Jürgen Potratz

Myocardial ischemia in generalized coronary artery–left ventricular microfistulae

Generalized (multiple) arterio-systemic fistulae are fistulae arising from all three major coronary arteries and drain into the left ventricle are rare and the clinical and hemodynamic sequelae are incompletely understood. This communication is based on the clinical and hemodynamic data of a series of patients (eight cases out of 7262 consecutive patients) incidentally identified at coronary angiography combined with data from cases previously reported in literature. The aim was to assess the role of generalized coronary artery fistulae as a non-atherosclerotic cause of myocardial ischemia by means of a coronary sinus lactate study. Coronary sinus lactate study demonstrated myocardial ischemia in 6/7 patients. Mean arterio-coronary venous lactate difference decreased from 0.31+/-0.18 mmol/l (lactate extraction ratio, LER, 29.4+/-13.9%) at rest to 0.04+/-0.13 mmol/l (LER -4.0+/-13.3%) at peak exercise. Five minutes after cessation of pacing, lactate difference increased to 0.22+/-0.21 mmol/l (LER -20.7+/- 13.2%). At peak pacing stress, 4/7 patients showed frank lactate production, and two patients presented with a reduced cardiac lactate extraction rate also indicating myocardial ischemia metabolically. In the present study, we demonstrated a possible role of a coronary steal mechanism due to microfistulae pathways in the pathogenesis of myocardial ischemia in patients with generalized coronary artery-left ventricular microfistulae.

Atrial sensing and AV synchrony in single lead VDD pacemakers: a prospective comparison to DDD devices with bipolar atrial leads.

Atrial Sensing and AV Synchrony in VDD and DDD Devices, Introduction: Single lead VDD pacing has offered an alternative to DDD systems in patients with isolated AV block. Up to now, however, the relative performance of these pacemaker systems was not systematically compared.

An Optimized AV Delay Algorithm for Patients with Intermittent Atrioventricular Conduction

Detection and promotion of an intermittent atrioventricular (A V) conduction is the objective of an AV delay hysteresis algorithm in dual chamber pacemaker (DDDj pacing. The AV delay following an atrial event is automatically extended by a programmable interval (AV hysteresis interval) if the previous cycle showed spontaneous AV conduction, i.e., a ventricular event was detected within the previous AV delay. An automatic search mode scans for spontaneous ventricular events during the hysteresis interval: a single AV delay extension (equal to the programmed AV delay hysteresis) will occur after a successive, programmable number of AV cycles with ventricular pacing. If a spontaneous AV conduction is present, the AV delay will remain extended by the hysteresis interval. Our first results in 17 patients with intermittent AV block disclosed a satisfactorily working algorithm with effective reduction of ventricular stimuli. In relation to the underlying conduction disturbance and pacemaker settings, the majority of our patients showed a reduction of ventricular pacing events up to 90% without any adverse hemodynamic or electrophysiological changes. Based on clinical (promotion of a physiological activation and contraction sequence) and technical (reduction of power consumption) advantages, the AV hysteresis principle could be of incremental value for future dual chamber pacing in patients with intermittent complete heart block.

Circadian Profile of QT Interval and QT Interval Variability in 172 Healthy Volunteers

BONNEMEIER, H., et al.: Circadian Profile of QT Interval and QT Interval Variability in 172 Healthy Volunteers. The limited prognostic value of QT dispersion has been demonstrated in recent studies. However, longitudinal data on physiological variations of QT interval and the influence of aging and sex are few. This analysis included 172 healthy subjects (89 women, 83 men; mean age 38.7 ± 15 years). Beat‐to‐beat QT interval duration (QT, QTapex [QTa], Tend[Te]), variability (QTSD, QTaSD), and the mean R‐R interval were determined from 24‐hour ambulatory electrocardiograms after exclusion of artifacts and premature beats. All volunteers were fully active, awoke at approximately 7:00 am, and had 6–8 hours of sleep. QT and R‐R intervals revealed a characteristic day‐night‐pattern. Diurnal profiles of QT interval variability exhibited a significant increase in the morning hours (6–9 am; P < 0.01) and a consecutive decline to baseline levels. In female subjects the R‐R and Tend intervals were significantly lower at day‐ and nighttime. Aging was associated with an increase of QT interval mainly at daytime and a significant shift of the T wave apex towards the end of the T wave. The circadian profile of ventricular repolarization is strongly related to the mean R‐R interval, however, there are significant alterations mainly at daytime with normal aging. Furthermore, the diurnal course of the QT interval variability strongly suggests that it is related to cardiac sympathetic activity and to the reported diurnal pattern of malignant ventricular arrhythmias. (PACE 2003; 26[Pt. II]):377–382)

