Chronic Steroid-Eluting Lead Performance: A Comparison of Atrial and Ventricular Pacing

It is generally believed that atrial pacing leads have higher stimulation thresholds and long-term complication rates than ventricular leads, and this is one of the factors limiting the use of dual chamber pacing. A study was undertaken to compare atrial and ventricular bipolar tined steroid-eluting leads in two designs: the Medtronic CapSure SP and the Telectronics Encor Dec. There were 123 pairs of leads: 81 CapSure SP and 42 Encor Dec. Bipolar atrial and ventricular stimulation thresholds, electrograms. and pacing impedance were measured using the Telectronics META DDDR pulse generator immediately postimplantation, and at 1, 3, and 6 months for all leads and at 12, 18, and 24 months for the CapSure SP. The only major lead complication was a 2% atrial lead dislodgment rate. All leads demonstrated low stimulation thresholds, with the CapSure SP leads having lower values than comparable Encor Dec leads. All leads had a mean range of 0.53–0.89 V at all testing periods with P < 0.05 for atrial leads only. There were no differences in electrogram size between manufacturers and no instances of atrial and ventricular undersensing. Pacing impedance was about 100 Ω higher for the Encor Dec leads (P < 0.05, atrial leads only), suggesting that these leads will result in lower pacing energy losses provided the pulse generators are at identical settings. More than 90% of patients could be paced chronically in the atrium and ventricle at 2.5 V, but for chronic 1.6-V pacing, the CapSure SP leads were superior. In conclusion, atrial and ventricular steroid-eluting leads of both manufacturers gave excellent stimulation threshold results allowing low energy dual chamber pacing.     

Intrapatient Comparison of Atrial and Ventricular Sensing, Pacing Threshold, and Impedance: Benefits with Steroid-Eluting Leads

We compared the atrial and ventricular bioelectrical effects relating to pacing threshold, pacing impedance, and pacing energy in each of 58 patients to determine the importance of pacing impedance in safe low energy stimulations. The study was conducted during 4 years of follow-up. Of the 58 patients in our study, 31 were stimulated in both chambers with steroid-eluting leads (Capsure 4503 and 4003) and 27 with platinum electrode catheters (Target Tip 4511 and 4011). The two groups were homogeneous in sex, age, cardiopathy, and reason for implant. At 6 months, the mean impedance values for the Target Tip were: 358 ± 72 Ω for the atrium and 443 ± 87 Ω for the ventricle (P < 0.00002): after 1 year, atrium = 386 ± 77 Ω, ventricle = 439 ± 42 Ω (P < 0.04); at 2 years, atrium = 409 ± 86 Ω, ventricle = 510 ± 94 Ω (P < 0.0001); at 3 years, atrium = 428 ± 81 Ω, ventricle = 494 ± 67 Ω (P < 0.02); and at 4 years, atrium = 424 ± 71 Ω and ventricle = 501 ± 69 Ω (P < 0.003). The mean impedance value (for the Capsure) was: atrium = 351 ± 43 Ω, ventricle = 431 ± 81 Ω at 6 months (P < 0.03); at 1 year, atrium = 359 ± 38 Ω, ventricle = 446 ± 83 Ω (P < 0.01); at 2 years, atrium = 304 ± 124 Ω, ventricle = 459 + 108 Ω (P <0.0003); at 3 years, atrium = 359 ± 108 Ω, ventricle = 461 ± 89 Ω (P < 0.02); and at 4 years, atrium = 419 ± 133 Ω and ventricle = 515 ± 75 Ω (P < 0.03;. In view of the chronic threshold, low energy stimulation was used at follow-up. The mean low energy stimulation values programmed for Target Tip were: atrium = 2.5 V/0.35 ms, ventricle = 2.5 V/0.30 ms; for Capsure, atrium = 2.5 V/0.25 ms, ventricle = 2.5 V/0.25 ms. The mean stimulation energy value was 31% higher in the atrium than in the ventricle with Capsure leads, and 39% higher with Target Tip. Pacing impedance was lower in the atrium than in the ventricle with both leads. Energy consumption in the atrium is significantly greater than in the ventricle with both leads, particularly with Target Tip.     

