Complete Elimination of Incessant Polymorphic VentricularTachycardia in an Infant with MIDAS Syndrome: Use ofEndocardial Mapping and Radiofrequency Catheter Ablation

THOMAS PAUL, M.D., PREECHA LAOHAKUNAKORN, M.D.,BLAKE LONG, M.D., and J. PHILIP SAUL, M.D.

From the Children’s Heart Program of South Carolina Medical University of South Carolina, Charleston, South Carolina

Catheter Ablation of Polymorphic VT. Experience with radiofrequency catheter ablation ofventricular tachycardia (VT) in pediatric patients is limited. A 5-month-old white female infant (bodyweight 5.5 kg) with MIDAS syndrome who suffered from incessant polymorphic VT (ventricular rates 250to 300 beats/min) and was unresponsive to medical treatment resulting in signi� cantly depressed leftventricular (LV) function underwent a total of four catheter ablation procedures during a 5-month period.Each of the procedures reduced the number of morphologies and the rate of the tachycardia, but VTreturned after each of the � rst three procedures, despite concomitant medical therapy. Activationmapping and pace mapping were used to identify the anatomic substrates, which were found at differentlocations at the LV septum and LV free wall. All forms of VT � nally were ablated successfully. There wereno signi� cant complications. After the fourth procedure, the patient was in continuous sinus rhythm.Follow-up examination 29 months after the last procedure while the child was not taking any medicationshowed normal sinus rhythm and normal LV function. This report demonstrates the usefulness and safetyof radiofrequency catheter ablation in an infant with polymorphic VT who was unresponsive to medicaltherapy. (J Cardiovasc Electrophysiol, Vol. 13, pp. 612-615, June 2002)

polymorphic ventricular tachycardia, radiofrequency catheter ablation, pediatrics

Introduction

Ventricular tachycardia (VT) in pediatric patients oftenis associated with structural cardiac anomalies, cardiac tu-mors, or myocardial ischemia/infarction.1 In infants with astructurally normal heart, VT most often is monomorphicand usually follows a benign course, with spontaneousresolution in a signi� cant number of patients.1 In contrast tomonomorphic VT, polymorphic VT can lead to severe car-diac dysfunction, congestive heart failure, and sudden car-diac death. Treatment is more dif� cult, usually requiringmultiple antiarrhythmic agents alone or in combination, oran implantable cardioverter de� brillator. To the best of ourknowledge, the use of radiofrequency (RF) catheter ablationin any patient with polymorphic VT has not been reported.

Case ReportThe patient was a 5-month-old white female infant (5.5 kg)

who was transferred to our institution for evaluation andmanagement of incessant polymorphic VT. Soon after birth,the diagnosis of MIDAS syndrome (microphthalmia, dermalaplasia, and sclerocornea) was established based on the char-acteristic features.2 Two weeks before her referral, she pre-sented to a local hospital with polymorphic VT with ventricu-lar rates between 200 and 250 beats/min. She was started onantiarrhythmic medications, including lidocaine, procain-amide, and propranolol, without any effect. Upon arrival atour institution, her ECG showed short periods of sinus rhythm

with intermittent long episodes of polymorphic VT having aright bundle branch block pattern and ventricular rates up to300 beats/min (Fig. 1). Echocardiography revealed global de-creased ventricular function. There were multiple areas ofincreased echogenicity in the muscular ventricular septum.Magnetic resonance imaging study of the heart demonstratedmultiple areas of signal loss in the ventricular septum, butimage quality was limited by the frequent ectopy.

Hemodynamic evaluation before the � rst electrophysiologicstudy revealed decreased ventricular function with a left ven-tricular (LV) end-diastolic pressure of 20 mmHg during a briefperiod of sinus rhythm. Right ventricular (RV) and LV an-giography did not reveal any abnormalities. Selective coronaryangiograms were normal. Endomyocardial biopsies obtainedfrom the RV showed disarray of the myocytes with numerousvacuolizations, a � nding compatible with this syndrome.

