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To quantify cardiac apex rotation (CAR), the authors recently proposed the use of a Coriolis force sensor (gyroscope) as an alternative to other complex techniques. The aim of this study was to evaluate the effects of right ventricular (RV) pacing on CAR. A sheep heart was initially paced from the right atrium to induce a normal activation sequence at a fixed heart rate (AAI mode) and then an atrioventricular pacing was performed (DOO mode, AV delay = 60 ms). A small gyroscope was epicardially glued on the cardiac apex to measure the angular velocity (Ang V). From AAI to DOO pacing mode, an increase (+9.2%, p < 0.05) of the maximum systolic twisting velocity (Ang VMAX) and a marked decrease (-19.9%, p < 0.05) of the maximum diastolic untwisting velocity (Ang VMIN) resulted. RV pacing had negligible effects (-3.1%, p = 0.09) on the maximum angle of CAR, obtained by integrating Ang V. The hemodynamic parameters of systolic (LVdP/dtMAX) and diastolic (LVdP/dtMIN) cardiac function showed slight variations (-3.8%, p < 0.05 and +3.9%, p < 0.05, respectively). Results suggest that cardiac dyssynchrony induced by RV pacing can alter the normal physiological ventricular twist patterns, particularly affecting diastolic untwisting velocity.

Efforts have been made to utilize biologic parameters for determining optimal cardiac pacing rates. In this study of 67 patients, a significant relationship between heart rate and respiratory rate was observed during dynamic exercise. A system using a radiofrequency activator to modify pacing rate is described. Eleven patients have received VVI pacemakers with a similar implanted radio receiver coil. In two patients the fully automatic system has been successfully implanted. The experience with respiratory rate as a determinant of pacing rate is encouraging.

A pacemaker that adapts heart rate in response to the patient's metabolic requirements has been developed. The pacemaker uses breathing frequency and tidal volume as the indicators of physiologic demand. Maximal physical work capacity, anaerobic threshold, oxygen uptake (16 patients) and hemodynamic variables (9 patients) were assessed with fixed rate (VVI), atrial synchronous (VDT/I) and respiration-dependent ventricular (VVI-RD) pacing. All subjects attained their anaerobic threshold in stress tests with VVI pacing. The maximal physical capacity (p less than 0.001), work time to attain the anaerobic threshold (p less than 0.01) and oxygen uptake (p less than 0.001) were significantly greater with VVI-RD than with VVI pacing. The transition from the supine to the standing position was characterized by a significant increase of cardiac index at rest with both VDT/I and VVI-RD pacing as compared with VVI pacing. Progressive increments in the cardiac index and average left ventricular stroke work index were significantly different at submaximal and maximal exercise when VVI and VVI-RD were compared. At maximal exercise, mean cardiac output was also significantly different: 10.21 +/- 2.5 (SD) liters/min with VVI, 11.2 +/- 0.8 liters/min with VDT/I (p less than 0.05) and 12.65 +/- 3.1 liters/min with VVI-RD (p less than 0.05) pacing. Maximal oxygen extraction values were greater with VVI and VVI-RD pacing than with VDT/I pacing. Pulmonary artery end-diastolic pressures at maximal exercise were within the normal range with the three different modes of pacing. In conclusion, there is a significant (25%) improvement in exercise performance with VVI-RD pacing as compared with VVI pacing.(ABSTRACT TRUNCATED AT 250 WORDS)

The rate responsive pacemaker using respiratory rate as a sensor was implanted in 22 patients, 19 patients for ventricular pacing and three for atrial pacing. The level of exercise achieved with this system was consistently higher than with a fixed ventricular pacing rate. In addition, no special chemical or mechanical sensors are required; the sensor itself is simple, long-lasting, and energy efficient. Thus, this system adapts easily to the individual patient.