Approximately how long does the total conduction pathway take, from initiation of the impulse in the SA node until depolarization of the ventricles is complete?

1. The conduction pathway has several timed stages: SA node to AV node (about 50 ms), the AV nodal delay (about 100 ms), the bundle branches to the apex (about 25 ms), and Purkinje fiber spread to the ventricular muscle (about 75 ms). 2. Adding these stages together gives the total time elapsed. 3. This total time, from initiation at the SA node until ventricular depolarization is complete, is approximately 225 ms. 4. 25 ms accounts only for the bundle-branch-to-apex portion of the pathway, not the whole route. 5. 500 ms is far longer than the actual total conduction time from SA node to full ventricular depolarization. 6. 1000 ms overstates the true total time even more, well beyond the roughly quarter-second window described. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 19 "The Cardiovascular System: The Heart", section 19.2, p. 850_