Leadless pacemaker implantation guided by transthoracic echocardiography with no iodinated contrast administration and minimal fluoroscopy in a 13-week pregnant woman

Key Teaching Points.

• •Transthoracic echocardiography (TTE)-guided leadless pacing (LP) implantation is a feasible and safe option for pregnant women.
• •Iodinated contrast medium is not necessary in the LP procedure, and it could be replaced by TTE.
• •TTE can monitor the position of the guidewire, the introducer sheath, the delivery catheter, and the LP in real-time. Therefore, TTE could replace the fluoroscopy to a great extent in special cases that need to avoid ionizing radiation.

Introduction

Leadless pacing (LP) is a compelling alternative for young patients requiring permanent pacing. However, for pregnant patients, there is no well-established approach for implanting LP and avoiding harm to the fetus simultaneously. Fluoroscopy and iodinated contrast administration which are necessary for LP implantation to guarantee the success and safety both pose potential risks to the fetus. In this scenario, we attempted to implant an LP with no iodinated contrast administration and minimal fluoroscopy in a pregnant woman, although a low-dose fluoroscopy was used ultimately.

Case report

A 13-week pregnant woman was referred for pacemaker implantation due to intermittent third-degree atrioventricular conduction block, with a maximum RR interval of 5.2 s (Figure 1). She had experienced multiple syncopal episodes over the past year. The ambulatory electrocardiography showed that the basic rhythm was sinus rhythm with a PR interval of 214 ms and an average heart rate of 68 bpm. Echocardiography showed mild mitral valve regurgitation and a left ventricular ejection fraction of 60%. As a dancer, she refused a traditional transvenous pacemaker. Following a detailed clinical consultation, the patient chose a transthoracic echocardiography (TTE)-guided LP (Micra AV, Medtronic, Minneapolis, MN) implantation strategy to reduce the harm to the fetus by avoiding iodinated contrast and minimal fluoroscopy.

Figure 1.

ECG illustrates the intermittent third-degree atrioventricular conduction block, with a maximum RR interval of 5.2 s. A: Third-degree atrioventricular block during the daytime. B: Mobitz type I second-degree atrioventricular block recorded during the daytime. C: Intermittent high-degree atrioventricular block with a maximum RR interval of 5.2 s at night. D: Second-degree atrioventricular block with 2:1 conduction recorded at night. ECG = electrocardiogram.

On March 26, 2025, she underwent LP implantation under the protection of lead shields around her waist and abdomen. Through the right femoral venous access, a super stiff guidewire was initially introduced to the superior vena cava guided by TTE in an apical 4-chamber view (Figure 2A). The introducer sheath was advanced into the right atrium along the guidewire under the real-time monitoring of TTE (Figure 2B). Subsequently, the delivery catheter was advanced to the tip of introducer sheath, withdrawing the latter into inferior vena cava (Figure 2C). The delivery catheter was advanced across the tricuspid annulus into the right ventricle and rotated clockwise to septum (Figure 2D–F). Each procedure was tracked by TTE in different views (Figure 2A–C apical 4-chamber view and Figure 2E–F parasternal 4-chamber view). The QRS waves of inferior leads shown in real-time electrocardiography which manifested not totally positive or negative waves were used to estimate the location of middle ventricular septum. After TTE ascertained the tip of delivery catheter in the middle septum, a gooseneck sign was given in the right anterior oblique 30° view under fluoroscopic guidance. The device was released and verified by pull-and-hold test to ensure tines engaged firmly in the cardiac tissue in extremely low-dose radiation (Figure 2G and H). The instant capture threshold was 2.5V/0.4 ms, with a sensed R wave of 4.0 mV and an impedance of 650 ohms. No iodinated contrast was used during the whole process. The radiation duration was 1.6 minutes and radiation dose was 4.2 mGy (Figure 2I). Finally, the echocardiogram ruled out an immediate pericardial effusion after the procedure.

Figure 2.

Positions of the guidewire, the introducer sheath, the delivery catheter, and the LP using TTE, and the fluoroscopy used in procedure. A: The super stiff guidewire was introduced into the superior vena cava guided by TTE in an apical 4-chamber view. B: The introducer sheath was advanced to the right atrium along the guidewire under the real-time monitoring of echocardiography. C: The delivery catheter was advanced to the tip of introducer sheath. D, E. and F: The delivery catheter continued to advance across the tricuspid annulus into right ventricle and rotated clockwise to septum. G and H: The device was released and verified by pull and hold test to ensure tines engaged firmly in the cardiac tissue in extremely low-dose radiation. I: The radiation duration was 1.6 minutes and radiation dose was 4.2 mGy. LP = leadless pacemaker; TTE = transthoracic echocardiography.

The device parameters remained stable at 2-week follow-up, with a capture threshold of 1.88 V/0.4 ms, a sensed R wave of 5.4 mV, and an impedance of 540 ohms. 4 months later, the capture threshold, sensed R wave, and impedance were 1.13V/0.4 ms, 4.6 mV, and 460 ohms, respectively. The percentage of ventricular pacing was 0.2% and the estimated battery longevity of LP was longer than 8 years. She remained asymptomatic following the implantation and ultimately delivered a healthy baby at term without complications.

