Abstract: Apparatus and method of antitachycardia pacing in a duel chamber pacing device including means for or steps of detecting the presence of a tachycardia, measuring the tachycardia cycle length, determining a VA interval value less than or equal to the tachycardia cycle length, determining an initial value of the AV delay interval, delivering pulses to the ventricle and to the atrium until the expiration of N VA intervals and N AV intervals thereby completing a first train of pulses, delivering a series of M trains of pulses similar to said first train pulses, and varying the AV delay interval value from the initial value at least once prior to the completion of the series of M trains of pulses. Monitoring of instrinsic QRS complexes between pulse trains is performed. If the tachyarrhythmia is deemed to be accelerating, one of cardioversion or defibrillation may be applied.

Abstract: An ultrasonic transducer for a system for determining liquid levels by echo ranging composed of a housing including a piezoelectric crystal mounted within the housing to transmit acoustic waves, an impedance matching medium mounted within the housing adjacent the crystal and including a window layer and a diaphragm layer to transmit acoustic waves between the crystal and a gaseous environment which window layer is composed of a material having hollow glass spheres dispersed therein, and a dampening backing mounted in said housing to abut the crystal which backing includes a plurality of solid lead spheres; a tube mounted to extend from the housing to form a beam of acoustic waves propagated from said crystal, the tube having an end which is telescoped into the housing and spaced a short distance from the diaphragm to form a gap for flow communication; and a reference reflector assembly mounted to extend from adjacent said housing, which assembly includes a U-shaped member having two legs extending in slideabl