Unstable tachyarrhythmia

A broken assembly line running wild

Imagine a factory assembly line where workers normally move along at a set pace—that's your sinus node setting the heart rate. One day, a foreman in the middle of the line starts yelling orders so fast that workers are told to pass items down before the next station has finished receiving the last one. The line speeds up to 200 cycles per minute. Now each station (the ventricles) receives almost empty boxes to process, so very little product gets shipped out the loading dock (cardiac output drops). The dock manager frantically tries to compensate by squeezing the supply trucks harder and blocking other routes to push pressure up, but it doesn't help—the boxes are still empty because there's no time to fill them. The factory (heart muscle) starts to run out of fuel because the loading dock is so chaotic it can't deliver oxygen supplies during breaks. Soon the line breaks down entirely and shuts off. That's unstable tachyarrhythmia: a hijacked pace, no time to fill, almost nothing shipped, and the factory starving itself.