Determining the Association of Chromosomal Variants With Non-PV Triggers and Ablation-outcome in AF (DECAF)
Condition: Atrial Fibrillation
MeSH terms: Atrial Fibrillation
Study type: Observational

Summary: 
      This prospective study aims to examine the association of specific genetic variants (single
      nucleotide polymorphisms) located on chromosome 1, 4 and 16, with presence of non-pulmonary
      vein triggers (NPVT) as well as ablation-outcome in AF patients
    

Detailed description: 
      Specific Aim: This prospective pilot study aims to examine the association of specific
      genetic variants (single nucleotide polymorphisms) namely rs2200733, rs6843082, rs10033464,
      rs17042171, rs2106261 and rs13376333 on chromosome 1, 4 and 16, with presence of
      non-pulmonary vein triggers (NPVT) as well as ablation-outcome in AF patients.

      Hypothesis: Genetic variants predict prevalence of non-PV triggers as well as long-term
      procedure-outcome.

      Background: Atrial fibrillation (AF) is the most common clinical arrhythmia affecting nearly
      3.0 million people in the United States. Its significant contribution to population morbidity
      and mortality is amplified by the fact that AF is associated with 3-5 fold increase in the
      prevalence of cerebrovascular stroke and 2-fold increase in the risk of death. Limited
      efficacy of the available therapeutic strategies makes the matter worse; failures being
      attributed to lack of clear-understanding of the pathophysiology of this complex arrhythmia.
      In addition to the traditional risk factors including advancing age, obesity, metabolic
      syndrome, ischemic/valvular heart disease and hyperthyroidism etc that predict the occurrence
      of AF, genetic predisposition to AF has been reported in recent years.

      Common AF often occurs with structural heart diseases but not all individuals with the same
      cardiac pathology develop AF, indicating that there must be genetic factors predisposing some
      individuals to AF. In 2007, the first Genome wide association study (GWAS) for AF in subjects
      of European descent was reported by investigators from Iceland. Two common variants on
      chromosome 4q25 were found that were strongly associated with AF. Following this initial
      report, several research groups provided independent replication analyses. So far, there are
      at least three distinct genomic loci, 4q25, 16q22, and 1q21 that have a strong association
      with AF.

      Although an SNP is generally not sufficient to cause AF, it may act in combination with other
      SNPs or pathological conditions (e.g., ischemia and stretch) to increase susceptibility to AF
      or it may have some regulatory role in the expression of nearby genes that are potential
      candidate genes for AF.

      Recent GWAS findings have left us with promising novel molecular pathways for AF and provide
      a starting point for the dissection of these novel pathways related to AF. However, the
      majority of these studies have not been replicated in independent populations or in different
      ethnic groups and none of the molecular pathways through which these SNPs lead to AF have
      been definitively determined. A better understanding and characterization of the genetic
      variants associated with AF in general population would facilitate new approaches to the
      diagnosis and efficient treatment of this arrhythmia.

      On the other hand, catheter ablation has become an established invasive procedure treating
      patients with AF and has offered the promise to free patients of symptoms as well as
      eliminate the need for use of chronic drug therapy with agents that sometimes have
      significant risks, cost, and inconvenience for the patient. However, despite of the rapid
      progress of this technique in the past decade, the success rate and outcome of AF ablation
      remain suboptimal and largely variable depending on the case volume and ablation strategy
      used at individual centers. Many risk factors have been associated with the procedural
      failure and arrhythmia recurrence after AF ablation, including the type of AF, size of left
      atrium, cycle length of AF, etc. Recently, we have demonstrated that the presence of NPVT
      strongly predicts failure of AF ablation while elimination of NPVTs during the procedure
      significantly improves the long term freedom from arrhythmia after ablation of AF of any
      type. Non-PV triggers are defined as ectopic triggers originating from sites other than
      pulmonary veins such as left atrial posterior wall, superior vena cava, left atrial
      appendage, ligament of Marshall and coronary sinus.

      Lately, a few published researches have shown that certain common genetic variants on
      different chromosomes are associated not only with an increased risk of AF itself, but also
      with the response to AF treatment or prognosis of AF patients. As we have observed a high
      incidence of NPVTs in AF patients and their role in determining the AF ablation outcome, we
      hypothesize that some common genetic variants at different chromosomal loci are associated
      with the occurrence of NPVTs, by which they subsequently predispose the development of AF and
      influence its response to management.

      Study Design:

      This prospective pilot study will enroll 400 consecutive AF patients undergoing catheter
      ablation. Baseline blood sample will be collected from all patients for genetic analysis.
      Quality of Life (QoL) surveys will be conducted at baseline and 1-year follow-up. All
      patients will be followed up for recurrence for one year.

