Cross-stimulation during lead impedance monitoring.

At the age of 4 years, a total cavopulmonary connection was performed in a boy with a complex congenital heart defect. On addition, a DDDR pacemaker was implanted for sick sinus syndrome. Atrial and ventricular leads were epicardially placed at the left atrium and left ventricle. At the age of 10 years, a new epicardial ventricular lead was placed because of malfunction of the existing lead. At the same operation the pulse generator was replaced by a Medtronic Kappa DR 731. After replacement, the boy experienced episodes of phrenic nerve stimulation associated with feelings of discomfort. Holter recordings revealed ventricular stimulation from the atrial stimulus for 2 consecutive beats. This phenomenon repeated exactly every 3 hours and was caused by the automatic lead impedance measurement that used a 5-V, 1-ms stimulus output.

Feasibility of pacemaker therapy after dynamic cardiomyoplasty.

A 54-year-old man presented with total atrioventricular (AV) block 3 months after dynamic cardiomyoplasty was performed because of heart failure due to idiopathic dilated cardiomyopathy. Though the cardiomyostimulator acted as a back-up pacemaker, a DDDR pacemaker was implanted to optimize hemodynamics. During testing no cross-sensing or cross-stimulation between the pacemaker and the cardiomyostimulator was demonstrable. The synchronization delay, however, had to be adjusted.

Comparison of longevity, pacing, and sensing characteristics of steroid-eluting epicardial versus conventional endocardial pacing leads in children.

OBJECTIVE: Because of either cardiac anatomy or small size, pacing in children often occurs by means of epicardial leads. The disadvantage of epicardial leads is the shorter longevity of these leads compared with endocardial leads. During short-term follow-up, improved stimulation thresholds were found for the newer steroid-eluting epicardial leads. The longevity of these leads may be better than that of conventional epicardial leads. An improved longevity of epicardial leads may influence the choice to either epicardial or endocardial pacing in children. METHODS: We studied the longevity and the pacing and sensing characteristics of 33 steroid-eluting epicardial pacing leads (group I, 15 atrial, 18 ventricular) implanted between November 1991 and October 1996 in 20 children with a mean age of 7.6 +/- 6.5 years (mean +/- SD), and 29 endocardial pacing leads (group II, 15 atrial, 14 ventricular) implanted during the same period in 21 children with a mean age of 11.7 +/- 4.7 years. RESULTS: The mean follow-up in group I was 2.9 +/- 1.6 years and in group II 3.1 +/- 1.7 years (P =.61). The 2-year survival of the leads in group I was 91% +/- 5% and in group II 86% +/- 7% (P =.97). Lead failure occurred in both groups in 4 leads (P =.85). Chronic stimulation and sensing thresholds were similar. CONCLUSIONS: Steroid-eluting epicardial leads have the same longevity as the conventional endocardial leads. Pacing and sensing thresholds were similar and did not change during follow-up. Therefore steroid-eluting epicardial pacing leads are a good alternative for endocardial leads in small children and in children with congenital heart disease.

Analysis of atrial sensed far-field ventricular signals: a reassessment.

Accurate detection of the spontaneous far-field ventricular signal may be used to determine the ventricular activation, and hence, the interval from atrial stimulus to the ventricular R wave (AR interval) using a standard atrial pacing lead. This can be useful in developing a physiological atrial rate responsive (AAIR) pacemaker and in further improving DDD(R) pacing algorithms. In order to better characterize the atrial sensed far-field ventricular signal, 200 consecutive patients undergoing pacemaker implantation were studied. The amplitude of the far-field ventricular signal was significantly smaller than that of the atrial deflection. In all recordings, the slew rate of the atrial deflection was larger than that of the far-field ventricular signal. Subdivision of the recordings by electrode position, pocket location, or QRS duration on the surface ECG resulted in significantly different signal characteristics. The amplitude and slew rate of the far-field ventricular signal were significantly smaller in bipolar versus unipolar sensing. Atrial sensed far-field ventricular recordings could also be obtained in the case of ventricular pacing. Our results indicate that accurate sensing of the far-field ventricular signal from an atrial pacing lead is conceivable in most patients. The different signal characteristics in relation to parameters, such as electrode position, sensing mode, and pocket location, may be useful in determining the optimal conditions for signal sensing.

Stimulation characteristics, complications, and efficacy of spinal cord stimulation systems in patients with refractory angina: a prospective feasibility study.

OBJECTIVES: In a prospective study with a 1-year follow-up we evaluated: (1) the feasibility of a method for the adjustment of spinal cord stimulator (SCS) parameters, (2) complications of SCS, and (3) efficacy of SCS. METHODS: In patients receiving an SCS for severe angina unresponsive to standard therapies, SCS characteristics were evaluated within 1 week and at 4, 14, 26, and 52 weeks after SCS treatment. Step-by-step adjustment of pulse output parameters was performed at the electrode configuration at which paresthesias occurred ("sensory threshold"), covered the anginal area ("adjusted setting"), or provoked pain ("motor threshold"). In addition, the number of anginal attacks and intake of glyceryl trinitrate (GTN) tablets were recorded at regular intervals. RESULTS: Twenty-two patients with either a bipolar (14) or a unipolar (8) system were evaluated. In the 14 patients with bipolar systems, alteration in paresthesias required 26 reprogrammings of the configuration. In the eight patients with bipolar systems who completed the follow-up without lead dislocation, the mean "sensory threshold" was 3.3 V (1.7-5.6), the mean "adjusted stimulation" output was 4.5 V (2.8-7.6), and the mean "motor threshold" was 4.9 V (2.8-7.7) after 4 weeks SCS. The mean stimulation duration per 24 hours was 14.1% (5%-24%), and the mean standardized impedance was 821 omega (748-893) after 4 weeks SCS. The unipolar group demonstrated comparable results. After 1-year follow-up the parameters had not changed significantly. During the 1-year follow-up, 6 of 22 patients experienced lead dislocation that required surgery. In all patients, anginal attacks (P < 0.003) and GTN intake (P < 0.005) were reduced significantly with SCS. The effect lasted during the 1 year. CONCLUSIONS: During a 1-year follow-up, the stimulation parameters did not change significantly in the 16 patients without lead dislocations. Our standardized method appears to be feasible for follow-up of SCS. Moreover, SCS seems to be an effective adjuvant therapy for intractable angina, despite a relatively frequent dislocation of the electrode.

Analysis of the morphology of the unipolar endocardial paced evoked response.

In a retrospective study we analyzed the unipolar endocardial evoked response signal (ERS) of 103 patients prior to pacemaker implantation. The objective of this study was to give a complete description of the ERS morphology and to evaluate influences on this morphology of both various electrode characteristics and pacing rate. In addition, spontaneous endocardial signals were studied. The results demonstrate that acute leads had both higher R wave and T wave amplitudes and a faster downslope of the T wave. In the acute leads those with porous titanium carbon coated tips showed a more pronounced T wave. Pacing rate influences the R wave amplitude and the stimulus to T wave interval. Both stimulus to maximum and stimulus to minimum T wave interval show an exponential correlation with the stimulus interval. The interval between maximum and minimum of the T wave and the absolute amplitude of T wave are not influenced by rate. Although there were significant correlations of the spontaneous endocardial signal with the ERS, the predictive value of the spontaneous signal for the ERS morphology is low. Prospective studies will be necessary to confirm the findings in this study.

Improved rate responsive algorithm in QT driven pacemakers--evaluation of initial response to exercise.

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.