Long-Term Performance of Bipolar Epicardial Atrial Pacing Using an Active Fixation Bipolar Endocardial Lead

Bipolar epicardial leads are not yet widely available for atrial use. Since September 1986, we have used a bipolar active fixation endocardial lead (Cardiac Pacemakers model number's 4266, 4268, and 4269) as a bipolar epicardial atrial lead by attaching the corkscrew tip to the atrial surface and imbricating atrial tissue around the more proximal electrode. A total of 77 bipolar epicardial atrial leads have been implanted using this approach in 72 patients with congenital heart disease (ages 3 months to 38.7 years; mean 8.9 ± 8.8 years). Indications for atrial pacing included AV block (n = 46), sinus node dysfunction (n = 17), and antitachycardial pacing (n = 9). Indications for epicardial pacing included the presence of an intracardiac right to left shunt (n = 33), concomitant cardiac surgery (n = 26), surgeon preference (n = 7), and lack of transvenous access to the atrial endocardium (n = 6). Follow-up (median 23 months; mean 28.0 ± 23.1 months; range 1–78 months) data beyond 1 month postimplantation were available for 44 leads. Atrial sensing was ≥ 2.0 mV for 26 leads (59%) with sensing possible at ≥ 0.75 mV for 42 leads (95%). Threshold data were available at 5 V for 37 leads and at 2.5 V for 36 leads with mean pulse width thresholds measuring 0.21 ± 0.33 ms and 0.34 ± 0.34 ms, respectively. Two leads failed (high capture thresholds at 5 days [n = 1], lead fracture at 42 months [n = 1]); one of which was replaced. Four additional leads were replaced electively (marginal thresholds [n = 1], intermittent phrenic nerve stimulation [n = 1], damaged during subsequent surgery [n = 1], clinically irrelevant insulation break [n = 1]) concomitant with additional cardiac surgery. Until a commercially available lead is developed and released, improvisation with a bipolar active fixation endocardial lead as a bipolar epicardial atrial lead is a reasonable approach to providing bipolar atrial sensing and pacing in patients for whom endocardial pacing is contraindicated.     

High Thresholds May Alter End-of-Life Behavior in a Dual Chamher Pacemaker

We noted a series of 12 consecutive patients with a DDD Genisis® pacemaker that showed an unexpected and a relatively rapid fall in battery voltage and output as these devices approached end-of-life (EOL). Twenty-one of 24 leads were Vitatron Helifix® leads and there was a relatively high mean threshold (atrial 2.5 ± 0.94 V: ventricular 2.9 ± 0.65 V) These devices were replaced after 65 ± 12 months. During the 9.3 ± 3.5 months before replacement, a striking fall in voltage from 2.7 ± 0.04 V to 2.49 ± 0.05 V was seen. Battery impedance rose from 3 ± 1.2 KΩ to 10.2 ± 4.3 KΩ during this same period. We unexpectedly observed a marked difference between programmed and telemetered output for both atrial (50%) and ventricular leads (30%). A discrepancy between measured and telemetered magnet rate was also seen. Despite this relatively rapid fall in battery voltage, several of these devices did not meet the manufacturer's recommended replacement time (RRT) criteria by magnet rate or according to the projected RRT determined by the relationship of battery impedance to current drain. These data have implications for the selection of RRT and EOL criteria for this device. Magnet rate measured by surface ECG was the safest indicator for RRT. Follow-up for this pulse generator should be increased to every 2 months when battery impedance is > 2 KOhms or if there is a difference between programmed and measured output amplitude of more than 15%. The data also highlight the effect of combining high threshold leads with modern pacemakers with relatively "small" batteries as well as certain problems with telemetered data     

