Paced Duration Research Articles

Effects of prolonged endocardial stimulation on left ventricular mechanical synchrony. A pilot study applying gated-SPECT phase analysis. Endocardial stimulation and dyssynchrony

To evaluate left ventricular mechanical dyssynchrony (LVMD) associated with prolonged right ventricular pacing through an innovative imaging technique as a pilot study in Uruguay. A 99mTc-MIBI gated-SPECT and phase analysis was performed in 12 patients with pace-makers implanted at least one year before scintigraphy, due to advanced atrioventricular block. Clinical data, QRS duration, rate, mode and site of pacing in right ventricle, chamber diameters, presence and extension of myocardial scar and ischaemia, as well as LVEF at rest, were recorded. Using V-Sync of Emory Cardiac Toolbox, a standard deviation (PSD) and bandwidth (PBW) from rest phase histogram was obtained and these indexes were compared with controls in the subgroups of patients with LVEF≥50% and <50%. Patients with prolonged RV endocardial pacing exhibited marked LVMD. More severe dyssynchrony was found in patients with impaired LVEF than in patients with preserved LVEF (PSD: 46.67o vs. 26.81o, P<.05; PBW: 144.33o vs. 77.41o, P<.05). Higher left ventricle diameters, extensive infarct, or significant ischaemia were found in patients with impaired LVEF. Chronic right ventricular pacing was invariably associated with LVMD, even when systolic function was preserved. Phase analysis could be a potentially useful technique to evaluate LMVD associated with myocardial scar in patients with pacemakers, and to decide promptly the upgrading to biventricular pacing.

Effects of Ambient Environmental Factors on the Stereotypic Behaviors of Giant Pandas (Ailuropoda melanoleuca).

Stereotypies are commonly observed in zoo animals, and it is necessary to better understand whether ambient environmental factors contribute to stereotypy and how to affect animal welfare in zoo settings. This study investigated the relationships between stereotypic behaviors and environmental factors including ambient temperatures, humidity, light intensity, sound intensity and number of visitors. Seven giant pandas were observed in three indoor enclosures and three outdoor enclosures. Environmental factors were measured for both indoor and outdoor enclosures and the effect they had on stereotypical behaviors was investigated. Our research found that light intensity significantly correlated with all stereotypies behaviors. Higher environmental temperature reduced the duration of pacing but increased the frequency of pacing, the duration and frequency of door-directed, meanwhile the duration of head-toss. However, we found no noticeable effect of humidity on stereotypic behaviors except for the frequency of head-toss. We also found that sound intensity was not correlated with stereotypies. Finally, the growth of visitors was negatively associated with the duration of door-directed. These results demonstrated that various environmental factors can have significant effects on stereotypic behaviors causing the expression of various stereotypies. Thus, stereotypies in zoo animals may not simply represent suboptimal welfare, but rather might be adopted as a means of coping with an aversive environment.

Key Role of Pacing Site as Determinant Factor of Exercise Testing Performance in Pediatric Patients with Chronic Ventricular Pacing.

Chronic right ventricular (RV) apical pacing has been associated with deterioration of functional capacity and chronotropic incompetence during exercise testing in children. The effects of alternative pacing site on exercise performance in pediatric population remain unknown. We evaluated the influence of ventricular pacing site on exercise capacity in pediatric patients with complete congenital atrioventricular block requiring permanent pacemaker therapy. Sixty-four children paced from RV apex (n=26), RV midseptum (n=15) and left ventricular (LV) apex (n=23) were studied cross-sectionally. Treadmill exercise stress testing was performed according to modified Bruce protocol. LV apical pacing was associated with greater exercise capacity. In comparison with the other study groups, children with RV apical pacing showed significantly lower VO2peak (37±4.11; p=0.003), O2 pulse (8.78±1.15; p=0.006), metabolic equivalents (7±0.15; p=0.001) and exercise time (6±3.28; p=0.03). Worse values in terms of maximum heart rate (139±8.83bpm; p=0.008) and chronotropic index (0.6±0.08; p=0.002) were detected in the RV apical pacing group although maximal effort (respiratory exchange ratio) did not differ among groups (p=0.216). Pacing from RV apex (odds ratio 9.4; confidence interval 2.5-18.32; Wald 4.91; p=0.0036) and low peak heart rate achieved (odds ratio 3.66; confidence interval 0.19-7.4; Wald 4.083; p=0.015) predicted significantly decrease in exercise capacity. Duration of pacing, gender, VVIR mode, baseline heart rate and QRS duration had not significant impact on exercise capacity. The site of ventricular pacing has the major impact on exercise capacity in children requiring permanent pacing. Among the sites assessed, LV apex is related to the better exercise performance.

