Practical aspects of automatic cardioverter/defibrillator implantation.
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Anti-Arrhythmia Agents↗
Biomedical subjects
R H Mead
Publications and source records attributed to R H Mead.
Therapy with investigational antiarrhythmic drugs.
The investigational antiarrhythmic agents available for use in this country are predominantly class I drugs with local anesthetic membrane effects. These drugs are often used successfully to control arrhythmias refractory to treatment with the standard antiarrhythmic drugs. Side effects often limit their use, and particular attention needs to be paid to their cardiac side effects, such as exacerbation of arrhythmia or enhanced conduction defects.
Amiodarone↗
Origin of the background sodium current and effects of sodium removal in cultured embryonic cardiac cells.
Cardiac automaticity is partly due to a diastolic sodium current. Possible mediators of this include tetrodotoxin-sensitive "fast" channels, cesium-sensitive time-dependent pacemaker current channels, calcium-gated nonspecific channels, and electrogenic sodium-calcium exchange. We have studied the effects of abrupt sodium removal on membrane current and conductance in voltage-clamped chick embryonic myocardial cell aggregates, in the presence of various sodium flux inhibitors. Total replacement of sodium by lithium, Tris, or tetraethylammonium ions in aggregates clamped in the pacemaker range caused a brief outward current followed by a sustained net inward current. The outward current reached a peak value of 1.1 +/- 0.5 microA/cm2 at a mean latency of 5.4 +/- 1.2 sec. (n = 6; V = -70.5 +/- 8.9 mV; Tris). Conductance often decreased during the outward current. The inward current developed exponentially (t = 19 +/- 5 sec) and reached a steady state value of -1.6 +/- 0.4 microA/cm2. This current was reversed by depolarization (mean reversal potential = -13 +/- 13 mV), and was accompanied by increased conductance and spontaneous mechanical activity. Neither of the sodium-removal currents was affected by 20 microM tetrodotoxin. Cesium (up to 20 mM) had no effect on the late inward current or the mechanical activity, but decreased the early outward current by 80 +/- 12%. Manganese (25 mM), which blocks sodium-calcium exchange, abolished the late inward current and the mechanical activity. Manganese also reduced the early outward current by 27 +/- 10%. Manganese and cesium together blocked all the effects of sodium removal. We conclude that removal of extracellular sodium interrupts a cesium-sensitive "background" current, that may be related to the time-dependent pacemaker current, If. Sodium removal also causes gradual activation of a nonspecific conductance, which can ultimately depolarize the cells, and which may be gated by cytoplasmic calcium.
Animals↗
Unusual manifestations of secondary syphilis occurring after orthotopic liver transplantation.
A 48-year-old actively homosexual man who had undergone liver transplantation for cirrhosis secondary to hepatitis B infection six years previously presented with a syndrome of diffuse pain, cholestasis, and low-grade fever. The development of thrombocytopenia and persistent hypoprothrombinemia precluded liver biopsy. Subsequently, a skin eruption and VDRL result of 1:128 indicated that most of the findings could be explained by a diagnosis of secondary syphilis with luetic hepatitis and periostitis. This impression was confirmed by a complete response to penicillin therapy. The relation of thrombocytopenia to lues in this case remains uncertain.
Hepatitis↗