Interatrial Conduction During Cardiac Pacing

DDD pacemakers sense and pace right-sided cardiac chambers. The relationship of atrial to ventricular systole on the left side of the heart is of importance for systemic hemodynamics. Effective atrioventricular synchrony is partially determined by interatrial conduction time (IACT). At the time of DDD pacemaker implantation, interatrial conduction was measured using an intraesophageal pill electrode in 25 patients who were on no cardiac medications. Mean interatrial conduction time for all patients prolonged from 95 ± 18 ms during sinus rhythm to 122 ± 30 ms during right atrial pacing (p < 0.001). In 16 patients with P wave duration < 110 ms interatrial conduction prolonged from 85 ± 10 ms during sinus rhythm to 111 ± 9 ms during right atrial pacing (p < 0.01) compared to 114 ± 20 ms prolonging to 111 ± 19 ms (p < 0.01] in 9 patients with P wave duration > 110 ms. In each patient, while atrioventricular conduction prolonged with incremental right atrial pacing, interatrial conduction times did not vary. Interatrial conduction prolongs from baseline during atrial pacing and remains constant at all paced rates from 60–160 heats per minute. In addition to longer interatrial conduction times during sinus rhythm, patients with electrocardiographic P wave prolongation have longer interatrial conduction times during right atrial pacing than do normals (p < 0.0001). Based on interatrial conduction times alone, the AV interval during DDD cardiac pacing should be approximately 25 ms longer during AV pacing as compared to atrial tracking.     

VDD(R) Pacing: Short- and Long-Term Stability of Atrial Sensing with a Single Lead System

Background: Recent studies have shown that the atrial signal can reliably be sensed for VDD(R) pacing via atrial floating electrodes incorporated in a single-pass lead. However, there remains concern about the long-term stability of atrial sensing and proper VDD function under real-life conditions. This study investigated the long-term reliability of atrial sensing and atrioventricular synchronous pacing using a new single lead VDD(R) pacing system. Methods and Results: In 20 consecutive patients (ages 71 ± 14 years) with normal sinus node function and high-degree heart block, a single lead VDD(R) pacemaker (Unity(tm), Intermedics) was implanted, Atrial sensing was studied at implantation, at discharge, and at 1, 3, 6, 12, and 18 months of follow-up. At implant, the measured P wave amplitude was 2.3 ± 1.2 mV. By telemetry, the atrial sensing threshold was 0.79 ± 0.41 mV at discharge, 0.75 ± 0.43 mV at 1 month, 0.73 ± 0.43 mV at 3 months, 0.76 ± 0.41 mV at 6 months, 0.79 ± 0.41 mV at 12 months, and 0.77 ± 0.35 mV at 18 months of follow-up (P = NS). Appropriate VDD pacing was assessed by the percentage of correct atrial synchronization (PAS = atrial triggered ventricular paced complexes ± total number of ventricular paced complexes) during repeated Holters. PAS was 99.99%± 0.01 % at 1 month, 99.99%± 0.02% at 3 months, and 99.98%± 0.05% at 12 months of follow-up (P = NS). No atrial oversensing with inappropriate ventricular pacing was observed, neither during isometric arm exercise testing nor spontaneously during Holier monitoring. Conclusion: The long-term stability of atrial sensing with almost 100% correct atrial synchronous tracking and the lack of inappropriate pacing due to atrial oversensing make the new Unity VDD(R) system a highly reliable single lead pacing system. In view of the lower costs and the ease of single lead implantation, this system may offer an interesting alternative to DDD pacemakers in patients with normal sinus node function.     

