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

Single-lead VDD pacing: a literature review on short-term and long-term performance

INTRODUCTION

VDD pacing system was introduced more than 30 years ago. Its use is considered by the 2021 European Society of Cardiology guidelines on cardiac pacing as a potential alternative to dual chambers system for patients with atrioventricular block and normal sinus node function.

AREAS COVERED

In this article, we performed a narrative review of current literature in order to identify the strengths and weaknesses of this pacing system. VDD system allows the maintenance of AV synchronous pacing and its hemodynamic advantages. Some disadvantages may be related to the non-negligible incidence of atrial undersensing and the possible subsequent need for upgrade to DDD system. On the other hand, shorter implantation time and lower complications rate may be advantages.

EXPERT OPINION

In the modern pacing era, VDD pacing system struggles to find its own space. However, it may still be considered as a valuable alternative to a dual-chamber pacemaker for selected patients, in specific clinical scenarios.

Outcomes of single‑lead VDD pacemakers in atrioventricular blocks: The OSCAR study

BACKGROUND

VDD pacemakers are regarded as a second choice in patients with atrio-ventricular blocks mainly due to the potential failure of atrial sensing, leading to a loss of atrio-ventricular synchrony. This single-centre study aimed to evaluate the prevalence of loss of atrial sensing and its potential determinants in patients with VDD pacemakers.

METHOD

142 patients with an implanted VDD device underwent long-term follow-up with clinical evaluation, electrocardiogram, device interrogation and echocardiogram.

RESULTS

Over a long follow-up period [median 110 (68-156) months], 17 patients (12%) in sinus rhythm presented loss of atrial sensing. This was most often intermittent, but three patients required a permanent switch to VVI mode. ECG showed higher prevalence of interatrial blocks (50% vs 26.6%, p = 0.057) and longer P wave duration (116 ± 19 vs 105 ± 15 ms, p = 0.019) in patients with loss of atrial sensing. Echocardiography revealed larger left atrial (LA) volumes (p < 0.05) in patients with loss of atrial sensing, and lower LA ejection fraction (0.40 vs 0.47, p = 0.0037) and expansion index (0.63 ± 0.26 vs 0.90 ± 0.31, p = 0.003). P wave duration on ECG proved to be independently associated with loss of atrial sensing on multivariable analysis (OR 1.062, 95% CI 1.015-1.110; p = 0.008). The prevalence of atrial fibrillation and subsequent switch to VVI mode was high (16%).

CONCLUSIONS

In the long-term follow-up, the loss of atrial sensing is present in 12% of patients with implanted VDD pacemakers. ECG and echocardiographic parameters may serve as screening tools for the detection of atrial myopathy which is associated with the loss of atrial sensing.

Long-term outcome in patients receiving permanent pacemaker implantation for atrioventricular block: Comparison of VDD and DDD pacing

A permanent pacemaker (PPM) with dual chamber pacing (DDD) offers atrioventricular synchronization for patients with atrioventricular block (AVB). Single lead atrial synchronous ventricular pacing mode (VDD) is an alternative, but there are concerns about its efficacy and risk of atrial undersensing. Whether VDD can be a good alternative in patients with AVB remains unknown. The aim of the present study was to compare the long-term risk of mortality of VDD with DDD pacing.A total of 207 patients undergoing PPM implantations for AVB with VDD mode were enrolled from 2000 to 2013. Another 828 age- and sex-matched patients undergoing DDD implantations during the same period of time were selected as the control group in a 1 to 4 ratio. The study endpoint was mortality.A total of 1035 patients (64.3% male) were followed up for 46.5 ± 43.2 months. The mean ages were 75.0 years for VDD, and 74.9 years for DDD. The Kaplan-Meier survival analysis showed no significant difference in long-term survival between the VDD and DDD groups (log-rank P = 0.313). After adjustment for baseline characteristics, the VDD and DDD groups had a similar long-term prognosis with an adjusted hazard ratio of 0.875 (P = 0.445). Further analyses for the risk of cardiovascular and noncardiovascular deaths also showed no significant differences between the 2 groups.The long-term prognosis of VDD mode is comparable to that of DDD mode. Single lead VDD can be considered as an alternative choice in patients with AVB without sinus nodal dysfunction.

