Biventricular pacing attenuates T-wave alternans and T-wave amplitude compared to other pacing modes

Background: The impact of altered ventricular activation, including biventricular (BV) pacing, on T-wave alternans (TWA) and arrhythmic substrates is unclear. We studied how differing ventricular activation sequence alters TWA; the interval from peak-to-end of the T-wave (TpTe) and T-wave amplitude during right (RV), left (LV), and biventricular (BV) pacing; and right atrial (RA) pacing in patients with preexisting conduction delay.
Methods and Results: We measured TWA during RA, RV, LV, and BV pacing in 33 patients receiving cardiac-resynchronization-therapy-defibrillators. TWA magnitude (V_alt) was lower during BV than RV (P < 0.01), RA (P < 0.01), or LV pacing. As a result, BV-TWA was more often negative than RV-TWA (P < 0.01), LV-TWA, and RA-TWA, particularly when discordant between pacing modes (P < 0.01). Overall, 83% of TWA recordings were abnormal (25% indeterminate), and 17% negative. BV pacing reduced T-wave amplitude (P < 0.05) and TpTe (P < 0.005) compared to RV pacing and LV pacing (P < 0.05; P < 0.005 respectively). Notably, TWA magnitude varied linearly with T-wave amplitude for all pacing modes (P < 0.001). Over 410 ± 252 days' follow-up, RV-TWA predicted the combined endpoint of death and ICD therapy with 86% negative predictive value (P < 0.05). BV-TWA, RA-TWA, and other repolarization indices were not predictive.
Conclusions: BV pacing attenuates TWA in tandem with reduced T-wave magnitude. In these patients with baseline QRS prolongation, RV-TWA predicted events more effectively than BV-TWA and RA-TWA. Further studies are required to understand how altered ventricular activation influences repolarization dynamics and arrhythmic tendency.     

Comparison of microvolt T-wave alternans measurements using atrial pacing compared to atropine administration

Background: Microvolt T-wave alternans (MTWA) has been associated with malignant ventricular arrhythmias in patients (pts) with structural heart disease. MTWA has been shown to be a strong heart rate-dependent arrhythmia marker. However, in clinical practice some pts in which MTWA should be assessed are unable to perform physical exercise to increase heart rate due to various reasons.
Methods: In this study, we investigated the feasibility of noninvasive MTWA measurement by using intravenous atropine to increase heart rate and compared the results to MTWA measurement by right atrial (RA) pacing during electrophysiologic (EP) study in 27 consecutive pts (53 ± 14 years; nine women). Determining the arrhythmia event-rate, a follow-up of 18 months was performed in all pts.
Results: Using atropine, five pts (18%) did not reach the target heart rate (105 bpm). In the remaining group of pts, concordant results for MTWA assessment could be found in 21 pts (96%). Comparing MTWA positive tests there were slightly higher amplitudes using right atrial (RA) pacing than atropine (7.0 ± 2.3μV vs 6.3 ± 2.2μV, P = 0.03; r = 0.97). During follow-up all pts with a positive MTWA test had documented ventricular arrhythmias. There were no arrhythmic events in the MTWA negative group.
Conclusion: Whenever target heart rate for MTWA evaluation is obtained by intravenous atropine, the results are comparable to RA pacing. In using atropine there has been observed no pharmacologically influenced increase of MTWA voltage leading to false positive MTWA results. Therefore the use of atropine can be recommended as a safe, non-invasive, and reliable method for MTWA assessment.     

Arrhythmic risk evaluation during exercise at high altitude in healthy subjects: role of microvolt T-wave alternans