A New Steroid-Eluting Screw-In Electrode

A new lead design was tested that combined a small microporous steroid-eluting electrode with an insulated, exposed helix for active fixation. This lead (model 5078, Medtronic, Inc., group I. n = 10) was compared to a conventional model (model Y 60 BP, Biotronik) with a larger surface of polished platinum-iridium, equipped with a fixed, noninsulated screw but without steroid elution (group II, n = 10). The two lead models were studied in the atrial position of dual chamber pacing systems, which all had a tined ventricular lead (model 5024, Medtronic, Inc.), with essentially the same steroid-aluting tip as the new active fixation lead design. Sensing and pacing data were recorded acutely and during 1 year of follow-up, via the telemetry of a Relay pulse generator (Intermedics. Inc.). Intraoperatively, unfiltered atrial electrogram amplitudes did not differ between groups (group I; 7.12 ± 2.56 mV vs group II: 6.42 ± 1.87 mV; P > 0.05), nor did sensing thresholds 1 year after implantation (group I: 5.33 ± 1.70 mV vs group II: 4.26 ± 1.40 mV; P > 0.05). Atrial pacing thresholds as measured during surgery at a pulse width of 0.5 msec were lower in group I (0.49 ± 0.15 V) than in group II (0.68 ± 0.19 V; P < 0.05). From day 5 through day 360 of follow-up, the difference in atrial pacing thresholds was highly significant (P < 0.01). with a smaller peaking of early thresholds and a much lower scattering of data for the steroid screw-in leads than for controls. Chronic thresholds as measured 1 year postimplant in terms of minimum charge delivered for capture were 0.20 ± 0.03 μC in group I versus 0.54 ± 0.11 μC in group II (P < 0.01). There was no difference between groups on the ventricular level, both acutely and during follow-up. If the active fixation atrial lead was compared to its tined ventricular counterpart in group I, pacing thresholds only differed within the early days postimplant, but they were virtually identical from week 3 through 1 year. It is concluded that the novel pacing lead design effectively combines low energy pacing with more versatility in electrode positioning by use of the active fixation mechanism.     

Insulation Lead Failure: Is it a Matter of Insulation Coating,Venous Approach,or Both?

Lead insulation material and implant route have a major impact on lead realiability and durability. We compare the incidence of lead insulation failure resulting from both the venous approach and insulation type. Two hundred ninty consecutive leads were followed for a mean period of 57 ± 30 months; leads with < 1 year follow-up were excluded. There were 116 Silicone Rubber insulated leads and 174 with polyurethane (151 Pellethane 80A and 23 Pellethane 55D) insulation; 279 leads were bipolar and 11 unipolar; 274 leads were implanted in the ventricle and 66 in the atrium. The venous route was the subclavian vein for 170 leads (58%) and the cephalic vein for 120 leads (42%). Insulation failure was diagnosed when a single sign of oversensing, undersensing, failure to capture, early pulse battery depletion, and lead impedance < 250 Ω was present. Measurement of lead impedance was performed intraopera-tively at implantation and during lead revision or pulse generator replacement. Lead failure caused by conductor coil fracture was not considered. There were 13 lead insulation failures, all among leads with polyurethane insulation (12 Pellethane 80A and 1 Pellethane 55D). Eleven failures (10%) occurred when the subclavian vein and 2 (3%) when the cephalic vein approach was used. The cumulative survival rate of polyurethane and silicone rubber insulated leads was 88.7% and 100%, respectively (P = 0.02); the cumulative survival rate of polyurethane insulated leads was 83.2% when the subclavian vein and 95.1% when the cephalic vein were used (P = 0.03). The mean time to polyurethane lead failure when the subclavian vein approach was used was 54 ± 17 months and when the cephalic route was 73 ± 4 months (P < 0.02). By multivariate analysis, the route of entry was found to be a significant variable related to polyurethane insulated lead failure (P < 0.05). At lead revision failure to capture was present in 7, over-sensing in 4, and undersensing in 2 instances; impedance was < 250 Ω in all cases. Pellethane 80A insulated leads are prone to insulation failure, but more when the subclavian vein is used, rather than the cephalic vein.     

Steroid Eluting High Impedance Pacing Leads Decrease Short and Long-Term Current Drain: Results from a Multicenter Clinical Trial.

