Determining Optimal Atrial Sensitivity Settings for Single Lead VDD Pacing: The Importance of the P Wave Histogram

In order to provide atrioventricular synchrony, VDD pacing systems require reliable atrial sensing. Variations in atrial signals with exercise and daily activities may lead to undersensing, with loss of physiological pacing. The aim of this study was to determine, for a single lead VDD pacing system, the maximal variation in atrial signals in order to facilitate optimal programming of atrial sensitivity. Fifteen patients underwent implantation of a Vitatron Saphir VDD pacemaker with a Vitatron Brilliant electrode. At a mean (± SD) follow-up of 67.3 ± 38.8 days, resting P wave amplitude was compared with the P wave amplitude histogram obtained from the pacemaker, which recorded atrial signals over the preceding 30 days. Resting P wave amplitude was also compared with P wave amplitudes during variations in posture, respiration, and during exercise. P wave amplitude showed great variation with changes in posture and respiration, but there was no consistent increase or reduction. During exercise, the mean P wave amplitude fell hy 36.6%± 31.3% compared with the resting value (P < 0.05). During daily activities, 22.6% of P wave amplitudes recorded on the P wave histogram were < 0.5 mV. The smallest P wave amplitudes were detected by the P wave histogram in 11 (79%) of 14 patients. These data suggest that atrial sensitivity may need to be programmed higher than that indicated by single readings or exercise. The P wave amplitude histogram is the most reliable indicator of the smallest atrial signal and should be used to opthnize atrial sensitivity settings.     

Initial Experience with 1.5-mm2 High Impedance, Steroid-luting Pacing Electrodes

In this human study, 21 atrial and 62 ventricular 1.5-mm² unipolar steroid-eluting pacing electrodes were implanted in 64 patients. Pacing thresholds, lead impedance, and sensing measurements were measured via pacemaker telemetry within 24 hours postimplont, and at 1, 2, 3, 4, 6, 12. 24. and 52 weeks. Acute pacing impedances measured via a pacing systems analyzer were 1,039 ± 292 (atrial) and 1,268 ± 313 ohms (ventricular). A10%-15% decline in the mean telemetered atrial and ventricular pacing impedances was observed at 1 week, but thereafter remained stable. Acute pacing thresholds at 0.5 ms were 0.5 ± 0.3 V (atrial) and 0.4 ± 0.1 V (ventricular). Filtered P and B wave amplitudes were 3.7 ± 2.3 mV and 14.9 ± 5.9 mV, respectively. In 21 patients, no complications related to the atrial electrode were observed. Of 62 patients with ventricular electrodes, 4 patients (6%) experienced complications and required surgical intervention. On these, causative factors included micro-dislodgment (l patient), and perforation (l patient). Sudden unexplained exit block occurred late (> 6 weeks) in two patients. In the remainder of patients, pacing thresholds and sensed electrogram amplitudes remained stable throughout the 52-week follow-up period. Conclusions: The- present study validates that smaller surface (i.e., 1.5 mm²) steroid- eluting electrode designs offer excellent pacing and sensing performance with significantly higher pacing impedances. Although questions remain as to the cause of late exit block in two patients in this series, this relatively small surface electrode design offers promise toward achieving greater pacing efficiency and a theoretical 13%-16% (minimum) enhancement in permanent pacemaker longevity.     

P Wave Recognition and Atrial Stimulation with Fractally Iridium Coated VDD Single Pass Leads

