FIGURE 2.

ECG recordings of Lowlanders identified with brady-arrhythmias during apnea (N.8) at 4330 m. Each frame (A–H) represents a single participant recording obtained preceding and/or proceeding volitional breakpoint. (A) sinus pause with junctional escape following volitional breakpoint; (B) ectopic atrial rhythm with junctional escape that began prior to volitional breakpoint and continued four beats following breakpoint; (C) premature atrial rhythm around volitional breakpoint; (D) sinus pause (4.3 s) immediately preceding volitional breakpoint; (E) ventricular bigeminy following breakpoint and 1st degree heart block (developed into 3rd degree); (2F) ventricular escape rhythm prior to volitional breakpoint; (G) premature ventricular contractions developed following breakpoint; (H) sinus pause with junctional escape preceding volitional breakpoint.