0386 : Direct thrombin inhibitors prevent atrial myocardial hypertrophy and atrial fibrillation susceptibility associated with heart failure in the rat

Atrial fibrillation (AF) is the most frequent cardiac arrhythmia, which is characterized by a high risk of stroke due to increased thrombogenesis and thrombin formation in poorly contractile atria. In addition to its role in the coagulation cascade, thrombin has pleiotropic effects on cardiovascular system through the activation of protease activated receptor 1 (PAR 1). Here we examined whether thrombin contributes to the atrial myocardial remodeling that occurs during heart failure (HF) and whether direct thrombin inhibitors can prevent this remodeling process and AF progression. The study was conducted in a well established rat model of atrial dilation and susceptibility to AF associated with ischemic HF secondary to myocardial infarction (MI). The endogenous thrombin potential increased in plasma after MI, and remained elevated in HF rats. Treating MI rats for one or two months with direct thrombin inhibitors reduced the area and diameter of left atria. After two months, there was also a reduction of the duration of burst pacing induced AF and a downregulation of the expression of hypertrophic markers such as brain natriuretic peptide and β myosin heavy chain. The transcription factor NFATc3, known to be activated in cardiac hypertrophy, and the plasminogen activator inhibitor 1, which has both thrombotic and fibrogenic activities were also downregulated. Treating rats with a PAR 1 antagonist reproduced the effect of thrombin inhibitors. To study the role of thrombin on atrial myocardium in absence of other cardiac stimuli, atrial explant cultures were performed. In cultured atria, thrombin upregulated hypertrophic markers and plasminogen activator inhibitor 1 through PAR 1 and the Rho/Rho kinase pathway. These results indicate that thrombin is a potent hypertrophic factor for atrial myocardium; they point to chronic inhibition of thrombin/PAR1 pathways as a potential therapeutic option to prevent atrial remodeling and AF substrate formation. The author hereby declares no conflict of interest

Myocardial injury during transfemoral transcatheter aortic valve implantation: an intracoronary Doppler and cardiac magnetic resonance imaging study.

Myocardial injury reflected by a post-procedural increase of serum troponin I (TnI) occurs frequently during transcatheter aortic valve implantation (TAVI). It is potentially caused by intraprocedural hypotension, periprocedural coronary microembolisation and post-procedural (para)valvular leakages (PVLs). We invasively assessed coronary flow dynamics including coronary flow velocity reserve (CFVR), embolic high-intensity transient signals (HITS) as well as rapid pacing induced hypotension and post-procedural PVLs to determine their contribution to post-procedural TnI increases. In 15 transfemoral TAVI patients, TnI was measured serially, and cardiac MRIs with late gadolinium enhancement (LGE) were performed pre- and post-interventionally. There were no significant correlations between coronary flow dynamics, CFVR and the area under the curve (AUC) of TnI over 72 hours. Despite the detection of HITS in all patients and during all procedural steps, there was also no correlation between the amount of HITS and the AUC of TnI. However, there were positive correlations between the duration of rapid pacing as well as the time of subsequent blood pressure recovery and the AUC of TnI. Both LGE and more than mild PVL were observed in a single case only. Myocardial injury after TAVI appears to be related more to hypoperfusion-induced ischaemia than to periprocedural microembolisation.

Evaluation of Long Term Effect of RV Apical Pacing on Global LV Function by Echocardiography.