Dual Chamber Pacing with a Single-Lead DDD Pacing System

The successful application of single-lead VDD pacing during the last few years has generated the idea of single-lead DDD pacing. Preliminary data from several single-lead VDD studies attempting to pace the atrium by a floating atrial dipole are unsatisfactory, causing an unacceptably high current drain of the device. We studied the feasibility as well as the short- and long-term stability of atrioventricular sequential pacing, using a new single-pass, tined DDD lead. In eight consecutive patients (age 73+/-16 years) with symptomatic higher degree AV block and intact sinus node function, this new single-pass DDD lead was implanted in combination with a DDDR pacemaker. Correct VDD and DDD function was studied at implantation; at discharge; and at 1, 3, and 6 months of follow-up. At implant, the atrial stimulation threshold was 0.6+/-0.1 V/0.5 ms. During follow-up, the atrial pacing thresholds in different every day positions averaged 2.1+/-0.5 V at discharge, 2.9+/-0.5 V at 1 month, 3.8+/-0.4 V at 3 months, and 3.4+/-0.4 V at 6 months (pulse width always 0.5 ms). The measured P wave amplitude at implantation was 4.5+/-2.2 mV; during follow-up the telemetered atrial sensitivity thresholds averaged 2.1+/-0.3 mV. Phrenic nerve stimulation at high output pacing (5.0 V/0.5 ms) was observed in three (38%) patients at discharge and in one (13%) patient during follow-up; an intermittent unmeasurable atrial lead impedance at 3 and 6 months follow-up was documented in one (13%) patient. This study confirms the possibility of short- and long-term DDD pacing using a single-pass DDD lead. Since atrial stimulation thresholds are still relatively high compared to conventional dual-lead DDD pacing, further improvements of the atrial electrodes are desirable, enabling lower pacing thresholds and optimizing energy requirements as well as minimizing the potential disadvantage of phrenic nerve stimulation.     

Atrial Septal Pacing to Synchronize Atrial Depolarization in Patients with Delayed Interatrial Conduction

The current method of pacing the right atrium from the appendage or free wall is often the source of delayed intraatrial conduction and discoordinate left and right atrial mechanical function. Simultaneous activation of both atria with pacing techniques involving multisite and multilead systems is associated with suppression of supraventricular tachyarrhythmias and improved hemodynamics. In the present study we tested the hypothesis that pacing from a single site of the atrial septum can synchronize atrial depolarization. Five males and two females (mean age 58 ± 6 years) with drug refractory paroxysmal atrial fibrillation (AF) were studied who were candidates for AV junctional ablation. All patients had broad P waves (118 ± 10 ms) on the surface ECG. Multipolar catheters were inserted and the electrograms from the high right atrium (HRA) and proximal, middle, and distal coronary sinus (CS) were recorded. The atrial septum was paced from multiple sites. The site of atrial septum where the timing between HRA and distal CS (d-CS) was ≤ 10 ms was considered the most suitable for simultaneous atrial activation. An active fixation atrial lead was positioned at this site and a standard lead was placed in the ventricle. The interatrial conduction time during sinus rhythm and AAT pacing and the conduction time from the pacing site to the HRA and d-CS during septal pacing were measured. Atrial septal pacing was successful in all patients at sites superior to the CS os near the fossa ovalis. During septal pacing the P waves were inverted in the inferior leads with shortened duration from 118 ± 10 ms to 93 ± 7 ms (P < 0.001), and the conduction time from the pacing site to the HRA and d-CS was 54.3 ± 6.8 ms and 52.8 ± 2.5 ms, respectively. The interatrial conduction time during AAT pacing was shortened in comparison to sinus rhythm (115 ± 18.9 ms vs 97.8 ± 10.3 ms, P < 0.05). In conclusion, simultaneous activation of both atria in patients with prolonged interatrial conduction time can be accomplished by pacing a single site in the atrial septum using a standard active fixation lead placed under electrophysiological study guidance. Such a pacing system allows proper left AV timing and may prove efficacious in preventing various supraventricular tachyarrhythmias.     

Interatrial septum pacing decreases atrial dyssynchrony on strain rate imaging compared with right atrial appendage pacing

Background: Interatrial septum pacing (IAS‐P) decreases atrial conduction delay compared with right atrial appendage pacing (RAA‐P). We evaluate the atrial contraction with strain rate of tissue Doppler imaging (TDI) during sinus activation or with IAS‐P or RAA‐P. Methods: Fifty‐two patients with permanent pacemaker for sinus node disease were enrolled in the study. Twenty‐three subjects were with IAS‐P and 29 with RAA‐P. The time from end‐diastole to peak end‐diastolic strain rate was measured and corrected with RR interval on electrocardiogram. It was defined as the time from end‐diastole to peak end‐diastolic strain rate (TSRc), and the balance between maximum and minimum TSRc at three sites (ΔTSRc) was compared during sinus activation and with pacing rhythm in each group. Results: There were no significant differences observed in general characteristics and standard echocardiographic parameters except the duration of pacing P wave between the two groups. The duration was significantly shorter in the IAS‐P group compared with the RAA‐P group (95 ± 34 vs 138 ± 41; P = 0.001). TSRc was significantly different between sinus activation and pacing rhythm (36.3 ± 35.7 vs 61.6 ± 36.3; P = 0.003) in the RAA‐P group, whereas no significant differences were observed in the IAS‐P group (25.4 ± 12.1 vs 27.7 ± 14.7; NS). During the follow‐up (mean 2.4 ± 0.7 years), the incidence of paroxysmal atrial fibrillation (AF) conversion to permanent AF was not significantly different between the two groups. Conclusions: IAS‐P decreased the contraction delay on atrial TDI compared to RAA‐P; however, it did not contribute to the reduction of AF incidence in the present study. (PACE 2011; 34:370–376)     

