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International Journal of Arrhythmia 2013;14(3): 28-33.
ECG & EP CASES
Ventricular Tachycardia
Originating from the Right
Ventricular Outflow Tract
Terminated by Steam Pop

Ki-Hun Kim, MD
Cardiology Division, Department of Internal Medicine, Haeundae Paik Hospital, Inje University College of Medicine, Busan, Korea




   Introduction

   Steam pops are infrequent in radiofrequency (RF) ablation for ventricular tachycardia (VT); although they have been reported to occur in only 1~1.5% of all RF ablations, they can cause cardiac tamponade, especially in the right ventricular outflow tract (RVOT).1-3

Case Report

   A 57-year-old woman presented to our emergency department with a 1-week history of waxing and waning palpitations that worsened and persisted on the day of admission, with associated dizziness and chest discomfort. Hypertension had been diagnosed 2 years earlier and was controlled by an angiotensin receptor blocker. Her family and social history were unremarkable. Her initial blood pressure (BP) was 130/98 mmHg, with a pulse rate of 170 beats/min and a respiration rate of 22 breaths/min. Her electrocardiogram showed a wide QRS tachycardia with left bundle branch block morphology, inferior axis, QRS width >140 ms, aVL size slightly greater than aVR, and a small r wave of >0.2 mV in the V2 lead, which suggested that the tachycardia originated from the left superior free wall of the RVOT (Figure 1).



Rapid administration of intravenous adenosine and slowly repeated infusions of diltiazem and verapamil had no effect. After sedation, biphasic direct cardioversion (50 J) was performed twice; however, the tachycardia continued, and her BP dropped to 70/56 mmHg. A flecainide infusion was started, and the tachycardia stopped during that infusion. Laboratory test results were within normal limits, and a transthoracic echocardiogram showed normal left ventricular ejection fraction (64%) and mild mitral regurgitation (grade I). The next day, an electrophysiology study was performed. With the patient fasting and unsedated, a 6 Fr quadripolar catheter was placed in the right ventricular (RV) apex and a 7 Fr deflectable non-irrigation catheter (CelsiusTM, Biosense Webster, Diamond Bar, CA, USA) via an SR-0 sheath (St. Jude Medical, St. Paul, MN, USA) was placed in the RVOT via the right femoral vein. After performing an angiogram of the RVOT area, 3D electroanatomic mapping (EnsiteTM, St. Jude Medical) was performed. The baseline rhythm was sinus with occasional ventricular premature contractions (VPC), whose morphology was compatible with the clinical VT. VT originating from the RVOT (cycle length 400 ms) was repeatedly induced by the RV burst pacing. The earliest ventricular potential was recorded at the left-superior area between the free wall and septum of the RVOT, and pace-mapping showed an identical VT morphology. The presystolic potential at the ablation catheter was earlier than the surface QRS onset at lead V2 by approximately 22 ms, and the 3D mapping point was compatible with the point. During RF ablation at the point on the VT state, VT was successfully terminated (Figures 2 and 3).



However, some VPCs and non-sustained VTs remained after several additional ablations, which might have been associated with improper power delivery because of impedances and temperature limitations. Therefore, we changed the ablation catheter to a 7 Fr unidirectional irrigated form (CelsiusTM Thermocool®, Biosense Webster) for increased power delivery. RF ablation (45 W, with the maximum catheter tip temperature set to 50°C) was repeated at the same ablated site. Catheter irrigation was started automatically at a flow rate of 30 mL/min at the start of the ablation. During ablation, a sudden audible steam pop developed (Figure 4).



Energy delivery was immediately stopped after the pop occurred. However, the patient’s BP suddenly dropped and she became stuporous. After confirmation of cardiac tamponade by portable transthoracic echocardiography, pericardiocentesis with drainage was performed. After drainage, the patient’s BP improved to 100/70 mmHg. Fortunately, after this event, no more VPCs or VTs were observed for >30 min (Figure 5). We finished the procedure, keeping the pericardial drainage in place. After 3 days of supportive care, she was discharged. There were no further events over the 2-year follow-up period.