We very often face pacemaker implanted patients during follow-up with shortness of breath and effort intolerance inspite of normal clinical parameters. The aim of our study is to evaluate the cause of effort intolerance and probable cause of sub-clinical Congestive Cardiac Failure (CCF) in a case of long term Right Ventricular (RV) apical pacing on global Left Ventricular (LV) function non- invasively by echocardiography. We studied 54 patients (Male 42, Female 12) of complete heart block (CHB) with RV apical pacing (40 VVI and 14 DCP). Mean duration of pacing was 58+4 months. All patients underwent 24 hours Holter monitoring to determine the percentage of ventricular pacing beats. 2-D Echocardiography was done to assess the regional wall motion of abnormality and global LV ejection fraction by modified Simpson's rule. These methods were coupled with the Doppler derived Myocardial Performance Index (MPI), tissue Doppler imaging, and mechanical regional dyssynchrony with 3-D Echocardiography. Data were analysed from 54 RV- apical paced patients and compared with age and body surface area of 60 controlled subjects (Male 46, Female 14). Evaluation of LV function in 54 patients demonstrated regional wall motion abnormality and Doppler study revealed both LV systolic and diastolic dysfunction compare with control subjects (regional wall motion abnormality 80±6% vs 30±3% with p-value<0.0001) which is proportional to the percentage of ventricular pacing beats (mean paced beat 78%). Global LVEF 50±4% vs 60±2% (p-valve <0.0001) and MPI 0.46 ±0.12 v/s 0.36±0.09 (p-value <0.0001). RV-apical pacing induces iatrogenic electrical dyssynchrony which leads to remodeling of LV and produces mechanical dyssynchrony which is responsible for LV dysfunction. Alternate site of RV pacing and/or biventricular pacing should be done to maintain biventricular electrical synchrony which will preserve the LV function.

Rapid Ventricular Transvenous Pacing via Pulmonary Artery Catheter: Deliberate Hypotension Technique for Precise Proximal Thoracic Aortic Stent Graft Deployment

Deliberate hypotension facilitates precise deployment of endovascular stent grafting in the thoracic aorta. We describe a practical technique using pulmonary artery catheter (PAC) guided transvenous rapid ventricular pacing via transjugular approach and delineate pertinent anesthetic considerations. Anesthesiologists performed PAC guided rapid ventricular pacing in thirty-nine (39) patients (27 men and 12 women, mean age 74 ± 11 years) undergoing thoracic endograft deployment for aneurysm repair. Patient characteristics, hemodynamic parameters, pacing rate, and number of pacing events were recorded. Post-operative complications were evaluated. PAC guided rapid ventricular pacing successfully provided controlled hypotension without technical complications. Mean pacing rate was 177 ± 17 beats/min with an average of 2.6 ± 2 pacing events/surgical procedure. Average pacing duration was 34 ± 29 seconds (MAP of 47 ± 5 mmHg). One intraoperative death occurred in a patient with severe valvular heart disease. In all other cases, recovery time to baseline hemodynamics was short. Postoperative complications included atrial fibrillation in five patients (12%), elevated troponin levels in eight (21%), and stroke in three (8%). No patients had PAC related complications. Pulmonary artery catheter guided rapid ventricular pacing allows for accurate deployment of thoracic aorta endovascular stent-grafts. Patients with severe valvular or ischemic heart disease are likely poor candidates for this technique.

Preserved prognostic value of preinterventional troponin T levels despite successful TAVI in patients with severe aortic stenosis

Elevated concentrations of troponin T have prognostic impact in patients with various cardiovascular diseases including those with severe aortic stenosis. Transcatheter aortic valve implantation (TAVI) has improved prognosis for patients without a surgical option. Whether this affects the prognostic value of preinterventional troponin T remains unclear. We therefore conducted a prospective study in 198 consecutive patients with subsequent, successful transfemoral TAVI and analyzed cardiac troponin T (cTnT) levels with a new generation, high-sensitive troponin T assay before and after TAVI, as well as their prognostic value after 12 months. Patients with severe aortic stenosis (AS) showed significant elevation of preinterventional cTnT levels. Postinterventional cTnT levels significantly rose further about sevenfold after transfemoral TAVI and peaked at day three until they steadily declined thereafter. Baseline renal function (P = 0.011), the duration of intraprocedural rapid pacing (P = 0.0012), and baseline cTnT (P = 0.0001) values predicted the magnitude of postinterventional cTnT elevations. Interestingly, Kaplan-Meier curve analysis revealed, that although cTnT levels were not predictive for short-term mortality, preinterventional as well as postinterventional peak cTnT showed prognostic value for 1-year mortality, regardless of successful TAVI. Pre- and postinterventional hscTnT levels signal adverse 1-year mortality in patients with severe AS independent of successful aortic valve replacement.

