Characteristics of Very High-Power, Short-Duration Radiofrequency Applications

Abstract

Introduction: Pulmonary vein isolation is the cornerstone of rhythm-control therapy for atrial fibrillation (AF). The very high-power, short-duration (vHPSD) radiofrequency (RF) ablation is a novel technology that favors resistive heating while decreasing the role of conductive heating. Our study aimed to evaluate the correlations between contact force (CF), power, impedance drop (ID), and temperature; and to assess their role in lesion formation with the vHPSD technique.

Methods: Consecutive patients who underwent initial point-by-point RF catheter ablation for AF were enrolled in the study. The vHPSD ablation was performed applying 90 W for 4 s with an 8 ml/min irrigation rate.

Results: Data from 85 patients [median age 65 (59-71) years, 34% female] were collected. The median procedure time, left atrial dwelling time, and fluoroscopy time were 70 (60-90) min, 49 (42-58) min, and 7 (5-11) min, respectively. The median RF time was 312 (237-365) sec. No steam pop nor major complications occurred. A total of 6,551 vHPSD RF points were analyzed. The median of CF, maximum temperature, and ID were 14 (10-21) g, 47.6 (45.1-50.4) °C, and 8 (6-10) Ohms, respectively. CF correlated significantly with the maximum temperature (p < 0.0001). A CF of 5 g and above was associated with a significantly higher temperature compared to those lesions with a CF below 5 grams (p < 0.0001). Bilateral first-pass isolation rate was 84%. The 6-month AF-recurrence rate was 7%.

Conclusion: The maximum temperature and CF significantly correlate with each other during vHPSD applications. A CF ≥ 5 g leads to better tissue heating and thus might be more likely to result in good lesion formation, although this clinical study was unable to assess actual lesion sizes.

Keywords: ablation; atrial fibrillation; pulmonary vein isolation; short duration; very high power.

Figure 1

Left atrial voltage map created with CARTO3 electroanatomical mapping system after successful PVI with vHPSD ablation (postero-anterior view). The inter-tag distances are <5 mm between all neighboring points (Heart and Vascular Center, Semmelweis University).

Figure 2

(A,B) QDOT Micro ablation catheter illustration. (A) The ablation catheter incorporates six thermocouples (columns with red disk) symmetrically embedded in the tip for the purpose of highly accurate local temperature measurement. The three distal thermocouples are positioned at a distance of 25 μm from the tip, while the proximal ones are positioned 3 mm proximally. (B) Three microelectrodes (blue dotted circles) are also located in the catheter tip. Each has a surface area of 0.17 mm² and an interelectrode spacing of 1.5 mm.

Figure 3

(A,B) Regulation of the temperature control mode with the QDOT irrigated catheter and vHPSD algorithm as registered by the CARTO3 electroanatomical mapping system (Heart and Vascular Center, Semmelweis University). (A) The 90 W of power is stably delivered throughout the 4 s when the temperature registered by any thermocouples located distally around the catheter tip does not reach the target temperature (55°C) during lesion formation. (B) When the target temperature is reached, the ablation power is immediately downregulated by the vHPSD algorithm to prevent overheating of the tissue. Yellow line, delivered power; red line, temperature; blue line, contact force; green line, impedance.

Figure 4

(A–C) Scatter plot diagrams of the correlations between different parameters registered during radiofrequency applications. (A) Correlation between contact force and the maximum temperature. (B) Correlation between contact force and temperature change. (C) Correlation between contact force and the mean delivered power. ρ, correlation coefficient.

Figure 5

Difference in the maximum temperature between lesions created with a CF <5 g and those with a CF ≥ 5 g. **** = p < 0.0001. Median and interquartile ranges.

Figure 6

(A,B) The association of the mean delivered power and maximum temperature to the different contact force ranges. Increasing contact force values result in higher temperatures but a lower delivered energy. This is the consequence of the appropriate regulation of the ablation generator. Median and interquartile ranges.