Background: Altitude‐induced sympathetic hyperactivity can elicit rhythm disturbances in healthy subjects, in particular during exercise. Aim: To asses the real susceptibility of healthy myocardium to malignant ventricular arrhythmias during exercise at high altitude using microvolt T‐wave alternans (MTWA). Methods: We evaluated eight healthy trained participants (one female, 42 ± 9 years) during a mountain climbing expedition on Gashembrum II (Pakistan, 8,150 m). MTWA and heart rate variability (HRV) were measured in each subject at sea level and at high altitude, both under rest conditions and during exercise. MTWA was determined with the modified moving average method. HRV was expressed as root mean square of successive differences. Results: Rest HRV at high altitude was significantly lower compared to rest HRV at sea level (36 ± 5 vs 56 ± 9 ms, P = 0.003). HRV during exercise was significantly lower with respect to rest condition both in normoxia (46 ± 7 vs 56 ± 9 ms, P = 0.0001) and hypoxia (27 ± 4 vs 36 ± 5 ms, P = 0.005). Moreover, HRV was significantly lower during exercise at high altitude compared to exercise at sea level (27 ± 4 vs 46 ± 7 ms, P = 0.0002) and arrhythmias were more frequent during exercise in hypoxia. Nevertheless, MTWA was absent under rest conditions both at sea level and at high altitude and minimally evoked during exercise in both conditions (22 ± 3 μV and 23 ± 3 μV, respectively, P = 0.2). Conclusions: In spite of an enhanced sympathetic activity, MTWA testing during exercise at high altitude was negative in all participants. Healthy trained subjects during exercise under hypoxia seem to be at low risk for dangerous arrhythmias.     

Polarization properties of small-surface-area pacemaker electrodes--implications on reliability of sensing and pacing.

The polarization characteristics of Pt-Ir and Elgiloy small-surface-area (10-12.5 mm2) pacemaker electrodes were studied at AC linear (sensing) and DC non-linear (pacing) conditions. The electrodes' AC polarization impedance was approximately equal to the demand pacemaker's input impedance, which causes waveform distortions ofthe sensed R-wave potentials. The pacemaker's coupling capacitor adds to the distortion's effect. As a result of amplitude attenuation (up to approximately 50%) and slew rate changes, the pacemaker may fail to recognize the ventricular complexes, reverting to hazardous competitive pacing. The impact of the DC polarization elements and of the coupling capacitor on the effectiveness of pacing was examined. The deficiency of small area electrodes was pointed out, this being counter-balanced to some extent by their lower pacing thresholds. The necessity to ensure a sufficient safety margin between the pacing pulse and the stimulation threshold, to avoid possible reasons for creation of exit blocks, was stressed. In reducing the electrode surface, it is advisable not to step down below a 15-20 mm2 effective area for Pt-Ir, and a 40-50 mm2 area for Elgiloy.     

Optimizing pacemaker longevity with pacing mode and settings programming: results from a pacemaker multicenter registry

Background: This study aimed to describe the influence on dual‐chamber devices' expected longevity of devices' settings. Methods: Data from patients implanted with dual chamber devices (Symphony?, SORIN CRM SAS, Clamart, France) from 2003 to 2006 were collected in registries. Programmer files were retrieved: device‐estimated longevity, assessed through algorithm prediction, was analyzed according to device settings. Results: One thousand sixty‐eight recipients of dual chamber pacemaker in sinus rhythm (75.3 ± 11.1 years, 54.5% male, ventricular block 30%, brady‐tachy syndrome 21%, and sinus node dysfunction 49%) were followed up to 14.2 ± 12.1 months (ranging from first quartile Q1: 2.9 months to fourth quartile Q4: 49.3 months) after implantation. DDD with automatic mode conversion and minimized ventricular pacing (SafeR) modes were programmed in 34.3%, 2.9%, and 62.8% of the patients, respectively. The mean total longevity estimated by the device was 134.1 ± 31.5 months (11.2 ± 2.6 years). Significant increase in longevity was observed in devices undergoing at least one reprogramming (134.4 ± 31.4 months) versus device presenting no reprogramming (103.4 ± 32.3 months, P = 0.0005). The parameters associated with the major increase in mean longevity were the mode (mean longevity increase of +23.9 months in SafeR as compared to DDD mode, P < 0.0001) and the atrial (A) and ventricular (V) amplitudes (mean longevity increase of +29.6 and +26.9 months for a decrease of less than 1V in A and V outputs respectively, P < 0.0001). Conclusion: This study provides information on dual chamber pacemakers’ longevity and highlights the impact of devices’ reprogramming on expected longevities. PACE 2012; 35:403–408)     

