Cryoablation versus RF Ablation for AVNRT
Cryoablation versus RF Ablation for AVNRT
In this meta-analysis of cryoablation versus RF ablation for AVNRT, both energy sources are shown to be safe and effective acutely and during follow-up. The reduced risk of permanent AV block (0.75% vs 0%) and shorter fluoroscopy time (13.5 minutes vs 15.9 minutes) observed with cryoablation is balanced by a higher risk of long-term AVNRT recurrence (9.7% vs 3.8%) and longer total procedure time (111.7 minutes vs 81.2 minutes). These results are in keeping with clinical observations noted at our center and others, and provide the best point estimate of differences between these energy sources for AVNRT available to date.
Interestingly, the success of cryoablation was not significantly affected by the choice of catheter size in this meta-analysis. This is in contrast to data from previously published work that reported that long-term outcomes (but not acute success) are inferior using a smaller (4 mm) cryoablation catheter. Many centers now exclusively use 6-mm-tip cryoablation catheters in adult patients due to a belief that long-term recurrence is greater using 4-mm-tip cryoablation catheters, but in our meta-analysis, long-term failure did not differ significantly between 4-mm-tip and 6-mm-tip cryoablation catheters. In addition, long-term recurrence remained greater with cryoablation even when only those studies that employed additional "insurance" cryoablations were considered and also after excluding studies with a follow-up duration of less than 6 months. This suggests that that the higher long-term recurrence noted with cryoablation is due to the source of energy used rather than other factors such as catheter size or duration of follow-up.
It is worth mentioning that there are other possible advantages to cryoablation that could not be systematically analyzed in this review. In contrast to RF ablation, cryoablation is associated with the well-described phenomenon of cryoadherence, which minimizes catheter movement during active ablation. Our observation that fluoroscopy use is significantly lower with cryoablation is likely a direct result this effect, since fluoroscopy is typically employed to ensure a stable catheter position during active RF ablation. In addition, the lower patient pain perception with cryoablation (reported in 2 studies; Refs. 3 and 5) is an additional advantage from a patient's point of view, although in practice, pain is readily managed with intravenous narcotics and sedatives in the electrophysiology lab. On the other hand, these possible additional benefits of cryoablation are further counterbalanced by a longer overall procedure time (related to longer lesion durations compared with RF) and the observation (in only 2 studies) that ablation device failure may be more frequent when cryoablation is used. These observations clearly require further confirmation in additional studies, but are worth keeping in mind when choosing a given treatment modality.
Surprisingly, no subgroup of patients could be identified from our data set that were at particularly high risk of AV block from RF ablation. Unfortunately, we did not have access to the primary data from the studies we included in this meta-analysis and therefore could not perform meta-regression to further explore possible high-risk groups for this complication. Also, it is possible that our study was relatively underpowered to thoroughly investigate this rare complication. On the other hand, even though the absolute risk of AV block from RF ablation appears to be similar in young patients and older patients in this analysis, the repercussions of a lifetime requirement for cardiac pacing is very different between these populations. Another limitation of our study involves the demographic information we reported. This was limited by the availability of this data in the published manuscripts. A large German registry by Schlosser et al. was available in abstract form only and demographic information was not available; therefore, the average age and gender of AVNRT patients may be different than what we reported.
Discussion
In this meta-analysis of cryoablation versus RF ablation for AVNRT, both energy sources are shown to be safe and effective acutely and during follow-up. The reduced risk of permanent AV block (0.75% vs 0%) and shorter fluoroscopy time (13.5 minutes vs 15.9 minutes) observed with cryoablation is balanced by a higher risk of long-term AVNRT recurrence (9.7% vs 3.8%) and longer total procedure time (111.7 minutes vs 81.2 minutes). These results are in keeping with clinical observations noted at our center and others, and provide the best point estimate of differences between these energy sources for AVNRT available to date.
Interestingly, the success of cryoablation was not significantly affected by the choice of catheter size in this meta-analysis. This is in contrast to data from previously published work that reported that long-term outcomes (but not acute success) are inferior using a smaller (4 mm) cryoablation catheter. Many centers now exclusively use 6-mm-tip cryoablation catheters in adult patients due to a belief that long-term recurrence is greater using 4-mm-tip cryoablation catheters, but in our meta-analysis, long-term failure did not differ significantly between 4-mm-tip and 6-mm-tip cryoablation catheters. In addition, long-term recurrence remained greater with cryoablation even when only those studies that employed additional "insurance" cryoablations were considered and also after excluding studies with a follow-up duration of less than 6 months. This suggests that that the higher long-term recurrence noted with cryoablation is due to the source of energy used rather than other factors such as catheter size or duration of follow-up.
It is worth mentioning that there are other possible advantages to cryoablation that could not be systematically analyzed in this review. In contrast to RF ablation, cryoablation is associated with the well-described phenomenon of cryoadherence, which minimizes catheter movement during active ablation. Our observation that fluoroscopy use is significantly lower with cryoablation is likely a direct result this effect, since fluoroscopy is typically employed to ensure a stable catheter position during active RF ablation. In addition, the lower patient pain perception with cryoablation (reported in 2 studies; Refs. 3 and 5) is an additional advantage from a patient's point of view, although in practice, pain is readily managed with intravenous narcotics and sedatives in the electrophysiology lab. On the other hand, these possible additional benefits of cryoablation are further counterbalanced by a longer overall procedure time (related to longer lesion durations compared with RF) and the observation (in only 2 studies) that ablation device failure may be more frequent when cryoablation is used. These observations clearly require further confirmation in additional studies, but are worth keeping in mind when choosing a given treatment modality.
Surprisingly, no subgroup of patients could be identified from our data set that were at particularly high risk of AV block from RF ablation. Unfortunately, we did not have access to the primary data from the studies we included in this meta-analysis and therefore could not perform meta-regression to further explore possible high-risk groups for this complication. Also, it is possible that our study was relatively underpowered to thoroughly investigate this rare complication. On the other hand, even though the absolute risk of AV block from RF ablation appears to be similar in young patients and older patients in this analysis, the repercussions of a lifetime requirement for cardiac pacing is very different between these populations. Another limitation of our study involves the demographic information we reported. This was limited by the availability of this data in the published manuscripts. A large German registry by Schlosser et al. was available in abstract form only and demographic information was not available; therefore, the average age and gender of AVNRT patients may be different than what we reported.