Detection of myocardial metabolic dysfunction caused by the right ventricular apical pacing using thallium 201/iodine 123-labeled beta-methyl iodophenyl pentadecanoic acid SPECT

Purpose: Many clinical trials have reported that right ventricular apical (RVA) pacing increases the risk of heart failure and atrial fibrillation, but the mechanism remains unknown. Using thallium 201 (Tl)/iodine 123-labeled beta-methyl iodophenyl pentadecanoic acid (BMIPP) single photon emission computed tomography (SPECT), we assessed the hypothesis that RVA pacing has a direct undesirable effect on myocardial metabolism. Methods: We reviewed the Tl/BMIPP SPECT studies that were performed more than one month after implantation of permanent pacemaker or implantable cardioverter defibrillator in our hospital. The ventricular pacing lead was located in right ventricular apex. Patients with ischemic heart disease, congenital heart disease and specific cardiomyopathy were excluded. All images were analyzed qualitatively in a blind manner. A positive finding was defined as reduced uptake on the BMIPP image compared with the Tl perfusion image. In quantitative analysis, a polar map was divided into 17 segments. Each segment was graded on a 5-point scale and mismatch score was calculated from the %uptake differences between the Tl and BMIPP. Results: Seventy one patients were included (mean age 65 years). Indications for device implantation were atrioventricular block (AVB) (n=31), sinus node dysfunction (SND) (n=22), both AVB and SND (n=1), ventricular tachyarrhythmia (n=10) and brady atrial fibrillation (n=2). Mean duration of pacing was 3369 days. Myocardial fatty acid metabolic dysfunction defined as a mismatch between Tl uptake and BMIPP uptake were detected in 39 patients mainly in inferior and apical segments. On multivariate analysis, percent ventricular beats that were paced (%VP) was identified as only independent factor for Tl/BMIPP mismatch, however, duration of pacing and pacing threshold were not. Cutoff value of %VP was determined (40%) by ROC analysis. Conclusions: RVA pacing leads to regional myocardial metabolic dysfunction, which may be the main cause of unfavorable clinical outcomes associated with RVA pacing.

GW24-e2163 Expressions of endothelin-converting enzyme in primary cultured atrial myocytes after rapid electrical-field stimulation

ObjectivesTo study the expressions of endothelin-converting enzyme (ECE2) at early stages of atrial fibrillation in a rapid paced primary cultured atrial myocyte model.MethodsPrimary rat atrial myocytes were cultured and a...

Transcutaneous lead implantation connected to an externalized pacemaker in patients with implantable cardiac defibrillator/pacemaker infection and pacemaker dependency

Systemic cardiac implantable electronic device (CIED) infection is a serious complication, especially in patients with pacemaker (PM) dependency. In those patients after infectious device removal temporary pacing is necessary, to obtain adequate haemodynamics. In this study, a new therapy option with temporary pacing by ipsilateral implantation of a new active-fixation right ventricular (RV)-lead was evaluated. Between September 2009 and November 2011, infectious lead removal was performed in 17 patients with systemic CIED infection. Temporary pacing was achieved by simultaneous implantation of a new active-fixation RV-lead, which then was connected extracorporally to the old CIED device. Antibiotic therapy was initiated. When laboratory infection parameters were in normal range and blood culture samples showed negative results, new CIED was implanted on contralateral side and temporary RV-lead was removed. Mean patients' age was 71.3 ± 9.1 years. Mean C-reactive protein values were 79.3 mg/dL, and mean leucocytes counts were 12.6 × 10(3). After lead extraction, temporary pacing was necessary in all patients due to severe bradycardia. Mean duration of temporary pacing was 12.7 (6-24) days. No major procedure-related peri- or post-operative adverse events occurred. Mean time of hospitalization was 20.8 (10-48) days. Mean follow-up time was 21.1 months (12-36), showing survival rate of 100% and freedom from reinfection in all patients. Ipsilateral implantation of a temporary active-fixation RV-lead connected to an externalized PM and pursued antibiotic therapy seems to be a good option for patients with CIED infection and PM dependency, showing no temporary pacing-related complications and no reinfection after mean follow-up time of 21.1 months.