The Importance of the Left Atrioventricular Interval during Atrioventricular Sequential Pacing

During atrioventricular (AV) sequential pacing from the right heart, the interval between the left atrium and ventricle may vary from the programmed AV interval depending on the position of the atrial and ventricular electrodes and interatrial and interventricular conduction. The aim of this study was to determine the hemodynamic effects of altering the left AV interval while keeping the programmed AV interval constant. Four male and 17 female patients, aged 49 ± 15 years were studied. The left AV interval was measured by a catheter in the coronary sinus. Stroke volume and mitral flow were measured by simultaneous echo Doppler during AV sequential pacing from the right atrial appendage and right ventricular apex at programmed AV intervals of 100. 60, and 6 ms. The atrial catheter was then positioned on the atrial septum and the measurements repeated. With the atrial catheter in the right atrial appendage, interatrial activation time (118 ± 20 ms) was similar to interventricular activation time (125 ± 21 ms) and the left AV interval was almost identical to the programmed right AV interval. There was a significant correlation between interatrial and interventricular activation times (r = 0.8; P < 0.001). Positioning the atrial electrode on the septum decreased interatrial activation time by 39 ± 12 ms and increased the left AV interval by a similar amount. At a programmed AV interval of 60 ms, the left AV interval increased from 67 ± 15 ms to 105 ± 17 ms after the atrial catheter was repositioned from the appendage to the septum (P < 0.001). Compared to pacing from the right atrial appendage, atrial septal pacing increased mitral A wave velocity integral (2.8 ± 1.4 vs 4.4 ±1.7 cm at a programmed AV interval of 60 ms, P < 0.01), decreased E wave velocity integral (8.1 ± 2.2 vs 6.1 ± 2.4 cm, P < 0.001) but did not alter stroke volume (44.8 ± 10.6 vs 44.9 ± 10.1 mL). In contrast, a 40 ms decrease in the programmed right AV interval from 100 to 60 ms decreased stroke volume from 48.0 ± 10.0 to 44.9 ± 10.2 mL (P < 0.001). There was a strong relationship between interatrial and interventricular conduction so that patients with prolonged interatrial conduction still had equivalent left and right AV intervals during atrioventricular sequential pacing from the right atrial appendage and right ventricular apex. Positioning the atrial electrode on the septum decreases interatrial activation time and increases the left AV interval by about 40 ms but has minimal hemodynamic effect in patients without heart failure.     

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% 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.     

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.     

Exercise Induced Sympathetic Influences Do Not Change Interatrial Conduction Times in VDD and DDD Pacing

Using telemetry, right atrial electrogram (RA), and marker channel of atrial sense events (M_A) in combination with the left atrial electrogram (LA), recorded by a filtered bipolar esophageal lead, interatrial conduction during submaximal exercise and at rest was examined in 46 DDD pacemaker patients. The RA-LA and M_A-LA conduction times measured in the presence of atrial sensing (VDD) as well as the conduction time S_A-LA from atrial stimulus (S_A) to LA, determined during atrial pacing (DDD) were found to be individual constants independent of exercise induced sympathetic influences. Thus, having determined an optima! mechanical interval (LA-LV)_mech/opt from left atrium to ventricle by other methods, the optimal AV delay for DDD as well as for VDD operation can be calculated by the sum of the appropriate interatrial conduction time (S_A-LA, respectively M_A-LA) and the (LA-LV)_mech/opt interval. Due to the constant S_A-LA and M_A-LA, the difference between these two values (AV delay correction interval) is a constant as well, which remains unchanged during exercise. Therefore, in selecting the rate responsive AV delay, only hemodynamic and not electrophysiologica] measurements need to be considered.     