Electrophysiologic Studies

The procedures were performed with the patient undergeneral anesthesia. A 4-French quadripolar electrode catheterwas positioned in the RV apex as a reference. As QRS complexmorphology during VT was consistent with an LV origin,detailed mapping was performed in the LV via the retrograderoute with a steerable 5-French mapping and ablation catheterhaving a tip size of 4 mm (Marinr(r); Medtronic/Cardio-rhythm, St. Paul, MN, USA) and containing an embebbedthermistor for temperature control. For the last study, a steer-able 7-French mapping and ablation catheter (Conductor(r);Medtronic/Cardiorhythm) was used in retrograde fashion. Iso-proterenol infusions were given at 0.02 to 0.16 m g/kg/min asneeded to promote spontaneous VT or paced induction of VT.VT could be induced with a critical range of atrial or ventric-ular burst pacing, was sensitive to the adrenergic state, andcame in paroxysmal bursts without stimulation, leading toclassi� cation as triggered activity.3

Address for correspondence: Thomas Paul, M.D., The Children’s HeartProgram of South Carolina, Medical University of South Carolina, 165Ashley Avenue, P.O. Box 250915, Charleston, SC 29425. Fax: 843-792-3284; E-mail: pault@musc.edu

Manuscript received 14 February 2002; Accepted for publication 5 April2002.

612 Reprinted with permission fromJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Volume 13, No. 6, June 2002Copyright ©2002 by Futura Publishing Company, Inc., Armonk, NY 10504-0418

Mapping of VT and AblationActivation mapping and pace mapping3 were performed

during the clinical ventricular arrhythmia. Locations for ap-plication of RF energy were identi� ed by stable catheter tipposition as assessed by � uoroscopy and electrogram stability.3The initial RF applications were performed in the unipolarmode using temperature control at a set point of 70°C with amaximum power of 50 W. In the second and third procedures(Table 1), RF applications also were performed “transseptally”in a bipolar mode using two ablation catheters (5 and 7French), with the larger tip used as a ground (anode) in the RVand the smaller as the active lead (cathode). Regardless ofmode, RF energy was delivered for 10 to 30 seconds unlessthere was success, in which case it was continued for 60 to 120seconds. After a successful RF application, programmed elec-trical stimulation (6 isoproterenol infusion) was repeated dur-ing the waiting period of 45 to 60 minutes.

Ablation 1Activation mapping revealed earliest activation on the an-

terior LV apical septum. No speci� c potentials, e.g., Purkinje-like spikes, were noted. RF energy delivered with the 5-Frenchcatheter resulted in elimination of all VTs (Table 1 and Fig. 2).Frequent premature ventricular complexes with a second mor-phology from the LV septum in a higher position were presentsubsequently (Table 1). RF applications resulted in transientsuccess. As VT had been stopped and only single ventricularpremature complexes were observed, the study was concluded.Twenty-four hours later, polymorphic VT recurred that wasunresponsive to a multiple drug regimen, including lidocaine,propranolol, and mexiletine.

Ablation 2The study was performed with a continuous infusion of

isoproterenol in an effort to exhibit all tachycardia morphol-

Figure 1. Multiform ventricular tachycardia with ventricular ratesbetween 250 and 300 beats/min exhibiting a right bundle branchblock pattern and variable axes.

TABLE 1Details of Electrophysiologic Studies

ProcedureNo.

VTMorphology Origin

ActivationTime(msec)

PaceMap

RF onto VTTerm.(sec)

No. RFApplications

Total RFTime(sec)

RFTechnique

Maximum/AverageTemperature (°C)

FluoroscopyTime (min)

1 1 Apical LV septum 20 11/12 2 1 60 Uni 66/52 49.92 Mid LV septum 15 11/12 4 (t) 7 193 Uni 70/65

2 1 Apical LV septum 18 12/12 7 5 214 Uni 70/61 43.32 Mid LV septum 11 11/12 5 7 300 Bi Power3 Mid LV septum 14 12/12 9 6 261 Bi Power

3 1 Apical LV septum 15 11/12 30 19 1006 Uni/bi 65/61 50.1Power

2 Sup LV septum 12 12/12 5 13 841 Uni 70/664 1 Lat MV annulus 12/12 9 4 253 Uni 68/66 35.1

2 LV free wall 11/12 12 5 203 Uni 74/683 LV apex 12/12 7 4 385 Uni 67/64

Ant anterior; bi transseptal bipolar RF con� guration with catheter ground; RF on to VT Term. interval between start of radiofrequency currentapplication and termination of ventricular tachycardia; Lat lateral; LV left ventricle; Mid middle; MV mitral valve; Power power mode inthe bipolar con� guration across the interventricular septum; RF radiofrequency current; Sup superior; t transient; uni unipolar RF con� gurationwith ground pad; VT ventricular tachycardia.