Permanent Cardiac Pacing in Children: Choosing the Optimal Pacing Site

Background— We evaluated the effects of the site of ventricular pacing on left ventricular (LV) synchrony and function in children requiring permanent pacing. Methods and Results— One hundred seventy-eight children (aged &lt;18 years) from 21 centers with atrioventricular block and a structurally normal heart undergoing permanent pacing were studied cross-sectionally. Median age at evaluation was 11.2 (interquartile range, 6.3–15.0) years. Median pacing duration was 5.4 (interquartile range, 3.1–8.8) years. Pacing sites were the free wall of the right ventricular (RV) outflow tract (n=8), lateral RV (n=44), RV apex (n=61), RV septum (n=29), LV apex (n=12), LV midlateral wall (n=17), and LV base (n=7). LV synchrony, pump function, and contraction efficiency were significantly affected by pacing site and were superior in children paced at the LV apex/LV midlateral wall. LV dyssynchrony correlated inversely with LV ejection fraction ( R =0.80, P =0.031). Pacing from the RV outflow tract/lateral RV predicted significantly decreased LV function (LV ejection fraction &lt;45%; odds ratio, 10.72; confidence interval, 2.07–55.60; P =0.005), whereas LV apex/LV midlateral wall pacing was associated with preserved LV function (LV ejection fraction ≥55%; odds ratio, 8.26; confidence interval, 1.46–47.62; P =0.018). Presence of maternal autoantibodies, gender, age at implantation, duration of pacing, DDD mode, and QRS duration had no significant impact on LV ejection fraction. Conclusions— The site of ventricular pacing has a major impact on LV mechanical synchrony, efficiency, and pump function in children who require lifelong pacing. Of the sites studied, LV apex/LV midlateral wall pacing has the greatest potential to prevent pacing-induced reduction of cardiac pump function.

What’s New in Shock, March 2012?

What’s New in Shock, March 2012?

N-3 polyunsaturated fatty acid supplementation does not reduce vulnerability to atrial fibrillation in remodeling atria

Prophylactic supplementation with omega-3 polyunsaturated fatty acids (PUFAs) reduce vulnerability to atrial fibrillation (AF). The effect of PUFAs given after cardiac injury has occurred is unknown. To investigate using a model of pacing-induced cardiac injury, the time course of development of injury and whether it was altered by postinjury PUFAs. Sixty-five dogs were randomized to undergo simultaneous atrial and ventricular pacing (SAVP, 220 beats/min) for 0, 2, 7, or 14 days. Twenty-two dogs received PUFAs (850 mg/d) either prophylactically or after some pacing had occurred (postinjury). Electrophysiologic and echocardiographic measurements were taken at baseline and sacrifice. Atrial tissue samples were collected at sacrifice for histologic and molecular analyses. With no PUFAs, the inducibility of AF increased with pacing duration (P < .001). Postinjury PUFAs (started after 7 days of pacing) did not reduce the inducibility of AF after 14 days of pacing (9.3% ± 8.8% no PUFAs vs 9.7% ± 9.9% postinjury PUFAs; P = .91). Atrial myocyte size and fibrosis increased with pacing duration (P < .05). Postinjury PUFAs did not significantly attenuate the cell size increase after 14 days of pacing (no PUFAs 38% ± 30% vs postinjury PUFAs 19% ± 28%; P = .11). Similarly, postinjury PUFAs did not attenuate the increase in fibrosis after 14 days of pacing (no PUFAs 66% ± 51% vs postinjury PUFAs 63% ± 76%; P = .90). PUFA supplementation begun after cardiac injury has already occurred does not reduce atrial structural remodeling or vulnerability to AF.

Invited Commentary

The dynamics of small body size at the time of implantation, somatic growth of the child, higher rates of pacing, and the total duration (a lifetime) of pacing differentiate pediatric permanent pacemaker procedures from their adult counterparts.

Temporary Transvenous Cardiac Pacing in Patients With Acute Myocardial Infarction Predicts Increased Mortality.

