Improving Safety in Catheter Ablation for Atrial Fibrillation
The most important limitation of this study is the nonrandomized design. To mitigate this, we attempted to minimize selection bias by collecting data on 100% of patients during the study period. However, as for any observational study we are inherently at risk of confounding, and this limits the strength of conclusions that can be drawn. As a longitudinal cohort study, it is theoretically possible that the benefits seen in the ultrasound-guided phase of the study were exaggerated by a general improvement of vascular access skills. However, all procedures were performed by highly experienced operators and so it is unlikely that this had a significant effect. This notwithstanding, the use of any new tool has the potential to introduce operator bias. Second, our choice of BARC 2+ bleeding as our primary endpoint may be considered too broad. The reason for choosing this was based on the publication of standardized criteria for clinical trials. Also, although physicians may be most interested in avoiding life-threatening complications, the effect on patient wellbeing of "lesser" events can be significant. Furthermore, our a priori calculations showed that to demonstrate a difference in potentially life-threatening (BARC 3+) complications, we would require an unfeasibly large sample size. Indeed, based on our results, an adequately powered study to look for a difference in BARC 3+ complications would require a sample size of around 5,000 patients. Another possible limitation of the study is the lack of patient blinding. This was inevitable given that most procedures were performed under local anesthesia and conscious sedation. However, in order to minimize potential bias the patient survey specifically avoided mentioning that comparison was being made between techniques. Finally, at our center all operators perform venous access using a uniform technique. It is therefore not possible to say whether alternative techniques, such as a strategy utilizing both groins or with femoral arterial blood pressure monitoring, might have demonstrated greater or lesser benefit of ultrasound use.
Limitations
The most important limitation of this study is the nonrandomized design. To mitigate this, we attempted to minimize selection bias by collecting data on 100% of patients during the study period. However, as for any observational study we are inherently at risk of confounding, and this limits the strength of conclusions that can be drawn. As a longitudinal cohort study, it is theoretically possible that the benefits seen in the ultrasound-guided phase of the study were exaggerated by a general improvement of vascular access skills. However, all procedures were performed by highly experienced operators and so it is unlikely that this had a significant effect. This notwithstanding, the use of any new tool has the potential to introduce operator bias. Second, our choice of BARC 2+ bleeding as our primary endpoint may be considered too broad. The reason for choosing this was based on the publication of standardized criteria for clinical trials. Also, although physicians may be most interested in avoiding life-threatening complications, the effect on patient wellbeing of "lesser" events can be significant. Furthermore, our a priori calculations showed that to demonstrate a difference in potentially life-threatening (BARC 3+) complications, we would require an unfeasibly large sample size. Indeed, based on our results, an adequately powered study to look for a difference in BARC 3+ complications would require a sample size of around 5,000 patients. Another possible limitation of the study is the lack of patient blinding. This was inevitable given that most procedures were performed under local anesthesia and conscious sedation. However, in order to minimize potential bias the patient survey specifically avoided mentioning that comparison was being made between techniques. Finally, at our center all operators perform venous access using a uniform technique. It is therefore not possible to say whether alternative techniques, such as a strategy utilizing both groins or with femoral arterial blood pressure monitoring, might have demonstrated greater or lesser benefit of ultrasound use.
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