Clinical Evaluation of Automatic Tachycardia Diagnosis by an Implanted Device

Reliable discrimination between sinus tachycardia (ST) and pathologic tachycardia has been a major problem for automatic implantable antitachycardia devices. In patients whose sinus response to activity is as rapid or faster than their pathologic tachycardia (rate crossover), these unsophisticated devices deliver the programmed tachycardia response to either the pathologic or sinus tachycardia. Over a one-year period, 50 Intermedics Intertach Model 262–12 antitachycardia pulse generators were implanted to evaluate the specificity of a new group of tachycardia recognition algorithms. Patients were subjected to exercise testing and noninvasive programmed stimulation to demonstrate the efficacy of this new approach. The five recognition algorithms tested were various combinations of the following criteria: high rate HR), sudden onset (SO), rate stability (RS), and sustained high rate (SHR). False positive rates (tachycardia response inappropriately triggered by ST) were as follows: HR (93%); HR + SO (3%); HR + RS (63%); HR + (RS or SHR) (87%); HR + HS + SO (8%). Pair-wise significance testing between HR only and HR + SO (p < 0.001), HR + RS (p = 0.01) and HR + SO + RS (p < 0.001), demonstrated a significant reduction in the rate of false positives through the use of the sudden onset and rate stability criteria in concert with the standard high rate criterion.     

MECHANISMS OF HALOTHANE ADSORPTION BY DRY SODA-LIME

Using fresh soda-lime (15% water by weight) the soda lime/airpartition coefficient of halothane was found to decrease asa function of vapour phase halothane concentration from 2 40at 0.3% halothane by volume to 1.15 at 2.6percnt;, but adsorptiongenerally followed Henry's law. However, soda-lime dried toa constant weight and subsequently exposed to various concentranonsof halothane adsorbed approximately 320 µlitre of vaporizedliquid halothane per 100 g before a measurable concentrationof halothane was detected in the vapour phase. Adding additionalhalothane then caused a linear increase in vapour concentration.We conclude that dry soda-lime can adsorb large quantities ofhalothane by a mechanism which is nimilar to that of a molecularsieve. After these "high affinity" sites are satisfied, additionalhalothane is adsorbed by a mechanism following Henry's law.