Dynamic Electrophysiology of Ventriculoatrial Conduction: Implications for DDD and DDDR Pacing

CAZEAU, S., ET AL.: Dynamic Electrophysiology of Ventriculoatrial Conduction: Implications for DDD and DDDR Pacing. The behavior of ventriculoatrial conduction (VAC) during exercise remains unknown. In order to determine its characteristics and the consequences it might have on dual chamber pacemaker technology and programming, 17 patients underwent an electrophysiological study (EPS) of atrioventricular conduction (AVC) and of VAC during a protocol including three steps: supine rest, upright position, and finally during cycloergometric exercise; the measurements were done at progressively increasing pacing rates. During a preimplantation EPS, Wenckebach points AVC-W and VAC-W and conduction times, AVCT and VACT (as a function of pacing rate), were measured in ten consecutive patients using temporary leads and an external device. In another study, AVCT, VACT, AVC-W, and VAC-W were measured by telemetric recordings under identical conditions in seven patients implanted earlier with a DDD pacemaker. A 1/1 VAC was observed in 7/17 patients (41%) at rest, and in 13/17 patients (76%) at the end of the protocol; VAC was never observed in 4/17 patients [23%], but occurred in six of the ten patients initially free, three standing at rest and three on exercise. For all patients, the VAC behavior remained of “nodal” type, indicated by a progressive increase in VACT as pacing rate rose up to the VAC-W point. Neither the existence of exercise-induced VAC nor the maximal VACT-W could be predicted from AVC or VAC data obtained at rest. However, at the same pacing rates, standing up and exercise induced a shortening effect on VACT, and improved the VAC-W by an average of 33%. These results suggest that the electrophysiological behavior of VAC does not obey any general rule and cannot be predicted individually. It would thus appear unwise to base pacemaker mediated tachycardia (PMT) protection solely on long postventricular atrial refractory period (PVARP) programming in DDD patients. This work also revealed the potential risks of a rate responsive auto-adaptive PVARP algorithm as proposed in certain new devices.     

Supriority of Multiprogrammable to Nonprogrammable VVI Pacing: A Comparative Study with Special Reference to Management of Pacing System Malfunctions

Analysis of pacing system malfunctions was performed in 374 patients at initial implantation or at pulse generator and lead replacement during a period of 55 months. A total of 150 nonprogrammable pacemakers were implanted in 148 patients, while 236 multiprogrammable pacemakers were implanted in 226 patients. The purpose of the analysis was to investigate the occurrence and management of malfunction unrelated to pacemaker/lead failure or lead dislodgement. The nonprogrammable group was followed for 3-53 months (median, 36). Malfunction occurred in 18 patients (12.0%): muscle stimulation in 14; exit block in three; sensing problem in one. Surgical correction was necessary in 14 of 18 cases. The multiprogrammable group was followed for 3-52 months (median, 12). Malfunction occurred in 30 cases (12.7%): muscle stimulation in 22; threshold increase in seven; sensing problem in one. Only seven of these patients required surgical correction as 23 cases were successfully managed by reprogramming alone. Malfunctions occurred during a period of several days to 36 months (median, 2.3 months). The difference in rate of secondary surgical intervention was significant (p less than 0.01). Measurements during reoperation in the nonprogrammable group showed that at least 40% of late malfunctions would have been correctable by reprogramming alone. Thus, multiprogrammability is of significant value for noninvasive correction of malfunctions unrelated to pacemaker and lead failures, predominantly muscle stimulation and threshold elevation.     

