title: Are QT measurements on body surface ECG indicative of ventricular refractory patterns?
abstract: OBJECTIVE
  Increased dispersion (DISP) of refractoriness (ERP) facilitates the induction of malignant ventricular arrhythmias. Accordingly, QT DISP on surface ECG, supposedly reflecting ERP DISP, has been proposed as a noninvasive marker for risk stratification. However, a comparative analysis of local ERPs and QT measurements is not available so far.
  
  
  RESULTS
  In 19 healthy dogs, standard 12 lead surface ECGs were recorded to measure QT and RR intervals. Based on these measurements, corrected QT intervals (QTc, Bazett formula) and DISP (maximum difference) of both QT and QTc intervals (QT-DISP and QTc-DISP, respectively) were calculated. Subsequently, 60 custom-made needle electrodes (12 mm long, 4 bipolar electrodes per needle, interelectrode distance 2.5 mm) were inserted into the left (LV) and right ventricle (RV). At each bipole of 14 randomly selected needle electrodes (8 LV, 6 RV) local ERPs were determined (extrastimulus technique, basic cycle length 1000 ms). Interventricular DISP of ERP (LV-RV-DISP) was defined as the difference between the longest and shortest ERP within both ventricles. Respective values were calculated for each ventricle (LV-DISP; RV-DISP). Scatter plots and correlation analysis did not reveal a significant correlation between QT, QTc, QT-DISP, QTc-DISP and any of the ERP measurements or calculations. Although not statistically significant, the closest correlation was found between QTc and mean ERP and between QTc-DISP and LV-RV-DISP.
  
  
  CONCLUSIONS
  QT measurements on surface ECG are poorly correlated with local ERPs. If anything, QT- or QTc-DISP might provide a rough estimate of interventricular, that is, global DISP of ERP. Local or even intraventricular DISP of ERP is definitely not reflected by these QT measurements.
authors.affiliation: Innere Medizin III, Universitätsklinikum Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany. frederik_voss@med.uni-heidelberg.de
authors.forename: Frederik
authors.initials: F
authors.lastname: Voss
authors.forename: Ruediger
authors.initials: R
authors.lastname: Becker
authors.forename: Alexander
authors.initials: A
authors.lastname: Bauer
authors.forename: Patrizia
authors.initials: P
authors.lastname: Kraft
authors.forename: Julia C
authors.initials: JC
authors.lastname: Senges-Becker
authors.forename: Hugo A
authors.initials: HA
authors.lastname: Katus
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Schoels
mesh_terms: D000818:Animals; D018780:Body Surface Potential Mapping; D004285:Dogs; D004562:Electrocardiography; D005260:Female; D008297:Male; D012032:Refractory Period, Electrophysiological / Q000502:physiology; D016276:Ventricular Function