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Background: During radiofrequency ablation of arrhythmias tissue heating and hence lesion size depend on electrode-tissue contact and cooling of the electrode tip caused by cavitary blood flow. These factors are unique and unknown for each catheter placement in the beating heart. A tool for assessing these factors prior to ablation may indicate the lesion size which will be obtained for any given catheter position., Methods and Results: Radiofrequency ablation was performed in vitro on strips of left ventricular porcine myocardium during two different levels of convective cooling (0 or 0.1 m/s), two different contact pressures (10 or 30 g) and parallel or perpendicular electrode-tissue orientation using 7F 4 mm tip catheters. Prior to ablation the impedance rise (DeltaIMP) caused by the obtained contact and the temperature rise with a 0.6 W 5 s test pulse (DeltaT) were measured. Subsequently, during unchanged conditions, radiofrequency ablation was performed as either temperature-controlled, power-controlled or irrigated tip ablation and lesion size was determined. DeltaIMP increased significantly (P < 0.05) by improved contact, whereas it was not affected by convective cooling. DeltaT was significantly increased by increasing contact pressure (P < 0.05) and significantly decreased by increased cooling (P < 0.001). DeltaT was not systematically affected by electrode orientation. The product of DeltaT and DeltaIMP showed a significant correlation between the obtained lesion size and power output for temperature-controlled and between lesion size and tip temperature for power-controlled ablation (P < 0.001)., Conclusions: Pre-ablation measurement of DeltaIMP and DeltaT can indicate the lesion size resulting after ablation in temperature-controlled, power-controlled and irrigated ablation in vitro, since DeltaT reflects cavitary cooling and to a smaller extent electrode-tissue contact, and DeltaIMP reflects only electrode-tissue contact.

Introduction: Irrigated tip radiofrequency ablation of cardiac arrhythmias was developed to increase the size of the radiofrequency-induced lesion, since cooling of the electrode tip allows use of higher power settings. The purpose of this study was to determine if the increased lesion size during irrigated tip ablation is caused by the cooling effect solely or if increased electrical conductivity around the tip also contributes by increasing the "current-delivering size" of the tip: the so-called "virtual electrode effect.", Methods and Results: In vitro strips of left ventricular porcine myocardium and in vivo canine left ventricles were ablated. In vitro closed loop tip and showerhead irrigated tip catheters were compared. In vitro and in vivo showerhead tip catheters irrigated with solutions having different ionic content were compared. We found no difference in lesion size for closed loop and showerhead-type catheters (998 +/- 345 vs. 811 +/- 313 mm(3) during power-controlled ablation and 227 +/- 76 vs 318 +/- 127 mm(3) during temperature-controlled ablation). For irrigation with liquids having increasing ionic strength we found a decrease in lesion volume in vitro (361 +/- 249 vs. 812 +/- 229 mm(3) (P < 0.001) for power-controlled and 156 +/- 78 vs. 318 +/- 127 mm(3) (P < 0.05) for temperature-controlled ablation and nonsignificant differences in vivo., Conclusions: The mechanism for enlarging lesion size during radiofrequency irrigated-tip ablation is that higher power levels can be used. There is no virtual electrode effect caused by the highly conductive surroundings of the tip during irrigation. In vitro this effect is shown to be opposite: it decreases lesion size.

During radiofrequency ablation sufficient power must be delivered to achieve a proper lesion, while tissue temperatures are kept below 100 degrees C. Tissue temperature and hence lesion size are determined by electrode to tissue contact and convective cooling, which vary with any obtained electrode position in the beating heart. A tool for evaluation of the combined effect of these parameters prior to ablation to predict the resulting lesion size for any actually obtained electrode position would be valuable. A low power pulse prior to ablation will cause a small increase in tip temperature, which will reflect tissue contact and convective cooling of the tip for that particular electrode position and may thereby predict lesion dimensions after subsequent ablation at that site. Ablation was performed in vitro on strips of left ventricular porcine myocardium during different levels of convective cooling, variable contact pressure, and two electrode orientations in temperature-controlled and power-controlled modes. A 4-mm tip catheter was used. Prior to ablation a 30-second, 0.6-W test pulse was delivered and the increase in tip temperature (DeltaT) registered. The study found that DeltaT and lesion size were mainly affected by the external cooling of the electrode tip and less by the electrode to tissue contact. Increased cooling caused a lower DeltaT (P < 0.001), and the effect on lesion dimensions depended on the ablation mode. For temperature-controlled ablation a larger lesion due to increased power output was obtained (P < 0.0001) for increased cooling, whereas for power-controlled ablation a smaller lesion was obtained for increased cooling (P < 0.05). DeltaT can predict lesion size, but the interpretation of DeltaT depends on the ablation mode. For temperature-controlled ablation a high DeltaT indicates a small lesion and for power-controlled ablation a high DeltaT indicates a large lesion.

