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Background: Elderly pacemaker patients with chronotropic incompetence (CI) may experience orthostatic hypotension (OH) upon standing. The objective of this study was to determine whether a transient increase in heart rate (HR) by overdrive pacing upon standing prevents OH in elderly pacemaker patients. Methods: We studied the effect of transient overdrive pacing upon standing in mitigating the drop in blood pressure (BP) in 62 pacemaker patients (77 ± 6 years, 32 F) implanted with DDD pacemaker for sick sinus syndrome (n = 40) or atrioventricular block (n = 22). All patients underwent two standing procedures in random order: a control, with backup (60 bpm) pacing and another with overdrive DDD pacing (at 35 bpm above their baseline rate) for 2 minutes upon standing. Systolic (SBP) and diastolic blood pressure (DBP) and HR were measured while supine (baseline) and 1, 2, and 3 minutes after standing. OH was defined as a drop in SBP ≥20 mmHg or DBP ≥10 mmHg during standing. Chronotropic incompetence (CI) was defined as an absence of HR increase of ≥10 bpm during standing. Results: A total of 17 (27%) patients developed OH upon standing during backup pacing. Baseline clinical characteristics (age, sex, prevalence of diabetes, use of vasoactive medications, and sick sinus syndrome) were similar between patients with or without OH. In patients with or without OH, transient overdrive pacing upon standing increased HR and DBP as compared with baseline (P < 0.05). However, in patients with OH, transient overdrive pacing did not prevent decrease in SBP upon standing and avoided the development of OH in only 10/17 patients (59%). Among those patients with OH, 10/17 (59%) patients had CI. In OH patients with CI, transient overdrive pacing upon standing maintained SBP and DBP as compared to baseline and prevented OH in the majority of patients (80%). By contrast, transient overdrive pacing in OH patients without CI had no significant effect on the decrease in SBP upon standing and prevented OH in only 20% of patients. Conclusions: OH is common (27%) in the elderly pacemaker population. In a subgroup of these patients, CI may be responsible for the occurrence of OH, and OH can be prevented by transient overdrive pacing upon standing. [ABSTRACT FROM AUTHOR]

TSE, H.F.,et al.: Blood Pressure Response to Transition from Supine to Standing Posture Using an Orthostatic Response Algorithm. Upon standing from a supine position, the normal response is an increase in heart rate to maintain blood pressure (BP). In patients with chronotropic incompetence, heart rate may not increase upon standing, and they may experience orthostatic hypotension (OH). We evaluated a new orthostatic response (OSR) pacing algorithm that uses an accelerometer signal to detect sudden activity following prolonged rest to trigger a 2 minutes increase in pacing rate to 94 bpm. Ten recipients of DDDR pacemakers which contain the OSR compensation algorithm (mean age= 77± 9 years, 8 women) with sick sinus syndrome (n= 6) or atrioventricular block (n= 4) were studied. In all patients BP was measured before and 0.5, 1, 1.5, 2, and 3 minutes after standing at their programmed base rate. A 20 mmHg fall in systolic BP upon standing was observed in five patients (OH patients), while the other five were considered non-OH patients. The measurements were repeated with the OSR algorithm turned on. Mean BP was defined as 1/3 systolic BP+ 2/3 diastolic BP. Baseline heart rate was significantly slower in OH patients (62± 2 bpm) than non-OH patients (71± 7 bpm, P<0.05). In OH patients mean BP increased significantly upon standing (P<0.05 for all comparisons) with the algorithm ON instead of decreasing with the algorithm OFF, at 1 minute (+3.4 vs−10.3 mmHg), 1.5 minutes (+7.0 vs−4.9 mmHg), 2 minutes (+1.6 vs−6.7 mmHg), and 3 minutes (+2.5 vs−8.5 mmHg). These preliminary results suggest that the OSR algorithm maintains BP upon standing in patients with OH.(PACE 2005; 28:S242–S245) [ABSTRACT FROM AUTHOR]

SPERZEL, J.,et al.: Evaluation of the Atrial Evoked Response for Capture Detection with High-Polarization Leads. AutoCapture™ based on the evoked response can be confounded by electrode polarization. In this study, polarization was measured in human subjects who had chronic atrial leads. The aim of the study was to determine whether electrode polarization can be measured using a time integral atrial evoked-response integral (AERI) of the negative portion of the atrial paced ER evoked-response signal and to determine whether high-polarization atrial leads unsuitable for AutoCapture™ can be identifieda priori.Atrial intracardiac-electrogram (IEGM) signals from 39 patients with implanted pacemakers were recorded and analyzed. The signals were recorded during conventional atrial-threshold searches. A total of 221 atrial-capture thresholds were recorded, ranging from 0.25 to 2.75 V with a mean of 0.79 V. Each evoked response was evaluated using the AERI in a 36 ms window following the 0.4 ms atrial stimulus. The polarization was estimated as a linear function of stimulus voltage using the evoked-response signal integral of captured beats identified on the IEGM. The 221 threshold-search datasets were obtained using leads with eight different electrode materials. Polarization could be measured using AERI as a function of stimulus voltage. Furthermore, this polarization measure can be used to identify high-polarization leads, which are ill suited for the atrial AutoCapture™ algorithm.(PACE 2005; 28:S57–S62) [ABSTRACT FROM AUTHOR]

Presents a study which devised a detection method that operates with unipolar and bipolar leads and covers all cardiac pacing and sensing combinations. Overview of the conventional cardiac pacemakers; Characteristics of bipolar-sensed evoked responses; Description of unipolar autocapture.