Long-term outcome of atrial synchronous mode pacing in patients with atrioventricular block using a single lead

BACKGROUND

Current guidelines suggest the use of atrial synchronous mode (VDD) pacemakers in patients with atrioventricular (AV) block and normal sinus node function. However VDD mode is being used much less than expected. The objectives of our study were to evaluate the efficacy of VDD pacing in long-term follow-up and to find risk factors for VDD loss.

METHODS

We retrospectively evaluated all patients with VDD pacemakers who were implanted in our center between 1995 and 2007.

RESULTS

During the study period, 123 consecutive patients with AV block (51% men, age 62 +/- 17.8 years) received a VDD pacemaker. Mean follow up duration was 4.5 +/- 3.2 years. At the last follow up visit, 21 patients (21.6%) lost their original VDD mode and were programmed to ventricular-based pacing (VVIR) (undersensing, 11; chronic AF, 7; SND, 3). In 28 patients, VDD mode was restored or maintained by increasing atrial sensitivity. No episodes of atrial oversensing were observed. In multivariate analysis history of paroxysmal AF (p = 0.007, odds ratio 36.6, 95% confidence interval 2.7-493.7) and p wave lower than 1 mv during the follow up (p = 0.021, odds ratio 7, 95% confidence interval 1.3-36.7), were found risk factors to VDD loss.

CONCLUSIONS

VDD pacing has good long-term performance. Absence of paroxysmal AF history predicts maintenance of VDD pacing mode. Taking into account that no atrial oversensing was observed, our recommendation is to increase atrial sensitivity when P wave amplitude declines to less than 1 mv.

The impact of the distance between the atrial electrode and the atrial wall on atrial undersensing in patients with VDD pacemakers: long-term follow-up

AIM

Atrial undersensing (AUS) in single-lead VDD pacemakers may be due to diminished P-wave amplitude secondary to local inflammation beneath the electrodes closer to atrial wall. The aim of this study was to assess the potential effect of distance between atrial electrode and atrial wall on immediate and long-term atrial sensing stability in VDD systems.

METHODS

A total of 275 patients with normal sinus node function who received VDD pacemakers were enrolled into the study and were followed up for a median duration of 33 months. During each control visit, a standard 12-lead electrocardiogram (ECG) was obtained and standard pacemaker function assessment was performed including testing for pacing threshold and atrioventricular synchrony. The distance between atrial electrode and atrial wall was measured from chest X-ray.

RESULTS

Of the 275 patients, AUS was detected in 59 patients. Univariate predictors of AUS were use of closely spaced bipolar ring atrial electrode (CSBR) (P = 0.01), wider atrial ring-spacing (P = 0.03), and atrial sensitivity programmed to a higher level (P = 0.001). Use of CSBR (P = 0.04) and atrial sensitivity > or =0.3 mV (P = 0.02) were observed to be the independent predictors for AUS. When the distance between atrial electrode and atrial wall was <7 mm, AUS was less with diagonally arranged bipolar ring electrodes (DABR) than it was with CSBRs (P = 0.02).

CONCLUSIONS

The distance between atrial electrode and atrial wall does not appear to affect AUS incidence in VDD pacemakers. For VDD electrodes closer to atrial wall, AUS was significantly less likely in DABR-type electrodes.

Incidence and Significance of Far-Field R Wave Sensing in a VDD-Implantable Cardioverter Defibrillator

BACKGROUND

A VDD-implantable cardioverter-defibrillator (ICD) provides atrioventricular (AV) synchronous stimulation when necessary and incorporates the advantages of dual chamber arrhythmia discrimination algorithms both at potentially lower costs and less periprocedural complications than a DDD-ICD system. A prerequisite for correct dual chamber ICD function is reliable atrial sensing.

METHODS

We evaluated atrial near- and ventricular far-field sensing and its impact on the dual-chamber detection algorithm in 106 patients with a single-lead VDD-ICD during a 12-month follow-up period.