双腔起搏器房室间期自动搜索功能对右心室起搏比例影响的临床研究

目的比较植入双腔起搏器患者房室（AV）间期自动搜索功能（Search AV）打开与固定长AV间期起搏,对右心室起搏比例的影响。方法入选60例病态窦房结综合征或间歇性Ⅱ度或Ⅲ度AV传导阻滞患者,均安装双腔起搏器。程控首先关闭Search AV功能,固定长AV间期（起搏房室间期220ms,感知房室间期200ms）起搏3个月,后程控打开Search AV 3个月,自身对照,比较其心房起搏比例、心室起搏比例及高频心房事件次数。再根据患者是否1：1房室传导分为2个亚组,自身对照分别比较其心房起搏比例、心室起搏比例及高频心房时间次数。结果58倒患者完成随访,固定长AV间期起搏时比Search AV（＋）自动搜索功能打开时的心室起搏比例、高频心房事件次数都高,分别为（70．5±12．4）％vs（22．4±8．3）％,（86±16）次VS（31±11）次（P=0．007,P=0．006）;而心房起搏比例二者差异无统计学意义。在1：1房室传导组（33例）及非1：1房室传导组（25例）两亚组比较中,均得出相同结果。结论Search AV功能可以减少不必要的右心室起搏,减少高频心房事件。     

Prevalence of T Wave Alternans in Healthy Subjects

WEBER, S., et al .: Prevalence of T Wave Alternans in Healthy Subjects. Beat-to-beat variations in the amplitude of the T wave (T wave alternans [TWA]) have been associated with malignant ventricular arrhythmias in patients with structural heart disease. TWA has also been observed sporadically in healthy persons during strenuous exercise. Therefore, it was the aim of this study to investigate the prevalence of TWA in healthy subjects at rest and during exercise. TWA was assessed in 48 healthy volunteers with a mean age of 30 ± 8 years (21–53 years) using the CH2000 system for measurement of microvolt level TWA. TWA was not observed in any individual at rest. Short transient intervals of TWA were observed during exercise in five (10.4%) subjects. Sustained TWA was observed in two (4.2%) individuals. In one of these two individuals sustained TWA was recorded at heart rates >110 beats/min. In the other TWA was observed at an onset heart rate of <110 beats/min, and therefore, was considered alternans positive. The prevalence of exercise related sustained TWA in healthy, young individuals is low (2.1%). Short transient intervals of TWA were observed in about 10% of healthy volunteers. These transient episodes of TWA had no clinical impact with respect to a higher vulnerability to ventricular arrhythmias. (PACE 2003; 26[Pt. I]:49–52)     

The influence of beta-adrenergic agonists and antagonists on T-wave alternans in patients with and without ventricular tachyarrhythmia

BACKGROUND: T-wave alternans (TWA) is an important noninvasive measurement of ventricular tachyarrhythmia (VT) and is known to be influenced by the sympathetic nervous system. We examined the correlation between TWA measurement and the sympathetic nervous system in patients with and without VT. METHODS AND RESULTS: Thirty-five patients (28 men, 7 women; mean age, 59 +/- 15 years) with tachyarrhythmia were assigned to two groups: VT group (n = 15) and supraventricular tachyarrhythmia (SVT) group (n = 20). Alternans voltage in lead vector magnitude (eVM) was measured during atrial pacing (90, 110 beats/min (bpm)). After eVM was measured at baseline, propranolol was administered, and eVM was measured again. In a subset of 18 patients (10 with VT and 8 with SVT), isoproterenol was administered prior to propranolol infusion. After propranolol infusion, eVM of both the VT and the SVT groups decreased significantly compared to baseline. The changes in absolute value of eVM at 110 bpm after propranolol infusion were greater in the VT group than in the SVT group (-1.3 +/- 0.8 microV vs -0.5 +/- 0.8 microV, P < 0.05). The eVM values of both the VT and the SVT groups increased after administration of isoproterenol compared to the baseline value. The changes in absolute value and percentile of eVM after isoproterenol infusion were smaller in the VT group than in the SVT group (2.0 +/- 1.8 microV vs 3.9 +/- 3.5 microV, P < 0.05; 21 +/- 18% vs 48 +/- 36%, P < 0.05). CONCLUSIONS: The sympathetic nervous system has an influence over microvolt-level TWA. Administration of a beta-adrenergic antagonist caused a significant decrease in TWA, particularly in the VT group. This may partially explain the mechanism by which adrenergic antagonists inhibit VTs.     