The bottleneck of VDD systems is the reliable detection of the small atrial signals by a floating atrial electrode. Fractally iridium coated electrodes offer excellent sensing and pacing performance. In this study, the performance of such a floating atrial lead in P wave sensing and synchronous ventricular stimulation was examined. Atrial pacing was also used as a test of atrial wall contact. Patients and Methods : A fractally iridium coated VDDlead was implanted in 18 patients. In 15 patients it was interfaced with a VDD pacemaker and in 3 patients with a DDD system depending on the P wave amplitude measured acutely (≥ 2 mV). Simultaneous recordings of the surface ECG and pacemaker telemetry were used to analyze P wave amplitudes and AV synchrony in different body positions, and during normal and deep breathing. Additionally, exercise tests based on daily life activities and 24-hour ECG monitoring were performed to test the pacemaker function. Results : During implantation P wave amplitudes were 1.86 mV ± 1.08 mV (range 0.5–4.9 mV) and during follow-up (6.6 ± 5.6 weeks) 0.18–3.8 mV. Holter recordings revealed reliable P wave sensing at a sensitivity setting of 0.5 mV (95.5%). P wave sensing was further improved by a higher atrial sensitivity. AV synchronous pacing ± 99.9% was achieved in all patients. In 7 patients the atrial electrode could be positioned close to the atrial wall enabling atrial stimulation thresholds at an average of 4.3 volts. Conclusion : This fractally iridium coated VVD lead allowed consistent and reliable P wave sensing at an atrial sensitivity as low as 0.5 mV in selected patients.     

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.     

Initial Clinical Experience with a Single Pass VDDR Pacing System

Although ventricular rate adaptive pacing (VVIR) improves exercise capacity and cardiac output compared to constant rate ventricular pacing (WI), this pacing mode does not provide benefit of atrioventricular (AV) synchrony. We evaluated the use of a custom-built VDDR pacing system using a single pass, ventricular lead, which detects end cavity P wave using a pair of diagonally arranged atrial bipolar (DAB) electrodes. In the VDDR mode, AV synchrony is enabled and the P wave rate is used in conjunction with an accelerometer based activity sensor for rate adaptive pacing. A VDDR pacemaker was implanted in three patients with complete AV block (mean age 63 ± 1 year) and the mean implantation time was 29 minutes. Mean P wave amplitude was 2.4 mV (1.2–4.2 mV) at implantation and telemeter P wave amplitude was stable over a follow-up of 6 months. At a sensitivity of 0.2 mV, stable P wave sensing was observed during breathing maneuvers, arm swinging, my potential induction, and Holter recording. Paired exercise tests performed in the VDDR and VVIR modes showed higher cardiac output at rest, during exercise, and in the recovery period in the VDDR pacing mode. Thus VDDR pacing using a single pass lead is superior to VVIR pacing by enabling P synchronous ventricular pacing without adding to the complexity of implantation.     

Evolution of Atrial Signals from a Single Lead VDD Pacemaker

The atrial sensing capabilities of a new single pass lead VDD pacing system (Pacesetter AddVent) were assessed in a prospective multicenter study of 101 implants during the period July 1994 through March 1996. The pacing lead (Pacesetter AV Plus) has a unique quadripolar 4-in-line connector and uses a pair of ring electrodes with an interelectrode spacing of 12 mm for atrial sensing. The mean age of the patients (51 men) was 73 years (range 19–91). Seventy-five patients had complete heart block; the others had 2:1 AV block. Wide variations were found in signal amplitude: mean P wave amplitude, measured over four cycles in the supine position, was 2.4 ± 1.9 mV at implant, dropping to 1.9 ± 1.7 mV predischarge, and remaining constant at follow-up but with a narrower range. Holter monitoring was undertaken in 24 patients, with a total of 550 monitored hours. Mean AV synchrony was 98.2%± 4.6% (excluding premature ventricular contractions), with 20 patients (83%) showing > 99% AV synchrony, with atrial sensing at 0.1 mV where needed. No oversensing was observed in any patient. There was a low incidence of atrial fibrillation (2%) and sinus bradycardia (0%). The findings show that the range of atrial signals, although wide initially, converges over the first year and remains adequate for reliable AV synchronous pacing.     

