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What is ventricular fibrillation?

  • Zhilin Qu
    Correspondence
    Address reprint requests and correspondence: Dr Zhilin Qu, Department of Medicine, David Geffen School of Medicine at UCLA, A2-237 CHS, 650 Charles E. Young Dr South, Los Angeles, CA 90095.
    Affiliations
    Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, California
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Published:October 28, 2021DOI:https://doi.org/10.1016/j.hrthm.2021.10.021
      The mechanisms of ventricular fibrillation (VF) have been in debate for more than a century.
      • Wiggers C.
      The mechanism and nature of ventricular fibrillation.
      ,
      • Aras K.K.
      • Kay M.W.
      • Efimov I.R.
      Ventricular fibrillation: rotors or foci?.
      Experimental and computer simulation studies in the last few decades have demonstrated that foci, reentry, or a mixture of the two are all possible electrical activities for VF, depending on the disease or experimental conditions.
      • Qu Z.
      • Weiss J.N.
      Mechanisms of ventricular arrhythmias: from molecular fluctuations to electrical turbulence.
      A reentry can occur around an anatomic structure, such as a scar, called anatomic reentry, or in structurally normal tissue, called functional reentry. A functional reentry is a spiral wave or a rotor whose rotation center is called a phase singularity (PS),
      • Gray R.A.
      • Pertsov A.M.
      • Jalife J.
      Spatial and temporal organization during cardiac fibrillation.
      a term first coined by Arthur Winfree.
      • Winfree A.T.
      Electrical instability in cardiac muscle: phase singularities and rotors.
      Experimental studies have shown that the number and lifetime of PSs during VF are highly variable over time.
      • Gray R.A.
      • Pertsov A.M.
      • Jalife J.
      Spatial and temporal organization during cardiac fibrillation.
      ,
      • Choi B.R.
      • Nho W.
      • Liu T.
      • Salama G.
      Life span of ventricular fibrillation frequencies.
      ,
      • Kay M.W.
      • Walcott G.P.
      • Gladden J.D.
      • Melnick S.B.
      • Rogers J.M.
      Lifetimes of epicardial rotors in panoramic optical maps of fibrillating swine ventricles.
      One common observation of the experimental studies is that the PS lifetime distribution decays exponentially. Based on this observation, Dharmaprani et al
      • Dharmaprani D.
      • Schopp M.
      • Kuklik P.
      • et al.
      Renewal theory as a universal quantitative framework to characterize phase singularity regeneration in mammalian cardiac fibrillation.
      ,
      • Dharmaprani D.
      • Jenkins E.
      • Aguilar M.
      • et al.
      M/M/infinity birth-death processes—a quantitative representational framework to summarize and explain phase singularity and wavelet dynamics in atrial fibrillation.
      hypothesized that the generation and disappearance of PSs can be described by a Markov birth-death process. They defined the death rate as the decay rate of the PS lifetime distribution, and the birth rate as the decay rate of the distribution of the time interval between 2 consecutive new PSs. In the first 2 studies, they demonstrated that the PS dynamics in experimental animal atrial fibrillation (AF), clinical human AF, and computer models could be well described by this Markov process.
      • Dharmaprani D.
      • Schopp M.
      • Kuklik P.
      • et al.
      Renewal theory as a universal quantitative framework to characterize phase singularity regeneration in mammalian cardiac fibrillation.
      ,
      • Dharmaprani D.
      • Jenkins E.
      • Aguilar M.
      • et al.
      M/M/infinity birth-death processes—a quantitative representational framework to summarize and explain phase singularity and wavelet dynamics in atrial fibrillation.
      In the current study reported in this issue of Heart Rhythm Journal, Dharmaprani et al
      • Dharmaprani D.
      • Jenkins E.V.
      • Quah J.X.
      • et al.
      A governing equation for rotor and wavelet number in human clinical ventricular fibrillation: implications for sudden cardiac death.
      further demonstrated that the PS dynamics in human VF could also be described by this simple Markov process. Mathematically, a Markov birth-death process is a purely random process without memory of the history. This implies that the PS dynamics in human VF and AF can be described by a purely random process. An issue arising is what are the underlying mechanisms/causes for this randomness. Answering this question could bring more insights into the understanding of the mechanisms of VF and AF.
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