Relationship Between Interatrial Conduction Times and Left Atrial Dimension in Patients Undergoing Atrioventricular Stimulation

Interatrial conduction time (IACT) and left atrial dimension (LAD) were determined in 75 patients (41 males, 34 females, mean age 78.2 ± 7,9 years) undergoing atrioventricular (AV) stimulation. The LAD was measured by M mode echocardiography as the distance between the posterior aortic wall and the posterior left atrial wall. The IACT was determined during a transvenous dual chamber pacemaker implant done under local anesthesia (lidocaine). The spontaneous interatrial conduction time (SIACT) was measured from the intrinsic deflection (ID) of the right atrium recorded in a unipolar mode (unipolar J-shaped had positioned in the right appendage) to the ID of the left atrium (bipolar esophageal lead, left atrial positive deflection equal to the negative one) during sinus rhythm. The right atrium then was paced at a rate slightly greater than the spontaneous one. The paced interatrial conduction time (PIACT) was measured from the stimulus artifact to the left atrial ID. The PIACT was also measured during incremental right atrial pacing (10 beats/min step increase to 180 beats/min) and, from these measurements, the maximum increase of PIACT (MIPIACT) was deduced. The LAD was measured at 39.5 ± 8.7 mm, SIACT at 70.3 ± 24.8 msec, PIACT at 118.8 ± 27.9 msec, and MIPIACT at 16.5 ± 16.4 msec. We found highly significant relationships between SIACT and LAD(P = 0.0006, r - 0.39), PIACT and LAD (P = 0.0001, r = 0.45), and MIPIACT and LAD (P = 0.0006, r = 0.38). We also noted that the LAD was greater in patients in whom MIPIACT was >10 msec than in patients in whom the MIPIACT was negligible (P < 0.002). However, the “r” values indicate that IACT is probably determined by multiple factors, and LAD appears to be one of the most important. Thus, we demonstrated the existence of highly significant relationships between the LAD determined by M mode echocardiography and the IACT when sensing and pacing the right atrium. We also demonstrated that the LAD was greater in patients in whom PIACT increased by an appreciable duration during fast atrial pacing. These results must be kept in mind when choosing a mode of stimulation and determining the AV delay (dual chamber pacemaker), particularly in patients with left atrial enlargement in whom the contribution of the atrial contraction and its timing are hemodynamically determinant.     

Ventricular activation sequence during left ventricular pacing promotes QRS complex oversensing in the atrial channel

Background: Left ventricular (LV)‐only pacing has a significant effect on delay in depolarization of parts of the ventricles that are likely oversensed in the right atrial channel. The study aimed to assess the impact of ventricular activation sequence on QRS oversensing and far‐field endless‐loop pacemaker tachycardia (ELT) in patients who received cardiac resynchronization therapy (CRT) devices. Methods: The study examined 102 patients with CRT devices. Oversensing artifacts in the atrial channel were inspected on intracardiac electrograms, and their timing with respect to the beginning of QRS was determined during DDD‐right ventricular (RV), DDD‐LV, DDD‐biventricular (BiV), and AAI pacing modes. The occurrence of ELT during DDD‐LV pacing with a postventricular atrial refractory period (PVARP) of 250 ms was also assessed. Results: The timing of oversensing artifacts (in relation to the beginning of surface QRS) was dependent on ventricular activation sequence, occurring promptly following intrinsic activation via the right bundle branch (47.1 ± 26.4 ms), later during RV pacing (108.7 ± 22.5 ms) or BiV pacing (109.4 ± 23.1 ms), and significantly later, corresponding to the final part of the QRS, during LV pacing (209.6 ± 40.0 ms, range: 140–340 ms, P < 0.001). Oversensing was significantly more frequent during LV than during RV pacing (35.3% vs 22.5%, P < 0.001). Far‐field ELT was observed in six patients. Conclusions: Oversensing artifacts in the atrial channel are likely caused by depolarization of the basal part of the right ventricle. The novel mechanism of QRS oversensing outside PVARP, caused by a reversed ventricular activation sequence during LV‐only pacing, may be important in some CRT patients. (PACE 2011; 34:1682–1686)     

Cardiac resynchronization therapy and obstructive sleep-related breathing disorder in patients with congestive heart failure

