Transcutaneous cardiac pacing

Transvenous cardiac pacing is currently the pacing procedure of choice in patients with severe, life-threatening bradyarrhythmias that do not respond to pharmacotherapy. However, pacing catheters can be difficult to insert and frequently fail to capture in severely hypotensive patients. Therefore, there has been a recent resurgence of interest in external pacing methods. Newer transcutaneous cardiac pacing units are easy to apply and especially suited for unconscious patients with severe, life-threatening bradyarrhythmias. There is no operator danger and, if need be, cardiopulmonary resuscitation can continue while the electrodes are in place and the unit is operating. Human and animal studies to date have shown that there are no significant short-term clinical hazards or pathologic abnormalities when using this technique.     

Physiologic pacing: new modalities and pacing sites

Right ventricular (RV) apical pacing impairs left ventricular function by inducing dys-synchronous contraction and relaxation. Chronic RV apical pacing is associated with an increased risk of atrial fibrillation, morbidity, and even mortality. These observations have raised questions regarding the appropriate pacing mode and site, leading to the introduction of algorithms and new pacing modes to reduce the ventricular pacing burden in dual chamber devices, and a shift of the pacing site away from the RV apex. However, further investigations are required to assess the long-term results of pacing from alternative sites in the right ventricle, because long-term results so far are equivocal. The potential benefit of prophylactic biventricular, mono-chamber left ventricular, and bifocal RV pacing should be explored in selected patients with a narrow QRS complex, especially those with impaired left ventricular function. His bundle pacing is a promising and evolving technique that requires improvements in lead technology.     

Pathological aspects of transcutaneous cardiac pacing

Although electrical energy has the potential to produce myocardial injury, the risk of tissue damage from transcutaneous cardiac pacing is largely unknown. This study reports the anatomical findings of a canine transcutaneous stimulation study. Ten dogs had 100-mA, 20-msec (pulse duration), transcutaneous impulses delivered across the thorax for 30 minutes at a rate of 80 stimuli per minute. Seventy-two hours later the animals were sacrificed, and the heart, lungs, and tissues of the chest wall were examined for pathological changes. Gross and microscopic lesions consistent with electrically induced myocardial damage were found in all hearts examined. These lesions included myocardial pallor and focal myofibril coagulation necrosis in the right ventricular outflow tract and perivascular microinfarcts in the posterior left ventricular myocardium. These lesions were not extensive; less than 5% of the right ventricular free wall and less than 1% of the left ventricular posterior wall were involved. Lesions of this extent would not be expected to cause clinically detectable changes in cardiovascular status. Short-term use of transcutaneous pacing appears to be safe. Determination of the potential for clinically significant injury with long-term use requires further study.     

Redundant pacing in a child

A 4-year-old boy with congenital complete atrioventricular block (CCAVB) and pacemaker (PM) dependency, received a redundant pacemaker. Two separate leads were implanted in the right ventricle, and connected to a dual chamber PM. The two pacing channels were both programmed so that each lead could compensate for the other in case of threshold elevation. The follow-up was uneventful despite exit block on one of the leads.     

Adaptive pacing during ventricular fibrillation

While it has been shown that pacing during ventricular fibrillation (VF) can capture a portion of the epicardium, little is known about the characteristics of the area captured or about whether adaptively changing the pacing rate during VF will increase the area captured. In six open-chested pigs, pacing during VF was performed from the center of a plaque containing 504 electrodes 2 mm apart in a21 x 24 array on the anterior right ventricle. Simultaneous recordings from the 504 electrodes were used to construct activation maps from which the area of epicardium captured by pacing was determined. Four pacing algorithms were examined: (1) fixed rate pacing at 95% of the median VF activation rate, (2 and 3) adaptive pacing in which the pacing timing and/or rate is reset in real time if capture is not obtained, and (4) pacing at a slowly increasing rate after initial capture. Regional capture, defined as control of the myocardium under at least 10 plaque electrodes, was achieved in 71% (92/129) of pacing episodes. The incidence of capture was not significantly different for pacing algorithms 1-3. The maximum area captured for each pacing episode with algorithms 1-3 was 3.8 +/- 2.0 cm2(mean +/- SD). Within each animal, the pattern of capture was similar among all pacing episodes, no matter which algorithm was use dr = 0.85 +/- 0.25). The region of greatest capture extended away from the pacing site along the long axis of the myocardial fibers. However, the area of captured epicardium toward the right ventricular side of the pacing electrode was 9.7 times greater than toward the left ventricular side. This principal direction toward the right ventricular side of the pacing electrode was the same direction traveled by the majority of VF activation fronts before capture occurred. The absence of recorded activations at the pacing site for 20 consecutive stimuli predicted 83% of the time that regional capture was present. With algorithm 4, the pacing rate could be increased 7.1%+/- 4.3%while maintaining capture; however, the area of capture progressively decreased as the pacing rate increased. While pacing from the anterior right ventricular epicardium during VF, the area of capture is repeatable and is markedly asymmetrical with almost 10 times as much epicardium captured on the side of the pacing electrode closest to the acute margin of the right ventricle as on the opposite side. This marked asymmetry is associated both with myofiber orientation and with the direction of spread of activation and hence the direction of dispersion of refractoriness during VF just before pacing is initiated. It is possible to perform adaptive pacing algorithms in real time during VF; however, the two adaptive algorithms tested did not capture significantly more epicardium than a simple fixed-rate pacing algorithm. Although it is possible to maintain capture while increasing the pacing rate during VF, the area of capture decreases.     

