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Figure 2 Six-lead electrocardiogram demonstrating VF produced by a 30-mph baseball impact to the chest wall directly over the anterolateral papillary muscle, timed to the upstroke of the T wave in an 11-kg juvenile swine. Ventricular fibrillation occurs immediately and is not preceded by ischemic electrocardiographic changes, ventricular tachycardia or heart block. Inset (lower right). Magnification of the LV pressure tracing obtained at the precise moment of impact; note the marked and immediate pressure rise within the LV. Left ventricular pressure increases abruptly to 290 mm Hg over a time period of 8 ms and falls to 0 mm Hg 12 ms later. LV = left ventricular; VF = ventricular fibrillation.