From Turbulence to Understanding: The Value of Bold Hypotheses in Atrial Fibrillation Research

The study of atrial fibrillation (AF) mechanisms represents one of the most formidable challenges in modern cardiac electrophysiology. For decades, the field has grappled with the extraordinary complexity of this arrhythmia, seeking conceptual frameworks that might illuminate its chaotic electrical dynamics 1, 2. For more than a century 3, 4, the mechanisms underlying atrial fibrillation have remained a subject of intense debate, with multiple competing hypotheses proposed and none achieving universal acceptance. Classical concepts include (1) rapidly firing automatic foci 5, 6. (2) A localized, rapidly discharging reentrant circuit producing fibrillatory conduction 7, 8. (3) Multiple unstable reentrant wavelets meandering through atrial tissue 2, 9 and (4) Endocardial–epicardial dissociation, which promotes breakthrough activations between atrial surfaces 10. Despite these advances, the failure to resolve AF's fundamental mechanism persists—a controversy so entrenched that contemporary clinical textbooks 11 and guideline statements 12-14 typically resort to vague, overly noncommital summaries that essentially summarize alternative possibilities for AF—so generalized and equivocal that they offer little actionable insight for clinicians and virtually no tangible benefit for patient treatment. Indeed, discussion of AF's fundamental mechanism has largely disappeared from mainstream clinical meetings, which have shifted toward technology-driven topics such as ablation tools and mapping systems, while basic science has become increasingly reductionist, focusing on molecular and cellular processes far removed from the clinically observable arrhythmia In this context, Chu et al. deserve genuine commendation for their intellectual courage in proposing a turbulence-based model of AF. The attempt to bridge classical fluid dynamics with cardiac electrophysiology is ambitious, and the authors should be applauded for taking on this difficult topic with conviction. Chu and colleagues propose that atrial fibrillation (AF) represents a turbulence-like state of myocardial electrical activity, borrowing concepts from fluid dynamics to explain AF's complex spatiotemporal organization. Unlike traditional rotor or multiple wavelet theories, this framework emphasizes multi-scale fragmentation of electrical wavefronts—from large coherent activations to micro-scale wavelets—within an anisotropic atrial substrate. The turbulence framework interprets the pulmonary vein–left atrial junction as a critical site for turbulence initiation, owing to its extreme structural and electrophysiological heterogeneity. PVI disrupts this “turbulence generator,” reducing system entropy and restoring order, explaining the partial effectiveness of AF ablation. The authors postulate that atrial electrical turbulence exhibits phenomenological parallels to conservation principles in fluid dynamics, notably the Navier-Stokes equations. At first glance, the hypothesis of Chu et al. is potentially attractive. The notion of scientific analogy is very powerful, and the notion of turbulence as a driver of AF could be seen as analogous to the phenomenon of wavelet formation or spiral wave breakup 15, 16. However, AF is not analogous to an eddy fragmenting upon collision with a static object. Rather, it is a well-characterized behavior of reaction-diffusion waves in excitable media, occurring when a propagating wavefront encounters tissue that remains in a refractory state. In AF, wavefront breakup occurs through the formation and annihilation of topologically chiral vortex pairs (±1) 17-19, a process that preserves overall topological charge balance 20 and underpins the statistical stability of phase singularity distributions 21-23. A remarkable parallel not identified by Chu et al. between turbulent fluid dynamics and AF is that due to the uncorrelated nature of phase singularity formation and destruction processes, the population of topological defects in both turbulent fluids 24, 25 and AF 21-23 tends to show a Poisson distribution 26, 27. However, while the turbulence analogy may possess superficial appeal and metaphorical resonance, a rigorous biophysical analysis reveals fundamental incompatibilities between fluid turbulence and cardiac electrical activity. The central pillar of the turbulence hypothesis is the claim that energy in AF exhibits cascade characteristics from macro-scale to micro-scale, consistent with classical Kolmogorov turbulence theory 28. This assertion represents perhaps the most significant conceptual error in the proposed framework, as it fundamentally misidentifies the nature of energy in the two systems. “Big whirls have little whirls that feed on their velocity and little whirls have lesser whirls and so on to viscosity.” However, whilst the turbulence analogy proposed by Chu et al. certainly offers an evocative metaphor or has allegorical similarity to fibrillation, closer examination reveals that it does not align with the underlying biophysics of excitable media and reaction-diffusion systems. The first issue is that the energy dynamics of AF operates under entirely different physical principles. AF is sustained by the dissipation of electrochemical gradients that are actively established and continually restored by membrane pumps—most prominently the Na⁺/K⁺-ATPase. With each action potential, sodium enters and potassium exits the cell, partially dissipating the transmembrane gradients that make excitability possible. The cell then spends metabolic energy (ATP) to reconstitute those gradients via active transport, moving ions against their electrochemical potentials. In AF energy dynamics are local and regenerative: each new depolarization draws on pre-established gradients that were actively rebuilt by ATP-dependent pumps, and the “dissipation” we observe is metabolic consumption required to maintain ionic homeostasis and excitability—not the transfer of mechanical kinetic energy across scales as in fluid turbulence. The second critical failure of the turbulence analogy lies in its conflation of two fundamentally different transport mechanisms: the advective transport of mass in fluids versus the propagation of electrical excitation through an excitable medium. In fluid turbulence, chaotic swirling motion is characterized by advection—the process by which substances or conserved quantities such as heat or momentum are transported by the bulk motion of the fluid itself. Fluid particles are physically displaced from one location to another, carrying their properties with them. The medium itself—the fluid—is what moves. This is the essence of flow: material transport through space. Cardiac electrical activity operates through an entirely different mechanism: propagation, not advection. It manifests as a nonlinear, regenerative wave moving through a medium of essentially stationary, interconnected cells. The cardiomyocytes that constitute the atrial walls do not travel with the electrical wave; they remain fixed within the structural architecture of the myocardial lattice. What propagates is not matter but a change in electrical state—specifically, membrane depolarization. The mechanism is fundamentally local and regenerative: an action potential in one cell causes ionic currents that flow through low-resistance gap junctions to adjacent cells. These currents raise the membrane potential of neighboring cells to their excitation threshold, triggering them to fire their own full action potentials by releasing their own locally stored electrochemical energy. The wave thus represents a propagating front of state change, with each cell sequentially transitioning from rest to excitation and back to rest. Chu et al. deserve recognition for their intellectual ambition in attempting to apply concepts from classical fluid mechanics to the complex problem of AF. Their work reflects commendable interdisciplinary creativity. However, rigorous analysis reveals that the turbulence analogy, while potentially evocative as a metaphor, is unlikely to succeed either as a quantitative physical model or a clinically applicable framework. The turbulence analogy, despite its intuitive appeal and the laudable intentions of its proponents, in our opinion, ultimately represents an inappropriate analogy between incompatible physical domains. The heart, after all, is not a turbulent fluid—it is an electrically excitable, metabolically active, structurally complex biological organ, and it demands models that honor that reality. Nonetheless, as a field, we must remain open-minded to new ideas, and Chu et al. should be commended for their contribution.