右心室起搏比例和不同部位起搏对老年患者心功能的影响

目的：探讨右心室起搏比例和不同部位起搏对老年患者心功能的影响。方法回顾性分析92例植入体内埋藏式双腔心脏起搏器（DDD）的老年患者的临床资料,根据术后1年起搏器程控仪获取的右心室起搏比例,将右心室起搏比例≥50%患者纳入A组,右心室起搏比例＜50%患者纳入B组,比较两组术前和术后1年彩色多普勒心脏超声的变化。同时,将A组分为右室心尖部（RVA）起搏者和右室间隔部（RVS）起搏者进行亚组分析。结果 A组术后1年左房内径（LAD）较术前增大,左室射血分数（LVEF）较术前和B组降低,差异均有统计学意义（t分别=2.43、4.20、6.37,P均＜0.05）;B组术后1年LAD、左室舒张末期内径（LVEDD）、LVEF和术前比较,差异均无统计学意义（t分别=0.73、0.78、1.16,P均＞0.05）。亚组分析结果显示两亚组术前LAD、LVEDD、LVEF比较,差异均无统计学意义（t分别=0.77、0.35、1.32,P均＞0.05）,两组术后LVEDD、LVEF比较,差异均有统计学意义（t分别=2.86、4.62,P均＜0.05）,RVS组术后LAD、LVEDD、LVEF与术前比较,差异均无统计学意义（t分别=1.45、0.14、0.48,P均＞0.05）;而RVA组术后LAD、LVEDD均较术前明显扩大,LVEF较术前明显下降（t分别=2.20、3.13、4.31,P均＜0.05）。结论老年患者中右室间隔部起搏与右室心尖部起搏相比更有利于保持患者心功能的稳定,但同时应尽量减少不必要的右心室起搏。     

Sequential biventricular pacing: evaluation of safety and efficacy

The study evaluated the clinical safety, performance, and efficacy of sequential biventricular pacing in the InSync III (Model 8042) biventricular stimulator in a multicenter, prospective 3-month study and assessed the proper functioning of features aiming at improving biventricular AV therapy delivery. The system was successfully implanted in 189 (95.9%) of 198 patients with symptomatic systolic heart failure and a prolonged QRS complex duration. Patients significantly improved their 6-minute hall walk distance (baseline 339 +/- 92 vs 3-month 422 +/- 127 meter, P < 0.001) and NYHA class (baseline 3.1 +/- 0.5 vs 3-month 1.9 +/- 0.7, P < 0.001). Echocardiographic optimization of sequential biventricular pacing showed an improvement in stroke volume compared to simultaneous stimulation (sequential 68 +/- 24 mL vs simultaneous 56 +/- 23 mL, P < 0.001) at baseline and at 3 months. In 88% (30/34) of the patients these improvements were seen within a small range of V-V delays of +/-20 ms and in 94% (32/34) within V-V delays of +/-40 ms. In contrast, programming beyond this range reduced stroke volume below that during simultaneous biventricular pacing. The device functioned as expected. LV lead dislodgement was observed in 12 patients and phrenic nerve stimulation required lead repositioning in 2 patients. Eight patients died during the study. Patient survival at 3 and 6 months was 97 +/- 2% and 94 +/- 2%, respectively. Cause of death was cardiac (n = 7), heart failure related (n = 3), arrhythmia related (n = 2), and unknown (n = 2). In conclusion, this sequential biventricular pacemaker was safe and efficacious.     