      The study will be conducted in collaboration with Dr. V. Iyer, professor at University of
      Texas at Austin. All genetic analyses will be performed at the UT core facility.

      Primary endpoints:

      Association of SNPs with non-PV triggers was considered as primary endpoints.

      Secondary endpoints:

        1. Association of SNPs with left atrial scar

        2. Association of SNPs with non-PV triggers stratified by AF type; paroxysmal (PAF) and
           non-paroxysmal AF (NPAF)

        3. association of SNPs with arrhythmia recurrence

      Study Procedure:

      1 ml of whole blood will be collected from each patient in a 4 ml Sodium-heparin tube before
      the ablation procedure. The blood sample will be labeled with an anonymous patient identifier
      that can only be identified by research staff. Following collection, blood sample will be
      stored at -200 C at the clinical lab of St. David's Medical Center until it is transferred
      (twice weekly in nitrogen bucket) to the lab of Dr. V. Iyer (Molecular Genetics and
      Microbiology, UT at Austin) where it will be stored at -70 degree C freezer until the end of
      the study, when all samples will be simultaneously analyzed. Genomic DNA purification and SNP
      analysis by Taqman assay will be performed for all samples at the end of the study, at the UT
      facility.

      DNA purification protocol:

      Qiagen QiaAMP 96 well blood kit will be used to lyse the white blood cells and purify genomic
      DNA.

      Overview of the procedure for using TaqMan SNP Genotyping Assays:

      Purified DNA samples will be used in a TaqMan qPCR assay. Briefly, a small quantity of each
      sample of DNA will be added to six wells in a 384 well qPCR plate. Next, Taqman fluorescent
      labeled probe will be added to the wells. Lastly, TaqMan master mix will be put in each well.
      This qPCR plate will be run on a Life Technologies ViiA7 real-time qPCR machine. To detect
      the presence or absence of each SNP in each patient, a plate reader will be used to detect
      fluorescence in each well.

      Ablation procedures:

      Standard mapping and ablation procedures will be performed at the discretion of the
      physician.

      Follow-up:

      Following ablation, patients will be discharged on their previously ineffective AADs which
      will be continued for 90 days (blanking period). The blanking period allows time for the
      inflammatory process to subside. AADs will be discontinued after the blanking period for all
      patients. If a patient suffers a recurrence of an atrial arrhythmia, AAD therapy may be
      administered at the discretion of the physician.

      All patients will be followed-up for minimum of 1 year following the PVAI. Recurrence will be
      assessed by event recording for 5 months and Holter monitoring at 1, 3, 6 and 12 months.
      Recurrence will be defined as freedom from atrial flutter (AFL), AF or atrial tachycardia
      (AT) of > 30 seconds duration, in the absence of anti-arrhythmic drugs (AADs) at follow-up.

      Risk Analysis:

      This study does not pose any additional risk to the patient. The risks are the same as those
      for a standard AF ablation.

      Minor risks associated with a venous blood draw may include fainting or bruising, pain or
      discomfort and a 1/1000 risk of infection at the site where blood is drawn.

      Benefits:

      The subject may not incur any benefit by participating in this study.

      Potential benefit for future patients: This information will enrich the knowledge about the
      molecular mechanism of AF and help in developing personalized ablation strategies for future
      patients that would be more effective in eliminating this arrhythmia.

      Statistical Methodology:

      Sampling Plan:

      Consecutive eligible patients will be approached for enrollment.

      Analysis Plan:

      Continuous variables will be reported as mean ± standard deviation (SD). The categorical
      variables will be reported as frequencies and percentage. Data analysis will be performed
      using the unpaired Student's t-test for continuous variables and chi-square test for
      categorical variables.

      For genotype-rhythm outcome correlations, 3 different models will be applied. The variant
      alleles will be assumed to be either dominant or recessive or having additive effects in
      these models. In the dominant model, an identical effect is expected in heterozygous and
      homozygous variant carriers. In the recessive model, an effect is only seen in homozygous
      variant carriers. Lastly, in the additive model, heterozygous variant carriers are assumed to
      have an intermediate effect as compared to the homozygotes.

      Multivariate regression analysis will be performed using Cox proportional hazards model to
      test the association of the SNPs with the prevalence of non-PV triggers and outcome variable.
      SAS 9.2 (SAS Institute Inc., Cary, NC) will be used for statistical analysis
    

Observational model: Cohort
Time perspective: Prospective
Sampling method: Probability Sample
Study population: 
        patients with atrial fibrillation
      
Biospecimen description: 
      Blood samples will be collected from which DNA would be extracted for SNP analysis
    
Keywords: AF, catheter ablation, non-PV triggers, SNP