Echocardiography-guided biventricular pacemaker optimization: role of echo Doppler in hemodynamic assessment and improvement

In spite of improvements in heart failure management and increasing utilization of cardiac resynchronization therapy (CRT), approximately 30–40% of CRT patients remain nonresponders and 50% or more are echocardiographic nonresponders (defined as less than 15% reduction in left ventricular end systolic volume post-CRT). Optimization guided by echocardiography has been studied as one of the methods to improve the nonresponder rate to CRT. Echo-guided biventricular (Biv) pacemaker optimization has been associated with improvement in acute cardiac hemodynamics and improvement in functional class. In this review, the authors discuss various methods to optimize Biv pacemaker by echocardiography, recent advances in pacemaker optimization and the limitations of echocardiography. The authors also demonstrate complex hemodynamic derangements in heart failure via multiple case examples highlighting the role of comprehensive echo Doppler in elucidating cardiac hemodynamics encountered in CRT nonresponders, as well as tailoring of Biv pacemaker optimization to the underlying physiologic derangement.     

Spontaneous ventricular tachycardia and fibrillation in a patient with a positive microvolt T wave alternans test and negative electrophysiological study

This report describes a patient with a previous myocardial infarction who presented with syncope. The patient had a positive microvolt T wave alternans test, a negative electrophysiological study, and a normal heart rate variability. In hospital, the patient had episodes of ventricular tachycardia and fibrillation. An implantable cardioverter defibrillator was implanted and during the following week it discharged appropriately.     

Long-term mortality and pacing outcomes of patients with permanent pacemaker implantation after cardiac surgery

Background: Approximately 20,000 permanent pacemakers (PPMs) are implanted annually for bradycardia or atrioventricular (AV) block after cardiac surgery. Little is known about the long‐term pacing and mortality outcomes and the temporal trends of these patients. Methods: We examined 6,268 consecutive patients who underwent cardiac surgery at the Minneapolis Veterans Administration Medical Center between 1987 and 2010. Patients who had a PPM within 30 days of cardiac surgery were identified. Pacemaker interrogation records were retrospectively reviewed and mortality was ascertained. Results: Overall, 141 (2.2%) patients underwent PPM implantation for high‐degree AV block (55%) and bradycardia (45%), 9 ± 6 days after surgery. Age, diuretic use, cardiopulmonary bypass time (CPBT), and valve surgery were independent predictors of PPM requirement. After 5.6 ± 4.2 years of follow‐up, 40% of the patients were PPM dependent. Longer CPBT (P = 0.03), PR interval >200 ms (P = 0.03), and QRS interval > 120 ms (P = 0.04) on baseline electrocardiogram predicted PPM dependency . In univariable analysis, PPM patients had a higher long‐term mortality than those without PPM (45% vs 36%; P = 0.02). However, after adjusting for age, sex, type of surgery, and CPBT, PPM requirement was not associated with long‐term mortality (hazard ratio 1.3; 95% confidence interval 0.9–1.9; P = 0.17). Compared to before, incidence of PPM implantation increased after the year 2000 (1.9% vs 2.6%; P = 0.04). Conclusion: The majority of patients who require PPM after cardiac surgery are not PPM dependent in the long term. Requiring a PPM after surgery is not associated with long‐term mortality after adjustment for patient‐related risk factors and cardiac surgical procedure. (PACE 2011; 34:331–338)     

Effects of continuous and triggered atrial overdrive pacing on paroxysmal atrial fibrillation in pacemaker patients

