Temporary transvenous external pacing for cardiac MRI in a pediatric patient

Cardiac magnetic resonance imaging (MRI) is a vital tool for diagnosing pediatric cardiac conditions, providing detailed tissue characterization and quantitative functional analysis without the ionizing radiation harmful to children [1‐5]. Temporary transvenous pacing stabilizes heart rhythm in patients with unstable arrhythmias, but its use during MRI is complex due to potential interactions between the magnetic field and pacing devices [2, 4]. This technique has been documented in adults, with a 44-patient series demonstrating its feasibility and safety under strict protocols [2]. Its use in pediatric literature is limited, potentially due to fewer pediatric patients requiring MRI during temporary pacing, although technical and safety concerns related to smaller anatomies and limited pediatric-specific data may also contribute [1, 3]. This report illustrates the integration of temporary externalized pacing with MRI for pediatric cardiac patients, offering a novel approach to diagnostic imaging in this population [6, 7].

This case was deemed exempt by the Institutional Review Board (IRB) and parental consent was obtained for anonymized data publication. A 6-year-old female presented with bradycardia secondary to type II Mobitz and intermittent complete heart block. Initial evaluation included laboratory tests that showed elevated inflammatory markers (CRP 5.6 mg/L, ESR 63 mm/h) and troponin T levels (peaking at 39 ng/L on day 3). Mild metabolic acidosis was evident (total CO₂ of 14 mmol/L). Infectious causes, such as Lyme disease and influenza, which are common etiologies for acute heart block in children, were investigated but ruled out through serologic testing [3]. Initial echocardiography confirmed bradycardia without structural abnormalities. An abdominal ultrasound ruled out systemic causes such as hepatic or renal pathology, but the etiology of the conduction abnormalities remained unclear. A temporary transvenous pacing lead was placed under fluoroscopic guidance to stabilize the patient for advanced imaging (Fig. 1) [6]. Cardiac MRI was performed to evaluate potential structural and inflammatory causes of AV block (see Fig. 2 for representative MRI images) [5]. There was no significant artifact related to the generator or transvenous lead. Imaging ruled out myocarditis and structural defects but identified a mildly reduced left ventricular ejection fraction (LVEF; 45%), suggesting primary conduction system involvement [5]. Her diagnosis remains non-specific but is classified as mitochondrial DNA-deletion syndrome. These findings guided further management, including genetic testing and permanent pacemaker implantation due to persistent heart block [3, 8].

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Parental consent for off-label cardiac device use in the magnetic environment was obtained, addressing risks of heating and malfunction. Temporary pacing was established using a transvenous active-fixation lead (Tendril STS Model 2088 T, 52 cm; Abbott, Chicago, IL, USA) connected to a Dual-Chamber Pacemaker (Assurity MRI™ Dual-Chamber Pacemaker Model PM2272, Abbott, Chicago, IL, USA) externalized and taped to the skin [6]. Gauze separated the pacemaker from the skin to reduce radiofrequency (RF)-induced heating risks. Pre-procedure, the electrophysiology (EP) team programmed the pacemaker to asynchronous ventricular pacing mode (VOO) at 70 beats per minute, with an output of 3.5 V at 0.4 ms, to prevent magnetic interference [2]. The atrial port was plugged per manufacturer MRI specifications to ensure safety [4]. After the MR protocol, specific absorption rate (SAR) was optimized, and institutional protocols for cardiac implantable electronic devices (CIEDs) were followed, involving EP-radiology collaboration. The MRI was conducted in a 1.5-T scanner (MAGNETOM Aera, Siemens Healthineers, Erlangen, Germany) using a 16-channel cardiac coil in a normal MR mode [7]. The imaging protocol included short-axis and four-chamber cine imaging, short-axis triple inversion recovery, T1 and T2 mapping, and late gadolinium enhancement (LGE) sequences, using segmented breath-hold techniques [5]. The patient remained awake and under close monitoring throughout the scan, facilitated by a short imaging protocol [1]. Continuous real-time non-invasive hemodynamic monitoring with electrocardiogram and pulse oximetry was performed. The surface temperature of the generator was monitored using MRI-compatible fiber-optic sensors (FOT-L-SD, FISO Technologies, Quebec, Canada) and no heating was detected [4].

This case demonstrates the feasibility of temporary transvenous pacing with an externalized permanent pacemaker during cardiac MRI in a pediatric patient, aligning with Kakarla et al., who reported safe cardiac MRI in three pediatric myocarditis cases with temporary pacing [1]. Unlike traditional temporary pacemakers (e.g., Model 5392, Medtronic, Minneapolis, MN, USA), which are not MRI-safe due to risks of heating and malfunction, the externalized Assurity MRI™ pacemaker system is MRI-conditional, offering a safer alternative for diagnostic imaging [2, 7]. The externalized Assurity MRI™ pacemaker generator, taped to the skin, and the transvenous lead, positioned in the right ventricle, minimized artifacts compared to traditional pacemakers [2]. Similar to Kakarla et al., our case showed minimal artifacts (<5% of the imaging field), enhancing diagnostic clarity [1]. Cardiac MRI provided critical diagnostic insights, identifying primary conduction system involvement without myocarditis and guiding permanent pacemaker implantation [5, 8].

Compared to echocardiography, which lacks detailed tissue characterization, and computed tomography (CT), which involves ionizing radiation and limited functional assessment, cardiac MRI is superior for pediatric patients requiring repeated imaging [5, 8]. In adults, Fyenbo et al. reported safe MRI with temporary external pacemakers in 44 patients, with minimal artifacts and no adverse events, using VOO mode and strict SAR limits [2]. Our case extends these findings to pediatrics, where smaller anatomies necessitated adjustments, such as precise lead placement and tailored pacing settings, to ensure safety and image quality [3, 6].

Pediatric patients present unique challenges for temporary pacing during MRI, including smaller venous anatomy requiring meticulous lead positioning and higher baseline heart rates necessitating customized pacing parameters [3, 7]. These factors, combined with limited pediatric-specific data on MRI-conditional devices, underscore the need for specialized protocols. Safety measures in our case included VOO pacing, SAR optimization below 2 W/kg, gauze insulation, and continuous real-time monitoring of hemodynamics and surface temperature using fiber-optic sensors, with no RF-induced heating detected [2, 4]. Institutional CIED protocols, involving pre-procedure EP consultations and real-time radiology coordination, ensured rigorous risk management [4, 7]. Unlike Kakarla et al., who used general anesthesia, our patient remained awake, reducing procedural complexity and resource use [1].

However, pediatric-specific data remain limited, and challenges include the need for specialized equipment and multidisciplinary expertise. Future multi-center studies should validate MRI-conditional pacing systems across diverse pediatric populations, while the development of smaller, pediatric-specific devices could further reduce artifacts and enhance safety [6, 7].

Temporary transvenous external cardiac pacing combined with cardiac MRI offers a powerful diagnostic tool for pediatric patients with severe conduction abnormalities. This approach provides high-quality imaging with minimal artifacts, enabling accurate diagnosis while minimizing risks through rigorous safety protocols. Further research is required to standardize protocols and confirm safety across diverse pediatric populations.