Note: VT accounts for up to 80 percent of cases of WCT in unselected populations, and more than 90 percent of cases in patients with a prior myocardial infarction (MI) . Making the presumption of VT guards against inappropriate and potentially dangerous therapies directed at an SVT (eg, adenosine, calcium channel blockers, or beta blockers), which can precipitate cardiac arrest in patients with VT. Treatment of SVT as if it were VT (eg, with IV amiodarone, procainamide, lidocaine, or external countershock) is safe and frequently effective in restoring sinus rhythm.