may cause cardiac arrest when applied at the right time and location of the precordium of an adult. The 50-joule threshold, however, can be considerably lower when the victim's heart is under ischemic conditions, such as in coronary artery insufficiency. Contusion of the heart, involving possible rupture of a heart chamber or damage to a heart valve as may occur in a violent vehicle accident, may be called contusio cordis (from Latin for "bruising of the heart"), but is unrelated to commotio cordis. Other situations Commotio cordis may also occur in other situations, such as in children who are physically abused, cases of torture, and frontal collisions of motor vehicles (the impact of the steering wheel against the thorax, although this has decreased substantially with the use of safety belts and air bags). In one fatality, the impact to the chest was the result of an exploding whipped cream canister. In contrast, the precordial thump (hard blows given over the precordium with a closed fist to revert cardiac arrest) is a sanctioned procedure for emergency resuscitation by trained health professionals witnessing a monitored arrest when no equipment is at hand, endorsed by the latest guidelines of the International Liaison Committee on Resuscitation. It has been discussed controversially, asin particular in severe hypoxiait may cause the opposite effect (i.e., a worsening of rhythm—commotio cordis). In a normal adult, the energy range involved in the precordial thump is five to ten times below that associated with commotio cordis. Mechanism The deviation of commotio cordis from the normal electrical rhythm of the heart is assessed scientifically in laboratory studies by analysis of the electrocardiograph (ECG) T wave (see ECG image). Only chest impacts occurring on a narrow band of the ECG during the upslope of the T wave (40 milliseconds (ms) before the peak of the T wave to the instant of the actual peak) will cause the ventricular fibrillation of commotio cordis, with an increased probability occurring when an impact happens from 30 to 10 ms before the peak of the T wave. These factors influence the onset of commotio cordis: Direction of impact over the precordium (precise area, angle of impact) Total applied energy (area of impact versus energy, i.e., the kinetic energy of the projectile ) Impact occurring within a specific 10- to 30-ms portion of the cardiac cycle. This period occurs in the ascending phase of the T wave