Acute unipolar intracardiac electrogram changes correlate with lesion size after pulsed field ablation in porcine left ventricle

Background

Pulsed field ablation (PFA) is becoming an established cardiac ablation modality. Although acute procedural success is easily achievable, it does not always translate into durable lesions. Despite dependence of lesion size on PFA dosing has been previously reported [1], an efficient intraprocedural lesion quality parameter is still lacking. It is also believed that such a parameter would be dependent on manufacturer-specific proprietary PFA waveform parameters.

Purpose

Current of injury (COI) phenomena, quantified from changes in unipolar intracardiac electrograms (iEGMs) after PFA, were correlated with lesion volumes determined by magnetic resonance images (MRI).

Methods

In total, 28 PFA lesions were created in the left ventricle of 4 pigs via a commercially available contact-force ablation catheter and investigational PFA generator. The PFA waveform and dose were varied by voltage (1500 V, 2000 V, 2500 V, 3000 V), pulse duration (0.5 µs, 1µs, 2 µs, 3 µs, 5 µs), number of pulses in a train (200, 400) and number of trains (1, 4, 8, 16 applications). Unipolar iEGMs were continuously recorded (bandpass: 0.5 Hz – 500 Hz) for 5 minutes after PFA delivery and COI recovery dynamics were analysed. Lesion volumes were determined by late gadolinium enhancement MRI obtained 24 hours after PFA deliveries as described previously [1].

Results

In total, 24 unipolar iEGMs with at least 5 minutes of artefact-free post-ablation duration were analysed with two COI evaluation approaches. First, COI was assessed with area under the curve (AUC) as shown in Figure 1A [1]. Second, unipolar iEGMs were decomposed into non-overlapping frequency sub-bands with discrete wavelet transform (DWT) and COI was determined by peak-to-peak amplitude measurement as shown in Figure 1C [2]. There was a good correlation between COI at 5 minutes and MRI lesion volumes shown, with coefficient of determination R2=0.67 and R2=0.61 for AUC and DWT, respectively (Figures 1B and D).

Discussion

As shown before, COI is observed after PFA and it is a low-frequency wave (resembling ST elevation) extending from QRS to T wave, reaching its peak value immediately after PFA and then gradually decreasing towards the end of observation period (Figure 1C) [1, 2, 3]. COI is a broad area phenomenon derived from electrical potential differences between extracellular spaces of affected (altered transmembrane voltage - depolarized) and non-affected (normal transmembrane voltage - hyperpolarized) regions. Best correlation was observed at 5 minutes post-ablation (i.e. the end of observation period); longer waiting periods may produce even better correlation. Further research with extended observation periods is warranted as shown by Amorós-Figueras [3].

Conclusion

Persistence of COI at 5 minutes after PFA is a potential marker of durable lesions irrespective of the PFA waveform and dose used, which could be the basis for developing a waveform independent PFA ablation index.