Optimal location for temporary epicardial pacing leads following open heart surgery

Temporary epicardial pacing wires are routinely placed in patients undergoing cardiac surgery. Eighteen suitable patients undergoing elective surgery were prospectively studied. Their sensing and stimulating characteristics were studied at various locations. Subepicardial pacing leads were applied to the lateral wall of the LV, apex of the LV, anterior wall of the RV, diaphragmatic wall of the RV, and diaphragmatic wall of the LV. Impedance, R wave amplitude, slew rate, and stimulation thresholds were measured on postoperative days 1 and 5. Impedance remained unchanged in time with no significant differences between locations. R waves and slew rates were significantly lower in the anterior RV wall. Stimulation thresholds displayed no differences on day 1, but they increased significantly in all locations on day 5. These thresholds were significantly lower in the lateral and diaphragmatic LV walls on day 5, and the rate of voltage increase was also lower in these two locations. Five patients presented phrenic nerve stimulation when stimulating the lateral LV wall. The authors advocate the diaphragmatic wall of the LV as the best location for placing temporary leads. The anterior wall of the RV is not recommended for pacing purposes.     

Hemodynamic and symptomatic consequences of ventricular pacing

After implantation of a ventricular demand pacemaker (VVI), occasional patients continue to have dizziness, syncope, or near syncope ("pacemaker syndrome"). To identify patients in whom VVI pacing may have deleterious effects, we compared cuff blood pressure responses to VVI pacing with blood pressure responses to atrioventricular sequential pacing (DVI) or sinus rhythm in 50 consecutive patients. Patients with intact ventriculoatrial conduction had a much greater decrease in systolic blood pressure with VVI pacing (24 +/- 11 mm Hg) than those with ventriculoatrial dissociation (-4 +/- 15 mm Hg) (P less than 0.005). Patients who were in heart failure had a lesser decrease in blood pressure with VVI pacing than did those without failure (P less than 0.05); 13 of the 14 heart failure patients lacked ventriculoatrial conduction. Ten patients had symptomatic dizziness after VVI pacing; the incidence of symptoms was higher in patients with ventriculoatrial conduction (9 of 23) than in those without ventriculoatrial conduction (1 of 27) (P less than 0.003). We conclude that the presence of intact ventriculoatrial conduction appears to be a crucial determinant of the hemodynamic response to VVI pacing, and its presence may identify patients who are at risk for "pacemaker syndrome."     

Triple-site ventricular pacing in a biventricular pacing system

This case report describes a patient with heart failure in whom a biventricular pacing system was successfully implanted. During control of the pacing system, three morphologies of the paced QRS complex could be elucidated. Right ventricular stimulation, biventricular stimulation, and biventricular pacing with additional stimulation from the anodal electrode of the right ventricular lead determined the morphologies.     

Ventricular pacing threshold variations in the young

Ventricular Capture Management (VCM) is a Medtronic Kappa pacemakers (PM) feature that automatically measures pacing threshold through detection of the evoked response after a pacing stimulus. The aim of this study was to evaluate the range of variation of ventricular pacing threshold in pediatric patients with endocardial and epicardial pacing leads. Thirty-one patients (median age 6.5 years) were implanted with a Kappa 901 PM for atrioventricular block or sinus node dysfunction. Congenital heart defects (CHD) were present in 58% of patients. Ventricular leads were epicardial in 52% of patients. VCM was programmed to automatically measure threshold every 2 hours. In a median follow-up of 12 months, 27,110 threshold measurements, 72% of which were successful, have been taken in 94% of patients. Measurement success was 99% in the endocardial leads group (age at implantation 12 +/- 6 years) and 31% in epicardial leads (age 4 +/- 5 years) (P < 0.05). Main reasons for unsuccessful measurements were high heart rate and, in a patient with an endocardial lead, competition with intrinsic rhythm. Undersensing or oversensing of the evoked responses was not detected. In all successful VCM measurements, epicardial pacing and CHD contributed to stability of thresholds (multivariate analysis). Pacing threshold showed specific circadian patterns: higher thresholds were found between 00.00 and 06.00 a.m., but the variation was low, 0.03 +/- 0.01 V. In conclusion, children and young patients show stable ventricular thresholds, especially in presence of CHD, and epicardial leads are at least as stable as endocardial leads. Ventricular pacing threshold showed a circadian variability similar to that described in adults, that does not seem to influence VCM functioning and PM programming.     