Comparison of Ramp and Stepwise Incremental Pacing in Assessment of Antegrade and Retrograde Conduction

. conduction. Conventional assessmenl of antegrade (AV) and retrograde (VA) conduction involves stepwise increments in pacing rates until block in conduction is observed. This study was designed to establish the comparative characteristics of ramp pacing, in which the rate is continuously and smoothly incremented until block occurs. Two hundred and ten patients participated in portions of this study. Stepwise pacing was performed in 10 beat/minute steps, with the rate held for at least 15 seconds at each step; if marked prolongation or variability in conduction was observed, the rate was held constant for up to 60 seconds to allow for accomodation. With ramp pacing, the rate was gradually increased at a steady 2–4 beats/minute/second. Whenever possible, both stepwise and ramp pacing were performed for assessment of both antegrade and retrograde conduction. All patients had conducted sinus rhythm as their baseline mechanism. Antegrade conduction was similar using incremental stepwise and ramp pacing. The AH interval at a cycle length (CL) of 500 ms, the maximum AH increment, the cycle length at AV block were all remarkably similar (p = NS). Assessment of retrograde conduction produced similar results, with insignificant differences between maximum conducted VA intervals, and cycle length at VA block using the two pacing techniques. Ramp pacing provides a useful and rapid alternative to conventional stepwise incremental pacing in the assessment of antegrade and retrograde conduction in patients using both normal and accessory pathways. Ramp pacing was better tolerated, and some correlations between antegrade and retrograde conduction were stronger with the ramp pacing technique.     

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.     

Long-Term Follow-Up of Biventricular Pacing Using a Totally Endocardial Approach in Patients with End-Stage Cardiac Failure

Background: Besides standard left ventricular (LV) stimulation via the coronary sinus, a transseptal approach allows left ventricular endocardial stimulation. We report our long-term observations with biventricular stimulation, using a strictly endocardial system for patients presenting with severe congestive heart failure .
Methods: Six patients with nonischemic cardiomyopathy (mean age = 60 ± 9.6 years, women) in New York Heart Association (NYHA) functional class III (n = 5) or IV, despite optimal drug therapy, and a mean LV ejection fraction of 24 ± 3%, underwent implantation of biventricular stimulation systems between April 1998 and March 1999. All presented with left bundle branch block and an increased LV end-diastolic diameter (mean = 66 ± 5 mm). In all patients, a bipolar pacing lead was implanted in the lateral LV wall using a direct transseptal approach. After implantation, all patients received oral anticoagulation.
Results: QRS duration decreased from 184 ± 22 ms to 108 ± 11 ms. NYHA functional class decreased to II in all patients within 1 month. Over a 85 ± 5 month follow-up, two patients underwent cardiac transplantation, 2 and 4 years after device implantation, respectively; two patients died of end-stage heart failure 4 years after system implantation; and two patients were alive in functional class II. One patient, who experienced syncope due to fast ventricular, underwent implantation of an ICD. One transient ischemic attack occurred in a patient whose anticoagulation was temporarily interrupted .
Conclusions: Long-term endocardial biventricular stimulation via a transseptal approach was safe and effective in this small population. This approach needs to be further compared with conventional epicardial pacing via the coronary sinus     

Characteristics of Ventriculoatrial Conduction in Patients with Enhanced Atrioventricular Nodal Conduction

To study the characteristics of the ventriculoatrial conduction system in palienfs capable of rapid antegrade atrioventricuiar conduction, eiectrophysiologic studies were performed in 23 subjects capable of 1:1 atrioventricular conduction at atrial cycle lengths < 300 ms (Group I). and in 23 subjects with normal 1:1 atrioventricular conduction (Group II). During venfricular pacing, ventriculoatrial block at all cycle lengths was seen in 5/23 (22%) in Group I and in 7/23 (30%) in Group II patients (p = NS). In the remainder, the minimum ventricuar pacing cycle length maintaining 1:1 ventriculoatrial conduction was 359 ± 85 ms in Group I, compared to 444 ± 118 ms in Group II (p < .02). Both flat and exponential VA conduction interval curves, drawn as a function of pacing cycle length, were observed in both groups. Discontinuous ventricuioatrial conduction curves were seen in 5/18 (28%) Group I and 1/16 (6%) Group II patients (p = NS). In conclusion, retrograde ventriculoatrial conduction, when present in patients capable of rapid 1:1 atrioventricular conduction, is maintained at shorter cycle lengths than in patients with normal atrioventricular conduction. Quantitative, rather than qualitative, differences distinguish the two groups.     