Pacemaker lead technology has changed considerably over the past decades. The widespread use of low polarization highly porous electrodes and steroid elution electrodes has resulted in low chronic pacing thresholds, as well as a decrease in the incidence of exit block. Efforts to develop pacing leads with high impedance might theoretically lead to lower lead current drain, which is a component of battery capacity. Pulse generator longevity can be increased without sacrificing pacemaker capabilities if pacing current drain can be decreased. Decreasing the size of the stimulation electrode results in increased pacing impedance, and if pacing thresholds are unchanged, a decreased current drain is predicted by Ohm's law (I = V/R). There is limited data available on the pacing characteristics of large numbers of patients with high impedance leads, despite their recent general availability and increasing widespread use. This multicenter, controlled trial examined the differences in performance between standard steroid-eluting pacing leads in the atrium (Medtronic model 5524) and ventricle (Medtronic model 5024), and new high impedance steroid-eluting pacing leads in the atrium (Medtronic model 5534) and ventricle (Medtronic model 5034). Measurements of bipolar pacing thresholds at 2.5 V, pacing impedance, and sensing thresholds were determined within 24 hours of pacemaker implantation, and at 0.5, 1, 3, 6 and 12 months after pacemaker implantation in 609 patients. Pacing and sensing thresholds were similar for the control and high impedance leads at all times except for a slightly larger R wave with the high impedance leads at implantation and 12 months. The mean impedance of the high impedance pacing leads in the atrium and ventricle at 12 months was 992 ± 175 and 1,080 ± 220 Ω, compared to 522 ± 69 and 600 ± 89 Ω for the standard pacing leads in the atrium and ventricle (P ≤ 0.001 for the high impedance leads compared to standard leads in each chamber). The mean atrial lead current (measured at 2.5 V) at 12 months was 2.6 ± 0.5 mA with the high impedance lead, and 4.9 ± 0.7 mA with the standard lead in the atrium (P ≤ 0.001). In the ventricle, the mean lead current at 12 months was 2.4 ± 0.4 mA with the high impedance pacing lead and 4.3 ± 0.6 mA with the standard lead (P ≤ 0.001). High impedance leads are associated with lower lead current drain than standard pacing leads in the atrium and ventricle for up to 1 year. No clinically important differences in sensing characteristics was noted with the high impedance leads in the atrium or ventricle compared to standard pacing leads. High impedance leads may result in increased pulse generator longevity.     

Telemetry Guided Pacemaker Programming: Impact of Output Amplitude and the Use of Low Threshold Leads on Projected Pacemaker Longevity

In a prospective study, a low threshold screw-in electrode (Medtronic 5078, group I. n = 9) was compared to a conventional active fixation lead (Biotronik Y60BP, group II. n = 9) to investigate whether lower pacing thresholds really translate into longer projected service life of the pacemaker. The leads were implanted in the atrium and were connected to a dual chamber pacing system which included the same ventricular lead (Medtronic 5024) and the same pulse generator model (Intermedics 294–03) in both groups. Eighteen months after implantation, atrial and ventricular pacing thresholds were measured as the charge delivered per pulse [μC] at 0.5, 1.0. 1.5, 2.0, and 3.5 V, respectively. For chronic output programming in both channels, patients capturing at 0.5 V were set to 1.0 V, those capturing at 1.5 V were permanently programmed to 2.0 V with the double of the charge threshold as the safety margin for pacing (“safety charge”). A combination of atrial and ventricular output settings was optimal, if it resulted in minimum battery current drain [μA] as measured by pacemaker telemetry. In both groups, current consumption [μA] decreased significantly as output amplitude was decreased, exhibiting its lowest value at 1.0 V in either channel. All ventricular leads could be programmed to the optimum output amplitude of 1.0 V in groups 1 and 2. As the 2:1 “safety charge” values were almost identical, the ventricular channel essentially contributes the same amount to the battery drain of the pacing system in both groups. In the atrium, all patients of group 1 could be programmed to the optimum output amplitude of 1.0 V with an average pulse duration of 0.42 ± 0.15 ms. In group 2, however, all patients had to be programmed to 2.0 V with a mean pulse width of 0.52 ± 0.15 ms. With the atrial and ventricular output being optimized, the average battery drain of the whole pacing system was 12.19 ± 0.63 μA in group 1 versus 14.42 ± 0.32 μA in group 2 (P < 0.001). As patients were chronically programmed to these output settings, this difference translates into a clinically relevant gain in projected pacemaker longevity of 17 months or 18.3 % (121 ± 4 vs. 104 ± 2 months; P < 0.001). Thus, programming a 2:1 safety margin in terms of charge and optimizing the output parameters by real-time telemetry of the battery current is a useful approach to reduce battery current drain. Making the most of modern lead technology with a different performance in only one channel of an otherwise identical DDD pacing system translates into a significant prolongation of projected pacemaker service life which is of great importance with the increasing awareness of health care expenditures. The gain in projected longevity is mainly due to the option of reducing the output amplitude which is still significantly beneficial well below the nominal voltage of the power source.     