Cardiac vein angioplasty for biventricular pacing

Biventricular pacing for the treatment of congestive heart failure has consistently demonstrated improvement in quality-of-life and reduction in heart failure symptoms. Though the over-the-wire systems will be helpful in overcoming many existing obstacles to optimal lead placement, anatomic variability will still limit overall success. Cardiac vein angioplasty may be required for deployment of leads into tortuous or obstructed cardiac veins. This case report describes the angioplasty of a focal cardiac vein stenosis allowing for successful implantation of a left ventricular pacing lead. The safety of this procedure is unknown, though the risks may be acceptable in certain patients.     

Effect of a pacing mode preserving spontaneous AV conduction on ventricular pacing burden and atrial arrhythmias

Background: Using dual‐chamber pacemakers with new algorithms: Manage Ventricular Pacing (MVP?), minimizes unnecessary ventricular pacing (VP). This function operates in AAI/R mode with backup VP during AV block. Aim: The aim of “Generation MVP” study was to assess the VP burden and atrial arrhythmias (AA) burden according to indication of pacing and MVP? function programming of AdaptaDR implantable pacemaker (Medtronic Inc., Minneapolis, MN, USA). Methods: The multicenter observational “Generation MVP” study included 220 patients aged 75.9 ± 11 years (men = 52%) implanted for sinus node dysfunction (SND; n = 115) or atrio‐ventricular block (AVB; n = 105). Programming MVP function has been left to the physician's discretion. Percentage of VP and AA burden (percentage of time spent in AA) stored in memories were assessed at 2 and 10 months. Results: 220 patients were followed at 2 months (174 MVP [On], 46 MVP [off]) and at 10 months (165 MVP [On], 55 MVP [off]). Median percentage of VP is significantly lower when MVP is programmed [On] versus [off] at 2 and 10 months follow‐up for SND and AVB indications of pacing (P < 0.001). Finally, programming MVP function is performed at middle term (10 months) for 84% of patients with SND and 65% of patients with AVB: median percentage of VP is as low as 0.6% for patients with SND and 12% for patients with AVB versus 95% for SND and 99% for AVB when MVP function is programmed [off](P < 0.001). Median AA burden was significantly lower when MVP function was programmed [On] versus [off] at 2 months (8.7% vs 28%; P < 0.001) and 10 months (1% vs 22%; P < 0.001). Conclusion: In this study programming MVP function decreases percentage of VP at 2 and 10 months for patients paced for SND or AVB. Moreover median AA burden is reduced when MVP function was programmed [On] vs [off] at two follow‐ups. (PACE 2012; 1–6)     

Adaptive bi-atrial pacing improves the maintenance of sinus rhythm

INTRODUCTION: Multiple pacing modalities have been shown to individually decrease atrial fibrillation (AF) burden and relieve symptoms of AF. This investigation retrospectively evaluated whether a combination of bi-atrial pacing with dynamic atrial overdrive (DAO) AF suppression would further decrease AF burden as compared to AF suppression (DAO) alone. METHODS AND RESULTS: A total of 33 patients were retrospectively evaluated. Patients (n = 16) were identified from the Deborah Heart and Lung Center pacemaker database with DAO programmed on at time of implantation. Patients (n = 17) were identified with bi-atrial pacing leads in right atrium and mid to distal coronary sinus who also had DAO programmed on at the time of implant. Evaluation of interrogated pacing data revealed Percent Time in Mode Switch (18.2%+/- 7.2% vs 0.59%+/- 0.08%) to be significantly lower (P = 0.014) in the bi-atrial paced group. In addition, there were less mode switches per day (MSPD) in the bi-atrial paced group (0.62 +/- 0.43 MSPD) versus control (4.40 +/- 3.24 MSPD) (P = 0.06). CONCLUSION: Bi-atrial pacing while used in conjunction with an adaptive pacing suppression algorithm (DAO) may successfully be used to inhibit PAF.     