Implantation strategy of the atrial dipole impacts atrial sensing performance of single lead VDD pacemakers.

WIEGAND, U.K.H., et al.: Implantation Strategy of the Atrial Dipole Impacts Atrial Sensing Perfor‐mance of Single Lead VDD Pacemakers. Intermittent atrial undersensing is observed in a considerable percentage of patients with single lead VDD pacemakers. Analyzing the 2‐year data of the Saphir Multicenter Follow‐Up Study, the authors investigated predictors for the occurrence of undersensing. The study included 194 patients with high degree AV block who received a VDD pacemaker system with an identical sensing amplifier. Placement strategy of the atrial dipole was left to the discretion of the implanting physician. At the final position, atrial potential amplitudes were measured during deep and shallow respiration. Atrial dipole position was determined by intraoperative fluoroscopy subdividing the right atrium in a high, mid, and low portion. Undersensing was defined by evidence of at least one not sensed P wave during Holter monitoring or exercise testing and by the presence of 0.1–0.2 mV amplitudes in the P wave amplitude histogram of the pacemaker. Incidence of undersensing was 25.8%; 9.3% of patients showed frequent (> 5%) or symptomatic undersensing. Patients with undersensing were older (76.6 ± 10.6 vs 64.2 ± 14.8 years), showed a lower minimum of intraoperative atrial potential amplitude (Pmin 0.86 ± 0.64 vs 1.43 ± 0.77 mV), a wider range of potential amplitude (ΔP 1.71 ± 1.44 vs 0.94 ± 0.84 mV), and a higher incidence of dipole placement in the low right atrium (50.0% vs 11.1%, P < 0.001 for all comparisons). In a multivariate regression analysis, patient age > 66 years, Pmin < 0.6 mV, > 1.3 mV and atrial dipol placement in the low right atrium were independently predictive for undersensing. Minimal atrial potential amplitude, range of potential amplitude, and atrial dipole position influence atrial sensing performance in single lead VDD pacing. Thus, implantation guidelines should reflect these rules to improve the outcome of VDD pacemaker recipients.

Age Dependency of Sensing Performance and AV Synchrony in Single Lead VDD Pacing

Implantation of single lead VDD pacemakers is an established therapeutic option in patients with AV block and normal sinus node function. However, related to occurrence of sinus node disease and atrial undersensing, there is concern whether VDD devices are appropriate in physically active young patients. Two hundred thirty‐two consecutive patients with isolated A V block and VDD pacemakers were investigated. This population was subdivided into quartiles of 58 patients according to age at time of inclusion: 26.2–59.4 years (group A), 59.5–70.1 years (group B), 70.2–81.0 years (group C), and 81.1–92.5 years (group D). Follow‐up visits included pacemaker telemetry, Holier monitoring, and exercise testing. Patients were visited at 2 and 12 weeks after implantation thereafter followed by 6‐month intervals. Mean follow‐up period was 35 ± 14 months. Three months after implantation, atrial sensing threshold was significantly higher in young patients: 1.18 ± 0.58 mV (group A) versus 0.79 ± 0.35 mV (group B), 0.68 ± 0.33 mV (group C), and 0.60 ± 0.25 mV (group D), P < 0.001 for comparison of group A to all other groups. Atrial undersensing was observed less frequently in young patients: 6.9% (group A) versus 17.2% (group B), 24.1% (group C), and 27.6% (group D), P = 0.025 for intergroup comparisons. Sinus node dysfunction did not occur in group A. Atrial arrhythmias and loss of AV synchronized pacing mode occurred rarely in young patients: 0.6% (0.4%) per year in group A versus 1.3% (1.3%) in group B, 3.9% (3.4%) in group C, and 5.7% (7.4%) per year in group D, P < 0.01 for intergroup comparisons. Our data show good atrial sensing performance, low incidence of sinus node dysfunction, and few atrial arrhythmias in young patients with VDD pacing for AV block. Thus, single lead VDD pacing can be recommended particularly for young patients with AV block.