BORIANI, G.,et al.:Atrial Evoked Response Integral for Automatic Capture Verification in Atrial Pacing . Beat-by-beat Autocapture is currently limited to operation in the ventricle with bipolar leads. The authors investigated the integral of the negative-going portion of the atrial evoked response integral (AERI) as a potential resource for verification of atrial capture. Intracardiac electrogram signals were collected from 59 patients (ages 67.8 ± 15.1 years) with bipolar, low polarization atrial leads. The signals were collected over a mean period of 6.1 months (minimum 4 days) after lead implantation. St. Jude Medical Affinity pulse generators were used to perform automatic capture threshold tests while the electrogram signals were recorded by a Model 3510 programming device. These signals were transferred to a personal computer in digital form for later analysis. The AERI was calculated at each programmable pacing voltage until capture was lost. The difference between the polarization integral at loss of capture and evoked response integral with successful capture was sufficient to justify enabling the atrial Autocapture feature in 53 of 59 patients in whom bipolar pacing and unipolar sensing was performed. The authors developed a calibration routine to identify automatically those patients in whom atrial Autocapture could be programmed On, based on the polarization integral at loss of capture, the estimated maximum polarization integral, and the AERI. Preliminary analysis indicated that the AERI is a practical resource for beat-by-beat atrial capture detection when used with low polarization leads. (PACE 2003; 26[Pt. II]:248–252). [ABSTRACT FROM AUTHOR]

The current pacing rates are clustered around a fixed base rate since pacemaker patients are usually sedentary, resting, or sleeping most of the time. This fixed base rate is either too low for daytime hemodynamic support or too high for nighttime rest and recovery. Multiple Holter studies involving normal individuals have suggested that the resting base rate fluctuates during the course of the day. The circadian base rate (CBR) algorithm was designed to provide patients with a circadian change in paced resting rate and a normal rate distribution. The CBR algorithm, using a sophisticated accelerometer sensor, was developed and tested using the downloaded activity data from patients implanted with Trilogy DR+ pacemakers. Twenty-five patients (19 men, 6 women, age 72 ± 9 years) were studied. Trilogy DR+ is able to record the detailed sensor and system behavior data for a week. During outpatient visits, the pacemaker was interrogated and the data accumulated in the pacemaker memory were downloaded. The CBR algorithm was applied to the activity variance histogram to calculate the base rate and to construct its histogram. The base rates in the CBR histogram are generally below 100 ppm with a distribution that mimics the natural sinus rate distribution of normal subjects. The CBR algorithm provides the highest daytime rates for hemodynamic support and the lowest nighttime rates for cardiac recovery, with a smoothly changing base rate modeling the normal circadian variation in heart rate. [ABSTRACT FROM AUTHOR]

Two advances in cardiac pacing have resulted in an internal conflict in some pacemakers. One is the development of a standard lead physiological sensor and the other is protection from electromagnetic interference (EMI). One popular type of standard lead sensor uses subthreshold pulses to measure intracardiac and intrathoracic impedance changes, i.e., minute ventilation. Recent clinical observations and extensive in vitro testing have verified that digital cellular phones can be troublesome. Large feedthrough capacitors (FCs), effective in blocking the EMI, will preclude sensing of the standard impedance-based signals. A variety of pulse configurations were studied that might be effective for a sensor-based impedance signal while allowing the pacemaker to continue to use large Fcs protecting them from environmental EMI. In comparison to both monophasic and biphasic pulse sequences, a pentaphasic pulse sequence was effective as an impedance sensor, still allows large FCs to function as an effective filter for environmental EMI, and would not produce artifacts on surface ECG. [ABSTRACT FROM AUTHOR]

Presents a study which examined the value of an impedance cardiography-based method of cardiac output measurement to optimize the atrioventricular interval in men and a woman during permanent left ventricular pacing. Methods; Results and discussion.

Determination of the optimal interventricular (VV) delay in cardiac resynchronization therapy currently relies on costly, time-consuming echocardiographic (ECHO) methods. This study evaluated the performance of a new intracardiac electrogram (IEGM)-based VV method compared to the aortic velocity time integral (AVTI) method of VV delay optimization. The study included two patient groups. Eleven patients enrolled by a single center in the Rhythm II ICD trial underwent prospective comparisons of the AVTI at the VV interval determined by the IEGM VV method versus the maximum AVTI at the echocardiographically determined optimal VV delay. In 61 patients enrolled in the RHYTHM VV trial, the same testing methods were compared retrospectively. In the prospective study, the maximum AVTI by the ECHO-based method (24.3 ± 7.9 cm), was closely correlated with maximum AVTI by the IEGM-based method (23.9 ± 7.9 cm; concordance correlation coefficient = 0.99; 95% confidence, lower limit of 98%. Likewise, in the retrospective analysis, the ECHO-determined maximum AVTI (22.1 ± 8.2 cm) was similar to that determined by the IEGM-based method (20.9 ± 8.3 cm; concordance correlation coefficient = 0.98; 95% confidence, lower limit of 97%). [ABSTRACT FROM AUTHOR]