Testing Objective Methods for Template Matching Ventricular Tachycardia and Pacemapping
Condition: Ventricular Tachycardia
MeSH terms: Tachycardia; Tachycardia, Ventricular
Study type: Observational

Summary: 
      Patients sometimes suffer from life-threatening abnormal heart racing that originates from
      the lower chamber of the heart. These patients will often need an implantable defibrillator
      which has the ability to shock the heart back to a normal heart rhythm, but this does not
      prevent them from getting frequent recurrences of the bad heart rhythm needing shocks from
      the device. This can be painful and potentially harmful. Medicines to prevent recurrences of
      shocks are not very effective and have many side effects. An alternative to medicines for
      this is a procedure called a catheter ablation in which a wire is passed up through the blood
      vessels of the leg into the heart and used to find the short circuits which cause the
      dangerous heart rhythm. When the spot causing the trouble is found, the investigators can
      burn it ("ablate" it). This procedure is challenging and methods are needed to make it more
      effective and easier to do. One of the main ways for finding the short circuits involves
      using the electrocardiogram (the "ECG"). The regular ECG is simplistic and only makes use of
      recordings from 10 sites (6 precordial sites and 4 sites on both upper and lower limbs) on
      the body surface. The investigators are testing whether making recordings from 120 sites on
      the chest and back and using special computerized analysis of the recordings can help make
      catheter ablation for dangerous heart rhythms more effective.
    

Detailed description: 
      Several conventional and advanced mapping techniques are frequently utilized to accomplish a
      successful catheter ablation. Many of these mapping techniques (activation mapping,
      entrainment mapping) are hampered by either hemodynamic instability of some tachycardias or
      non-sustainability of others. Pacemapping is a commonly used tool for mapping non-sustained
      or hemodynamically unstable VT, which is based upon the principle that activation of the
      heart from a given site will yield a reproducible body surface electrocardiogram (ECG)
      morphology and that pacing from a site very close to the site at which VT activates the heart
      will result in a matching ECG morphology. This technique, however, is limited by imperfect
      accuracy and spatial resolution, subjectivity of interpretation leading to marked
      inter-observer variability in the perceived quality of a morphologic match, and by the need
      for an intuitive interpretation of the ECG to direct catheter manipulation. We hypothesize
      that one can improve the accuracy with which the origin of VT is localized by applying body
      surface potential mapping (BSPM), using data derived from 120 simultaneously acquired ECGs.

      Objectives:

        1. To quantify the similarity between BSPM waveforms during induced VT and during
           pacemapping or between two different pacing sites using two waveform comparison metrics,
           the correlation coefficient (CORR) and the root mean square error (RMSE) and to test the
           validity of these metrics as markers of proximity of the pacing site to the site of
           earliest ventricular activation.

        2. To compare the accuracy with which the origin of ventricular tachycardia is localized
           via pacemapping by applying (BSPM), which uses data derived from 120 simultaneously
           acquired ECGs, to the accuracy of localization with different ECG subsets e.g. 12-lead
           ECG and X, Y and Z leads.

      Patient and methods:

      We anticipate that our patients will fall in one of the flowing 4 groups:

      Group A:Patients with focal VT in structurally normal heart. Group B:Patients with scar
      related VT in which the exit site can be identified. Group C:Patients with scar related VT in
      which the exit site cannot be identified.Group D:Patients presenting with SVT.

      For all groups, data for body-surface potential mapping (BSPM) will be recorded during
      induced VT (Group A& B), pacing from virtual VT exit sites which are several points selected
      around the scar margin to represent the VT exit site (group C) or index pacing site which is
      a pacing site selected as a reference in the RV of patients presented with SVT (group D) and
      from different pacemapping sites including successful and unsuccessful ablation sites if
      applicable. All data will be imported into customized software.

      The improvement in the arithmetic value of the two comparison metrics will be tested as the
      site of pacing approaches the site of earliest ventricular activation (Groups A&B) or virtual
      VT exit sites in group C or the index pacing site (in group D). The best CORR and RMSE
      between the BSPM obtained during VT (in group A and B)/virtual VT exit sites (in group C) or
      index pacing site (group D) and different pacing sites (including successful and unsuccessful
      ablation sites) will be recorded. A simple linear regression will be used to compare the CORR
      and RMSE difference at each pacing site to distance between this pacing site and the
      successful ablation site as a surrogate of the best pace-match (in group A and B) or the
      corresponding virtual VT exit site (in group C) or index pacing site (group D). P value <0.05
      will be considered significant. The mean sensitivity, specificity, and positive- and
      negative-predictive accuracies of the arithmetic metrics in determining the VT origin/exit
      site will be determined. We will repeat the previous protocol using different ECG subsets
      including 12 lead ECGs and X, Y and Z leads. The predictive accuracies for different subsets
      of electrodes will be measured and compared to those derived from using the whole BSPM
      obtained from the 120 ECG leads.
    

Intervention name(s): 12-lead body surface mapping
Intervention type(s): Other
Intervention description(s): An average of 20 distinct left ventricular sites will be mapped using 12-lead body surface mapping electrodes and recorded for 15 seconds, then sent to a computer for further analysis.
Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Patients will be recruited from consecutive patients referred for ablation of sustained
        ventricular tachycardia with or without structural heart disease or Patients referred for
        ablation of supraventricular tachycardia to the QEII Health Sciences Centre, in Halifax,
        NS.
      
Keywords: Ventricular Tachycardia; Body Surface Mapping