Discussion:
Over the last decade, the utilization rate of catheter ablation (CA) has steadily increased as an important therapy for ventricular tachycardia (VT). [7] Despite significant advancements in electroanatomic mapping systems and imaging technologies, VT ablation is still associated with a risk of significant complications. A decision to perform the procedure includes balancing those risks against potential benefits. [8] Typically, patients with VT have complex underlying comorbidities that contribute to morbidity and mortality following the ablation procedure. [9] Previous clinical trials have been conducted to assess the efficacy and safety of VT ablation. [10] However, many of these studies have excluded specific populations, such as those with renal dysfunction. [11] Our study aims to fill this gap by addressing the association of chronic kidney disease (CKD) with in-hospital mortality and complications following VT ablation using a real-world large administrative database. Proper understanding of the risks of VT ablation in this population will have significant clinical implications on CKD patients with VT, by identifying therapeutic strategies that can improve survival and by guiding patient counseling.
In-hospital mortality has been widely used in the literature as an important outcome measure for invasive cardiology procedures. In this multi-center registry, in-hospital mortality was our primary outcome, and it occurred in 3.2% of VT patients undergoing CA, higher than the mortality rates reported in previous similar studies. A retrospective study from National Inpatient Sample (NIS) database (2006-2013), have revealed a 2.8% in-hospital mortality rate among 25,451 patients undergoing VT ablation. [5] The higher mortality rate in recent years could be due to the increased number of patients with a higher burden of comorbidities undergoing VT ablation or due to a rising number of low-volume centers performing VT ablation with decreased access to equipment and personnel. [7] Our study adds to the current literature by highlighting the association between in-hospital mortality and CKD status (OR=2.24; 95% CI: 1.29-3.88, p=0.004), particularly CKD stage IV (OR=4.48 95% CI 1.79 – 11.2, p<0.01). These findings are comparable with Palanismawy et al. who reported a similar association between CKD and in-hospital mortality following CA (OR=2.15; 95% CI: 1.12-4.14, p=0.022), among 81,539 patients with postinfarct VT identified through NIS. [7]
Thirty-day readmission is another important indicator for the success of the VT ablation procedure in high-risk patients. [12] According to Sharma et al, who used NRD data from 2010 to 2014, 1 in 6 patients was readmitted within 30 days after undergoing VT ablation. The most common cause of 30-day readmission after the index hospitalization for VT ablation was ventricular arrhythmia (39.51%) followed by acute congestive heart failure (11.83%). Moreover, they investigated the different predictors of 30-day readmission and found a significant association with CKD (OR=1.3; 95% CI: 1.1-1.6, p=0.01). [3] Our study using the same database from 2016 to 2018 did not find a statistically significant association between CKD status and 30-day readmission rates due to ventricular arrhythmia after adjusting for confounders (OR=1.35; 95% CI: 0.78-2.31, p=0.27).
Given the complexity of VT catheter ablation procedure and the high comorbidity burden among patients undergoing this procedure, the length of stay and the hospital costs hospitalizations following the procedure are significant. [13] A study conducted by Cheung et al reported a median length of stay of the index admission of 4.3 days, while the mean length of stay in our study was 6.4 days (8.73 in CKD patients). [12] Moreover, we found that the mean hospital charges in CKD patients undergoing VT ablation were 226,796 USD, compared with 176,249 USD in patients without CKD. These associations were most significant in patients with CKD stage V. This remarkable difference in length of stay and hospital costs could have important implications on resource allocation in hospitals performing VT ablation.
The association between CKD and worse outcomes in patients undergoing VT ablation is complex and could be related to structural cardiac abnormalities caused by CKD, in addition to several triggers in this population. Firstly, CKD leads to progressive coronary calcification and coronary artery disease, which is considered the most common etiology of VT in these patients also CKD can make intra-op volume management more challenging, thus CKD may be related to less complete ablation. [14] CKD patients are also at risk for QTc-prolongation due to impairment of cardiac repolarization mechanisms. [15] In addition, CKD patients undergoing hemodialysis are affected by electrolyte shifts, such as sudden potassium and calcium shifts, leading to a mechanical and electrical imbalance in the cardiac myocytes. [16] Other underlying mechanisms for this imbalance could be attributed to oxidative stress, increased levels, and the accumulation of several cardiotoxic substances such as homocysteine b2-microglobulin, and parathyroid hormone [17] The present study contributes to a better understanding of this high-risk subgroup of patients undergoing VT ablation. Development of a nationally valid risk stratification model and improving post-hospital care have the potential to offset some of the risks inherent to ablating VT in CKD patients.