ABSTRACT
The QT pacemaker is a rate modulated pacemaker that uses the evoked QT interval as an indicator to determine its optimal pacing rate. Despite the generally favorable clinical results with this form of pacing, some flaws in the system have been reported, such as the frequently observed rather slow initial response of the pacing rate to physical exercise, and the phenomenon of oscillation of the heart rate. These problems can be attributed to the rate adaptive algorithm used in the current QT pacemaker. Recently, in a reexamination of the relationship between evoked QT interval and pacing rate, a curvilinear relationship between these parameters has been demonstrated. As a result, a new algorithm has been developed for the next generation of the QT pacemaker. Before this new algorithm was implemented in new implantable devices, it was evaluated in a multicenter clinical investigation, with emphasis on the initial response of the pacing rate to exercise. This study was carried out by means of special software in the programmer of the QT pacemaker. By employing real-time bidirectional telemetry, it was possible to submit the study population, consisting of 37 patients with implanted QT pacemakers of the current generation, to identical exercise tests. Comparing these exercise tests, it appears that a considerable gain in speed of response to exercise can be achieved by using the same sensor with a faster reacting, nonlinear rate adaptive algorithm.
Subject(s)
Algorithms , Electrocardiography , Exercise , Pacemaker, Artificial , Aged , Arrhythmias, Cardiac/therapy , Exercise Test , Female , Heart Rate , Humans , Male , Multicenter Studies as Topic , SoftwareABSTRACT
Hypertension as a result of stenosis of a renal artery was diagnosed in three patients, aged 20, 17, and 9 respectively, among 14 siblings from one family. The oldest patient was treated by vasoplasty; a hypoplastic kidney had previously been removed in an unsuccessful attempt to control hypertension. Nephrectomy was performed in the other two patients. The pathological picture of the main renal artery that could be examined differed from that usually seen in the fibromuscular dysplasia group. The absence of microscopic signs of atrophy in the small kidneys behind the stenosis argues for a developmental defect. More than three years after operation blood pressure and renal function in all three patients have remained normal.