Discussion

   RF ablation causes lesion development by inducing cell death when tissue temperature exceeds 50°C; however, it can also cause steam pops when the tissue temperature is >100°C, sometimes far exceeding the catheter tip temperature.1,3 When steam explosions occur, which maybe audible as steam pops, they can cause cardiac perforation. This dangerous situation occurs more commonly in the RV than in the left ventricle because of the thin-walled structure of the RV.2,4 Externally irrigated RF ablation can cool the catheter-tissue interface, making it possible to increase power delivery and reduce coagulum formation. However, irrigated RF also causes an imbalance between tissue and catheter tip temperatures during ablation, causing difficulty in predicting steam pops.3 Cooper et al. found a relationship between pops and electrode temperature during atrial ablation and recommended maintaining a catheter tip temperature <40°C to prevent steam pops.5 However, steam pops were observed when the mean catheter tip temperature was 39°C with open irrigation and even occurred with catheter tip temperatures as low as 34°C.1 Yokoyama et al. demonstrated that steam pops occurred more frequently as power was increased from 30 to 50 W.6 Hsu et al. suggested that pops occurred when power exceeded 48 W, and pop formation was limited when power remained under 42 W.7 However, Seiler et al. showed no significant difference between power settings for lesions with and without pops, and found that limiting RF power to achieve an impedance decrease of <18 Ω is a feasible method of reducing steam pops.1 Nonetheless, higher maximum energies and larger impedance falls are associated with steam pops.4 Koruth et al. demonstrated that steam pops can be predicted by the rate of temperature rise and the maximum volumetric temperature measured by microwave radiometry during irrigated RF ablation.3 Increasing contact force also was proportionally associated with more steam pops.8 In our case, the relatively high power (45 W) and technically increasing contact force may have been related causes of the steam pops, but we could not check the spike in impedance because of the unstable situation. Whether the VT focus was abolished by elevated RF power delivery or the steam pop, the interpretation was tangled. Anyway careful handling of the ablation catheter and monitoring of impedance and catheter tip temperature, and possibly a low power setting, is required to prevent steam pops.


References

  1. Seiler J, Roberts-Thomson KC, Raymond JM, Vest J, Delacretaz E, Stevenson WG. Steam pops during irrigated radiofrequency ablation: feasibility of impedance monitoring for prevention. Heart Rhythm. 2008;5:1411-1416.
  2. Tokuda M, Kojodjojo P, Epstein LM, Koplan BA, Michaud GF, Tedrow UB, Stevenson WG, John RM. Outcomes of cardiac perforation complicating catheter ablation of ventricular arrhythmias. Circ Arrhythm Electrophysiol. 2011;4:660-666.
  3. Koruth JS, Dukkipati S, Gangireddy S, McCarthy J, Spencer D, Weinberg AD, Miller MA, D'Avila A, Reddy VY. Occurrence of Steam Pops During Irrigated RF Ablation: Novel Insights from Microwave Radiometry. J Cardiovasc Electrophysiol. 2013 [Epub ahead of print].
  4. Tokuda M, Tedrow UB, Stevenson WG. Silent steam pop detected by intracardiac echocardiography. Heart Rhythm. 2012 [Epub ahead of print].
  5. Cooper JM, Sapp JL, Tedrow U, Pellegrini CP, Robinson D, Epstein LM, Stevenson WG. Ablation with an internally irrigated radiofrequency catheter: learning how to avoid steam pops. Heart Rhythm. 2004;1:329-333.
  6. Yokoyama K, Nakagawa H, Wittkampf FH, Pitha JV, Lazzara R, Jackman WM. Comparison of electrode cooling between internal and open irrigation in radiofrequency ablation lesion depth and incidence of thrombus and steam pop. Circulation 2006;113:11-19.
  7. Hsu LF, Jais P, Hocini M, Sanders P, Scavee C, Sacher F, Takahashi Y, Rotter M, Pasquie JL, Clementy J, Haissaguerre M. Incidence and prevention of cardiac tamponade complicating ablation for atrial fibrillation. Pacing Clin Electrophysiol. 2005;28 Suppl 1:S106-109.
  8. Yokoyama K, Nakagawa H, Shah DC, Lambert H, Leo G, Aeby N, Ikeda A, Pitha JV, Sharma T, Lazzara R, Jackman WM. Novel contact force sensor incorporated in irrigated radiofrequency ablation catheter predicts lesion size and incidence of steam pop and thrombus. HCirc Arrhythm Electrophysiol. 2008;1:354-362.