Background: The aim of the study was to compare the effects of different pacing strategies to prevent paroxysmal atrial fibrillation (AF): triggered atrial overdrive pacing versus the combination of triggered and continuous overdrive pacing.
Methods : Patients with an indication for dual-chamber pacing (Selection 9000, Prevent AF; Vitatron B.V., Arnhem, the Netherlands) and a history of paroxysmal AF were randomized to triggered atrial pacing (three pacing functions, "triggered group": PAC Suppression™, Post-PAC Response™, and Post-Exercise Response™) or to the combination of continuous (Pace Conditioning™) and triggered atrial pacing (four pacing functions, "combined group"). After 3 months, there was a crossover to the other pacemaker setting.
Results : In 171 enrolled patients, the median AF burden of the combined group was with 2.1% versus 0.1% in the triggered group (P = 0.014). Fewer AF episodes were observed in the triggered (median: 7) than in the combined group (median: 116; P = 0.016). The combined group had more frequent atrial pacing (median 97%) than the triggered group with 85% (P < 0.001), but ventricular pacing was not significantly different with 95% and 96% in the combined and triggered group, respectively. After the crossover, the AF burden increased in the triggered group to 0.3% and decreased in the combined group to 0.4%.
Conclusions : Triggered atrial pacing functions alone resulted in a low AF burden. The additional activation of continuous atrial overdrive pacing increased the percentage of atrial pacing, but had no beneficial effects on the prevention of paroxysmal AF.     

The strength-duration curve and its importance in pacing efficiency: a study of 325 pacing leads in 229 patients

Pacemaker battery life is dependent on programmable parameters, principally pulse amplitude and pulse duration. High factory default settings cause excessive current drain. The strength-duration curve relates pacing threshold to pulse duration. The most energy efficient pacing occurs at chronaxie, a value of pulse duration derived from the curve. Strength-duration curves were calculated for 325 acutely implanted pacing leads. Chronaxie and rheobase were compared for atrial and ventricular leads. Chronaxie was compared with actual programmed pulse duration. There were 101 atrial and 224 ventricular leads, all passive fixation. The curve fit was good, (mean error +/- SD) 0.024 +/- 0.06 V for atrial curves and 0.008 +/- 0.034 V for ventricular curves. Mean (+/- SD) atrial and ventricular chronaxies were 0.24 +/- 0.07 ms and 0.25 +/- 0.07 ms, respectively. A "Z" value of 1.4 indicated that chronaxies might have been from the same population. Mean (+/- SD) atrial and ventricular rheobases were 0.51 +/- 0.2 V and 0.35 +/- 0.13 V, respectively. A "Z" value of 7.1 (P < 0.001) suggested atrial and ventricular rheobases were from differing populations. All patients had factory default pulse durations of 0.45 ms or 0.5 ms, exceeding acute chronaxie by a factor of two, thus, demonstrating suboptimal pacing. We conclude that understanding the strength-duration curve is critical. Sensible programming of other pacing functions optimizes longevity. Battery drain is reduced by programming pulse duration to chronaxie with a doubling of voltage threshold at this point to achieve a safety margin. Further study of chronaxie drift with time is required.     

Relationship between ventricular dyssynchrony and T-wave alternans in patients with coronary artery disease

Introduction: Coronary artery disease (CAD) is associated with increased dispersion of repolarization and sudden cardiac death. We sought to investigate whether ventricular dyssynchrony is associated with proarrhythmic repolarization dispersion as measured by T‐wave alternans (TWA) in patients with CAD. Methods and Results: We evaluated 154 patients (67 ± 9 years, 123 men) with documented CAD, who underwent exercise treadmill testing and echocardiographic examination. TWA was analyzed continuously during treadmill testing in all standard precordial leads by time‐domain method. Tissue Doppler imaging was performed to measure inter‐ and intraventricular dyssynchrony. Increased TWA ≥ 60μV was observed in 42 (27%) patients. There was higher prevalence of females (31 vs 16%, P = 0.04) and greater body mass index (25.7 ± 2.6 vs 24.6 ± 3.0 kg/m², P = 0.04) in the TWA ≥ 60μV group of patients than the TWA < 60μV group. The index of interventricular dyssynchrony, Ts‐RL, was significantly increased (75.6 ± 37.8 vs 59.9 ± 35.9 ms, P = 0.03) but not intraventricular dyssynchrony (all P > 0.05) in patients with TWA ≥ 60 μV compared with those with TWA < 60 μV. In addition, a weak but significant positive correlation was observed between TWA and Ts‐RL (r = 0.25, P = 0.003). Multivariate analysis revealed that only Ts‐RL (odds ratio 1.02, 95% confidence interval 1.00–1.03, P = 0.013) was independent predictor for increased TWA. Conclusions: Our results demonstrated that interventricular dyssynchrony in patients with CAD is associated with increased TWA. This suggests that interventricular dyssynchrony may contribute to proarrhythmic repolarization dispersion. (PACE 2011; 34:1503–1510)     