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.     

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.     

Interpretation of electrocardiograms produced by a new unipolar multiprogrammable "committed" AV sequential demand (DVI) pulse generator

This paper describes our approach to the interpretation of electrocardiograms produced by a new unipolar multiprogrammable "committed" DVI pulse generator (Intermedics) during normal function. The arrhythmias engendered by this new DVI pacemaker may be better understood by conceptualizing the recycling mechanism in terms of a simple atrial pulse generator with two important qualification: 1) the ventricular stimulus obligatorily follows the atrial stimulus after 155 ms (AV sequential interval); 2) the pulse generator senses ventricular events (via the ventricular electrode) but recycles according to its atrial timing cycle (AA interval). These characteristics lead in turn to two important consequences: a) the QA interval (from the onset of a sensed QRS complex to the succeeding atrial stimulus) must be longer than the VA interval (from a ventricular stimulus to the succeeding atrial stimulus) by a period equal to or slightly greater than the AV sequential time. This may be considered to represent a form of hysteresis. b) the pacemaker refractory period always starts at the onset of an atrial cycle (AA interval( and therefore occurs after the delivery of an atrial stimulus or after a sensed ventricular event. The above characteristics may cause pacemaker stimuli to fall within the P wave, PR interval, QRS, ST segment and the ascending limb of the T wave during normal function of the pulse generator. Superficially, these peculiarities resemble malfunction and may be quite befuddling but they all occur predictably according to the electronic design of the pulse generator.     

Automatic pace-sense polarity switch as an indicator of early lead corrosion: the usefulness of impedance trend graphing

A rate responsive dual chamber pacemaker system (Medtronic Inc.) was implanted without complications. At 6-week postimplantation a routine pacemaker check showed a spontaneous switch from programmed bipolar pace-sense to unipolar pace-sense on the atrial and ventricular leads. Pacing and sensing thresholds were not significantly changed from implantation. The atrial and ventricular lead impedances increased from 680 and 720 ohms at implantation to 1,290 and 2,400 ohms, respectively. The device was reprogrammed to bipolar pace-sense and the continuous lead telemetry trend option was programmed On. Evaluation of the system 1 month later revealed a decrease in atrial and ventricular lead impedances, 680 and 2,100 ohms, without a change in pace-sense polarity. One month later, the lead polarity had again switched from programmed bipolar to unipolar pace-sense. The lead trend data revealed stable atrial impedances with sporadic increases in the ventricular lead impedance to values > 3,000 ohms. The pacemaker lead system was invasively investigated and visible gross corrosion of the ventricular lead distal connector pin was discovered.     

快速心室起搏犬心房颤动模型研究

目的建立快速起搏心室致心力衰竭犬房颤模型,研究其电生理及心房结构和功能改变。方法 15只健康杂种犬分两组:对照组6只,实验组9只[240次/min心室起搏(25±3)d]。超声心动图测定起搏前后心房面积、面积缩小分数及左心室功能,利用心内电极测定心房有效不应期、传导速度及房颤诱发情况。结果实验组7只犬完成了实验。快速心室起搏(25±3)d后,犬的收缩末期和舒张末期左、右心房面积显著增大(与起搏前比较,P<0.01),左、右心房面积缩小分数显著减小(左心房:(35.7±1.9)%和(20.7±2.7)%,P<0.01;右心房:(35.0±2.3)%和(18.0±2.3)%,P<0.01),左室射血分数从(65.3±2.1)%降至(31.6±2.8)%(P<0.01)。实验组犬左、右心房有效不应期显著延长,心房内传导速率较对照组减慢。实验组有5只犬诱发出超过30 min的房颤,平均房颤持续时间较对照组显著延长(687±290)s和(13±9)s,P<0.01)。实验组平均房颤持续时间与左、右心房面积及面积缩小分数相关(P<0.05)。结论 快速心室起搏致心衰模型能稳定地诱发出房颤,房颤持续时间与心衰引起的显著心房结构和功能异常相关。     