Permanent Left Atrial Pacing with a Specifically Designed Coronary Sinus Lead

This article reports the original use of a specifically designed coronary sinus (CS) lead for permanent left atrial (LA) pacing. The device is characterized by its distal end shape featuring a double 45° angulation. which ensures very close contact with the CS upper wall. The device was successfully implanted in 39 out of 40 patients (97.5%). The tip electrode was eventually positioned in the distal CS in 9 patients, in the middle CS in 21 patients, and close to the ostium in the proximal CS in 9 patients. The mean acute pacing threshold voltage was 0.9 ± 0.5 V with a mean impedance of 578 ± 144 Ω as measured in unipolar distal configuration at 0.5 ms pulse width (PW). The mean A wave amplitude was 3.5 ± 2.1 mV. Early lead dislodgment occurred only once (3%) when the tip electrode was placed in the distal or middle CS, but more often (4/9 cases) when it was placed in the proximal CS. After a mean follow-up duration of 14 ± 8.5 months, 35 of the 39 successfully implanted leads (89.7%) were still functional in terms of LA pacing and sensing. The mean chronic pacing threshold voltage was 1.5 ± 0.8 V and the mean A wave amplitude was 2.7 ± 1.6 mV. There were no lead related complications. In conclusion, the device proved to be safe and highly effective for permanent LA pacing, provided the distal tip could be positioned in the distal or middle part of the CS.     

Sinus and paced P wave duration and dispersion as predictors of atrial fibrillation after pacemaker implantation in patients with isolated sick sinus syndrome

The aim of this study was to prospectively evaluate the sinus and the paced P wave duration and dispersion as predictors of AF after pacemaker implantation in patients with isolated sick sinus syndrome (SSS). The study included 109 (69 women, mean age 72 +/- 11 years) patients with SSS, 59 with bradycardia-tachycardia syndrome (BTS). A 12-lead ECG was recorded before pacemaker implantation and during high right atrial and septal right atrial pacing at 70 and 100 beats/min. The ECGs were scanned into a computer and analyzed on screen. The patients were treated with AAIR (n = 52) or DDDR pacing. The P wave duration was measured in each lead and mean P wave duration and P wave dispersion were calculated for each ECG. AF during follow-up was defined as: AF in an ECG at or between follow-up visits; an atrial high rate episode with a rate of > or =220 beats/min for > or =5 minutes, atrial sensing with a rate of > or =170 beats/min in > or =5% of total counted beats, mode-switching in >/=5% of total time recorded, or a mode switching episode of > or =5 minutes recorded by the pacemaker telemetry. The ECG parameters were correlated to AF during follow-up. Mean follow-up was 1.5 +/- 0.9 years. None of the ECG parameters differed between patients with AF and patients without AF during follow-up, nor was there any difference between groups after correction for BTS and age. BTS was the strongest predictor of AF during follow-up (P < 0.001). P wave duration and dispersion measured before and during pacemaker implantation were not predictive of AF after pacemaker implantation in patients with isolated SSS.     

Efficacy of single lead VDD pacing in patients with impaired and normal left ventricular function

Atrial synchronous ventricular pacing seems to be the best pacing mode for patients with advanced AV block and impaired LV function. The long-term follow-up of single lead VDD pacing was studied in 33 patients with impaired LV function and compared to 42 patients with normal LV function. All patients received the same VDD lead and VDDR pacemaker. The lead model with 13-cm AV spacing between the atrial and ventricular electrode was implanted in 89% of the patients. Follow-ups were 1, 3, 6, and 12 months after implantation. The percentage of atrial sensing and the P wave amplitude were determined at each follow-up. Minimal P wave amplitude at implantation was 2.0 +/- 1.4 mV in patients with impaired and 1.7 +/- 0.9 mV with normal LV function (not significant). At the 12-month follow-up, 33 patients with normal and 23 patients with depressed LV function remained paced in the VDD mode. The remaining patients died in five (impaired LV function) and seven cases (normal LV function) or their pacemakers were programmed to the VVI/VVIR pacing mode in four (impaired LV function) and three cases (normal LV function). P wave amplitude did not differ in the two groups (e.g., at month 12: impaired: 1.17 +/- 0.42 mV; normal: 1.09 +/- 0.49 mV). The atrial sensitivity was programmed in most patients to sensitive settings with no differences between the two groups (e.g., at month 12: impaired: 0.13 +/- 0.06 mV; normal: 0.13 +/- 0.05 mV). The diagnostic counters indicated nearly permanent atrial sensing (e.g., at month 12: impaired: 99.3 +/- 2.2%; normal: 99.0 +/- 1.0 mV). In conclusions, single lead VDD pacing restored AV synchronous ventricular pacing in patients with normal and with impaired LV function indicating that it could be an alternative to DDD pacemakers, but not to dual-chamber pacing.     