Direct comparison of a contractility and activity pacemaker sensor during treadmill exercise testing

There are limited data about the chronotropic capacity of the peak endocardial acceleration (PEA) sensor. This study directly compared the chronotropic function from the PEA and the activity (ACT) sensor. The study included 18 patients (age 73 ± 7 years) with ≥ 75% pacemaker-driven heart rate (HR) and a PEA sensor and 11 healthy controls (age 67 ± 7 years) underwent a chronotropic assessment exercise protocol (CAEP) exercise test with the pacemaker patients in VVIR mode after programming the sensors in the default setting with adjustment of the upper sensor rate as an age related maximum value (220-age). The ACT sensor was externally strapped on the thorax. Achieved exercise duration for the patients and controls was, respectively, 9.2 ± 3 vs 18.4 ± 4 minutes (P < 0.001). The maximal achieved HR with the PEA sensor was 124 ± 25 beats/min, versus the ACT with 140 ± 23, versus the controls with 153 ± 26 beats/min (P < 0.001 between the groups). For the PEA, ACT, and controls, the time to peak HR was, respectively, 11 ± 3, 7 ± 3.6, and 18 ± 4 (P < 0.001 between groups) and HR after 10 minutes recovery was, respectively, 80 ± 20, 65 ± 15, and 82 ± 4 beats/min (P < 0.001 between groups). The PEA sensor functions hypochonotroop during exercise programmed as a single sensor system. It is, therefore, preferable to combine the PEA sensor with an activity-based sensor in a dual sensor system. Although both groups had normal left ventricular functions, the exercise capacity of pacemaker patients is significantly lower than in the controls.     

Adverse effects of long-term right ventricular apical pacing and identification of patients at risk of atrial fibrillation and heart failure

In patients needing a pacemaker (PM) for bradycardia indications, the amount of right ventricular (RV) apical pacing has been correlated with atrial fibrillation (AFib) and heart failure (HF) in both DDD and VVI mode. RV pacing was linked with left ventricular (LV) dyssynchrony in almost 50% of patients with PM implantation and atrioventricular (AV) node ablation for AFib. In patients with normal systolic function needing a PM, apical RV pacing resulted in LV ejection fraction (LVEF) reduction. These negative effects were prevented by cardiac resynchronization therapy (CRT). Algorithms favoring physiological AV conduction are possible useful tools able to maintain both atrial and ventricular support and limit RV pacing. However, when chronic RV pacing cannot be avoided, it appears necessary to reconsider the cut-off value of basic LVEF for CRT. In HF patients, RV pacing can induce greater LV dyssynchrony, enhanced by underlying conduction diseases. In this context, a more deleterious effect of RV pacing in implantable cardioverter-defibrillator (ICD) patients with low LVEF can be expected. In some major ICD trials, DDD mode was correlated with increased mortality/HF. This negative impact was attributed to unnecessary RV pacing >40-50%, virtually absent in VVI-40 mode. However, some data suggest that avoiding RV pacing may also not be the best option for patients requiring an ICD. In patients with impaired LV function, AV synchrony should therefore be ensured. The best pacing mode in ICD patients with HF should be defined on an individual basis.     

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。     

Accelerometer-derived time intervals during various pacing modes in patients with biventricular pacemakers: comparison with normals