Left Atrial Size and Wall Motion in Patients with Permanent Ventricular and Atrial Pacing

KUBICA, J., ET AL.: Left Atrial Size and Wall Motion in Patients with Permanent Ventricular and Atrial Pacing. It is well known that during permanent ventricular pacing atrial arrhythmias and embolic complications occur much more frequently in comparison to permanent atrial or sequential pacing. He-modynamic disturbances caused by ventriculoatrial conduction (VAC) are thought to be responsible for those complications. The aim of this study was to compare the left atrial size and its wall motion in three groups of patients with sick sinus syndrome. Group 1: 58 patients with VVI pacing and VAC observed (22 males, 36 females, aged 31–86, mean 62.3). Group 2: 43 patients with primary AAI pacing (13 males, 30 females, aged 27–74, mean 57.8). Group 3: 13 patients with AAI or DDD replacing the primary VVI mode due to pacemaker syndrome and/or heart failure, all with VAC present during VVI pacing (7 males, 6 females, aged 26–80, mean 59.8). Two-dimensional/M-mode echocardiography was performed in all these patients. In group 1 mean diastolic as well as mean systolic atrial diameters were significantly greater (p < 0.005) and wall motion significantly smaller (p < 0.005) in comparison to the other groups. Left atrial wall motion amounted to only 7.4% of the mean diastolic diameter in this group. Mean left atrial diastolic and systolic diameters and wall motion in patients with pacemakers preserving atrioventricular synchrony (group 2 and group 3) were almost identical and wall motion amounted to about 22% of the diastolic diameter in both these groups. We conclude that ventriculoatrial conduction leads to significant enlargement of left atrium and to the atrial wall-motion decrease. This predisposes to arrhythmias and embolic complications. Changes in atrial size and performance seem to be reversible with restoration of the physiological atrioventricular synchrony.     

Ventricular and Dual Chamber Pacing for Treatment of Carotid Sinus Syndrome

Thirty-nine consecutive patients with recurrent syncope and either cardioinhibitory or mixed type carotid sinus syndrome were studied to determine the efficacy of ventricular (VVI) pacing in 16, and dual chamber (DDD/DVI) in 23 patients. Only those patients affected by the isolated vasodepressor form were excluded. Follow-up lasted 12 ± 5 months. Symptoms were totally eliminated in 67% of patients and ameliorated with persistence of minor symptoms in 33%. All patients underwent an initial 2-month follow-up in the VVI mode. Evaluation of the 19 patients who remained symptomatic and the 20 who became asymptomatic with VVI pacing demonstrated that factors observed prior to pacemaker implant were related to failure of the VVI mode. These included symptomatic pacemaker effect (42% vs 0%), mixed carotid sinus syndrome (95% vs 65%), orthostatic hypotension (47% vs 15%), or ventriculoatrial conduction (68% vs 38%). In the 23 patients with dual chamber pacing, random 2 month comparisons were performed between VVI and DVI/DDD pacing. The dual chamber mode was preferred by 14 patients, none preferred the VVI mode and nine noted no difference. Comparison of the two groups found that the factors linked to DVI/DDD preference were symptomatic pacemaker effect (50% vs 0%), ventriculoatrial conduction (78% vs 44%), or orthostatic hypotension (50% vs 11 %). VVI pacing is efficacious in a high proportion of patients affected by cardioinhibitory or mixed carotid sinus syndrome. The identification of causes of VVI pacing failure allows determination of those who will benefit from VVI pacing and those who should have DVI/DDD. VVI pacing is suggested for the cardioinhihitory type with no symptomatic pacemaker effect and for the mixed type with no symptomatic pacemaker effect or orthostatic hypotension or ventriculoatrial conduction. Dual chamber pacing should be used in all other instances.     

