Originally Posted by
Carbonfiberboy
The Afibbing riders I've been with definitely noticed their HRM giving readings maybe 40 beats over what was appropriate for their effort and possibly above their noted MHR. These are riders using standard 4 electrode chest straps with diagnosed and treated Afib. We'd stop and wait for their HRs to return to normal, then proceed at reduced effort, below the HR which triggered their Afib. Observed in the wild.
Are you saying that even during Afib, the ventricle is also firing at that extreme rate? If so, why did the riders feel faint?
In AF the ventricle keeps contracting, otherwise there would be cardiac arrest and death. However, it is no longer under the control of the of the sinus node and is driven by ectopic activity from elsewhere in the atrium or associated structures.. The resulting ventricular rate is usually high, but can be “normal” or even slow. An abnormally high ventricular rate prevents the ventricle from filling completely and reduces cardiac output, sometimes drastically. That’s why people experiencing pathological tachycardia feel faint or collapse, or die.
The big danger in AF, however, is not from tachycardia, but from clot forming in the non-contracting atrium and causing strokes, etc.