Late Potentials and Ablation Index in Ventricular Tachycardia Ablation
Condition: Ventricular Tachycardia
MeSH terms: Tachycardia; Tachycardia, Ventricular
Study type: Interventional

Summary: 
      There is an increasing evidence regarding the efficacy of a substrate-based ablation approach
      to ventricular tachycardia (VT). This approach involves identifying regions of scar and also
      areas displaying late potentials and fractionated activity. Automated mapping systems are now
      available which may be able to generate high density maps displaying regions containing both
      late potentials and ventricular scar. Such an automated approach has not been validated.
      Furthermore, most patients presenting for VT ablation have pacing devices in situ. It is not
      known how the pacing modality affect the substrate maps generated for these procedures. Once
      an area felt to be important to ablate has been identified, the next key step is to perform
      effective ablation. An algorithm has now been made available (Ablation index - Biosense
      Webster Inc.,) which in preclinical studies is an effective predictor of radiofrequency
      lesion depth. This algorithm has been studied extensively in the atrium but not in the
      ventricle. This study would also seek to collect ablation index data during ablation to
      assess the algorithm during ventricular ablation.
    

Detailed description: 
      The study would propose to use the Carto3 mapping system with the Confidense automated
      tagging module (Biosense Webster Inc.,) and a high density mapping catheter to generate
      substrate maps of the ventricle, with maps generated with varying pacing modes. A SmartTouch
      catheter (Biosense Webster Inc.,) would then be used for ablation with data collected during
      each ablation.

      The study hypotheses are:

        -  High density automated mapping systems can be used to generate accurate ventricular
           substrate maps.

        -  There will be a significant change in the late potential maps based on the presence and
           type of ventricular pacing.

        -  The relationship between impedance drop and ablation index during ablation will be
           stronger than FTI and will allow formulation of an upper limit for clinical ventricular
           ablation.

        -  The relationship between FTI and AI with impedance drop will be stronger than with
           electrogram attenuation.

      Protocol:

      15 patients, listed on clinical grounds for a left ventricular VT ablation in the context of
      structural heart disease (including redo ablation) would be recruited for the trial. All
      patients would need to have a pacing device in situ and have underlying sensed ventricular
      rhythm (with or without atrial pacing), or in the absence of a sensed ventricular rhythm, a
      biventricular pacing device. As part of their clinical work-up for the procedure, patients
      will have cardiac MRI scans wherever possible.

      All procedures would be undertaken with Carto3, using a PentaRay catheter for mapping in
      concert with the Confidense module, and a SmartTouch or SmartTouch SF catheter for ablation
      (Biosense Webster).

      Procedures would be conducted under moderate ('conscious') sedation or general anaesthetic.

      Mapping Phase Mapping would be performed antegrade, retrograde or a combination of both. The
      first map taken would be without ventricular pacing using the PentaRay catheter and
      Confidense. Confidense maps would be displayed showing bipolar voltage and late potentials in
      Carto3. The aim would be for maximal coverage of the ventricle. A remap would then be
      undertaken with pacing from the patient's right ventricular pacing lead. In patients with an
      additional left ventricular lead, maps would also be made with left ventricular only and
      biventricular pacing. In those patient without underlying ventricular sensed rhythm, maps
      would be taken with right ventricular only, left ventricular only and biventricular pacing.

      The automatically collected maps would then be validated. The PentaRay would be moved over to
      2 areas where there is agreement between the maps over the presence of late potentials and,
      while the PentaRay was kept in the same place, manual points would be taken with one pacing
      mode and then with the pacing mode changed. This would also be repeated for 2 areas where
      there is disagreement over the presence of late potentials. This process would also be
      repeated for areas identified as showing scar. All points would be taken with respiratory
      gating. Off line, the areas identified as showing abnormal signal - either scar or late
      potentials - would be manually checked to ensure the system has correctly identified them.

      Ablation Phase Ablation would be undertaken using a Smart Touch Surround Flow Catheter
      (Biosense Webster). Ablation power would be restricted to 40-50W based on the operator's
      choice. Steerable sheath usage would be encouraged but not mandatory. Each radiofrequency
      application would be delivered with the catheter stable prior to the ablation. A mapping
      point would be taken with the catheter stable, and then a static ablation would be delivered
      and an ablation point manually taken. Following cessation of ablation, a further mapping
      point would be taken. All points would be respiratory gated. Ablations would be
      non-overlapping. If there was displacement of the catheter during the ablation, this ablation
      would be removed from the impedance analysis.

      Quantitative comparisons Mapping Study The percentage of the maps showing scar and late
      potentials would be quantitatively analysed by exporting the data from Carto3. As comparisons
      would be made between pacing modes, each patient would act as their own control. Based on
      prior work, bipolar scar would be defined as <0.5mv for dense scar and 0.5-1.5mV for low
      voltage areas12, while unipolar scar would be <5mV. The characteristic of the late potentials
      - specifically how late they were compared to the QRS and their size would be compared
      quantitatively for electrograms taken manually at the same location with the PentaRay.
      Quantitative analyses of the data exported from Carto 3 would be conducted using novel
      algorithms programmed in Matlab (Mathworks, Natick, MA, USA).

      Ablation Study The Carto3 data export would be utilized to obtain the impedance, contact
      force, temperature and location data and electrogram data (pre- and post-ablation) for each
      ablation. These data would then be analysed using custom Matlab scripts to undertake an
      incremental AI and FTI based analysis of the impedance drop during ablation. The curves would
      then be analyzed with the target of quantitatively describing the relationships with
      impedance drop and if possible providing the plateau points in the curve to generate an upper
      limit for ablation.

      Value of Results This study would assess automated electrogram collection as a valid
      methodology for rapidly generating ventricular substrate maps. This will help to shorten
      procedure times for VT ablation by guiding the physician to the areas of interest more
      rapidly. At present, it is unknown how the pacing mode affects substrate maps in the
      ventricle and consequently the mode in which to leave pacing. The study will help to guide us
      to maximise the appropriate identification of the VT substrate by picking the correct pacing
      mode for the procedure.

      The study would validate the use of ablation index for clinical ventricular ablation as well
      as aiming to provide guidance as to how to use this for maximal safety and efficacy.
    

Intervention name(s): Mapping and ablation
Intervention type(s): Device
Intervention description(s): High density substrate map. Data collection during ablation
Intervention model: Single Group Assignment
Intervention model description: Ventricular Substrate maps in patients undergoing ablation for VT - maps collected with automated tagging in different pacing modalities. Validation of collected substrate. Collection of impedance and ablation index data during ablation
Masking: None (Open Label)
Primary purpose: Diagnostic
Keywords: Ventricular Tachycardia; Catheter Ablation; Late Potential; Ablation Index; Pacing