Right Ventricular Outflow Tract Septal Pacing: Long-Term Follow-Up of Ventricular Lead Performance

Background: The detrimental effects of right ventricular apical pacing on left ventricular function has driven interest in selective site pacing, predominantly on the right ventricular outflow tract (RVOT) septum. There is currently no information on long-term ventricular lead electrical performance from this site.
Methods: A total of 100 patients with ventricular lead placement on the RVOT septum undergoing pacemaker implantation for bradycardia indications were analyzed retrospectively. Lead positioning was confirmed with the use of fluoroscopy. Long-term (1 year) follow-up was obtained in 92 patients. Information on stimulation threshold, R-wave sensing, lead impedance, and lead complications were collected.
Results: Lead performance at the RVOT septal position was stable in the long term. Ventricular electrical parameters were acceptable with stable long-term stimulation thresholds, sensing, and impedance for all lead types. One-year results demonstrated mean stimulation threshold of 0.71 ± 0.25 V, mean R wave of 12.4 ± 6.05 mV, and mean impedance values of 520 ± 127 Ω. There were no cases of high pacing thresholds or inadequate sensing.
Conclusions: This study confirms satisfactory long-term performance with leads placed on the RVOT septum, comparable to traditional pacing sites. It is now time to undertake studies to examine the long-term hemodynamic effects of RVOT septal pacing.     

The Incidence of Retrograde Conduction in Children

With the increasing use of "physiological" pacemakers in the pediatric age group, retrograde conduction in children has become of clinical importance. Pacemakers which sense atrial depolarization may sense "retrograde" P waves. The pacemaker may then act as the antegrade limb of a reciprocating tachycardia circuit, while the patient's own conduction system acts as the retrograde limb. We reviewed the data of 127 patients who underwent antegrade and retrograde electrophysiologic study at Texas Children's Hospital, with regard to retrograde conduction. Sixty percent of the patients had ventriculo-atrial conduction through the A-V node; the incidence of retrograde conduction in patients after surgical correction of a tetralogy of Fallot was significantly lower (33%). None of the patients with third-degree A-V block had retrograde conduction. The mean retrograde conduction time was 162 ms (range 70-335 ms) at the slowest pacing rate and 257 ms (range 80-475 ms) at the fastest pacing rate. This high incidence of retrograde conduction and the variability of conduction times must be taken into account when "physiological" pacemakers are to be implanted.     

Long-Term Follow-Up of Patients Treated with Automatic Scanning Antitachycardia Pacemaker

The long-term efficacy of an automatic antitachycardia pacemaker was evaluated in 13 patients with supraventricular tachycardia and in two patients with ventricular tachycardia. Patients were followed for 4–53 months (median 16). The concertina scanning mode with 2–7 extrastimuli proved to be effective in all patients but one. During follow-up, two patients had to be reoperated due to sensing problems. Atrial flutter was induced during scanning in one patient, termination mode was triggered by sinus tachycardia in one patient despite beta blocker therapy, and in one patient after cessation of beta blocker treatment. The pacemaker did not induce any serious arrhythmias and no sudden deaths occurred. Seven patients were given beta blockers, one patient with ventricular tachycardia was additionally administered amiodarone. In conclusion, the PASAR 4171 (Telectronics, Englewood, CO, USA) automatic scanning pacemaker is an alternative or adjunctive means to chronic antiarrhythmic drug therapy in patients with supraventricular tachycardia, but further versatility with regard to sensitivity, refractory period, and tachycardia recognition is required to eliminate the shortcomings observed, including the need for additional beta blocker therapy.     