Paul et al. Catheter Ablation of Polymorphic VT 613

ogies. Again, activation during VT was earliest in the apicalLV septum, but slightly more superior than before (Table 1).One RF application completely eliminated 1 of 3 dominant VTmorphologies present, but all other applications resulted inonly transient success. Because RV septal activation was onlya few milliseconds later than on the LV septum, the bipolarcon� guration was used (Fig. 3). RF application resulted inelimination of the last two VT morphologies (Table 1). Rarepremature ventricular complexes were noted during isoproter-enol provocation. The patient was discharged on propranololand mexiletine. LV function recovered (shortening fraction30%). Three months later, polymorphic VT recurred and LVfunction again deteriorated (shortening fraction of 24%).

Ablation 3During this study, VT was mostly suppressed by the anes-

thetic state. RF applications were delivered along the LVseptum (Table 1). Although the RF applications initially ap-peared to be successful, VT returned during recovery fromanesthesia.

Ablation 4At the � nal study, a different anesthesia protocol (propofol/

midazolam instead of iso� urane) was used, but ectopy still wasinfrequent. Pace mapping was used primarily, and three loca-tions were identi� ed at the LV apex and free wall, with aperfect 12/12 lead match achieved in two forms and an 11/12lead match in one form. All VTs were successfully ablated

(Table 1 and Fig. 4). Follow-up examination 29 months laterwhile the patient was not taking any medication showed nor-mal sinus rhythm and normal LV function.

Figure 2. Endocardial mapping and radiofrequency catheter ablationduring the � rst electrophysiologic study. Top: Endocardial mapping withsurface ECG leads I, aVF, II, V1, and V6 displayed with intracardiacbipolar electrograms from the distal (ds) and proximal (px) electrode pairsof the mapping and ablation catheter (RF), esophageal lead (Esoph), andright ventricular catheter (RV). With the tip of the mapping catheter (RF)located at the anterior left ventricular apical septum, the local electro-grams during ventricular tachycardia (RF ds) preceded the onset of theQRS complex on surface ECG by 20 msec. Bottom: With start of radio-frequency current delivery (RF), there was almost immediate cessation ofany repetitive ventricular response.

Figure 3. Catheter positions during bipolar radiofrequency energy appli-cations across the interventricular septum (anteroposterior view). The5-French catheter is at the target site in the left ventricle and the 7-Frenchcatheter is positioned in the right ventricle at a site that was anatomicallyas close as possible to the left ventricular site and had the earliest rightventricular activation.

Figure 4. Catheter positions and surface ECGs during pace mapping in thefourth electrophysiologic study. Three locations on the left ventricular wallwere identi�ed with excellent pace maps. Pace mapping with a 12/12 leadmatch at one location and an 11/12 lead match at the remaining twolocations was achieved. Successful ablation could be accomplished at thelateral free wall close to the mitral valve annulus (left panel), low on theleft ventricular free wall (middle panel), and at the left ventricular apex(right panel). The patient subsequently was in continuous sinus rhythm.

614 Journal of Cardiovascular Electrophysiology Vol. 13, No. 6, June 2002

Discussion

We report for the � rst time successful RF catheter abla-tion in an infant with incessant polymorphic VT. MIDASsyndrome is a rare condition, and sudden death secondary toVT has been reported.2 Polymorphic VT is seen commonlyin patients with myocardial ischemia or in those with pro-longation of QT interval,1 but it is uncommon in otherconditions. In the patient reported here, the most likelymechanism was triggered activity in multiple parts of theLV myocardium at the free wall and interventricular sep-tum.

