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In eleven patients serum levels of amiodarone and its desethyl metabolite were determined after a single dose of 400 mg amiodarone given with and without subsequent administration of colestyramine. In addition, the elimination half-life was measured in three patients after discontinuation of long-term amiodarone therapy. Mean serum levels of amiodarone at 7 1/2 hours after dosing (n = 11) were 0.42 +/- 0.11 micrograms/ml without colestyramine and 0.21 +/- 0.14 micrograms/ml with colestyramine (P less than 0.01). Elimination half-life after discontinuing long-term amiodarone therapy (n = 3) was 23 1/2, 29 and 32 days, respectively (half-life in eight controls: 35-58 days). The results indicate that colestyramine significantly reduces the enterohepatic circulation of amiodarone. Therefore, colestyramine should be capable of accelerating the regression of dose-dependent side-effects of amiodarone by enhancing its elimination.

Muscle potentials as a cause of pacemaker malfunction are often unrecognized, because control examinations are usually performed without physical exercise. Two observations are cited to illustrate how malfunctioning of different modes of stimulation can be caused by interference from muscle potentials. In addition to the known suppression of impulse production, fixed-rate stimulation may occur. These observations indicate that pacemaker function should be tested also during physical activity. Any malfunction can almost always be stopped by re-programming amplifier sensitivity.

The implantable defibrillator is a device to treat refractory ventricular tachyarrhythmias. This study was done to evaluate the determinants of defibrillator performance which are not known completely. Different defibrillation electrodes were attached to beating and non-beating isolated pig-hearts (n = 15) and the electric field resulting from defibrillation measured over a distance of 3 mm. From 5 to 20 J a non-linear relation was found between delivered shock energies and the amplitudes of the recorded voltage waveforms. Using two patch electrodes maximal amplitudes were monitored apical in the right (4.6 +/- 0.5 V) and left ventricle (2.1 +/- 0.3 V). The atria only showed 10-25% of the maximal amplitudes. The combination of a patch and a catheter electrode showed similar efficiency. Two catheter electrodes reduced the apical (1.2 +/- 0.1 V) and increased the atrial amplitude (0.75 +/- 0.06 V). The recorded amplitudes in myocardium were half as much compared with blood-/sodium chloride indicating the twofold higher resistance of myocardial tissue. These experiments quantify the dependence of the efficiency of automatic implantable defibrillator systems on the sort and localization of the defibrillation electrodes.