Predictors of all-cause 1-year mortality in implantable cardioverter defibrillator patients with chronic Chagas' cardiomyopathy

Background: Implantable cardioverter defibrillators (ICDs) have been used in the treatment of either sustained ventricular tachycardia or ventricular fibrillation in patients with Chagas’ cardiomyopathy. This study aimed at determining mortality rate and risk factors of all‐cause 1‐year mortality in primary and secondary ICD patients with Chagas’ cardiomyopathy. Methods: One hundred and forty‐eight Chagas’ patients with ICDs were included from the Medtronic ICD Registry Latin America. All patients were followed for 1 year. Results: At implant, mean age was 60.1 ± 9.4 years and 72.9% were male. Mean left ventricular ejection fraction (LVEF) was 40.1 ± 11%. Mean follow‐up was 12 ± 7 months. During the follow‐up, 15 patients died (10.2%). Patients who died were older (64 ±10.8 years vs 59 ± 9.1; P = 0.04), had more atrial fibrillation (13.3% vs 3.8%; P = 0.02), had lower LVEF (33.4%± 9.8 vs 40.9%± 11.3; P = 0.01), and worse functional class (III/IV 40% vs 21.8%; P = 0.03). The multivariate analysis showed that two independent predictors of all‐cause 1‐year mortality remained statistically significant: age more than 65 (hazard ratio [HR] = 2.85, 95% confidence interval [CI] 1.77–3.92; P = 0.03) and LVEF less than 30% (HR = 2.68, 95% CI 1.57–3.79; P = 0.04). Conclusion: This analysis showed that patients older than 65 years of age and with LVEF less than 30% were independent predictors of all‐cause 1‐year mortality in patients with chronic Chagas’ cardiomyopathy. (PACE 2011; 34:1063–1069)     

Long-term outcome of leads and patients following robotic epicardial left ventricular lead placement for cardiac resynchronization therapy

Introduction: In cardiac resynchronization therapy (CRT), positive clinical response and reverse remodeling have been reported using robotically assisted left ventricular (LV) epicardial lead placement. However, the long‐term performance of epicardial leads and long‐term outcome of patients who undergo CRT via robotic assistance are unknown. In addition, since the LV lead placement is more invasive than a transvenous procedure, it is important to identify patients at higher risk of complications. Methods: We evaluated 78 consecutive patients (70 ± 11 years, 50 male) who underwent robotic epicardial LV lead placement. The short‐ (<12 months) and long‐term (≥12 months) lead performance was determined through device interrogations. Mortality data were determined by contact with the patient's family and referring physicians and confirmed using the Social Security Death Index. Results: All patients had successful lead placement and were discharged in stable condition. When compared to the time of implantation, there was a significant increase in pacing threshold (1.0 ± 0.5 vs 2.14 ± 1.2; P < 0.001) and decrease in lead impedance (1010 ± 240 Ω vs 491 ± 209 Ω; P < 0.001) at short‐term follow‐up. The pacing threshold (2.3 ± 1.2 vs 2.14 ± 1.2; P = 0.30) and lead impedance (451 ± 157 Ω vs 491 ± 209 Ω; P = 0.10) remained stable during long‐term follow‐up when compared to short‐term values. At a follow‐up of 44 ± 21 months, there were 20 deaths (26%). These patients were older (77 ± 7 vs 67 ± 11 years; P = 0.001) and had a lower ejection fraction (EF) (13 ± 7% vs 18 ± 9%; P = 0.02) than surviving patients. Conclusion: Robotically implanted epicardial LV leads for CRT perform well over short‐ and long‐term follow‐up. Older patients with a very low EF are at higher risk of death. The risks and benefits of this procedure should be carefully considered in these patients. (PACE 2011; 34:235–240)     