RESULTS

Six hundred and thirty-nine follow-ups were included. Mean near-field amplitude was 3.82 +/- 1.76 mV; mean far-field amplitude was 0.31 +/- 0.15 mV. 46% of patients had far-fields >0.35 mV and 35% of patients showed atrial EGM markers corresponding to a ventricular far-field in at least one follow-up. Six hundred and forty-five tachycardia episodes were evaluated. Due to far-field sensing, three of 66 episodes (4.5%) of sinus tachycardia were misclassified as ventricular tachycardia (VT), leading to antitachycardia therapies. Delayed detection of VT was seen in a 12 of 323 episodes (3.7%) in five of 62 patients (8%) having VT events (delay 6.4 +/- 6.0 seconds (range 2-24 seconds)). Stable far-field amplitudes <0.2 mV in a follow-up had a high negative predictive value for the occurrence of malfunction during tachycardia-conversely, high far-field amplitudes or a high incidence of far-field markers are only moderately correlated with malfunction.

CONCLUSIONS

Ventricular far-field sensing in a VDD-ICD is not uncommon, however, tachycardia detection by the dual chamber algorithm is not seriously impaired by far-field sensing.

Unusual VDD-pacing

The case of an 80-year-old woman who underwent permanent VDD-pacemaker implantation for recurrent syncope in the presence of second-degree type 2 AV-block is reported. During follow-up, low atrial sensing with AV-synchrony of only 58-73% was noted. Four years after the pacemaker implantation, the patient was hospitalized for non-cardiac reasons and the chest radiograph showed displacement of the atrial dipole into the right ventricular outflow tract (RVOT). It is hypothesized that AV-synchrony was maintained by left atrial sensing due to the anatomic proximity of the RVOT to the left atrial appendage.

Seguridad y eficacia de los sistemas de estimulación VDD monosonda

INTRODUCTION AND OBJECTIVES

Single-lead VDD pacing provides the physiological benefits of atrioventricular synchrony with the convenience of a single-lead system. However, concern remains about the method's safety and effectiveness.

METHOD

In total, 700 patients with single-lead VDD pacemakers were evaluated retrospectively. The following parameters were recorded: age, sex, etiology, the symptoms and electrocardiographic diagnosis that justified pacemaker implantation, the venous access route used for implantation, atrial sensing at implantation, atrial undersensing at follow-up, the occurrence of supraventricular tachyarrhythmias, and final pacing mode.

RESULTS

Third-degree atrioventricular block was the main indication for pacemaker implantation (66.4%). The most commonly used venous access route was via the right cephalic vein (49.1%). At implantation, the mean atrial signal was 1.8 (4 1.15) mV. During follow-up, significant atrial undersensing occurred in 7.7% of patients; in 1.9%, it could not be corrected by device reprogramming. Uncontrollable supraventricular arrhythmias were observed in 6.4% of patients. Symptomatic sinus node disease was rare. By the end of follow-up, 91.4% of patients were still on VDD pacing, while, in 8.3%, the pacemaker had to be reprogrammed to the VVI mode. Only 0.3% required atrial lead implantation for DDD pacing. Left-side venous access during implantation was a independent predictora of atrial undersensing at follow-up. Low values of atrial detection at implant did not reach statistical signification although it showed a remarkable trend.

CONCLUSIONS

Single-lead VDD pacing seems to be safe and effective when appropriately indicated. Our findings are consistent with those of previously published studies.

VDD pacemaker replacement is safe and reliable independently of the previously implanted lead: a prospective and controlled study

Theoretically, replacement of a VDD device requires using a similar pacemaker to provide the best match between the filtering characteristics of the pacemaker and the atrial dipole of the lead. This study evaluated the performance of newly implanted Vitatron VDD pacemakers connected to dedicated leads and compared the results with those of the same Vitatron pacemakers used as replacement but connected to a variety of nondedicated leads.

METHODS

23 consecutive patients (15 M, 8 F, 78 +/- 6 years) in Group 1 underwent pacemaker replacement with a VDD(R) Saphir 3 (Vitatron BV, Arnhem, The Netherlands) device designed for an 8.6 mm atrial dipole. Atrial dipoles of the previously implanted leads ranged from 5 to 30 mm. Another 22 consecutive patients (14 M, 8 F, 80 +/- 7 years) in Group 2 received a Saphir 3 pacemaker with the related dedicated lead.

RESULTS

P-wave amplitude measured by the same Pacing Sensing Analyzer (PSA) at the first implantation was 1.7 +/- 0.8 vs. 1.7 +/- 0.5 mV (P = NS) in groups 1 and 2 respectively. P-wave amplitudes measured at 1 month follow-up after replacement in Group 1 and at 1 month follow-up after implantation in Group 2 were 0.69 +/- 0.5 vs. 0.85 +/- 0.3 mV (P = NS) respectively. The percentage of atrial sensing at the same follow-up was 97 +/- 3 vs. 95 +/- 5% (P = NS) in groups 1 and 2 respectively.