Since its introduction into clinical practice, RF catheterablation has been used with high success rates in childrenand adults having supraventricular tachycardias.4 However,the success rates were lower in patients with VT, whichre� ects, in part, the variety of underlying pathologies. Rea-sonable success rates have been achieved in patients withidiopathic RV out� ow tract tachycardia and idiopathic LVVT,4 both of which often result from single automatic focior triggered activity. In contrast to these entities, for VTinvolving a larger area of diseased myocardium as in myo-cardial ischemia, the success rate of RF current applicationis much lower. The mechanism is much more complex andoften there are multiple morphologies in a particular patient,making localization of the critical area that would be thebest target of ablation more dif� cult.5 Because a 7-Frenchcatheter was used in this patient without any adverse effects,the electroanatomic mapping system might have been help-ful and safe despite the patient’s low body weight. Inaddition, it can be speculated whether application of RFcurrent ablation lines, rather than focal ablation, to isolatethe arrhythmogenic area would have been helpful in thisparticular patient, because the origin of ventricular tachy-cardia was most often the apical or mid-LV septum in the� rst three ablation attempts.

Antiarrhythmic drug therapy has been the � rst-line ther-apy in pediatric patients with polymorphic VT. However,surgical removal of small areas of LV myocardium has beenreported in a series of patients with incessant monomorphicor polymorphic VT.6 RF ablation has not been reported ineither children or adults with polymorphic VT. Ablation ininfants generally is reserved for only the most severe casesbecause of concerns with the unknown long-term effects of

RF energy application in the growing heart.7 ,8 In this pa-tient, multiple drugs were used without adequate effects.Because of tachycardia-induced cardiomyopathy and therisk of sudden death, control of VT in this patient seemedmandatory. All morphologies of VT eventually were ab-lated in four successive procedures. Successful sites werelocated at multiple areas of the LV septum and free wall.The total number of RF current lesions in this young patientde� nitely is of concern. However, no wall-motion abnor-malities attributable to the induced RF current lesions werenoted on echocardiographic evaluation. Most importantly,since the last ablation, the patient has done well from bothan arrhythmia and structural standpoint.

Conclusion

This report demonstrates the usefulness and safety of RFcatheter ablation in an infant with polymorphic VT who didnot respond to medical therapy.

References

1. Alexander ME: Ventricular arrhythmias in children and young adults.In Walsh EP, Saul JP, Triedman JK, eds: Cardiac Arrhythmias inChildren and Young Adults. Lippincott Williams & Wilkins, Philadel-phia, 2001, pp. 201-234.

2. Happle R, Daniels O, Koopman RJ: MIDAS syndrome (microphthal-mia, dermal aplasia, and sclerocornea): An X-linked phenotype dis-tinct from Goltz syndrome. Am J Med Genet 1995;57:117-118.

3. Buxton DJ, Waxman H, Marchlinski FE, Simson MB, Cassidy D,Josephson ME: Right ventricular tachycardia: Clinical and electro-physiological characteristics. Circulation 1983;68:917-927.

4. Morady F: Radio-frequency ablation as treatment for cardiac arrhyth-mias. N Engl J Med 1999;340:534-544.

5. Stevenson WG, Khan H, Sager P, Saxon LA, Middlekauff HR, Natter-son PD, Wiener I: Identi� cation of reentry circuit sites during cathetermapping and radiofrequency ablation of ventricular tachycardia lateafter myocardial infarction. Circulation 1993;88:1647-1670.

6. Garson A, Smith RT, Moak JP, Kearney DL, Hawkins HP, Titus JT,Cooley DA, Ott DA: Incessant ventricular tachycardia in infants:Myocardial hamartomas and surgical cure. J Am Coll Cardiol 1987;10:619-626.

7. Saul JP, Hulse JE, Papagiannis J, Van Praagh R, Walsh EP: Lateenlargement of radiofrequency lesions in infant lambs. Implicationsfor ablation procedures in small children. Circulation 1994;90:492-499.

8. Paul T, Bokenkamp R, Mahnert B, Trappe, HJ: Coronary arteryinvolvement early and late after radiofrequency current application inyoung pigs. Am Heart J 1997;133:436-440.

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