Adverse Pacemaker Hemodynamics Evaluated by Pulmonary Venous Flow Monitoring

The pacemaker syndrome refers to symptoms and signs in the pacemaker patient caused by an inadequate timing of atrial and ventricular contractions. The lack of normal atrioventricular synchrony may result in a decreased cardiac output and venous cannon A waves. The objective of this study was to define the left atrial and pulmonary venous flow response to ventricular pacing in a group of 14 unselected consecutive patients with total heart block and sinus rhythm. Pulmonary venous flow was assessed by transesophageal pulsed Doppier echocardiography in the VVI and ODD pacing modes. An inappropriate atrial timing caused a marked augmentation of the normally small pulmonary venous z wave in all patients (“negative atrial kick” peak z wave in DDD pacing 14.5 ± 4.6 cm/s, VVI pacing 51.8 ± 15.0 cm/s). Restoration of AV synchrony (DDD pacing, AV interval 100 ms) abolished these “cannon z waves” in all patients, and a normal pattern of pulmonary venous flow was achieved. Abnormal pulmonary venous flow characteristics were observed in 2 of 14 patients during DDD pacing with short AV intervals (100 ms). The Doppier pattern was similar to the findings seen in VVI pacing. Assessment of pulmonary venous flow by transesophageal pulsed Doppier echocardiography may provide a simple, sensitive, and relatively noninvasive technique to evaluate patients with suspected pacing induced adverse hemodynamics.

Long-term superiority of steroid elution in atrial active fixation platinum leads.

Steroid elution reduces the acute increase in stimulation threshold particularly in active fixation leads. The aim of this study was to investigate the long‐term efficacy of steroid elution in atrial screw‐in leads compared to conventional lead design. Two different bipolar active fixation platinum lead designs were implanted. Leads were similar except for the presence (group S, n = 66) or absence (group N, n = 68) of steroid elution. Patients received dual chamber pacemakers with the following atrial leads in consecutive order: Medtronic 4058 M (group N, n = 30), Medtronic 4068 (group S, n = 40), Vitatron IMS 13 (identical to 4058 M, group N, n = 38), and Vitatron IMX 13 (identical to 4068, group S, n = 26). The. mean follow‐up period was 40.7 ± 16.1 months (range 10 to 84 months). Stimulation thresholds, pacing impedances, P wave potentials, and sensing threshold were assessed for both groups immediately, 10 days, 6 weeks, and 3 months after implantation followed by 6‐months intervals. Energy thresholds, chron‐axie‐rheobase products, and energy consumption of atrial pacing were calculated. Chronic values were deduced from the most recent measurement performed in an individual patient. Within the first 10 days after implantation, atrial voltage threshold at pulse duration of 0.4 ms increased from 0,91 ± 0.42 to 2.06 ± 0.45 V in group N (P < 0.001). Less increase was observed in group S (0.83 ± 0.39 to 1.08 ± 0,53 V, P = 0.003). Atrial voltage thresholds remained markedly lower in steroid‐eluting leads during whole follow‐up (1.12 ± 0.49 V in group S vs 1.58 ± 0.71 V in group N, P < 0.001). Chronic energy consumption was markedly reduced in group S (4.0 ± 2.7 μJ) compared to group N (9.8 ± 7.5 μJ, P < 0.001). An atrial voltage threshold below 1.25 V at 0.4 ms was achieved in 92.3% of patients of group S allowing programming of an output of 2.5 V. Such low outputs were feasible in only 49.3% of patients in group N (P < 0.001). Chronic P wave amplitudes did not differ significantly between groups (3.27 ± 1.81 mV in group N vs 3.24 ± 1.18 mV in group S, P = 0.91). Steroid elution diminishes the increase of stimulation thresholds of non‐steroid atrial active fixation platinum leads resulting in a long‐term reduction of energy consumption. Thus, use of steroids can be recommended for general use in atrial active fixation lead designs.

