title: Extraction of buried P waves from printed electrocardiograms.
abstract: BACKGROUND
  Morphologic identification of ectopic P-waves from surface ECGs can be challenging, particularly when the P-wave is buried in the QRST wave complex. Because ECGs are often available on paper and not digitally, we developed a method of subtracting the T-wave from the buried P-wave complex on paper ECGs.
  
  
  METHODS
  To validate our system, an atrial extrastimulus was introduced during and following the T-wave. The ECGs were scanned and then transformed from an image format to a digital format. A computer algorithm digitally subtracted a QRST with no buried P-wave from one with a buried P-wave, thus resulting in an extracted P-wave. The extracted P-waves were compared to the nonburied P-wave by determining correlation coefficients and by visual grading by two independent reviewers.
  
  
  RESULTS
  Visual grading comparing the buried P-wave with the exposed paced P-wave was 94%. The median correlation coefficient was 85%.
  
  
  CONCLUSIONS
  An ectopic atrial P-wave obscured by a coincident QRST wave complex can be accurately derived from printed ECG using this PC-based system. Addition of this technique to the existing methods may aid in the localization and ablation of ectopic atrial foci.
authors.affiliation: New England Cardiac Arrhythmia Center, Division of Cardiology, Department of Medicine, Tufts-New England Medical Center, USA.
authors.forename: Bryant
authors.initials: B
authors.lastname: Lin
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Wang
authors.forename: Srijoy
authors.initials: S
authors.lastname: Mahapatra
authors.forename: Munther
authors.initials: M
authors.lastname: Homoud
authors.forename: Mark
authors.initials: M
authors.lastname: Link
authors.forename: N A Mark
authors.initials: NA
authors.lastname: Estes
authors.forename: Amin
authors.initials: A
authors.lastname: Al-Ahmad
mesh_terms: D000465:Algorithms; D001145:Arrhythmias, Cardiac / Q000175:diagnosis; D016280:Atrial Function, Right; D018880:Atrial Premature Complexes / Q000175:diagnosis*; D002304:Cardiac Pacing, Artificial; D004562:Electrocardiography; D006801:Humans; D012815:Signal Processing, Computer-Assisted