BackgroundTemporary pacemakers (TP) are used in emergency situations for severe bradyarrhythmias secondary to acute myocardial infarction (AMI) and to non-AMI related cardiac disorders. TP have been studied previously in AMI patients treated with thrombolytic therapy; limited information is available on current outcomes in AMI patients treated with percutaneous coronary intervention.MethodsWe reviewed the indications, complications, and mortality associated with TP insertion over a four year period (2003 - 2007) at a university hospital.ResultsSeventy-three temporary pacemakers were inserted (47 men, 26 women) during this period. The mean age was 65.2 years. TP were used in 29 AMI patients (39.7 % of total) and 44 non-AMI patients (60.3% of total). The duration of TP use was 2.6 ± 0.4 days in the whole cohort, 2.46 % of all AMI patients (29/1180) admitted during this period required a TP. Six of these patients requiring a TP required a permanent pacemaker. Eight patients with AMI and a TP died (27.6%). In contrast 8.9 % of AMI patients not requiring a TP died (P < 0.01). There were no statistically significant differences between the AMI and non-AMI groups in the duration of temporary pacing (2.4 ± 0.6 days vs. 2.8 ± 0.4 days), in complications (27.6% vs. 29.5%), or in mortality (27.6% vs. 15.9%). The need for a permanent pacemaker (PPM) differed significantly between the AMI and non-AMI patients (20.7% vs. 54.5%; P < 0.05).ConclusionOur results indicate that AMI patients infrequently require a TP and that approximately 20% of these patients require a PPM. These results suggest that early revascularization of the conduction system with current interventional techniques has decreased the need for TP in AMI patients. However, this group requires more intensive monitoring as the mortality rate in this group of patients is significantly higher than the other AMI patients not requiring TP.

Pacing-induced cardiomyopathy in patients with right ventricular stimulation for &gt;15 years

The prevalence of pacing-induced cardiomyopathy (PiCMP) has been reported to be 9% 1 year after implantation. As long-term data are sparse, the aim of our study was to evaluate the prevalence of PiCMP in a cohort of patients with at least 15 years of right ventricular (RV) pacing. Inclusion criteria were RV stimulation for at least 15 years due to atrioventricular block III° and absence of structural heart disease at the time of initial implantation. All patients were examined by echocardiography and spiroergometry. Pacing-induced cardiomyopathy was pre-defined as left ventricular (LV) ejection fraction (LVEF) ≤45%, dyskinesia during RV pacing and absence of other known causes of cardiomyopathy. Twenty-six patients from our outpatient department met the inclusion criteria. Pacing-induced cardiomyopathy was diagnosed in four patients (15.4%). Echocardiography showed significant LV remodelling in PiCMP patients [LVEF 41.0 ± 4.5%, LV end-diastolic diameter (LVEDD) 54.0 ± 2.7 mm] compared with patients with preserved LVEF (LVEF 61.2 ± 5.8%, P = 0.002, LVEDD 45.6 ± 4.0 mm, P= 0.004). There were no significant differences regarding age, gender, duration of RV pacing, heart rate, interventricular mechanical delay, QRS duration or prevalence of sinus rhythm, and arterial hypertension between both groups. The longest intraventricular delay was significantly shorter in patients with preserved LVEF (65.5 ± 43.0 ms) compared with PiCMP patients (112.5 ± 15.0 ms, P= 0.043). Exercise capacity and quality of life did not differ significantly between both groups. Considering the very long duration of RV stimulation in our study population (24.6 ± 6.6 years), the prevalence of PiCMP was remarkably low. Pacing-induced cardiomyopathy was associated with more pronounced intraventricular dyssynchrony.

154 Patients receiving standard pacemaker generator replacements frequently have impaired left ventricular function and exercise intolerance, related to the percentage of right ventricular pacing