CONCLUSIONS

Replacement of VDD pacemakers with the Saphir 3 model designed for a short dipole is safe and reliable when used in combination with previously implanted nondedicated leads.

Radiation Doses to Patients and Cardiologists from Permanent Cardiac Pacemaker Implantation Procedures

BACKGROUND

The purpose of this study was to determine the patient and cardiologist doses during the implantation of permanent cardiac pacemakers under fluoroscopic control.

METHODS

For 55 procedures concerning three different types of pacemakers (DDD, VDD, and VVI), the dose-area product (DAP) meter readings and fluoroscopy times were recorded. From these data, the dose to the operating cardiologist was estimated.

RESULTS

The median values of DAP and fluoroscopy time for all the procedures monitored were 11.4 Gycm(2) and 6.6 minute, respectively. For the 22 DDD, 21 VDD, and 12 VVI pacemakers implanted, the respective DAP median values were 14.7, 9.9, and 7.3 Gycm(2) and the respective median fluoroscopy times were 8.4, 5, and 2.9 minutes. The median doses to the hands, chest, eyes, and legs of the cardiologist conducting the manipulations were estimated to 0.21, 0.06, 0.03, and 0.11 mGy, respectively, per procedure.

CONCLUSIONS

Compared to the existing literature, the median DAP value of this study is almost identical to the 11.2 Gycm(2) reported from a sample of 627 patients in 17 different x-ray rooms, whereas the fluoroscopy times are within the range of values reported by other authors. Concerning the cardiologist exposure, the estimated values indicate that the implantation of pacemakers is a procedure that does not involve a severe risk, especially if it is taken into account that lead aprons and collars are routinely used.

Optimal Side of Implant for Single-Lead VDD Pacing: Right-Sided Versus Left-Sided Implantation

BACKGROUND

Atrial undersensing occurs in a considerable number of patients with single-lead VDD pacing. This study tried to determine the role of implant side in maintenance of the VDD mode in patients with isolated atrioventricular (AV) block.

METHODS

Eighty-two patients with isolated AV block (46 females; mean age, 58 +/- 17 years) received a single-lead VDD pacemaker (Medtronic Kappa, n = 70 and St. Jude Medical Affinity, n = 12). The patients were randomly assigned to one of two implantation groups (group I: right-sided VDD and group II: left-sided VDD). In each group, the P-wave amplitudes were determined at implantation, predischarge, 2-month, and 6-month follow-up. At each follow-up visit, stored event histograms of pacemaker were also retrieved. The atrial sensing measurements were compared between two groups.

RESULTS

Implantation was easier from right side (1.7 +/- 1.0 vs 2.8 +/- 1.7 attempts, P = 0.001). Implant P-wave was higher in group I compared to group II (4.2 +/- 1.7 vs 2.7 +/- 1.0 mV, P < 0.0001). During follow-up, higher P-wave amplitudes were obtained in group I both at predischarge (2.6 +/- 1.3 vs 1.4 +/- 1.1 mV, P < 0.0001), 2-month (2.8 +/- 1.8 vs 1.3 +/- 1.0 mV, P < 0.0001), and 6-month (2.9 +/- 1.7 vs 1.3 +/- 0.9 mV, P < 0.0001) evaluations but remained stable throughout the 6 months in both groups. After implantation, VDD function was better maintained in group I than group II (100% vs 90%, P = 0.026). Incidence of atrial undersensing was lower in group I than group II (P = 0.026) in last follow-up visit.

CONCLUSIONS

Implant side has a significant influence on atrial sensing performance in single-lead VDD pacing. Thus, right-side implantation should be the preferred approach for the implantation of VDD single-lead systems.

Long term complications in single and dual chamber pacing are influenced by surgical experience and patient morbidity

OBJECTIVE

To determine how short and long term complication rates after pacemaker implantation are influenced by patient morbidity, operator experience, and choice of pacing system.

