Should fast pathway ablation be reconsidered in typical atrioventricular nodal re-entrant tachycardia?

INTRODUCTION: Atrioventricular nodal re-entry tachycardia (AVNRT) is the most common, regular narrow-complex tachycardia. The established treatment is catheter ablation of the AV nodal slow pathway (SP). However, in a select group of patients with long PR intervals in sinus rhythm, SP ablation can lead to AV block due to the absence of robust anterograde conduction through the fast pathway (FP). This report aims to demonstrate that AV nodal FP ablation is a reasonable approach in patients with AVNRT and poor or absent anterograde FP conduction. METHODS AND RESULTS: Standard electrophysiology study techniques were used in the electrophysiology laboratory. Catheter ablations were performed using radiofrequency energy. Mapping of intracardiac activation was performed with electroanatomical mapping systems. Outcomes were assessed acutely during the procedure and during routine clinical follow-up. Six patients with first-degree AV block and recurrent AVNRT who underwent ablation of their tachycardia at our institution are presented. One patient underwent ablation of AV nodal SP resulting in high-degree AV block necessitating pacemaker implantation. The remaining five patients underwent ablation of the AV nodal FP guided by electroanatomical mapping of the earliest atrial activation in tachycardia. These five had successful treatment of the tachycardia with preservation of anterograde AV nodal conduction. Mapping and ablation approach to eliminate retrograde FP conduction are described. CONCLUSION: In select patients with AVNRT and poor anterograde FP conduction, retrograde FP ablation is reasonable and is less likely to result in AV block and pacemaker dependency.

Catheter ablation as a treatment of atrioventricular block.

BACKGROUND: Symptomatic second-degree atrioventricular (AV) block is typically treated by implantation of a pacemaker. An otherwise healthy AV conduction system can nevertheless develop AV block due to interference from junctional extrasystoles. When present with a high burden, these can produce debilitating symptoms from AV block despite an underlying normal AV node and His-Purkinje system properties. OBJECTIVE: The purpose of this study was to describe a catheter ablation approach for alleviating symptomatic AV block due to a ventricular nodal pathway interfering with AV conduction. METHODS: Common clinical monitoring techniques such as Holter and event recorders were used. Standard electrophysiological study techniques using multipolar recording and ablation catheters were utilized during procedures. RESULTS: A 55-year-old woman presented with highly symptomatic, high-burden second-degree AV block due to concealed and manifest junctional premature beats. Electrophysiological characteristics indicated interference of AV conduction due to a concealed ventricular nodal pathway as the cause of the AV block. The patient's AV nodal and His-Purkinje system conduction characteristics were otherwise normal. Radiofrequency catheter ablation of the pathway was successful in restoring normal AV conduction and eliminating her clinical symptoms. CONCLUSION: Pathways inserting into the AV junction can interfere with AV conduction. When present at a high burden, this type of AV block can be highly symptomatic. Catheter ablation techniques can be used to alleviate this type of AV block and restore normal AV conduction.

Low penetrance breast cancer predisposition SNPs are site specific.

Large scale association studies have identified low penetrance susceptibility alleles that predispose to breast cancer. A locus on chromosome 8q24.21 has been shown to harbour variants that predispose to breast, ovarian, colorectal and prostate cancer. The finding of risk variants clustering at 8q24 suggests that there may be common susceptibility alleles that predispose to more than one epithelial cancer. The aim of this study was firstly to determine whether previously identified breast cancer susceptibility alleles are associated with sporadic breast cancer in the West of Ireland and secondly to ascertain whether there are susceptibility alleles that predispose to all three common epithelial cancers (breast, prostate, colon). We genotyped a panel of 24 SNPs that have recently been shown to predispose to prostate, colorectal or breast cancer in 988 sporadic breast cancer cases and 1,016 controls from the West of Ireland. We then combined our data with publicly available datasets using standard techniques of meta-analysis. The known breast cancer SNPs rs13281615, rs2981582 and rs3803662 were confirmed as associated with breast cancer risk (P (allelic test) = 1.8 x 10(-2), OR = 1.17; P (allelic test) = 2.2 x 10(-3), OR = 1.22; P (allelic test) = 5.1 x 10(-2), OR = 1.15, respectively) in the West of Ireland cohort. For the remaining five breast cancer SNPs that were studied there was no evidence of an association with breast cancer in the West Ireland population (P (allelic test) > 6.5 x 10(-2)). There was also no association between any of the prostate or colorectal susceptibility SNPs, whether at 8q24 or elsewhere, with breast cancer risk. Meta-analysis confirmed that all susceptibility SNPs were site specific, with the exception of rs6983269 which is known to predispose to both colorectal and prostate cancer. This study confirms that susceptibility loci at FGFR2, 8q24 and TNCR9 predispose to sporadic breast cancer in the West of Ireland. It also suggests that low penetrance susceptibility SNPs for breast, prostate and colorectal cancer are distinct. Although 8q24 harbours variants that predispose to all three cancers, the susceptibility loci within the region appear to be specific for the different cancer types with the exception of rs6983269 in colon and prostate cancer.