Leadless pacing using induction technology: impact of pulse shape and geometric factors on pacing efficiency.

AIMS: Leadless pacing can be done by transmitting energy by an alternating magnetic field from a subcutaneous transmitter unit (TU) to an endocardial receiver unit (RU). Safety and energy consumption are key issues that determine the clinical feasibility of this new technique. The aims of the study were (i) to evaluate the stimulation characteristics of the non-rectangular pacing pulses induced by the alternating magnetic field, (ii) to determine the extent and impact of RU movement caused by the beating heart, and (iii) to evaluate the influence of the relative position between TU and RU on pacing efficiency and energy consumption. METHODS AND RESULTS: In the first step pacing efficiency and energy consumption for predefined positions were determined by bench testing. Subsequently, in a goat at five different ventricular sites (three in the right ventricle, two in the left ventricle) pacing thresholds using non-rectangular induction pulses were compared with conventional pulses. Relative position, defined by parallel distance, radial distance, and angulation between TU and RU, were determined in vivo by X-ray and an inclination angle measurement system. Bench testing showed that by magnetic induction for every alignment between TU and RU appropriate pulses can be produced up to a distance of 100 mm. In the animal experiment pacing thresholds were similar for non-rectangular pulses as compared with conventional pulse shapes. In all five positions with distances between 62 and 102 mm effective pacing was obtained in vivo. Variations in distance, displacement and angle caused by the beating heart did not cause loss of capture. At pacing threshold energy consumptions between 0.28 and 5.36 mJ were measured. Major determinants of energy consumption were distance and pacing threshold. CONCLUSION: For any given RU position up to a distance of 100 mm reliable pacing using induction can be obtained. In anatomically crucial distances, up to 60 mm energy consumption is within a reasonable range.

Changes in right ventricular pressures between hemodialysis sessions recorded by an implantable hemodynamic monitor.

Intermittent and chronic volume overload might contribute to the onset and progression of cardiovascular disease in patients who are undergoing maintenance hemodialysis (HD). Continuous monitoring of central hemodynamic variables may provide valuable information to improve volume control, particularly in patients with left ventricular dysfunction. Sixteen patients with end-stage renal disease who were undergoing long-term HD received an implantable hemodynamic monitor consisting of a subcutaneously implanted memory device and transvenous right ventricular (RV) lead with a pressure sensor. The implantable hemodynamic monitor continuously records heart rate, RV pressures, and estimated pulmonary arterial (PA) diastolic pressure, an estimate of left ventricular filling pressure. All patients underwent HD 3 times per week, and averages of rest hemodynamic values from the first, second, and third nights after HD during 12 weeks were analyzed. The third night always occurred after the weekend, when there was an extended interval between dialysis sessions. From the first night to the second night, RV systolic pressure increased by 10 +/- 8% (p <0.001), and estimated PA diastolic pressure increased by 16 +/- 14% (p <0.001). On the third night, RV systolic pressure increased by 14 +/- 12% (p <0.001), and estimated PA diastolic pressure increased by 23 +/- 18% (p <0.001) compared with the first night. In conclusion, the progressive pressure increments between dialysis sessions seen in this study suggest that the implantable hemodynamic monitor was a sensitive indicator for changes in volume load in patients who were undergoing HD treatment. The results also suggest that more frequent dialysis may avoid excessive pressure increase, but this needs to be investigated further in future studies.