This case demonstrates that TTE-guided positioning of the guidewire and LP is feasible with no iodinated contrast administration. Minimal fluoroscopy ensures an adequate gooseneck sign before the release and the safety of operation. For the pregnant woman, it is of great value to use echocardiography to replace iodinated contrast to guide the position of LP.

Discussion

In this report, we described an LP (Micra AV) implantation in a pregnant woman with no iodinated contrast medium and minimal fluoroscopy. TTE represents a viable alternative to contrast media for guiding device navigation, significantly reducing the reliance on fluoroscopy during the procedure.

For this cardio–obstetrics patient, the use of imaging must incorporate additional safety measures to maximize fetal well-being. According to the guidance on the use of diagnostic imaging during pregnancy and lactation from the American College of Obstetricians and Gynecologists,^1,2 we should minimize fluoroscopy radiation exposure and avoid exposing to ionizing radiation. However, the 2021 European Society of Cardiology (ESC) guidelines on cardiac pacing and cardiac re-synchronization therapy strongly recommend implanting LPs in electrophysiology laboratories or hybrid operating rooms equipped with high-resolution fluoroscopy to guide safe implantation and provide a detailed assessment of the mechanical fixation.³ As discrimination of a septal and free-wall position may be difficult using standard X-ray projections, additional right ventriculography may facilitate proper positioning. A position paper by the European Heart Rhythm Association/Heart Rhythm Society/Latin American Heart Rhythm Society/Asia Pacific Heart Rhythm Society on leadless and extravascular cardiac implantable electronic devices suggests contrast injection via the delivery system should be considered for confirmation of wall contact.⁴

The primary concern when exposing a pregnant woman to ionizing radiation from medical imaging is fetal exposure resulting in an elevated risk of childhood cancer, not teratogenesis.² It is also important to keep in mind that the absolute risk to the fetus remains small. According to the Image Wisely Taskforce, the added cancer risk to the fetus following exposure to 10 mGy of radiation is estimated to range from 0.022% to 0.06%. Radiation exposure exceeding a threshold of 50 mGy should be avoided due to potential non-stochastic effects of radiation to the fetus.⁵ Although exposure to the fetus primarily occurs when the uterus is within the direct beam, we used lead shields placed around the waist and abdomen to avoid the direct irradiation.

Intravenous iodinated contrast media can traverse the placenta and enter the fetal circulation with only 0.003% of the injected dose.^6,7 Depression of fetal thyroid function is the most important potential harmful effect of iodinated contrast media when injected in pregnant woman. A few studies on amniography using both Lipiodol and meglumine diatrizoate injected into the amniotic fluid was associated with marked elevated thyroid-stimulating hormone levels in 6 of 7 neonates at 5 days and 2 babies developed hypothyroidism which we treated with thyroxine.⁸ Therefore, its use in pregnancy should be limited to situations in which the diagnostic information obtained will alter care.

In this scenario, we used TTE to guide LP implantation with minimal fluoroscopy and no iodinated contrast utilization. TTE could help us ascertain each position of the guidewire, the introducer sheath, and the delivery catheter as they needed to be advanced, such as inferior vena cava, right atrium, tricuspid valve, right ventricle, and interventricular septum. Although most of the operation time was consumed by TTE, the fluoroscopy time was decreased to 1.6 mins and the dose was 4.2 mGy without iodinated contrast utility. TEE and intracardiac echocardiography were both available to guide LP implantation, whereas TTE was non-invasive and did not need any narcotic drug.9, 10, 11, 12, 13, 14 It was difficult not to use any fluoroscopy during the whole process as TTE could not clearly show the LP release process. So, fluoroscopy was still used in this case to illustrate an enough gooseneck sign and examine a pull-and-hold test to guarantee the safe fixation. Although the implant capture threshold was relatively high, it decreased over time in our case. Results from the Micra Transcatheter Pacing System Global Clinical Trial showed that patients with high and very-high thresholds decreased significantly by 1 month, with 87% and 85% having 6-month thresholds lower than the implant value.¹⁵ The implant impedance was another important electrical indicator. In patients with a high implant threshold, a low implant impedance (<600 ohms) might suggest the need for repositioning.¹⁶ As for this patient, we finally decided not to reposition the LP considering both the implant threshold and impedance, and the young, healthy myocardium.

Limitation

The procedure of LP implantation under TTE guidance was highly demanding. The operator must possess both mature experience in LP implantation and proficient echocardiography skills. It is time-consuming to determine each position of the guidewire, the introducer sheath, the delivery catheter, and the LP. Furthermore, TTE could not replace fluoroscopy in confirming the gooseneck sign before delivering and tine engagement by pull-and-hold test after delivering. The image quality of echocardiography is another key factor. For patients with a thick chest wall or emphysema resulting in poor acoustic windows, transesophageal echocardiography or intracardiac echocardiography may be a good choice. Sometimes, poor acoustic windows would create difficulty in distinguishing the ventricular septal wall from free wall in patients with abundant trabeculae.

Conclusion

We report a case of TTE-guided LP implantation in an early pregnant woman. TTE-guided LP implantation is feasible and safe, with no iodinated contrast administration and minimal fluoroscopy.

Funding Sources

The Multi-center Clinical Research Project for Major Diseases in Suzhou, (Grant Number: DZXYJ202302).

Disclosures

The authors have no conflicts of interest to disclose.