Predictive Value of the P Wave at Implantation for Atrial Fibrillation After VVI Pacemaker Implantation

This study assesses the value of P wave measurements on the surface EGG at implantation, in the prediction of atrial fibrillation in VVI paced patients. From a consecutive series of 320 pacemaker implantations 172 WI paced patients for symptomatic atrioventricular block (AVB) (n = 126; mean age 69 ± 14) or sick sinus syndrome (SSS) (n = 56; mean age 68,6 ± 12] and in sinus rhythm at implantation were used in this study. P wave duration in VI is correlated with the incidence of atrial fibrillation during 5 years of follow-up. VI at implantation was significantly longer (114.6 ± 2.7 msec) in the patients who developed atrial fibrillation than in those who did not (91.9 ± 2.7 msec) (P < 0.001). Although positive predictive accuracy increases progressively for higher VI values for AVB and SSS, the negative predictive and diagnostic accuracy of V1 criteria were Jess in SSS. Application of the Bayes' theorem showed that in SSS the probability to develop atrial fibrillation is 33% for V1 < 110 msec and is for V1 < 90 msec still higher than that reported in DDD paced patients. In the AVB group the probability to develop atrial fibrillation is 8% for V1 < 110 msec and 6% for V1 < 100 msec. It seems, therefore, that atrial stimulation (AAI or DDD) is always indicated in SSS. In AVB with V1 < 100 msec, DDD pacing, if not needed for other indications, apparently does not offer much benefit in the prophylaxis of atrial fibrillation.     

Long-Term Experience with a Preshaped Left Ventricular Pacing Lead

OLLITRAULT, J., et al. : Long-Term Experience with a Preshaped Left Ventricular Pacing Lead. This study describes a long-term experience with a new LV pacing lead. The study population consisted of 62 patients (85% men,   71 ± 10   years old) with advanced dilated cardiomyopathy, in NYHA Class III or IV despite optimal drug therapy, and a QRS duration >150 ms. Patients in sinus rhythm were implanted with a triple chamber pacemaker to maintain atrioventricular synchrony. A dual chamber pacemaker was implanted in patients in atrial fibrillation for biventricular pacing only. A clinical evaluation and interrogation of the resynchronization pacemaker were performed at implant, at 1 week (W1), one (M1), four (M4), and seven (M7) months after implantation. A longer follow-up (2 years) is available for patients implanted at the authors institution. LV measurements were pacing threshold at 0.5-ms pulse duration and pacing impedance. R wave amplitude (mV) was measured at the time of implantation only. The system was successfully implanted in 86% of patients with the latest design of the lead. Mean R wave amplitude at implant was   15 ± 7 mV   and mean pacing impedance was   1054 ± 254 Ω   . Between implant   (n = 38)   and M7   (n = 15)   , pacing threshold rose from   0.73 ± 0.54   to   1.57 ± 0.60 V (P < 0.001)   . In conclusion, the situs lead was successfully implanted in a high percentage of patients. In addition, low pacing threshold and high impedance measured during follow-up are consistent with a low pacing current drain, ensuring a durable pulse generator longevity. (PACE 2003; 26[Pt. II]:185–188)     

Experience and Implantation Techniques with a New Single-Pass Lead VDD Pacing System