Objectives: To assess the impact of cardiac resynchronization therapy (CRT) with or without atrial overdrive pacing, on sleep‐related breathing disorder (SRBD). Introduction: CRT may have a positive influence on SRBD in patients who qualify for the therapy. Data are inconclusive in patients with obstructive SRBD. Methods: Consenting patients eligible for CRT underwent a baseline polysomnography (PSG) 2 weeks after implantation during which pacing was withheld. Patients with an apnea hypopnea index (AHI) ≥15 but <50 were enrolled and randomized to atrial overdrive pacing (DDD) versus atrial synchronous pacing (VDD) with biventricular pacing in both arms. Patients underwent two further PSGs 12 weeks apart. Results: Nineteen men with New York Heart Association class III congestive heart failure participated in the study (age 67.2 ± 7.5, Caucasian 78.9%, ischemic 73.7%). The score on Epworth Sleepiness Score was 7.3 ± 4.0, Pittsburgh Sleep Quality Index 7.4 ± 3.1, and Minnesota Living with Heart Failure Questionnaire 36.9 ± 21.9. There were no differences between the groups. At baseline, patients exhibited poor sleep efficiency (65.3 ± 16.6%) with nadir oxygen saturation of 83.5 ± 5.3% and moderate to severe SRBD (AHI 21.5 ± 15.3) that was mainly obstructive (central apnea index 3.3 ± 6.7/hour). On both follow‐up assessments, there was no improvement in indices of SRBD (sleep efficiency [68.3 ± 17.9%], nadir oxygen saturation of 82.8 ± 4.6%, and AHI 24.9 ± 21.9). Conclusion: In a cohort of elderly male CHF patients receiving CRT, CRT had no impact on obstructive SRBD burden with or without atrial overdrive pacing. (PACE 2011; 34:593–603)     

Atrial Stimulation by Means of Floating Electrodes: A Multicenter Experience

It is well established that single lead VDD pacing is a physiological, reliable, and easy to use mode of pacing. The major limitation of VDD pacing is the need of a normal sinus node function, confirming its indication to patients with isolated atrioventricular conduction disturbances. The Phymos 830 pacing lead was originally designed for VDD pacing in association with the Phymos MPS pulse generator; it has a floating atrial dipole with an interelectrode distance of 3 cm; the distal electrode is 11, 13, or 15 cm proximal to the tip. As a result of the incidental observation of atrial captures occurring at very low pulse amplitudes delivered from the floating dipole of this lead, a 13-center Italian study was initiated to test the systematic feasibility of this type of atrial pacing. Pacing parameters were set and strength-duration curves were acquired with the PSA Master 470 external device. The investigation was performed at pacemaker implant in 114 patients in the supine position. The tip of the electrode was positioned at the right ventricular apex and the atrial dipole at the site of the highest endocavitary signal. Atrial bipolar pacing was performed with the proximal electrode as the cathode. Stable atrial capture was obtained in 108 of 114 patients (94.7%); pacing threshold was < 3.5 V with a pulse width of 1 msec in 85 of 108 patients. Results of voltage threshold were: 2,99 ± 1.25 and 2.59 ± 1.13 V at pulse widths of 0.5 and 1 msec, respectively. The mean value of atrial pacing impedance (5 V, 1 msec) was 601.2 ± 221 Ohm; the mean value of the endocavitary signal amplitude was 1.53 ± 0.48 mV. During deep breathing loss of capture was observed in only 8.3% of patients; these patients regularly had an atrial pacing threshold higher than 3.5 V. Diaphragmatic stimulation occurred in 19.2% of patients at an output of 5 V and 1 msec. Our results suggest that stable atrial pacing is possible with floating electrodes in a high percentage of patients; in 85/114 patients (74.5%) atrial capture was reliable at a satisfactory mean pacing threshold. This experience shows that single lead DDD pacing is possible and may be reliable in acute conditions; and supports the availability of this pacing mode in selected patients. It can be considered a starting point for improvements in techniques and materials.     

