Thermal Injury Leading to Myocardial Perforation During Cavotricuspid Isthmus Ablation: A Case Report

Introduction

Radiofrequency ablation is an established and generally safe treatment for atrial arrhythmias, including atrial fibrillation and atrial flutter. However, rare complications related to thermal myocardial injury can occur [1]. One such complication is steam pop, which results from rapid tissue overheating with intramural water vaporization [2]. Clinically, steam pop may be recognized by an audible “pop” sound, tactile catheter kickback, or abrupt changes in generator parameters, although these warning signs are not always present [3,4]. Despite its low reported incidence, steam pop can occasionally lead to life-threatening complications such as myocardial rupture and cardiac tamponade, requiring immediate termination of energy delivery and prompt hemodynamic management [5]. This report describes the case of a 70-year-old man with myocardial perforation and hemopericardium associated with thermal steam pop during radiofrequency ablation of the cavo-tricuspid isthmus (CTI) for atrial fibrillation.

Case Report

A 70-year-old man with a history of hypertension and hyperuricemia had been receiving outpatient care at a local hospital. Six months before presentation, he developed palpitations and dyspnea on exertion and was found to have atrial flutter and atrial fibrillation on electrocardiography. Transthoracic echocardiography demonstrated a left ventricular end-diastolic diameter of 44.7 mm, an end-systolic diameter of 26.4 mm, a left atrial diameter of 38.4 mm, and a preserved left ventricular ejection fraction of 72%, with no regional wall motion abnormalities.

The patient had been taking rivaroxaban 15 mg once daily, which was withheld on the morning of the procedure. Catheter ablation for atrial fibrillation and atrial flutter was performed under general anesthesia with intravenous propofol. Airway management was achieved using a laryngeal mask airway with mechanical ventilation. Intravenous unfractionated heparin was administered to maintain an activated clotting time between 250 and 350 s, measured every 20 min. No respiratory instability or patient movement occurred, and catheter stability was maintained throughout the procedure.

Pulmonary vein isolation was first performed using a cryo-balloon (Arctic Front Advance™, Medtronic), with each pulmonary vein isolated using a single application. Subsequently, cavo-tricuspid isthmus (CTI) ablation was performed to treat the atrial flutter.

A non-irrigated IntellaTip MIFI XP™ catheter (Boston Scientific) was introduced via a Swartz™ SL0 sheath (Abbott) under fluoroscopic guidance alone. Radiofrequency energy was delivered at 70 W and 65°C in a point-by-point manner, with each application lasting 60 s. Bidirectional conduction block across the CTI was achieved during the fourth application (Figure 1).

At 58 s after the onset of the fourth radiofrequency application, the operator perceived a sudden tactile impulse (“pop”) at the catheter tip. Although the temperature abruptly increased with a corresponding power reduction, no significant impedance change was observed throughout the application (Figure 2). Radiofrequency delivery was immediately terminated.

Several minutes later, the patient’s blood pressure decreased, and transthoracic echocardiography revealed a large pericardial effusion. Emergency pericardial drainage evacuated more than 1200 mL of blood; however, bleeding persisted. Protamine sulfate (50 mg) was administered to reverse the heparin, but the hemorrhage could not be controlled. Despite aggressive fluid resuscitation and continuous intravenous norepinephrine infusion, systolic blood pressure remained in the 80-mmHg range. Percutaneous cardiopulmonary support was therefore initiated, and emergency thoracotomy was performed.

Intraoperative inspection revealed a 1-cm myocardial rupture on the right atrial wall between the inferior vena cava and the tricuspid annulus. The surrounding myocardium appeared darkly charred, consistent with thermal coagulation necrosis (Figure 3). The lesion was successfully repaired with suturing.

The postoperative course was uneventful, and the patient was discharged on postoperative day 16. No recurrence of atrial fibrillation or atrial flutter was observed during the 1-year follow-up period.