Thirty-six patients were implanted with a single-lead atrial-synchronous ventricular pacing (VDD) system at our center in the first and second phases of a clinical trial between October 1987 and December 1989. The clinical system comprised a pulse generator in conjunction with a pacing lead incorporating two diagonal atrial bipolar (DAB) electrodes designed to lie in the mid-to upper-right atrium and a distal tip electrode for ventricular pacing and sensing. Twenty five of the patients had complete heart block, ten had second-degree block, and one had AV nodal block. A modified Bruce protocol limiting treadmill speed to 1.7 miles per hour was used to establish sinus node competency as evidenced by sustained sinus rate increase in a more-or-less linear fashion. The mean acute P wave amplitude measured at implant was 1.66 mV +/- 1.04 SD; the mean P wave amplitude (minimum and maximum, both sitting and supine) for all patients at all follow-up (N = 420) was 1.54 mV +/- 0.9 SD. The follow-up interval for all patients ranged from a minimum of 13 days and a maximum of 762 days, with a mean of 261 +/- 206 days as of December 1, 1989. Four dislodgments of the ventricular electrode occurred with the more pliable of two passive fixation mechanisms used on the lead; atrial sensing remained intact at all times with both fixation systems. Changes in atrial sensing threshold were quite frequent during the early follow-up visits due to electrode movement in the right atrium; however, adequate ventricular tracking of the atrial rate was achieved in all cases once the threshold values were established initially, even though several patients required atrial sensing of 0.2 mV at some of the follow-up visits. Two patients presented with pacemaker-mediated tachycardia associated with retrograde conduction, which was resolved with reprogramming; they are presently maintaining atrial synchrony in the VDD mode. Successful single-lead VDD pacing with consistent P wave sensing has been achieved with this atrial rate responsive system.     

U.S. Experience with the AddVent VDD(R) Pacing System

The AddVent pacemaker generator and model 1328C AV single-pass lead is a new pacemaker system capable of VDD or VDDR modes. The purpose of this study was to present the initial experience with AddVent in the United States and Canada. Between May 10, 1995 and May 3, 1996, 53 devices were implanted in 52 patients and followed for a mean of 217 (±39) days. At the predischarge, 1-, 3-, and 6-month follow-up evaluations, atrial sensing thresholds and ventricular sensing and capture thresholds were measured in the supine, sitting, and standing positions to evaluate stability of atrial sensing with respect to body posture at rest. At the 1-month follow-up, a treadmill exercise test was performed to evaluate atrial sensing during exercise and to evaluate two new features of the AddVent called "sensor-mediated rate smoothing" and "preferential P wave sensing." Atrial sensing thresholds were not significantly different (P > 0.05) among body postures for any follow-up period or among follow-up periods for each posture. At rest, the percentage of appropriately tracked P waves observed was > 99% at each follow-up period. During treadmill exercise, the percentage of appropriately tracked P waves was > 98.7%. Appropriate preferential P wave sensing and sensor-mediated rate smoothing (VDDR mode) was observed. The AddVent pacing system provides safe and effective pacing therapy. Several features of VDDR pacing offer advantages over standard VDD pacing.     

A New Orthogonal Lead for P Synchronous Pacing

P synchronous pacing has long been identified as advantageous for patients with atrioveniricular conduction defects and intact sinus node function. Prior endocavitury systems have been infrequently employed, because of unreliable P wave sensing from standard ring electrodes in the atrium or the requirement for a second atriaJ sensing lead. A single endocardial lead employing a unipolar ventricular stimulating electrode and an orthogonal P wave sensing design was developed and tested in 22 patients undergoing electrophysiologic study or pacemaker implantation. Thirteen centimeters from the stimulating tip of a standard permanent pacing lead, three or four electrodes with a surface area of one millimeter squared, equidistant from the tip, were placed circumferentially about the catheter. With the catheter tip normally placed in the right ventricular apex, atrial sensing eJectrodes were positioned in the mid-high lateral right atrium, adjacent to, but not affixed to, the right atrial wall. Bipolar orthogonal leads X and Y were obtained. In 22 patients, during sinus rhythm, atrial electrogram voltages in the X axis of 2.47 plus or minus 1.6 millivolts and 2.32 plus or minus 1.6 millivolts in the Y axis were recorded. QRS voltages of 0.078 millivolts and 0.073 millivolts, respectively, allowed dramatic ability to discriminate P from QRS complexes (P/QRS equals 32/1). There was no change in QRS voltages recorded during spontaneous premature ventricular contractions, bipolar or unipolar ventricular pacing. A single catheter designed for P synchronous pacing empJoying circumferentially placed atrial sensing electrodes has demonstrated unique atrial sensing voltages with excellent QRS signal rejection. (PACE, Vol. 4, November-December, 1981)     