Relationship between Amplitude and Timing of Heart Sounds and Endocardial Acceleration

Objective: To study the correlation between heart sounds and peak endocardial acceleration (PEA) amplitudes and timings, by modulation of paced atrioventricular (AV) delay in recipients of dual chamber pacemakers.
Methods: Ten recipients of dual chamber pacemakers implanted for high-degree AV block were studied. Endocardial acceleration (EA) and phonocardiographic and electrocardiographic signals were recorded during performance of an AV delay scan in VDD and DDD modes.
Results: First PEA (PEA I) and first heart sound (S1) changed similarly with the AV delay. A close intrapatient correlation was observed between S1 and PEA I amplitudes in all patients (P < 0.0001). The interpatient normalized PEA I to S1 amplitudes correlation was r = 0.89 (P < 0.0001) in DDD mode, and r = 0.81 (P < 0.0001) in VDD mode. The mean cycle-by-cycle PEA I to S1 delay was −4.3 ± 22 ms and second PEA (PEA II) to second heart sound (S2) delay was −7.7 ± 15 ms.
Conclusions: A close correlation was observed between PEA I and S1 amplitudes and timings, and between PEA II and S2 timings. These observations support the hypothesis that PEA and heart sounds are manifestations of the same phenomena. EA might be a useful tool to monitor cardiac function.     

Is Local Myocardial Contractility Related to Endocardial Acceleration Signals Detected by a Transvenous Pacing Lead?

The availability of sensors monitoring cardiac function parameters may offer many interesting new applications in cardiac pacing. A microaccelerometer sensor (BEST, Biomechanical Endocardial Sorin Transducer) located at the tip of a pacing lead (PL) has been developed by Sorin Biomedica. The signal detected by the accelerometer, peak Endocardial acceleration (PEA), was shown to reflect cardiac contractility and to be related to the dP/dt signal. Whether the PEA detected by the BEST sensor in different cardiac locations is the expression of local acceleration forces or reflects the whole heart contractility has not yet been demonstrated in humans. Endocardial acceleration and PEA were evaluated in five patients (4 males, 1 female, mean age 68 years) who underwent cardiac catheterization. Sinus rhythm was present in four patients and chronic atrial fibrillation was present in one. The BEST PL was introduced through the left subclavian vein and PEA signals were recorded: (1) at the apex of the right ventricle (RV), (2) within the coronary sinus (CS), (3) at the right atrial appendage (RAA), and (4) floating in the right atrium. The PEA signals were recorded simultaneously with surface ECG, intracardiac electrograins, and RV pressure. At each recording site, PEA signals with significant amplitude were always recorded during the preelection period, during the isovolumic contraction phase, independently of the recording site and cardiac rhythm. The PEA amplitude was higher in the RV (mean value 1.32 g) and it decreased in the RAA and CS (0.75 and 0.45 g, respectively). The same behavior of PEA was observed during sinus rhythm or atrial fibrillation. The amplitude and the timing of the PEA signals detected by the BEST accelerometer were independent of the recording site and atrial rhythm; they appeared to be strictly related to the global ventricular contractility. These results suggest that the BEST could be used either as an effective sensor in closed loop pacing systems, or primarily as a diagnostic hemodynamic sensor.     

Atrial Electromechanical Sequence and Contraction Synchrony during Single- and Multisite Atrial Pacing in Patients with Brady-Tachycardia Syndrome

Objectives: Investigation of which atrial pacing modality provides atrial synchrony and the most physiological atrial contraction pattern in patients with brady-tachycardia syndrome.
Methods: Fifteen healthy subjects and 57 patients with sinus node dysfunction, atrial fibrillation recurrences, and prolonged P-wave on the electrocardiogram treated with multisite atrial (MSA) pacing were studied. One atrial lead was implanted in the coronary sinus (CS) ostium area, the other at the right atrial appendage (RAA): RAA+CS group (28 patients), or Bachmann's bundle (BB) region: BB+CS group (29). Sinus rhythm (SR) and CS, RAA, BB, RAA+CS, and BB+CS pacing modalities were evaluated. Electromechanical delay (EMD) in atrial walls was assessed by tissue Doppler echocardiography. Interatrial (ΔinterA), intra-right (ΔRA), and intra-left (ΔLA) atrial dyssynchrony were calculated.
Results: During SR, in the study group versus controls, important ΔinterA: 55 ± 23 versus 22 ± 11 ms (P < 0.01) and ΔLA: 47 ± 21 versus 21 ± 6 ms (P < 0.001) were present. Single-site BB and both MSA pacing modes restored ΔinterA and ΔLA (ΔinterA: 24 ± 16, 20 ± 13 and 14 ± 9 ms, ΔLA: 28 ± 18, 28 ± 13 and 20 ± 10 ms during BB, RAA+CS and BB+CS pacing, respectively). CS pacing prolonged lateral RA EMD, while RAA pacing LA walls EMD, which resulted in ΔinterA persistence. CS pacing induced ΔRA (50 ± 23 vs 16 ± 8 ms, P < 0.0001 vs controls). Atrial contraction sequence during BB pacing resembled that observed in controls.
Conclusions: (1) Single-site BB and both MSA pacing modes restored atrial synchrony. (2) Single-site RAA and CS ostium pacing retained interatrial dyssynchrony; moreover, CS pacing created RA dyssynchrony. (3) Single-site BB pacing provided physiological atrial contraction sequence.     