The limited success rate of radiofrequency catheter ablation in patients with ventricular tachycardias related to structural heart disease may be increased by enlarging the lesion size. Irrigated tip catheter ablation is a new method for enlarging the size of the lesion. It was introduced in the power-controlled mode with high power and high infusion rate, and is associated with an increased risk of crater formation, which is related to high tissue temperatures. The present study explored the tissue temperatures during temperature-controlled irrigated tip ablation, comparing it with standard temperature-controlled ablation and power-controlled irrigated tip ablation. In vitro strips of porcine left ventricular myocardium were ablated. Temperature-controlled irrigated tip ablation at target temperatures 60 degrees C, 70 degrees C, and 80 degrees C with infusion of 1 mL saline/min were compared with standard temperature-controlled ablation at 70 degrees C and power-controlled irrigated tip ablation at 40 W, and infusion of 20 mL/min. Lesion size and tissue temperatures were significantly higher during all modes of irrigated tip ablation compared with standard temperature-controlled ablation (P < 0.05). Lesion volume correlated positively with tissue temperature (r = 0.87). The maximum recorded tissue temperature was always 1 mm from the ablation electrode and was 67 +/- 4 degrees C for standard ablation and 93 +/- 6 degrees C, 99 +/- 6 degrees C, and 115 +/- 13 degrees C for temperature-controlled irrigated tip ablation at 60 degrees C, 70 degrees C, and 80 degrees C, respectively, and 112 +/- 12 degrees C for power-controlled irrigated tip ablation, which for irrigated tip ablation was significantly higher than tip temperature (P < 0.0001). Crater formation only occurred at tissue temperatures > 100 degrees C. We conclude that irrigated tip catheter ablation increases lesion size and tissue temperatures compared with standard ablation in the temperature-controlled mode at the same or higher target temperatures and in the power-controlled mode. Furthermore, tissue temperature and delivered power are the best indicators of lesion volume during temperature-controlled ablation.

Background: A variety of basic factors such as electrode tip pressure, flow around the electrode and electrode orientation influence lesion size during radiofrequency ablation, but importantly is dependent on the chosen mode of ablation. However, only little information is available for the frequently used temperature-controlled mode. The purpose of the present experimental study was to evaluate the impact during temperature-controlled radiofrequency ablation of three basic factors regarding electrode-tissue contact and convective cooling on lesion size., Methods and Results: In vitro strips of porcine left ventricular myocardium were ablated in a tissue bath. Temperature-controlled ablation at 80 degrees C for 60 s was performed using a 7F 4 mm tip electrode in either perpendicular or parallel contact with the endocardium at a pressure of 10 or 20 g. Increased flow around the electrode was induced by circulating the saline in the tissue bath at a flow-velocity of 0.1 m/s. Lesion volume was determined by cutting lesions in 1 mm thick slices, staining with nitroblue tetrazolium and planimetering. A total of 107 lesions was created. Lesion size was significantly larger for perpendicular electrode orientation compared to parallel for both pressure-settings and both levels of flow around the electrode (p < 0.05). Increased flow around the electrode enlarged lesion size (p < 0.005). Electrode-tissue contact pressure had no significant impact on lesion size., Conclusions: During temperature-controlled radiofrequency ablation increased external cooling of the electrode tip due to either flow of the surrounding liquid or poor electrode tissue contact, as exemplified by perpendicular versus parallel electrode orientation, increases lesion size significantly. This is in contrast to the impact of these factors during power-controlled ablation due to the lack of increased power-delivery in the latter situation.

Introduction: In patients with ventricular tachycardias due to structural heart disease, catheter ablation cures < 60% partly due to the limited lesion size after conventional radiofrequency ablation. Irrigated tip radiofrequency ablation using power control and high infusion rates enlarges lesion size, but has increased risk of cratering. The present study explores irrigated tip catheter ablation in temperature-controlled mode, target temperature 60 degrees C, using an irrigation rate of 1 mL/min, comparing this to conventional catheter technique, target temperature 80 degrees C., Methods and Results: In vivo anesthetized pigs were ablated in the left ventricle. In vitro strips of porcine left ventricular myocardium were ablated in a tissue bath. Lesion volume was significantly larger after irrigated tip ablation both in vivo (544 +/- 218 vs 325 +/- 194 mm3, P < 0.01) and in vitro (286 +/- 113 vs 179 +/- 23 mm3, P < 0.001). The incidence of cratering was not significantly different between the two groups. In vivo, no coagulum formation on part of the catheter tip was seen after irrigated tip ablation as opposed to 52% of the applications with conventional ablation (P < 0.05)., Conclusion: We conclude that temperature-controlled radiofrequency ablation with irrigated tip catheters using low target temperature and low infusion rate enlarges lesion size without increasing the incidence of cratering and reduces coagulum formation of the tip.

This study was designed to investigate the effect of the convective cooling of the tip of the ablation electrode during temperature controlled radiofrequency ablation. In vivo two different application sites in the left ventricle of anaesthetised pigs were ablated and in vitro ablation was performed during two different flow-velocities in a tissue bath, while electrode contact pressure and position were unchanged. Target temperature was 80 degrees C. Obtained tip temperature, power consumption and lesion dimensions were measured. In vivo lesion volume, depth and width were found significantly larger for septal applications than apical applications (p < 0.01) and more power was used (p < 0.001). Obtained tip temperature was significantly lower in the septal applications (p < 0.001). In vitro increased convective cooling by induction of flow yielded larger lesion volume, depth and width (p < 0.01), and had higher power consumptions (p < 0.01). Obtained tip temperature did not differ significantly. For the given chosen target temperature power consumption was positively related to lesion volume (r = 0.66 in vivo and 0.65 in vitro), whereas obtained tip temperature was not (r = -0.49 in vivo and -0.61 in vitro). We conclude that during temperature controlled radiofrequency ablation lesion size differs for septal and apical left ventricular applications. Differences in convective cooling might play an important role in this respect. This is supported by our in vitro experiments, where increased convective cooling by induction of a flow around the electrode tip increases lesion dimensions and power consumptions. Furthermore we conclude that for the given target temperature the power consumption is positively correlated with lesion volume (p < 0.001), whereas the obtained tip temperature is not.