The right ventricular outflow tract: the road to septal pacing

BACKGROUND: Pacing from the right ventricular apex is associated with long-term adverse effects on left ventricular function. This has fuelled interest in alternative pacing sites, especially the septal aspect of the right ventricular outflow tract (RVOT). However, it is a common perception that septal RVOT pacing is difficult to achieve. METHODS AND RESULTS: In this article, we will review the anatomy of the RVOT and discuss the importance of standard radiographic views and the 12-lead electrocardiogram in aiding lead placement. We will also describe a method utilizing a novel stylet shape, whereby a conventional active-fixation, stylet-driven lead can be easily and reliably deployed onto the RVOT septum.     

External cardiac pacing for out-of-hospital bradyasystolic arrest

Cardiac pacing has been used successfully in patients with asystole or bradycardia compromising hemodynamics when it was applied soon after the onset of the event. An external cardiac pacemaker was used as part of initial resuscitative efforts for patients in primary, out-of-hospital, cardiac arrest who arrived in the emergency department in asystole, agonal rhythm, pulseless idioventricular rhythm, or bradycardia with hemodynamic compromise. A pulse was successfully generated in only one of twelve patients. That patient developed complete atrioventricular dissociation while in the emergency department. The nonresponding patients were in asystole or pulseless idioventricular rhythm when the pacemaker was applied. Pacing was initiated 1-13 minutes (mean 7 minutes) after arrival in the emergency department, but 27-90 minutes (mean 59 minutes) after arrest. The interval between arrest and application of the pacemaker was prolonged because of long periods for ambulance response, field resuscitation, and transport. It is concluded that the external cardiac pacemaker is a useful instrument for the treatment of bradyarrhythmias. While it may also be useful in the first few minutes after development of asystole, pulseless idioventricular rhythm, or agonal rhythm, it is of no benefit if applied long after the event.     

Microdislodgment of ventricular pacing lead undetectable during rapid pacing one year after implantation

A 71-year-old woman had undergone valvular heart surgery in 1981, and implantation of a permanent ventricular pacemaker for ventricular pauses during atrial fibrillation in 2001. One year after pacemaker implantation, she complained of faintness. When pacing at 100 beats/min the pacemaker functioned properly. However, pacing and sensing failure was detected at a pacing rate of 60 beats/min. At rapid pacing rates, the lead tip was in closer contact with the endocardium, and its microdislodgment was undetectable. The symptoms have resolved since the lead was repositioned.     

Increasing left ventricular pacing output decreases interventricular conduction time in patients with biventricular pacing systems

OBJECTIVE: To evaluate the effect of increasing LV pacing output on interventricular timing in patients with biventricular pacing systems. BACKGROUND: Clinical improvement with biventricular pacing is likely related to reduction in ventricular dysynchrony in patients with cardiomyopathy. We hypothesized that increasing left ventricular pacing output would reduce interventricular conduction time and could affect ventricular synchrony. METHODS: Forty-two sequential patients with biventricular pacing systems that permitted independent LV pacing were selected at the time of routine device interrogation. The interval between LV pacing stimulus and onset of the RV electrogram was measured during LV pacing at capture threshold and at maximum pacing output for each patient. RESULTS: The average time from LV pacing stimulus to right ventricular electrogram onset was 142.5 +/- 32.5 ms (range 90-230 ms) at threshold and 132.3 +/- 30.4 ms (range 90-220 ms) at maximum pacing output, with a mean decrease in conduction time of 10.2 +/- 10.9 ms (range 0-45 ms). There was significantly greater interventricular conduction shortening with increased pacing output in patients with ischemic cardiomyopathy compared to others (14.9 +/- 11.9 ms vs 4.0 +/- 4.6 ms; P < 0.01). CONCLUSIONS: Conduction time from LV to RV shortens as LV pacing output is increased. This effect is seen to a greater degree in patients with ischemic cardiomyopathy, possibly related to the presence of myocardial scar near the pacing electrode. Further investigation is needed to assess the clinical outcomes related to this new method for optimizing resynchronization therapy.     

Unusual pacing observed in a biventricular pacemaker with epicardial pacing leads

In this case report, we describe inappropriate pacing in a patient with a newly implanted biventricular pacing system with three epicardial leads. Very high pacing thresholds resulted from the use of nonsteroid eluting leads, and unusual pacing behavior was due to the chosen implant locations for the right atrial and right ventricular epicardial leads. The interplay between the programmed pacemaker parameters, the very late ventricular sensing in the setting of intrinsic right bundle branch block, and atrial lead oversensing led to ineffective biventricular pacing. The persistently elevated pacing thresholds and sensing problems led to very early battery depletion and the need to replace the epicardial system with three new endocardial leads.