DESIGN

Retrospective analysis of 1884 patients who received VVI (n = 610), VDD (n = 371), or DDD devices (n = 903) between 1990 and 2001. Follow up period was 64 (34) months. The influence of age, sex, coronary artery disease, myocardial infarction, reduced left ventricular (LV) function, right ventricular (RV) dilatation, atrial fibrillation, device type, and operator experience on operation time and complication rate were analysed.

RESULTS

Operation time was prolonged in patients with coronary artery disease, inferior myocardial infarction, reduced LV function, and RV dilatation. Implantation of DDD pacemakers prolonged operation time, particularly among operators with a low or medium level of experience. The overall complication rate was 4.5%. Sixty seven per cent of these complications occurred within the first three months. Complication rate was increased by age, reduced LV function, and RV dilatation. Implantation of DDD systems led to a higher complication rate (6.3%) than implantation of VVI (2.6%) or VDD pacemakers (3.2%). These differences were present only among operators with a low or medium level of experience.

CONCLUSIONS

Operation time and complication rate increased with age, impaired LV function, and RV dilatation. Complication rates were higher with DDD than with VVI or VDD implantation and were excessive among inexperienced but not experienced operators.

Development of atrial fibrillation in patients with atrioventricular block after atrioventricular synchronized pacing

Many studies have evidenced an increased incidence of AF in patients receiving single chamber ventricular pacing (VVI) when compared with those undergoing an atrial-based system (AAI or DDD). However, the difference in incidence of AF between two atrial-based systems (VDD, DDD) in patients with AV block was still controversial. This study was conducted to compare the development of AF between different modes of pacemakers (VDD and DDD) in patients with symptomatic AV block. A retrospective review was conducted of the detailed records of all consecutive patients who received permanent pacemakers due to symptomatic bradycardia from March 1995 to March 2000. The occurrence of AF was documented when there was presence of AF in the free-run or 12-lead ECG, any ECG strips, or persistent AF on 24-hour Holter ECG during the follow-up. The study included 152 patients (44 women, 108 men; mean age 73). The patients were divided into two groups: VDD (n = 100) and DDD (n = 52). The mean follow-up was 48.9 +/- 22.9 months. The incidence of AF was 7.9%. A higher incidence of AF was noted in the DDD group (15.4%) when compared with the VDD group (4.0%, P = 0.023). The incidence of development of AF in patients with AV block was higher in those receiving DDD cardiac pacing when compared with those who received the VDD system. The authors suggest that VDD pacing may be a better choice than the DDD system for patients with AV block, but without clinical evidence of sinus node dysfunction, and if an atrial lead is required, it should be placed close to the Bachmann's bundle.

Optimal Pacing for Symptomatic AV Block:. A Comparison of VDD and DDD Pacing

VDD pacing provides the physiological benefits of atrioventricular synchronous pacing with the convenience of a single lead system, but is hampered by uncertainty regarding long term atrial sensing and potential development of sinus node disease. To examine the long-term reliability and complication rates of VDD pacing, we compared the outcome of 112 consecutive patients (age 70 +/- 13 years, 59% men) with symptomatic AV block who received a single pass bipolar VDD system, to 80 patients (age 63 +/- 16 years, 70% men) who received DDD pacing for the same indication. All patients were judged to have intact sinus node function based on submitted ECGs and monitoring results at the time of implant. Implant time was reduced in VDD patients compared to DDD patients (63 +/- 20 vs 97 +/- 36 minutes, P < 0.0001). Implant complications occurred in 5 (6%) DDD patients compared to 3 (3%) VDD patients (P = 0.15). The implant P wave was lower with VDD pacing compared to DDD patients (2.91 +/- 1.48 vs 4.0 +/- 1.7 mv, P < 0.0001), but remained stable during long-term follow-up in both groups. During 17.7 +/- 10.0 months of follow-up in the VDD group, only two VDD patients were reprogrammed to VVIR mode, compared to three DDD patients. Physiological atrioventricular activation was maintained in 94%-99% of beats throughout the follow-up period in the VDD group. VDD pacing is an excellent strategy for treatment of patients with symptomatic AV block. The lower cost, high reliability, and abbreviated implantation time suggest that VDD pacing is a viable alternative to DDD pacing in patients with high degree AV block and normal sinus node function.

