The Road to Hell Is Paved With Plugged Ports—Leadless EGM Findings and Their Potential Clinical Implications

A 33-year-old woman with a complex cardiac history, including heart failure with reduced left ventricular ejection fraction (LVEF 25%) of non-ischemic etiology, prior bioprosthetic mitral valve replacement and tricuspid ring annuloplasty, and recurrent ventricular arrhythmias and signs of systemic infection was transferred from the Emergency Department. The patient had received an implantable cardioverter-defibrillator (ICD) device in 2023 as a mean of primary prevention of sudden cardiac death. She was admitted this time due to an electrical storm, with a total of eight episodes of ventricular tachycardia (VT), treated with four successful antitachycardia pacing episodes, and four episodes with unsuccessful antitachycardia pacing (ATP), however, each terminated by the first shock. The trans-esophageal echocardiography revealed vegetations on the implanted leads, and the patient underwent complete, uneventful transvenous device extraction due to cardiac device-related infective endocarditis (CDRIE). Having completed systemic antibiotic therapy, a dual-chamber right-sided Abbott Neutrino NxT ICD was implanted, with a Durata DF-4 single-coil right ventricular (RV) lead, and the right atrial (RA) port was plugged (Figure 1A). After the procedure, the ECG showed sinus rhythm with a rate of approximately 63 bpm (Figure 1B), and the device interrogation revealed optimal RV lead parameters (RV impedance: 680 Ohm, high-voltage impedance: 82 Ohm, sensing amplitude: > 12.0 mV, capture threshold: 0.5 V/0.5 ms). However, a peculiar pattern was noted on the Leadless ECG tracing immediately post-operatively (Figure 1C). Distinct deflections of major amplitude, and repeatable morphology (some indicated by the arrows) were observed between QRS complexes, appearing periodically. P wave QRS complex T wave Artifacts The correct answer is (d) Artifacts. This pattern reflects pseudo-electrical activity due to an inactive vector configuration in the Leadless ECG channel, arising from the plugged atrial port in a dual-chamber ICD system. In this case, the Leadless ECG—by default set to A-tip to RV-coil configuration in Abbott ICD-DR and CRT-D devices—becomes functionally invalid once the atrial port is plugged [1]. The resulting tracing can resemble any of the ECG elements, including both P waves, QRS complexes, or even T waves, potentially mimicking AV block patterns. However, these are artifactual signals, as no atrial lead is present. In this patient, there were initial caveats, on why each of the provided answers could not have been automatically excluded. The pseudo-regular signals seen in Figure 1C may resemble Mobitz type I AV block (with pseudo-prolongation of PR interval), which could indicate that signals annotated below with “VS” marker are P waves, and deflections of interest may be QRS complexes. Although high sensing on the lead should suggest that the sensing of “ventricular” events occurs in the RV, the risk of P wave oversensing as in this case cannot be completely omitted. Post-surgical changes from tricuspid valve ring repair and mitral valve replacement often impact the electroanatomical geometry, bringing atrial structures closer to ventricular leads—and coils. In this case, the RV coil, may have inadvertently sensed atrial activity and thus, may have generated ambiguous deflections, exacerbating confusion. In this patient, the dual chamber Abbott Neutrino, despite the need to plug the RA port was chosen due to multiple reasons. First, of all available leads, the Abbott Durata lead, is the sole widely available true bipolar lead deliverable via the 7F sheath, and as the patient was of very small height, and frailty, the Abbott system was chosen to mitigate the trauma associated with lead insertion. Second, the Neutrino family is enabled with smartphone, app-based Merlin.net remote monitoring, which due to the young age of the patient, was considered as a major possible benefit. The dual chamber device was chosen as there were no single chamber devices in the facility. Moreover, the patient was discharged on high doses of antiarrhythmic drugs, and if needed, the dual chamber device allowed for future upgrade to DR system. Finally, the patient's right-sided implant of the single coil lead was dictated by the patient's low height, and small cranio-caudal dimension of the thorax—had the dual-coil lead been implanted, the RV coil would have probably been almost in the subclavicular region, posing risk for its stability and fracture. The choice of non-transvenous devices was excluded, as the patient had a substantial risk of monomorphic VTs, benefitting from ATP therapy (thus limiting the use of subcutaneous ICD in this patient), while her history of sternotomy excluded her from being an optimal candidate for an extravascular implantable cardioverter-defibrillator (EV-ICD). Given her optimal functional status, and no prior decompensations of HF, the patient was not considered for an urgent heart transplant, limiting the usability of a wearable cardioverter-defibrillator as a bridge [2]. The patient underwent device interrogation with ECG custom electrodes, what resulted in the confirmation that the device optimally identified QRS complexes (Figure 2). Another important signal may be the lower amplitude of the signals annotated by the “VS” markers—in this case, it must be noted that a high amplitude of artifacts in leadless ECG result in a significant (more than 8×) change of channel gain, when compared with standard electrode ECG. However, without such knowledge, and the possibility to connect the patient in-person, such image obtained, for example, from remote monitoring may raise suspicion of inappropriate sensing [3]. Such suspicion could be even more pronounced, considering the patient's high risk of arrhythmias already at the young age. Later on, the defibrillation threshold test (DFT) was performed, confirming effective detection and treatment of ventricular tachycardia with 20 J energy. However, importantly, despite the presence of the artifacts on the leadless ECG channel, it should be noted that the observed signals would not participate in arrhythmia detection or discrimination algorithms, as sensing and arrhythmia classification are based on ventricular sensing channel, and the far-field “discrimination” channel nominally set in the “RV coil to can” configuration, as presented in Figure 1D, rather than the leadless ECG preview channel. Our tracing highlights the importance of recognizing potential artifacts in the Leadless ECG tracing in dual-chamber ICD systems with a plugged atrial port. In this patient, the pseudo-electrical activity seen on the Leadless ECG tracing was due to the inactive A-tip to RV-coil configuration, producing non-physiological signals that mimicked meaningful atrial or ventricular activity. Although rare, such findings may trigger misinterpretation, including the risk of unnecessary reintervention (reposition) of the ICD lead to address incorrectly stated diagnosis of the presented findings as oversensing. The authors have nothing to report. The authors received no specific funding for this work. Ethical approval was not required for this single case report in accordance with institutional policies. Written informed consent was obtained from the patient for participation in the present analysis. The authors declare no conflicts of interest. Despite almost all data presented in the text, the detailed patient and device data are available upon reasonable request to the corresponding author.