Analyzing the QRS Complex

■ QRS ≤ 0.10 sec: Considered normal.
■ QRS > 0.10 sec, “wide and bizarre”: Consider ventricular ectopy.
■ QRS > 0.10 sec (2.5 small boxes), with notched or “rabbit ears” appearance: Consider BBB (see differentiating right and left BBB).
■ QRS preceded by 1–2 very narrow “spikes”: Consider pacemaker.