequency Energy,” Circulation, V. 78, No. 2 (August 1988), pp. 416-427.

TAN91 Tanaka M, Satake S, Kawahara Y, Sugiura M, Hirao K, Tanaka K, Kawara T, Masuda A, Nishikawa T, and Kasajima T, “Pathological Aspects of Radiofrequency Ablation of the Canine Atrioventricular Node and Bundle of His: With Special Reference to Chronic Incomplete Atrioventricular Block,” Acta Pathol Jpn, V. 41, No. 7 (1991), pp. 487-498.

HUA91 Huang SKS, Graham AR, Lee MA, Ring ME, Gorman GD, and Schiffman R, “Comparison of Catheter Ablation Using Radiofrequency Versus Direct Current Energy: Biophysical, Electrophysiologic and Pathologic Observations,” JACC, V. 18, No. 4 (October 1991), pp. 1091-1097.

HUA87 Huang SK, Bharati S, Graham AR, Lev M, Marcus FI, and Odell RC, “Closed Chest Catheter Dessication of the Atrioventricular Junction Using Radiofrequency Energy- A New Method of Catheter Ablation,” JACC, V. 9, No. 2 (February 1987), pp. 349-358.

DAV78 Davies MJ, Moore BP, and Braimbridge MV, “The floppy mitral valve: Study of incidence, pathology, and complications in surgical, necropsy, and forensic material,” British Heart Journal, V. 40 (1978), pp. 468-481.

KIN82 King BD, Clark MA, Baba N, Kilman JW, Wooley CF, “Myxomatous Mitral Valves: Collagen Dissolution as the Primary Defect,” Circulation, V. 66, No. 2 (August 1982), pp. 288-296.

COS89 Cosgrove DM and Stewart WJ, “Mitral Valvuloplasty,” Curr Probl Cardiol, V. 14, No. 7 (July 1989), pp. 353-416.

ZOO83 Zook BC, Blackbourne BD, Katz RJ, and Bradley EW, “Mitral Valve Prolapse,” Comparative Pathology Bulletin, Vo. 15 (August 1983), pp.3-4.

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