Cardiovascular collapse caused by electrocardiographically silent 60-Hz intracardiac leakage current : Implications for electrical safety

• Published in: Circulation (New York, N.Y.) N.Y.), 1999-05, Vol.99 (19), p.2559-2564
• Main Authors: SWERDLOW, C. D, OLSON, W. H, O'CONNOR, M. E, GALLIK, D. M, MALKIN, R. A, LAKS, M
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Diseases of the cardiovascular system; Electric Stimulation - adverse effects; Electrocardiography; Heart - physiopathology; Humans; Medical sciences; Radiotherapy. Instrumental treatment. Physiotherapy. Reeducation. Rehabilitation, orthophony, crenotherapy. Diet therapy and various other treatments (general aspects); Ventricular Fibrillation - physiopathology; Ventricular Fibrillation - therapy
• ISSN: 0009-7322; 1524-4539
• DOI: 10.1161/01.CIR.99.19.2559

The national standard for safe 60-Hz intracardiac leakage current under a single-fault condition is 50 microA. This standard is intended to protect patients from alternating current (AC) at levels below the threshold for sensation, but the minimum unsafe level for AC in closed-chest humans is not known. To determine this value, we studied 40 patients at testing of implantable cardioverter-defibrillators using a programmable source of 60-Hz AC. We applied AC for 5-second test periods in increasing strengths until ventricular fibrillation (VF) was induced or 1 mA was reached. Two current paths were tested: bipolar, between tip and ring electrodes of a right ventricular pacing catheter, and unipolar, from tip to a remote electrode. We observed a characteristic sequence of 3 responses as AC was increased: (1) intermittent ventricular capture with QRS morphology identical to pacing through the electrodes (minimum value, 20 microA); (2) continuous capture at cycle length 282+/-88 ms (minimum value, 32 microA); and (3) VF persisting after AC termination (minimum value, 49 microA). Continuous capture caused loss of pulsatile arterial pressure and cardiovascular collapse (mean arterial pressure, 32+/-8 mm Hg) for the duration of AC with no ECG evidence of AC stimulation. Thus, the clinical picture was that of hypotensive ventricular tachycardia (VT). The continuous-capture threshold was /=5 seconds should be