Anatomical predictors of sensing amplitudes for extravascular implantable cardioverter defibrillator implantation

Introduction

The extravascular implantable cardioverter-defibrillator (EV-ICD) provides defibrillation and antitachycardia pacing while avoiding complications associated with transvenous systems. However, anatomical predictors for successful implantation remain unclear.

Methods

We retrospectively analyzed patients who underwent implantation of the Aurora EV-ICD (Medtronic) between March and September 2025. All patients underwent pre-procedural computed tomography (CT) or magnetic resonance imaging (MRI), with some imaged during both inspiration and expiration. At the level of the inferior border of the aortic valve, the shortest distances from the right atrium and right ventricle to the left sternal border were measured (Figure 1A and B). The latest P- and R-wave amplitudes in the Ring 1–2 sensing vector obtained during follow-up were analyzed. P-wave amplitude was manually measured on stored electrograms (Figure 2).

Results

For P-wave stratification at 0.2 mV, patients with higher amplitudes had a shorter right atrium–to–left sternal border (RA–LSB) distance during expiration than those with lower amplitudes (46 ± 16 mm vs 23 ± 7 mm, P = 0.01). The RA–LSB distance also tended to be longer in expiration than in inspiration (43 ± 15 mm vs 39 ± 17 mm, P = 0.06; Figure 3A and B). For R-wave stratification at 1.0 mV, patients with lower amplitudes had a longer right ventricle–to–LSB (RV–LSB) distance during inspiration (22 ± 1 mm vs 12 ± 6 mm, P = 0.04), and the RV–LSB distance did not differ by respiratory phase overall (13 ± 7 mm vs 14 ± 6 mm, P = 0.56).

Conclusion

Anatomical measurements on preoperative CT may predict P- and R-wave amplitudes and help determine eligibility for EV-ICD implantation.

In addition, analyzing preoperative CT images obtained during expiration may be particularly relevant for predicting P-wave amplitudes.