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.     

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.     

Comparison of Electrical Characteristics Between a Steroid-Eluting Single-Pass VDD Lead and a Standard Steroid-Eluting Ventricular Lead

Compared to regular ventricular leads, single-pass VDD leads have two additional floating electrodes proximal to the ventricular tip, which enables them to detect atrial signals. Because of the latter, VDD leads are thicker than ventricular leads, which could affect ventricular pacing. The purpose of the present study was to compare ventricular pacing of a steroid-eluting single-pass VDD lead (CapSure VDD, Medtronic; n = 107) with the same steroid-eluting regular lead (CapSure SP, Medtronic; n = 39) implanted in the ventricle; both leads were connected to the same types of pacemakers. At implantation, pacing thresholds were measured at 0.5-ms pulse duration and impedance by means with the PSA. At discharge, as well as after 1 and 3 months, pulse duration thresholds were determined at 2.5 V pulse amplitude and impedance by telemetry. At implantation, pacing thresholds and impedance were not different in the VDD (0.38 ± 0.16 V; 691 ± 122 Ω) and ventricular lead group (0.44 ± 0.17 V; 648 ± 150 Ω). During follow-ups, no differences in pulse duration threshold were detected between the two groups neither at discharge (VDD = 0.05 ± 0.03 ms; ventricular 0.05 ± 0.02 ms), nor after 1 (VDD = 0.05 ± 0.02 ms; ventricular 0.08 ± 0.07 ms) and 3 months (VDD = 0.06 ± 0.03 ms; ventricular 0.09 ± 0.10 ms). There were also no significant differences for impedance at discharge (VDD = 675 ± 113 Ω; ventricular = 594 ± 113 Ω), after 1 (VDD = 678 ± 131 Ω,; ventricular = 627 ± 112 Ω) and 3 months (VDD = 652 ± 99 Ω; ventricular = 628 ± 105 Ω). Pacing thresholds and impedance were neither significantly different at implantation nor during follow-ups between patients with steroid-eluting VDD leads and patients with an equivalent ventricular lead indicating that the thicker VDD lead does not affect ventricular pacing.     

A Simplified Approach to Temporary DDD Pacing Using a Single Lead, Balloon-Tipped Catheter with Overlapping Biphasic Impulse Stimulation

Temporary DDD pacing offers significant hemodynamic benefits in emergency management of bradyarrhythmias but is underused because of its complexity (two leads) and unreliability. Single lead VDD pacing with atrial sensing via a floating dipole is feasible, but atrial pacing is limited by high thresholds and phrenic nerve stimulation (PNS). Overlapping biphasic impulse (OLBI) stimulation may avoid these problems. The authors designed a single lead balloon-tipped catheter for temporary transvenous DDD pacing, incorporating noncontact atrial dipoles for OLBI stimulation. This catheter was deployed using fluoroscopic guidance in 74 patients (43 men, 31 women) with mean age 56.9 +/- 17.0 years. Pacing parameters were assessed at implantation and follow-up. The median procedural time was 6.6 (range 1.2-25.0) minutes and fluoroscopy time 1.9 (range 0.2-7.8) minutes. Stable VDD pacing was achieved in all cases. Atrial capture was achieved in 73 of 74 cases with both modes at maximum output but was restricted by PNS at outputs below atrial capture threshold in 3 of 74 cases with OLBI and 10 of 74 cases with standard bipolar mode (P = 0.04). At outputs > or = 1.0 V above atrial threshold, reliable DDD pacing without PNS was achieved and maintained in 67 (91%) of 74 patients in OLBI compared to 53 (72%) of 74 patients in bipolar mode (P = 0.003). Pacing parameters were stable during follow-up (median 53 hours, range 6-168 hours). In conclusion, the single lead catheter with OLBI stimulation allows temporary VDD and DDD pacing without PNS to be achieved in > 90% of patients. This rapid and convenient approach should facilitate DDD pacing in emergency settings.