Efficacy and Safety of Bipolar Sensing with High Atrial Sensitivity in Dual Chamber Pacemakers

In dual chamber pacemakers, atrial sensing performance is decisive for maintenance of AV synchrony. Particularly, the efficacy of mode switching algorithms during intermittent atrial tachyarrhythmias depends on the sensitive detection of low potential amplitudes. Therefore, a high atrial sensitivity of 0.18 mV, commonly used in single lead VDD pacemakers, was investigated for its efficacy and safety in DDD pacing. Thirty patients received dual chamber pacemakers and bipolar atrial screw‐in leads for sinus node syndrome or AV block; 15 patients suffered from intermittent atrial fibrillation. Pace makers were programmed to an atrial sensitivity of 0.18 mV. Two weeks, 3, 9, and 15 months after implantation, P wave sensing threshold and T wave oversensing thresholds for the native and paced T wave were determined. The myopotential oversensing thresholds were evaluated by isometric contraction of the pectoral muscles. Automatic mode switch to DDIR pacing was activated when the mean atrial rate exceeded 180 beats/min. The patients were followed by 24‐hour Holter monitoring. Two weeks after implantation, mean atrial sensing threshold was 1.81 ± 0.85 mV (range 0.25–2.8 mV) without significant differences during further follow‐up. Native T wave sensing threshold was < 0.18 mV in all patients. In 13% of patients, paced T waves were perceived in the atrial channel at the highest sensitivity. This T wave sensing could easily be avoided by programming a postventricular atrial refractory period exceeding 300 ms. Myopotential oversensing could not be provoked and Holter records showed no signs of sensing dysfunction. During a 15‐month follow‐up, 1,191 mode switch events were counted by autodiagnostic pacemaker function. Forty‐two of these events occurred during Holter monitoring. Unjustified mode switch was not observed. In DDD pacemakers, bipolar atrial sensing with a very high sensitivity is efficient and safe. Using these sensitivity settings, activation of the mode switch algorithm almost completely avoids fast transmission of atrial rate to the ventricle during atrial fibrillation.

Diagnosis of Atrial Undersensing in Dual Chamber Pacemakers: Impact of Autodiagnostic Features

Atrial undersensing occurs in a considerable number of patients, both with single lead VDD pacemakers and with DDD devices. The aim of this study was to investigate the diagnostic efficacy of electrocardiographic methods and autodiagnostic pacemaker features to detect atrial sensing dysfunction. Two hundred and thirty‐one patients with AV block received single lead VDD pacemakers or DDD devices. Atrial sensitivity was programmed to 0.1 or 0.18 in VDD devices and to 0.5 mV in DDD devices; the rate limits were set to 40 and 160 beats/min. Twelve‐lead ECG recording for 1 minute during deep respiration and change of body position, 24‐hour Holter ECG recording, and treadmill exercise were performed 2 weeks and 15 months after pacemaker implantation. AV synchrony and, if available, P wave amplitude histogram were sampled by autodiagnostic pacemaker features and compared to electrocardiographic findings. Atrial undersensing was assumed, if AV synchrony was below 100% or if minimal P wave amplitude (PWA) was equal to the programmed atrial sensitivity. Intermittent atrial undersensing occurred in 20.7% of patients. The diagnostic sensitivities of the various methods used to detect atrial sensing failures were: 24‐hour Holter monitoring 97.5%, P wave amplitude histogram 90.0%, stored AV synchrony 68.0% without significant difference between the various devices, treadmill exercise testing 58.8%, and 12‐lead ECG recording 21.3%. In one patient, atrial undersensing was exclusively detected by exercise testing. In conclusion, autodiagnostic pacemaker features facilitate the evaluation of atrial sensing performance. However, to exclude intermittent atrial malsensing, routine Holter monitoring and treadmill exercise are still needed.