Mapping the Coronary Sinus and Great Cardiac Vein

GIUDICI, M., et al. : Mapping the Coronary Sinus and Great Cardiac Vein. The purpose of this study was to develop a better understanding of the pacing and sensing characteristics of electrodes placed in the proximal cardiac veins. A detailed mapping of the coronary sinus (CS) and great cardiac vein (GCV) was done on 25 patients with normal sinus rhythm using a deflectable electrophysiological catheter. Intrinsic bipolar electrograms and atrial and ventricular pacing voltage thresholds were measured. For measurement purposes, the GCV and the CS were each subdivided into distal (D), middle (M), and proximal (P) regions, for a total of six test locations. Within the CS and GCV, the average atrial pacing threshold was always lower (  P < 0.05  ) than the ventricle with an average ventricular to atrial ratio > 5, except for the GCV-D. The average atrial threshold in the CS and GCV ranged from 0.2– to 1.0-V higher than in the atrial appendage. Diaphragmatic pacing was observed in three patients. Atrial signal amplitude was greatest in the CS-M, CS-D, and GCV-P and smaller in the CS-P, GCV-M, and GCV-D. Electrode spacing did not significantly affect P wave amplitude, while narrower electrode spacing attenuated R wave amplitude. The average P:R ratio was highest with 5-mm-spaced electrodes compared to wider spaced pairs. The P:R ratio in the CS was higher (P < 0.05) than in all positions of the GVC. It is possible to pace the atrium independent of the ventricle at reasonably low thresholds and to detect atrial depolarization without undue cross-talk or noise using closely spaced bipolar electrode pairs. The areas of the proximal, middle, and distal CS produced the best combination of pacing and sensing parameters.     

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.     

T-wave alternans testing in pacemaker patients: comparison of pacing modes and long-term prognostic relevance

Background: T‐wave alternans (TWA) is a useful method for identifying patients who are at risk for sudden cardiac death. We aimed to determine the effects of different pacing modes on test results and long‐term prognostic relevance of TWA in patients following a dual‐chamber (DDD) pacemaker implantation. Methods: Sixty‐three patients (mean age 68 ± 13 years) with structural heart disease and recently implanted DDD pacemakers were enrolled. Left ventricular (LV) function was normal or moderately impaired (mean LV ejection fraction 61 ± 13%). All patients underwent sequential TWA testing using atrial and ventricular pacing. Results: During atrial pacing requiring physiologic conduction to the ventricles, 21% of TWA tests were positive, 43% negative, and 36% indeterminate. When using right ventricular (RV) pacing in the same patients, 19% of tests were positive, 40% negative, and 41% indeterminate. When positive and indeterminate tests were grouped as nonnegative, the concordance between atrial and ventricular pacing was 62% (κ= 0.22). After a mean follow‐up of 5.9 ± 1.9 years, 18 (29%) patients had died. Improved survival was predicted by a negative TWA test using atrial pacing (P = 0.028), but not with ventricular pacing (P = 0.722). Conclusions: In patients with dual‐chamber pacemakers, there is a low concordance of TWA test results between atrial pacing with intrinsic conduction to the ventricles and apical RV pacing via pacemaker electrode. However, TWA during atrial pacing clearly exerts long‐term prognostic relevance in a patient group with preserved LV function and structural heart disease. (PACE 2011; 34:1054–1062)     

Intramyocardial pacing and sensing for the enhancement of cardiac stimulation and sensing specificity

BACKGROUND: Intracardiac electrodes create an "antenna" capable of unintentionally recording and stimulating tissue beyond the chamber in which they are positioned, resulting in far-field R wave oversensing in pacemakers and inappropriate detection in defibrillators. This feasibility study sought to determine whether a specially constructed lead with two distal totally intramyocardial electrodes could overcome these limitations. METHODS: Two mongrel dogs were anesthetized and a median sternotomy performed. Epicardial intramyocardial pacing and sensing function was assessed and compared to standard active fixation pacing and sensing placed at the same atrial and ventricular sites. Right ventricular pacing was also assessed. RESULTS: For the novel intramyocardial lead, the average R wave amplitude was 7.2 mV, compared to an average R wave of 8.4 mV for the standard active fixation lead placed at identical ventricular sites; P-waves were also similar. Cross-chamber sensing was present in the ventricle and atrium with the standard lead, and absent with the intramyocardial lead. The average pacing threshold was 0.7 mA at 0.2 ms for the novel lead compared to 1.1 mA for the standard lead. With the standard lead, phrenic stimulation was seen at threshold (cathode distal) and at 3 mA (cathode proximal electrode). No phrenic stimulation was seen with the novel intramyocardial lead despite outputs up to 20 mA at sites located 3-5 mm from the phrenic nerve. CONCLUSION: Totally intramyocardial pacing is feasible, and results in site-specific pacing and sensing function. This may eliminate far-field signal oversensing and phrenic stimulation in future devices.     