Optimal Pacing for Symptomatic AV Block:

VDD pacing provides the physiological benefits of atrioventricular synchronous pacing with the convenience of a single lead system, but is hampered by uncertainty regarding long-term atrial sensing and potential development of sinus node disease. To examine the long-term reliability and complication rates of VDD pacing, we compared the outcome of 112 consecutive patients (age 70 +/- 13 years, 59% male) with symptomatic AV block who received a single pass bipolar VDD system to 80 patients (age 63 +/- 16 years, 70% male) who received DDD pacing for the same indication. All patients were judged to have intact sinus node function based on submitted ECGs and monitoring results at the time of implant. Implant time was reduced in VDD patients compared to DDD patients (63 +/- 20 vs 97 +/- 36 minutes, P < 0.0001). Implant complications occurred in 5 (6%) DDD patients compared to 3 (3%) VDD patients (P = 0.15). The implant P wave was lower with VDD pacing compared to DDD patients (2.91 +/- 1.48 vs 4.0 +/- 1.7 mV, P < 0.0001), but remained stable during long-term follow-up in both groups. During 17.7 +/- 10.0 months of follow-up in the VDD group, only 2 VDD patients were reprogrammed to VVIR mode, compared to 3 DDD patients. Physiological atrioventricular activation was maintained in 94%-99% of beats throughout the follow-up period in the VDD group. VDD pacing is an excellent strategy for treatment of patients with symptomatic AV block. The lower cost, high reliability, and abbreviated implantation time suggest that VDD pacing is a viable alternative to DDD pacing in patients with high-degree AV block and normal sinus node function.

Long-Term Complication Rates in Ventricular, Single Lead VDD, and Dual Chamber Pacing

A higher incidence of pacemaker related complications has been reported in DDD systems as compared to VVI devices. The implantation of single lead VDD pacemakers might reduce the complication rate of physiological pacing in patients with AV block. In a retrospective study, the data records of 1,214 consecutive patients with pacemaker implantation for AV block between 1990 and 2001 (VVI 36.5%, DDD 32.9%, VDD 30.6%) were analyzed. Complications requiring surgical interventions were compared during a follow-up period of 64 +/- 31 months. Operation and fluoroscopic times were longer in DDD pacemaker implantation compared to VDD and VVI devices:58 +/- 23 versus 39 +/- 10 and 37 +/- 13 minutes (P<0.001), 9.2 +/- 5.2 versus 4.1 +/- 2.4 and 3.5 +/- 2.3 minutes, respectively. Differences remained significant after correction for covariates. In a multivariate Cox regression model, the corrected complication hazard of a DDD pacemaker implantation was increased by 3.9 (1.4-11.3) compared to VVI and increased by 2.3 (1.1-4.5) compared to VDD pacing. Higher complication rates in DDD pacing were mainly due to a higher incidence of early reoperation for atrial lead dysfunction, whereas the long-term complication rate was not different from VDD or VVI pacing. Early and long-term complication rates did not differ between VDD and VVI pacemaker systems. In conclusion, operation time and complication rates of physiological pacing are reduced by VDD pacemaker implantation achieving values comparable to VVI pacing. Thus, single lead VDD pacing can be recommended for patients with AV block.

Mechanism of decrease in the atrial potential after implantation of a single-lead VDD pacemaker: atrial histological changes after implantation of a VDD pacemaker lead in dogs

The single-lead VDD pacemaker system (VDDPS) enables atrial synchronous ventricular pacing with only one lead in patients with an atrioventricular block. There are some cases in which the atrial potential decreases after implantation of a VDDPS, making physiological pacing difficult. The mechanism of this decrease has not been elucidated yet. To elucidate the possible relationship between the decrease of the atrial potential after implantation of a VDDPS and histopathological changes of the atrium. We implanted a VDDPS from the jugular vein under anesthesia in 10 adult dogs. The tip of the pacing lead was fixed in the right ventricular apex of the heart under fluoroscopic guidance. Then, the lead was ligated and fixed to the jugular vein at a point where a favorable atrial potential was obtained. The end of the lead was passed from the neck to the back subcutaneously; then pulled outside and fixed there to measure the atrial potential. The atrial potential was measured using a pacing system analyzer under anesthesia on days 3 (n = 9) and 7 (n = 8), as well as on weeks 2 (n = 6), 3 (n = 4), and 4 (n = 3), after the implantation. The heart was removed from the dogs on day 3 (n = 2), day 7 (n = 2), week 2 (n = 2), and week 4 (n = 4) to examine the atrial histological findings. The atrial potential was 2.7 +/- 0.7 mV at the time of the implantation, 1.7 +/- 1.1 mV (P < 0.05) on day 3, and 1.7 +/- 0.7 mV on week 4 after the implantation. Macroscopically, the pacemaker lead was covered with thrombus, and adhered to the atrial wall in 80% of animals. Microscopically, the endocardium was hypertrophic due to fibrous tissue; besides RBC extravasation, inflammatory cells infiltration and degeneration of myocardial cells, were observed under the endocardium. Inflammatory changes developed in the atrial wall after implantation of the VDDPS, and this seemed to be one of the mechanisms for the decrease of the atrial potential of the VDDPS.