<h3>Background</h3> Right ventricular (RV) pacing is an accepted treatment for symptomatic bradycardia. However, long-term RV pacing is increasingly recognised to be detrimental to left ventricular (LV) systolic function. We wanted to establish the prevalence, associated features and predictors of LV systolic dysfunction (LVSD) and outcome in a contemporary group of patients with long–term RV pacemakers. <h3>Methods</h3> We prospectively recruited consecutive patients listed for PGR between 2008 and 2010 at Leeds General Infirmary. We performed echocardiography, exercise testing and recorded indications for pacing, pacing variables and duration of pacing, co-morbidities, current medication and renal function. <h3>Results</h3> Of 399 PGR procedures 342 subjects (86%), 184 men, attended. Non-attendees had similar pacing variables and were of similar age as attendees. Mean age (SE) was 76 (1), and mean duration of pacing was 10 (0.3) years. Comorbidites were common: diabetes mellitus in 11%, previous myocardial infarction in 15%, previous cardiac surgery in 26% and atrial fibrillation (AF) in 26%. Medical therapy included β-blockers in 60% and ACE inhibitors in 70%. Dual chamber devices were implanted in 77% (45% of all patients had rate responsive (RR) pacing programmed). Mean percentage of ventricular pacing (%VP) was 61 (2)%. Mean left ventricular ejection fraction (LVEF) was 49 (1)%, (44% had an LVEF &lt;50%). Mean peak oxygen uptake (pVo₂) (in 107 subjects) was 17 (1) ml/kg/min and mean creatinine was 108 (3) μmol/l. There was an inverse relationship between LVEF and %VP (0.42; p&lt;0.0001), and years since first implanted (p=0.09) but there was no effect on LVEF of age, the presence of AF and the pacing mode. In single chamber devices, RR pacing was associated with higher %VP (p=0.01), and a trend to worse LVEF (p=0.09). These differences were not seen in RR programmed dual chamber devices. There was a negative relationship between pVo₂ and %VP (r=0.21; p&lt;0.03). Even with a short follow-up period of 16 (0.5) months, 23 (7%) patients are dead. Patients dead at the censor date were older at the time of the assessment (p&lt;0.005), had a higher %VP (p&lt;0.03) and worse renal function (p&lt;0.001), but did not have significantly worse LVEF or pVo₂. The presence of a single chamber device was associated with a poorer outcome (p&lt;0.002) despite patients with a single chamber device being of similar age as those with a dual chamber device. <h3>Conclusions</h3> Patients receiving standard pacemaker generator replacements frequently have cardiovascular comorbidities, left ventricular dysfunction and impaired pVo₂ and suffer a high mortality rate. In an unselected population of patients with pacemakers, we have established that the amount of RV pacing is related not only to important surrogate measures of outcome such as exercise tolerance and LVEF but also mortality. Whether an aggressive policy of limiting RV pacing in patients at risk reduces mortality is unknown.

Initial clinical experience with implantation of left ventricular lead guided by Overlay Ref for the treatment of congestive heart failure

Cardiac resynchronization therapy (CRT) improves clinical outcome in selected patients with advanced congestive heart failure. The Overlay Ref technique may facilitate the procedure for implanting left ventricular (LV) pacing leads to deliver CRT. To assess the feasibility of deploying a LV pacing lead into a coronary sinus side branch guided by Overlay Ref. Data from 88 consecutive patients who met the CRT implantation criteria in our hospital between 28 November 2007 and 30 December 2009 were randomly assigned to two groups. Forty-four patients underwent CRT device implantation using Overlay Ref to guide target vein selection and advance a specifically designed pacing lead into the target vein (Overlay Ref group); 44 patients were conventionally implanted (control group). LV lead implantation was successful in all patients. Mean CRT total procedure times (skin-to-skin) were: Overlay Ref group, 80.7 ± 18.0 min; control group, 98.5 ± 32.2 min; p = 0.029. Mean placement of LV pacing lead into target vein times were: Overlay Ref group, 16.2 ± 7.7 min; control group, 36.4 ± 23.4 min; p=0.004. Mean total fluoroscopy times were: Overlay Ref group, 13.6 ± 4.3 min; control group, 23.8 ± 15.7 min; p=0.007. Mean LV lead fluoroscopy times were: Overlay Ref group, 5.7 ± 2.9 min; control group, 14.4 ± 4.6 min; p=0.003. No major complications occurred. Overlay Ref facilitates location of and entry into the coronary sinus, and shortens the duration of LV pacing lead implantation into the target vein.

Roles of Autonomic Nerve System on the Evolution of PAF to PRAF

Atrial fibrillation (AF) can be either paroxysmal or sustained. Not all patients with paroxysmal AF progress to sustained forms. The mechanisms by which paroxysmal AF progresses to sustained AF remain poorly understood. Intermittent rapid atrial pacing in large animals can initially induce paroxysmal AF followed by transition to persistent AF. Pacing-induced shortening of the effective refractory periods were thought to underlie the mechanisms of AF progression. However, the time course of changes in atrial refractoriness did not completely run parallel with the time course of development of sustained AF. We analyzed long-term recording of nerve activities in ambulatory dogs, and used an intermittent high rate atrial pacing protocol to determine the duration of pacing needed to induce sustained (>48 hrs) of AF. We found that differential patterns of interactions among cardiac autonomic structures naturally exist at baseline (before pacing). We also noted that dogs with good linear sympathovagal correlation and higher vagal tone at baseline have more paroxysmal atrial tachycardias at baseline and faster induction of sustained AF by rapid pacing, as compared to dogs with an L-shaped sympathovagal correlation and lower vagal tone at baseline. These findings suggest that simultaneous sympathovagal discharges, which simultaneously increase Ca2+ entry and shortens the action potential duration, are important in the development of persistent AF.