Long-Term Performance of Endocardial Pacing Leads

To assess the performance of endocardial pacemaker leads and to identify factors associated with structural lead failure, medical records of 2,611 endocardial pacing leads (in 1, 5W patients) implanted between 1980 and 1991, having at least 1 month of follow-up, were reviewed. Leads without structural failure had normal function at the last follow-up date, or were discontinued for reasons other than structural failure (patient death, infection, dislodgment, lead-pacemaker incompatibility, operative complication, or abandonment by telemetry not related to failure). Leads with suspected structural failures were invasively or noninvasively disconnected because of clinical malfunction (loss of capture or sensing, oversensing, elevated thresholds, or skeletal muscular stimulation). Leads with verified structural failures met the criteria for suspected lead failure and also had a visible defect seen in the operating room or on chest roentgenograms, a change in the impedance interpreted by the physician as lead disruption, or a manufacturer's return product report that confirmed structural failure. Variables analyzed included patients’ age and gender, paced chamber, venous access, insulation materials, fixation mechanism, coaxial design, polarity, and different lead models. The cumulative lead survival at 5 and 10 years were 97.4% and 92.9%, respectively, for suspected failures; and 98.7% and 97.3%, respectively, for verified failures. Leads in older patients (≥ 65 years old), and leads in atrial position had fewer verified failures (P = 0.014 and P = 0.007, respectively). Unipolar leads also tended to perform better according to the verified definition (P = 0.07). The lead Medtronic 4012 had more suspected (P < 0.05) and more verified failures (P < 0.01), the lead CPI 4010 had more verified failures (P < 0.05) than the entire group of ventricular leads. Conclusions: Endocardial pacing leads implanted in atrial position, and implanted in older patients (> 65 years old) seems to have better long-term survival. Some lead models (Medtronic 4012 and CPI 4010) had poor survival rates, that could not be explained by the analyzed variables. The expected performance of endocardial pacing leads varies according to how failure is defined.     

Long-Term Follow-Up of Patients with Single Lead VDD Stimulation

The purpose of this study was to assess the long-term results of a single lead VDD pacing system (Phymos MPS) in 85 patients (48 males, 37 females, mean age 74 ± 9 years). The system, which incorporates two atrial floating electrodes (Phymos 830-S). was implanted for second- or third-degree Mobitz II AV block. The percentage of AV synchronized pacing, the presence of fusion beats due to short AV delay, and the occurrence of supraventricuiar arrhythmias was evaluated by Holter monitoring at 6-month intervals. Over a mean period of follow-up of 44 months (range 2–56), over 90% of AV synchronized pacing events were noted in 74 patients (87%). The presence of persistent fusion beats was detected in 12 patients (14%). In ten patients the pacemaker was reprogrammed to VVI mode for supraventricuiar arrhythmias (7 patients, 8.2%) or unsatisfactory atrial sensing (3 patients, 3.5%). One pacemaker was removed for pocket infection and two for battery depletion. These observations support the use of VDD single lead pacing to combine a physiological mode of stimulation with simple implantation techniques.     

The Effect of VVI Pacing and Resultant Atrioventricular Dyssynchrony on Segmental Volumes

Left and right ventricular volumes were monitored simultaneously in four anesthetized dogs by intracardiac impedance ventriculography during normal sinus rhythm, spontaneous ventricular rhythm, and VVI and VDD pacing. Cardiac output was found to increase with VVI pacing rate but remained somewhat lower than normal sinus or VDD values. The dissynchronous atrial contraction was found to distort the volume waveforms but had little effect on right ventricular volumes. Left atrial contraction had the greatest impact on left ventricular filling at near normal AV delays. Cardiac output during VDD pacing was found to be a maximum at 170 msec and decreased in three of four dogs at 220 msec. Examination of volume waveforms during "filling" indicates that the right ventricle is dominated by passive filling while the left ventricle demonstrates a large active or "fast" filling phase.     