INTRODUCTION: Changes due to biventricular pacing have been documented by shortening of QRS duration and echocardiography. Compared to normal ventricular activation, the presence of left bundle branch block (LBBB) results in a significant change in cardiac cycle time intervals.Some of these have been used to quantify the underlying cardiac dyssynchrony, assess the effects of biventricular pacing, and guide programming of ventricular pacing devices. This study evaluates a simple noninvasive method using accelerometers attached to the skin to measure cardiac time intervals in biventricularly paced patients. METHODS: Ten patients with biventricular pacemakers previously implanted for congestive heart failure were paced in the AAI mode, then in atrioventricular (AV) sequential mode from the right and left ventricles followed by biventricular pacing. Simultaneous recordings were obtained by 2D, Doppler echocardiography as well as by accelerometers. Similar recordings were obtained from 10 gender, aged matched, normal controls during sinus rhythm. RESULTS: Compared to normals, heart failure patients paced in AAI mode had prolonged isovolumetric contraction time (IVCT), shorter ventricular ejection time (LVET), and prolonged isovolumetric relaxation (IVRT). With biventricular pacing the IVCT decreased, but the LVET and IVRT did not change significantly. There was excellent correlation between the echo and accelerometer-measured intervals. CONCLUSIONS: Shortening of the IVCT measured by an accelerometer is a consistent time interval change due to biventricular pacing that probably reflects more rapid acceleration of left ventricular ejection. The accelerometer may be useful to assess immediate efficacy of biventricular pacing during device implantation and optimize programmable time intervals such as AV and interventricular (VV) delays.     

Effect of right ventricular apex pacing on the Tei index and brain natriuretic peptide in patients with a dual-chamber pacemaker

BACKGROUND: Asynchronous electrical activation induced by right ventricular apex (RVA) pacing can cause various abnormalities in left ventricular (LV) function, particularly in the context of severe LV dysfunction or structural heart disease. However, the effect of RVA pacing in patients with normal LV and right ventricular (RV) function has not been fully elucidated. The aim of this study was to characterize the effects of RVA pacing on LV and RV function by assessing isovolumic contraction time and isovolumic relaxation time divided by ejection time (Tei index) and by assessing changes in plasma brain natriuretic peptide (BNP). METHODS: Doppler echocardiographic study and BNP measurements were performed at follow-up (mean intervals from pacemaker implantation, 44+/-75 months) in 76 patients with dual chamber pacemakers (sick sinus syndrome, n=30; atrioventricular block, n=46) without structural heart disease. Patients were classified based on frequency of RVA pacing, as determined by 24-hour ambulatory electrocardiogram (ECG) that was recorded just before echocardiographic study: pacing group, n=46 patients with RVA pacing>or=50% of the time, percentage of ventricular paced 100+/-2%; sensing group, n=30, patients with RVA pacing<50% of the time, percentage of ventricular paced 3+/-6%. RESULTS: There was no significant difference in mean heart rate derived from 24-hour ambulatory ECG recordings when comparing the two groups (66+/-11 bpm vs 69+/-8 bpm). LV Tei index was significantly higher in pacing group than in sensing group (0.67+/-0.17 vs 0.45+/-0.09, P<0.0001), and the RV Tei index was significantly higher in pacing group than in sensing group (0.34+/-0.19 vs 0.25+/-0.09, P=0.011). Furthermore, BNP levels were significantly higher in pacing group than in sensing group (40+/-47 pg/mL vs 18+/-11 pg/mL, P=0.017). With the exception of LV diastolic dimension (49+/-5 mm vs 45+/-5 mm, P=0.012), there were no significant differences in other echocardiographic parameters, including left atrium (LA) diameter (35+/-8 mm vs 34+/-5 mm), LA volume (51+/-27 cm3 vs 40+/-21 cm3), LV systolic dimension (30+/-6 mm vs 29+/-7 mm), or ejection fraction (66+/-9% vs 63+/-11%), when comparing the two groups. CONCLUSIONS: These findings suggest that the increase of LV and RV Tei index, LVDd, and BNP are highly correlated with the frequency of the RVA pacing in patients with dual chamber pacemakers.     

病态窦房结综合征伴房室传导延迟AAI与DDD起搏模式右心功能的超声评价

目的探讨AAI与DDD起搏模式下病态窦房结综合征伴房室传导阻滞患者的右心功能。方法 35例病态窦房结综合征伴Ⅰ度房室传导阻滞植入DDD双腔起搏器患者,先用程控仪将起搏器程控为DDD模式,最后程控为AAI模式。超声心动图检测患者2种起搏模式下的各参数变化情况。结果 DDD起搏模式下的RVPEP、RVPEP/RVET、Sm、Tei指数明显高于AAI起搏模式（P〈0.05）,E/Em低于AAI起搏模式（P〈0.05）。结论 AAI起搏模式右心的收缩和舒张功能均优于AV间期优化的DDD起搏模式。