Discussion

INCIDENCE AND CLINICAL SEVERITY OF STEAM POPS:

Steam pop is a known complication of radiofrequency ablation. Although its overall incidence is approximately 2% in a large-scale study [5], it can lead to serious complications such as myocardial rupture and cardiac tamponade. Nevertheless, steam pop-related rupture requiring emergency surgery remains extremely rare.

BIOPHYSICS AND MECHANISM OF STEAM POP FORMATION:

Steam pop occurs when myocardial tissue is rapidly heated above 100°C, causing intramural water to vaporize and expand explosively. Haines demonstrated that non-irrigated catheters allow rapid temperature rise, whereas irrigated catheters mitigate overheating through convective cooling [2]. Furthermore, irrigated-tip design influences thermal behavior. Suga et al reported that an irrigated TactiFlex SE catheter showed a lower steam pop frequency than a SurroundFlow porous-tip catheter, suggesting that improved irrigation efficiency can reduce risk [7].

PROCEDURAL FACTORS AND LIMITATIONS OF IMPEDANCE MONITORING:

Multiple procedural variables affect steam pop occurrence. Previous studies have suggested that excessive or rapid energy delivery may increase the risk of steam pop; however, no specific radiofrequency power or duration threshold has been definitively established to prevent this complication [2]. Reddy et al demonstrated that steam pop incidence increases sharply when contact force exceeds 40 g, recommending ≤20 g [8]. Olszewski et al reported that steam pops consistently produce a sudden impedance rise, whereas preceding decreases do not reliably predict risk [4].

Impedance monitoring also has intrinsic limitations. Theis et al found that approximately 80% of audible steam pops occurred without preceding impedance change [3]. In our case, no impedance warning was observed, and contact force could not be measured because a non-irrigated, non-CF catheter was used. Excessive or unstable contact – combined with the known limitations of impedance monitoring – may have contributed to the myocardial rupture.

ANATOMICAL VULNERABILITY OF THE INFERIOR CAVO-TRICUSPID ISTHMUS:

The inferior CTI, especially near the inferior vena cava, has variable myocardial thickness and limited convective cooling. Wang et al identified this region as a high-risk anatomical site for steam pop formation [1]. The rupture site in our patient corresponded precisely to this vulnerable region.

EMERGING ALTERNATIVE MODALITIES: CRYOABLATION AND PFA:

Cryoablation produces tissue injury through controlled freezing rather than heating and therefore avoids the mechanism of intramural vaporization that leads to steam pops. Previous reports have demonstrated its safety in CTI ablation [9]. Pulsed field ablation produces irreversible electroporation without thermal injury and entirely eliminates the steam pop mechanism [10]. These modalities may be safer alternatives in anatomically vulnerable regions.

STRATEGIES TO PREVENT STEAM POPS:

Evidence-based preventive strategies include using conservative power and duration settings, real-time monitoring of contact force (≈10–20 g), ensuring adequate irrigation when using irrigated catheters. Selecting irrigated-tip catheters with favorable thermal behavior (eg, TactiFlex SE), considering alternative non-thermal modalities such as PFA or cryoablation, and maintaining stable catheter contact by experienced operators. Research is needed to establish the safety and long-term efficacy of these strategies, especially for cavo-tricuspid isthmus ablation.

LIMITATIONS:

This case report has several limitations. First, mechanical perforation due to excessive contact force cannot be completely excluded, as no definitive impedance or temperature changes were observed prior to the event. Second, although echocardiography was performed during the procedure, no echocardiographic images were preserved because the situation was an emergency. Third, histological confirmation of thermal injury was not obtained; however, the intraoperative finding of darkly charred myocardium was suggestive of a thermally induced lesion rather than a purely mechanical tear. Finally, this is a single case report, and further studies are required to clarify the underlying mechanisms of atypical steam pop events and their prevention.

Conclusions

This case demonstrates that a steam pop-related myocardial rupture can occur abruptly during cavo-tricuspid isthmus ablation using a non-irrigated catheter, even in the absence of significant impedance changes, showing that stable generator parameters do not necessarily exclude the risk of severe complications during radiofrequency ablation.