Because of the advent of open-heart surgery, the 1960s saw a dramatic increase in the use of cardiac catheterization procedures. More and more patients with externalized transarterial catheters, usually enclosing leads that could be quickly connected to an external cardiac pacemaker, were appearing in the new cardiac care or special care units of hospitals. Once physicians realized that this highly conductive pathway not only bypassed the usual protective layers of relatively resistive body tissues, but also that it directed current to the most electrically sensitive areas of the inner walls of the heart, concerns arose about the possibility that these patients could be electrocuted by currents much lower than those that could pose a threat of electrocution when applied to the exterior of the body.
