Myocardial ischemia caused by exercise versus total coronary occlusion.

Because we consider the last paragraph of our editorial4 ger-mane to our concern, reiteration will serve to emphasize its vital importance: "In the absence of such a reporting system and lacking new scientifically based data to supersede the old, we strongly urge manufacturers of electromedical equipment to continue to design their systems so as to meet the 1975 AHA committee recommendations and the 1978 ANSI standard. Although we understand the desirability for standards of individual countries to be in harmony with a single international standard, that alone cannot justify a relaxation of limits that may be hazardous to some patients. In the absence of credible data, the increases in risk current permitted by the new standard constitute unconsented-to human experiments to determine the safe range of such currents. There is a clear need for clinical studies (ethically approved) to provide robust information to resolve this issue. We strongly urge clinical investigators and members of industry to collaborate in gathering the appropriate data and designing a reporting system to establish a new realistic basis for safe current limits." In summary, both dog and human studies dictate the need to limit current through patient leads to 10 ,uA under single-fault conditions. As recommended previously by the AHA, enclosure leakage current under single-fault conditions should also be limited to 10 ,uA. With no accessible conducting surface, the leakage current should be limited to 100 ,uA, providing a reasonable safety factor for strong sensations as documented by Tan and Johnson.5 These current limitations are within the capabilities of modern engineering design and have been met by electrocardiographs of various manufacturers for many years. Amendment of recommendations for standardization of specifications for instruments in electrocardiography and vectorcardiography concerning safety and electrical shock hazards: report of the Committee on Electrocardi-ography, American Heart Association. D. Will relaxing safe current limits for electromedical equipment increase hazards to patients? The study by Borges-Neto et al' reports interesting findings regarding the extent of myocardial ischemia caused by exercise versus total coronary occlusion, but the conclusions expressed in the "Discussion" section and in the "Summary" may be misleading to clinicians. Indeed, they suggest that studies investigating the "myocardial demand" side of myocardial ischemia may prove to be inadequate prognostic indicators because the extent of myocar-dium in jeopardy from a stenostic lesion would be larger in the case of sudden coronary occlusion than that expected from exercise studies. Although this latter proposal …