Dual chamber cardiac pacing in children: Single chamber pacing dual chamber sensing cardiac pacemaker or dual chamber pacing and sensing cardiac pacemaker?

BACKGROUND

Dual chamber pacemakers (single chamber pacing dual chamber sensing cardiac pacemaker (VDD) and dual chamber pacing and sensing cardiac pacemaker (DDD)) are being used frequently in children and adolescents. The aim of this study was to verify the safety and performance of the VDD and DDD pacing systems, and to evaluate the differences between two pacing modes with regard to atrial sensing and tracking functions.

METHODS

In this study, we evaluated 14 patients with VDD pacing and 15 patients with DDD pacing between 1994 and 2000. In the patient group with VDD pacing, all had congenital or acquired atrioventricular (AV) block. In the patient group with DDD pacing, 11 had congenital or acquired AV block, three had sinus node dysfunction with AV conduction disturbance and one had idiopathic hypertrophic subaortic stenosis. Twenty-eight devices were implanted in the subpectoral area using the transvenous route. After implantation the atrial tracking capabilities of the pacing systems were analyzed by telemetry, Holter monitoring, and treadmill exercise testing.

RESULTS

The mean age of patients in the VDD pacing group was younger. The percentage of congenital heart disease was higher in the DDD pacing group. There was no significant difference regarding fluoroscopy time during implantation and follow-up time between the two groups. During implantation, in the VDD pacing group the mean sensed atrial signal was 3.1 +/- 1.3 mV and this decreased to 1.37 +/- 0.68 mV (P < 0.05) during follow-up. This pattern was also observed in DDD group (3 +/- 2 mV vs 1.9 +/- 1.5 mV, P < 0.05). Although the P wave measurement at implantation did not differ between the two groups, it was significantly higher in the DDD pacing group at the last control. Three patients with VDD pacing were reprogrammed to VVI or single chamber pacing and sensing, rate adaptive cardiac pacemaker because of complete loss of AV synchrony. There was no atrial sensing problem in the DDD pacing group. During the follow-up, one patient with VDD pacing developed diaphragmatic stimulation and required lead revision. In one patient with DDD pacing, venous thrombosis occurred in the right subclavian vein and was treated with thrombolytic therapy. During treadmill exercise testing, in one patient with VDD and one patient with DDD pacing temporary failure of atrial sensing occurred. At 24 h Holter monitoring, intermittent loss of atrial sensing was documented in two patients with VDD pacing.

CONCLUSIONS

Dual chamber pacing in children with DDD or VDD pacemakers is a suitable method for bradycardia treatment. Atrial sensing problems may occur in VDD pacemakers. Therefore, DDD pacing mode should be preferred whenever suitable for the patient to maintain the AV synchrony.

Cardiac pacing. A review

Pacing is a field of rapid clinical progress and technologic advances. Clinical progress in the 1990s included the refinement of indications for pacing as well as the use of pacemakers for new, nonbradycardiac indications, such as the treatment of cardiomyopathies and CHF and the prevention of atrial fibrillation. Important published data and studies in progress are shedding new light on issues of pacing mode selection, and they may influence future practice significantly. Important technologic advances include development of new rate-adaptive sensors and sensor combinations and the evolution of pacemakers into sophisticated diagnostic devices with the capability to store data and ECGs. Automatic algorithms monitor the patient for appropriate capture, sensing, battery status, and lead impedance, providing better patient safety and pacemaker longevity.

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 AV 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, Holter 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.