Long-Term Follow-Up of Patients with Sick Sinus Syndrome: A Comparison of Clinical Aspects Among Unpaced, Ventricular Inhibited Paced, and Physiologically Paced Groups

To analyze the prognosis of the sick sinus syndrome (SSS), we compared the clinical aspects among unpaced, ventricular paced, and physiologically paced patients who were followed over a long period. Unpaced intrinsic SSS was not always progressive and patients did not necessarily require permanent pacing. The incidence of concomitant AV conduction disturbance was 65.6% before pharmacologic autonomic block, (PAB), but this was significantly reduced to 31.7% after PAB. Follow-up study of the physiologically paced groups revealed no development of either new or more than second degree AVB. The VVI group had significantly more complications (68%) than the physiologically paced groups, mainly chronic atrial fibrillation (36%) and thromboembolism (20%). In addition, cardiothoracic ratio (CTR) in the VVI group was significantly greater compared with that in the physiologic groups. Nine deaths occurred during the follow-up period in the pacing groups, including six with VVI and three with physiologic pacing. In the VVI pacing group, heart failure and thromboembolism were most commonly the causes of death, while in the physiologic pacing groups, the causes of death were noncardiac. Although the survival rate in the ventricular paced group was not significantly different from that in the physiologic pacing groups, cardiac deaths were fewer in the latter group. Considering our clinical data, the decision to use ventricular pacing needs to be carefully weighed in patients with sick sinus syndrome, and physiologic pacing is more highly recommended. (PACE, Vol. 11. November 1988)     

Long-Term Performance of Epimyocardial Pacing Leads in Adults: Comparison with Endocardial Leads

The long-term performance of epimyocardiaJ pacing leads in children is well established, but few studies have analyzed the performance in adults. This issue has clinical relevance in view of the increased use of epimyocardial leads with implantable cardioverter defibrillator and antitachycardia pacing systems. We analyzed 93 epimyocardial pacing "systems" (121 leads: 65 unipolar, 28 bipolar) in adult patients (age 57 ± 16 years), implanted since January 1980. Two different models were studied: Medtronic 4951 "Stab–on" (n = 35) and Medtronic 6917/6917A "Screw-in" (n = 58). A control group was created by randomly matching each epimyocardial system with two endocardial leads, according to age and year of implant. Epimyocardial and endocardial leads were followed-up for 44 ± 35 and 43 ± 35 months, respectively (P = NS). Freedom from failure for epimyocardial leads was 0.91 (95% Confidence Interval [95% CI] = 0.82 to 0.96) at 5 years, and 0.91 f95% CI = 0.69 to 0.98) at 10 years. No difference was found between the two analyzed models. Freedom from failure for endocardial leads was 0.97 (95% CI = 0.93 to 0.99) and 0.90 (95% CI = 0.61 to 0.97) at 5 and 10 years, respectively. Epimyocardial Jeads had a significantly poorer short-term survival than endocardiaJ leads, secondarily to earlier "technique related" failures (P = 0.03; relative riskc 3.0; Wilcoxon test). However, overall long-term performance was similar to endocardial leads. Epimyocardial pacing leads, meticulously implanted and tested, have a long-term performance similar to endocardial pacing leads.     

Five-Year Follow-Up of a Bipolar Steroid-Eluting Ventricular Pacing Lead

Steroid-eluting pacing leads are known to attenuate the threshold peaking early after implantation. Long-term performance, however, is not yet settled. The lead design tested in this prospective study combines a 5.8-mm2 tip of microporous platinum-iridium with elution of 1.0 mg of dexamethasone sodium phosphate and tines for passive fixation (model 5024, Medtronic Inc.). In 50 patients (mean age 69 +/- 10 years), the electrode was implanted in the right ventricular apex. Follow-up was performed on days 0, 2, 5, 10, 28, 90, 180 and every 6 months thereafter for 5-years postimplant. At each visit, pacing thresholds were determined as pulse duration (ms) at 1.0 V and as the minimum charge (microC) delivered for capture. Lead impedance (omega) was telemetered at 2.5 V-0.50 ms, and sensing thresholds (mV) were measured in triplicate using the automatic sensing threshold algorithm of the pacemaker implanted (model 294-03, Intermedics Inc.). On the day of implantation, mean values were 0.10 +/- 0.03 ms, 0.12 +/- 0.03 microC, 758 +/- 131 omega, and 13.1 +/- 1.8 mV, respectively. Beyond 1-year postimplant, pacing thresholds did not vary significantly. Sensing thresholds and lead impedance values were stable during long-term follow-up. Five years after implantation, mean values were 0.23 +/- 0.11 ms, 0.24 +/- 0.07 microC, 670 +/- 139 omega, and 11.6 +/- 3.1 mV for pulse width and charge threshold, lead impedance, and sensing threshold, respectively, and all leads captured at 1.0 V with the longest pulse duration available (1.50 ms). It is concluded that the bipolar steroid-eluting tined ventricular lead showed stable stimulation thresholds, lead impedance values, and sensing thresholds for 5 years after implantation.     