Delayed Cardiac Perforation by Defibrillator Lead Placed in the Right Ventricular Outflow Tract Resulting in Massive Pericardial Effusion

A 76‐year‐old man received a dual‐chamber implantable cardioverter defibrillator (ICD), with the defibrillator lead positioned within the right ventricular outflow tract. The lead parameters at the time of implantation were satisfactory and the postprocedure chest X‐ray showed the leads were in place. The patient was cardioverted from atrial fibrillation during defibrillation threshold testing and commenced on anticoagulation immediately. One month post implantation, he experienced multiple ventricular tachycardia episodes all successfully treated with antitachycardia pacing and shocks by his ICD, but he fell and hit his chest against a hard surface during one of these attacks. He developed a massive pericardial effusion and computed tomography confirmed cardiac perforation by the defibrillator lead. Pericardiocentesis was performed and the defibrillator lead replaced with a different model positioned at the right ventricular apex. The patient made an uneventful recovery. The management and avoidance of delayed cardiac perforation by transvenous leads were discussed.     

Factors Influencing Pacemaker Generator Longevity: Results from the Complete Automatic Pacing Threshold Utilization Recorded in the CAPTURE Trial

Objectives: The CAPTURE study evaluated the accuracy of automated atrial and right ventricular (RV) threshold algorithms. Background: Modern pacemakers include many added features designed to improve the ease of patient follow‐up, as well as algorithms to reduce pacing outputs and/or reduce the atrial or ventricular pacing percentages, thus improving longevity. Methods: Automated atrial and RV threshold measurements were assessed versus manual measurements at 6 months. The projected longevity was assessed and compared between subjects with the threshold‐tracking feature On versus Off. In addition, the projected longevity effect of device features to reduce atrial pacing and reduce ventricular pacing, and device characteristics such as battery size and high impedance leads (≥1,000 ohms), was investigated. Results: Atrial and RV manual versus automatic measurements were equivalent in 683 of 691 subjects (98.8%) and 736 of 746 subjects (98.7%), respectively. Thresholds were stable with 99.6% of atrial and 99.2% of RV consecutive measurements within ±0.25V. Algorithms for threshold tracking, reducing ventricular pacing, and reducing atrial pacing were associated with 0.8, 0.9, and 0.2 years projected longevity improvements. High impedance leads were associated with a 0.8‐year projected longevity improvement. Approximately 2 years of longevity improvement was projected for a 1‐cc increase in device size. Conclusions: The atrial and RV algorithms were accurate and reliable in all leads tested. Threshold tracking, reduced ventricular pacing, and high impedance leads result in increased device longevity. Battery capacity was the strongest determinant of increased projected longevity. (PACE 2010; 33:1020–1030)     

Should Unipolar Leads Be Implanted in the Atrium? A Holter Electrocardiographic Comparison of Threshold Adapted Unipolar and High Sensitive Bipolar Sensing

The accuracy ofatrial sensing plays a central role in dual chamber pacing. Recent Holter electrocardiographic studies showed a high incidence of atrial malsensing. We investigated the efficacy of bipolar atrial sensing at high sensitivity compared to threshold adapted unipolar sensing. One h undred consecutive patients with identical dual chamber pacemakers and bipolar atrial leads were investigated. Mean and individual range of 40 unipolar and bipolar telemetered atrial potentials were calculated; sensing threshold was determined by a semiautomatic sensing test. Oversensing was investigated with the help of a muscle provocation test. Twenty-four-hour Holter monitoring was performed at the highest bipolar sensitivity as well as at a unipolar sensitivity of half the measured sensing threshold. Mean atrial potential was significantly lower during bipolar mode compared to the unipolar sensing configuration, 3.66 ± 1.75 versus 3.85 ± 1.62 mV, P = 0.02. The bipolar atrial potentials showed a higher individual range than the unipolar signals, 2.44 ± 2.62 versus 1.79 ± 0.92 mV, P < 0.01. Sensing threshold did not differ significantly, 2.76 ± 1.33 versus 2.67 ± 1.29 mV. Mean oversensing threshold was 1.21 mV at unipolar configuration, whereas oversensing could not be provoked at a bipolar sensitivity of 0.5 mV. The incidence of atrial undersensing was significantly higher at threshold adapted unipolar sensing compared to bipolar sensing at highest atrial sensitivity, 35% versus 22%, P = 0.04. Oversensing did not occur at bipolar sensing, but was observed in 56% of patients at unipolar mode. Thirty-two percent of patients showed both atrial undersensing and over- sensing at the unipolar sensing configuration. The muscle provocation test reached a sensitivity of 89% and a specificity of 95% in prediction of atrial oversensing during daily life. In conclusion, unipolar atrial potentials are more stable than bipolar ones. On the other hand, bipolar atrial sensing is less prone to the perception of myopotentials. Programming a high bipolar sensitivity significantly improves atrial sensing. Th us, bipolar leads should generally be implanted in the atrium.     

