Effect of accessory pathway location on the efficiency of heating during radiofrequency catheter ablation

During radiofrequency catheter ablation of accessory pathways there is a poor correlation between applied power and temperature at target sites for catheter ablation. This study was designed to examine the relation between power and temperature during radiofrequency catheter ablation in patients with accessory pathways and to identify the factors that affect the efficiency of heating, defined as the ratio of applied power and temperature. Twenty-nine patients underwent radiofrequency catheter ablation of an accessory pathway. Among 257 energy applications, 108 were applied for ablation of a right-sided accessory pathway, 105 for a left-sided accessory pathway, and 44 for a posteroseptal accessory pathway. During each application of radiofrequency energy, temperature was continually monitored by use of an ablation catheter with a thermistor embedded in the tip of the distal electrode. During some applications of energy, fluctuations in temperature were observed. The average power, impedance, temperature, and efficiency of heating for all applications of radiofrequency energy was 37 ± 11 W, 100 ± 9 ohms, 53 ± 9° C, and 1.7 ± 0.8° C/W (range 0.9° to 6.6° C/W), respectively. The efficiency of heating varied by location (p < 0.0001), with the greatest efficiency of heating for posteroseptal energy applications (2.3 ± 1.2° C/W, which were significantly greater than for left-sided (1.8 ± 0.8° C/W; p < 0.01) or right-sided (1.2 ± 0.4° C/W; p < 0.0001) applications. Phasic fluctuation in temperature was observed during 127 (49%) energy applications, and the efficiency of heating was 1.5 ± 0.7° C/W. For the 130 applications with a stable temperature curve, the efficiency was 1.8 ± 0.9° C/W (p < 0.02). The mean impedance during energy applications correlated weakly with efficiency (r = 0.2, P = 0.0012). In conclusion, the efficiency of heating varies according to the location of the application of radiofrequency energy. Inadequate contact, as manifested by fluctuating temperature during ablation, results in less efficient heating