Feasibility Of Temporary Biventricular Pacing In Patients With Reduced Left Ventricular Function After Coronary Artery Bypass Grafting

Background and Methods: Biventricular pacing improves hemodynamics after weaning from cardiopulmonary bypass in patients with severely reduced left ventricular (LV) function undergoing coronary artery bypass grafting (CABG). We examined the feasibility of temporary biventricular pacing for 96 hours postoperatively. Unipolar epicardial wires were placed on the roof of the right atrium (RA), the right ventricular (RV) outflow tract, and the LV free lateral wall and connected to an external pacing device in 51 patients (mean LV ejection fraction 35 ± 4%). Pacing and sensing thresholds, lead survival and incidence of pacemaker dysfunction were determined.
Results: Atrial and RV pacing thresholds increased significantly by the 4th postoperative day, from 1.6 ± 0.2 to 2.5 ± 0.3 V at 0.5 ms (P = 0.03) at the RA, 1.4 ± 0.3 V to 2.7 ± 0.4 mV (P = 0.01) at the RV, and 1.9 ± 0.6 V to 2.9 ± 0.7 mV (P = 0.3) at the LV, while sensing thresholds decreased from 2.0 ± 0.2 to 1.7 ± 0.2 mV (P = 0.18) at the RA, 7.2 ± 0.8 to 5.1 ± 0.7 mV (P = 0.05) at the RV, and 9.4 ± 1.3 to 5.5 ± 1.1 mV (P = 0.02) at the LV. The cumulative overall incidence of lead failure was 24% by the 4th postoperative day, and was similar at the RV and LV. We observed no ventricular proarrhythmia due to pacing or temporary pacemaker malfunction.
Conclusions: Biventricular pacing after CABG using a standard external pacing system was feasible and safe.     

Atrial Fibrillatory Electrogram Measurement Allows Atrial Lead Placement in Patients Who Develop Atrial Fibrillation During Permanent Dual Chamber Pacemaker Implantation

The benefit of DDD(R) pacing is proven even in patients with intermittent atrial fibrillation. Atrial fibrillation developing during dual chamber pacemaker implantation creates a difficult problem. Maneuvers to reestablish a stable atrial rhythm often are required if atrial fibrillation sets in. This study was performed to determine if atrial lead placement can be performed with acceptable long-term results in the presence of atrial fibrillation. Twenty-one patients in whom atrial fibrillation developed during permanent pacemaker implantation were included in this study. In 12 patients, episodes of intermittent atrial fibrillation had been documented before the procedure. Screw-in leads were used in 15 patients and J-shaped passive fixation leads in 6 patients. AH leads were bipolar. The intraoperative atrial fibrillation electrogram amplitudes ranged from 0.9 to 3.2 mV (mean 1.8 ± 0.6 mV). One patient required lead revision due to a high atrial pacing threshold after conversion to SR. One patient remained in atrial fibrillation at 3-month follow-up. The other 20 patients converted to SR, 11 of whom had intermittent atrial fibrillation with successful mode switch activation. P wave amplitudes were 2.8 ± 6 mV (range 1.4 to 4.0 mV) after conversion to SR. The mean atrial pacing threshold was 1.1 ± 0.5 V (range 0.5 to 3.5 V). Placement of atrial leads in patients who develop atrial fibrillation during pacemaker implantation is feasible; fibrillatory electrogram amplitudes showed a good correlation with the atrial signal after conversion to an organized atrial rhythm (r = 0.698). Acceptable atrial pacing thresholds can be expected as well.