Time Course of Transvenous Pacemaker Stimulation Impedance, Capture Threshold, and Electrogram Amplitude

To examine the time course of atrial and ventricular stimulation impedance, capture threshold, and electrogram amplitude, we obtained noninvasive telemetric data in 63 patients who underwent implantation of unipolar, endocardial pacing leads and a second-generation dual chamber pacemaker with expanded bidirectional telemetry, including stimulation impedance, endocardial electrograms, and automatic capture threshold determination. On follow-up of 9-20 months (mean, 15 months), all but six patients continued to pace in the DDD mode. To validate measurements made with telemetry, invasive measurements made directly with a pacing system analyzer at time of implant were compared with immediate postimplant telemetric measurements. Significant correlation of acute stimulation impedance was noted in both atrial (r = .7, p less than .001) and ventricular (r = .8, p less than .001) lead systems. The atrial stimulation impedance decreased from 538 ohms at implant to 471 ohms at 13 months (p less than .01); the ventricular stimulation impedance similarly declined from 545 ohms to 485 ohms at 13 months (p less than .01). Capture thresholds peaked at one month, then declined: atrial, 1.2 V at implant vs 2.2 V at 1 month (p less than .008) and 1.4 V at 13 months; ventricular, 1.1 V at implant vs 1.9 V at 1 month (p less than .001) and 1.3 V at 13 months. There were no significant changes noted in atrial or ventricular electrogram amplitude following implantation. We conclude that there is close correlation of invasive recordings with those made telemetrically with this pacemaker at time of implant.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of Polarity Reversal on de-fibrillation Success with Biphasic Shocks and a Transvenous/Subcutaneous Defibrillator System in a Porcine Animal Model

Clinical studies show that polarity reversal affects de-fibrillation success in transvenous monophasic defibrillators. Current devices use biphasic shocks for de-fibrillation. We investigated in a porcine animal model whether polarity reversal influences de-fibrillation success with biphasic shocks. In nine anesthetized, ventilated pigs, the de-fibrillation efficacy of biphasic shocks (14.3 ms and 10.8 ms pulse duration) with “initial polarity” (IP, distal electrode = cathode) and “reversed polarity” (RP, distal electrode = anode) delivered via a transvenous/subcutaneous lead system was compared. Voltage and current of each defibrillating pulse were recorded on an oscilloscope and impedance calculated as voltage divided by current. Cumulative de-fibrillation success was significantly higher for RP than for IP for both pulse durations (55% vs 44%, P = 0.019) for 14.3 ms (57% vs 45%, P < 0.05) and insignificantly higher for 10.8 ms (52% vs 42%, P = n.s.). Impedance was significantly lower with RP at the trailing edge of pulse 1 (IP: 44 ± 8.4 vs RP: 37 ± 9.3 with 14.3 ms, P < 0.001 and IP: 44 ± 6.2 vs RP: 41 ± 7.6 Ω with 10.8 ms, P < 0.001) and the leading edge of pulse 2 (IP: 37 ± 5 vs RP: 35 ± 4.2 Ω with 14.3 ms, P = 0.05 and IP: 37.5 ± 3.7 vs RP: 36 ± 5 Ω with 10.8 ms, P = 0.02). In conclusion, in this animal model, internal de-fibrillation using the distal coil as anode results in higher de-fibrillation efficacy than using the distal coil as cathode. Calculated impedances show different courses throughout the shock pulses suggesting differences in current flow during the shock.