Thresholds and Complications with Right Ventricular Septal Pacing Compared to Apical Pacing

Background: Right ventricular septal pacing has been proposed as an alternative to apical pacing. However, data concerning thresholds and requirement for lead repositioning with this technique are scant.
Methods: We reviewed data at implantation and follow-up of 362 consecutive recipients of the same model of active fixation lead (Medtronic 5076-58, Minneapolis, MN, USA) to avoid differences due to lead characteristics. Patients were divided into two groups according to whether the lead was positioned on the interventricular septum (n = 157) or at the right ventricular apex (n = 205). Thresholds, lead impedance, and requirement for lead repositioning were compared between groups at implantation and follow-up.
Results: There were no differences between the septal and apical groups in sensing and pacing thresholds or lead impedance, either at implantation or during a 24-month follow-up. In the septal group, the lead had to be repositioned in four patients (2.5%) due to lead dislodgement in two patients, acute threshold rise in one patient, and pericardial effusion in another patient (the lead had unintentionally been positioned on the anterior free wall in these last two patients). In the apical group, the lead had to be repositioned in eight patients (3.9%, P = 0.56) due to lead dislodgement in three patients and acute threshold rise in five patients.
Conclusions: Acute and chronic thresholds associated with septal pacing are similar to those observed with apical pacing, and risk of lead dislodgement is low. However, multiple radioscopic views must be used to avoid inadvertent positioning of the lead on the anterior free wall .     

Noninvasive Assessment by Doppler and M-Mode Echocardiography of Hemodynamic Responses to Temporary Pacing and to Ventriculoatrial Conduction

A new, dual-chamber temporary pacing lead was introduced via the subclavian vein in 20 patients who needed a temporary pacemaker. Stroke volume (SV) was measured continuously by combining M-mode and noninvasive Doppier echocardiography during spontaneous rhythm (SR), AV sequential pacing at a positive AV interval (DP), ventricular pacing (VP) and AV sequential pacing at a negative AV interval (VA pacing). The valvular functions were determined by Doppler echocardiography. Left ventricular dimensions and function, and left atrial size were measured by M-mode echocardiography. In the nine patients with no valvular heart disease and with no ventriculoatrial (VA) conduction (group I) the CO increased 83 ±11% during DP and 42 ± 9% during VP as compared to during SR when the heart rate (HE) was increased from 34 ± 3 to 72 ± 1 beats/min. The CO was 29 ± 3% higher during DP than that during VP. In the seven patients with valvulox heart disease and with no VA conduction (group II), the increment in CO compared to that during Sfi was SZ ± 12% during DP and 31 ±17% during VP: the CO was 17 ± 4% higher during DP than that during VP. In the four patients with spontaneous VA conduction (group III), the CO during DP was 35 ± 10% greater than that during VP, which did not result in an increase in the CO compared to that during SR in spile of an increase in HR from 52 ± 8 to 74 ± 2 beats/min. The study demonstrated that DP is the preferred temporary pacing mode and also that VA conduction during VP resulted in a mean decrease of 20% in CO compared to that during VP without VA conduction. The hemodynamic benefit from DP compared to SR seems to decrease when the left ventricular end-diastolic dimension increases. Furthermore, patients with large left ventricular end-systolic dimensions seem to have a lower increase in stroke index during DP as compared to that during VP than patients with smaller end-systolic dimensions.     

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)