Spatially discordant voltage alternans cause wavebreaks in ventricular fibrillation.
BACKGROUND
Ventricular fibrillation (VF) is characterized by complex ECG patterns emanating from multiple, short-lived, reentrant electrical waves. The incessant breakup and creation of new daughter waves (wavebreaks) perpetuate VF. Dispersion of refractoriness (static or dynamic) has been implicated as a mechanism underlying wavebreaks.


OBJECTIVE
The purpose of this study was to investigate the mechanisms underlying wavefront instability in VF by localizing wave fractionation sites (the appearance of multiple waves) and their relationship to local spatial dispersion of voltage (V(m)) oscillations.


METHODS
Wave fractionations were identified by tracking V(m) oscillations optically at unprecedented spatial (100 x 100 pixels) and temporal (2,000 frames per second) resolution using a CMOS camera viewing the surface (1 x 1 cm(2)) of perfused guinea pig hearts (n = 6). VF was induced by burst stimulation, and wavefront dynamics were highlighted using region-based image analysis to automatically detect wavebreaks. Direct detection of wavebreak locations by image analysis was more reliable than the phase reconstruction method because baseline noise obstructed the correct identification of phase singularities by detecting false-positives.


RESULTS
Wave fractionations (34 +/- 4 splits/s.cm(2)) fell into three categories: decremental conduction (49% +/- 7%), wave collisions (32% +/- 8%), and wavebreaks (17 +/- 2%). Wavebreaks occurred at a frequency of 5.8 +/- 1 splits/s.cm(2) and did not preferentially occur at anatomic obstacles (i.e., coronary vessels) but coincided with discordant alternans where V(m) amplitudes and durations shifted from high to low to from low to high on opposite sides of wavebreak sites.


CONCLUSIONS
Spatial discordant alternans cause wavebreaks most likely because they are sites of abrupt dispersion of refractoriness.
Department of Cell Biology and Physiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA. bchoi@lifespan.org
Bum-Rak
BR
Choi
Woncheol
W
Jang
Guy
G
Salama
D000200:Action Potentials; D000465:Algorithms; D000818:Animals; D006168:Guinea Pigs; D006329:Heart Conduction System / Q000503:physiopathology*; D006352:Heart Ventricles / Q000503:physiopathology; D007091:Image Processing, Computer-Assisted; D066298:In Vitro Techniques; D008297:Male; D008955:Models, Cardiovascular; D014693:Ventricular Fibrillation / Q000503:physiopathology*