Trichamber pacing in dilated myocardiopathy. TTDR pacing?

This article describes the first case in Mexico city that received a three chamber pacing system. A 40 year-old man with dilated cardiomyopathy with variant cardiac rhythm and bradycardia. The three leads were introduced by right subclavian approaches. The right chamber leads were placed in atrial's appendage and in the right ventricular outflow tract and the last one was placed in the great cardiac vein. The two ventricular lead were connected a Y-connector to the ventricular channel of a standard bipolar DDDR pacemaker. The right ventricular lead was connected to the distal pole (anode) and the left ventricular lead to the proximal pole (cathode). Eight days later, the patient's clinical status improved, his functional class improved from IV to II and his left ventricular ejection fraction increased from 30% to 35% by conventional ventriculography. In this type of patients the improvement in cardiac output is this result an of increase in left ventricular filling, reduced mitral and tricuspid regurgitation a better synchronization of ventricular contraction. Multisite pacing has added a mayor complexity to contemporary pacing and a modification of the standard pacer-maker code should be considered to accommodate multisite pacing. The letter in the first and second position might be T (three) or F (four) according to number of pacing chamber and also the letter "t" may be suitable to designate trigger in the third position. We conclude that implant of three chamber pacing in patients with dilated cardiomyopathy is technically feasible. An improvement in the patient's condition may be obtained and a modification in standard pacemaker code is necessary.     

Doppler ultrasound measurement of cardiac output in patients with physiologic pacemakers. Effects of left ventricular function and retrograde ventriculoatrial conduction

Dual-chamber cardiac pacing (DDD) offers obvious theoretical advantages over traditional ventricular demand (VVI) pacing. Nevertheless, no widely agreed upon criteria exist for the selection of patients for physiologic DDD pacemakers compared with the simpler VVI systems. Accordingly, a non-invasive method for measuring cardiac output (Doppler ultrasound) was used to identify candidates for pacing who would derive the greatest hemodynamic benefit from DDD vs VVI pacing. Among 29 patients studied at rest during VVI-mode pacing, the average cardiac output by Doppler ultrasound was 4.3 +/- 0.3 liters/min (mean +/- standard error of the mean). In the DDD mode, the average cardiac output was 5.0 +/- 0.3 liters/min (p less than 0.001). Baseline left ventricular ejection fraction did not identify a group that improved more with DDD pacing. Patients who showed either retrograde ventriculoatrial conduction or described symptoms consistent with the "pacemaker syndrome" during VVI pacing, however, showed greater increases in cardiac output during DDD pacing. In these patients, the mean improvement in cardiac output was 30.4 +/- 8.6% with DDD vs VVI pacing, as opposed to an average increase of only 14.4 +/- 3.4% in the remaining 20 patients (p = 0.02). Thus, Doppler ultrasound can be used to quantitate the change in cardiac output at rest that occurs with DDD vs VVI pacing. The change is independent of the level of left ventricular function but is substantially higher when there is evidence of ventriculoatrial conduction or the pacemaker syndrome.     

Hemodynamic compromise associated with ventriculoatrial conduction following transvenous pacemaker placement

Ventriculoatrial conduction complicating ventricular pacing in a patient with ischemic heart disease led to severe clinical disability and hemodynamic compromise. Data obtained at cardiac catheterization documented that ventriculoatrial conduction of the patient's paced beats led to inadequate left ventricular filling pressures, pulmonary congestion and depressed cardiac output. This complication of ventricular pacing can be suspected at bedside examination and emphasizes the importance of considering the possible hemodynamic effects of ventricular pacing when long-term pacemaker therapy is contemplated.     

The importance of avoiding unnecessary right ventricular pacing in clinical practice

Symptomatic bradycardia is effectively treated with the implantation of a cardiac pacemaker. Although a highly successful therapy, during recent years there has been a focus on the negative effects associated with long-term pacing of the apex of the right ventricle (RV). It has been shown in both experimental and clinical studies that RV pacing leads to ventricular dyssynchrony, similar to that of left bundle branch block, with subsequent detrimental effects on cardiac structure and function, and in some cases adverse clinical outcomes such as atrial fibrillation, heart failure and death. There is substantial evidence that patients with reduced left ventricular function (LVEF) are at particular high risk of suffering the detrimental clinical effects of long-term RV pacing. The evidence is, however, incomplete, coming largely from subanalyses of pacemaker and implantable cardiac defibrillator studies. In this group of patients with reduced LVEF and an expected high amount of RV pacing, biventricular pacing (cardiac resynchronization therapy) devices can prevent the negative effects of RV pacing and reduce ventricular dyssynchrony. Therefore, cardiac resynchronization therapy has emerged as an attractive option with promising results and more clinical studies are underway. Furthermore, specific pacemaker algorithms, which minimize RV pacing, can also reduce the negative effects of RV stimulation on cardiac function and may prevent clinical deterioration.     

用三维超声心动图评价右室起搏对左室功能的影响

应用三维超声心动图测定了13例植入ⅤⅥ起搏器病窦综合征病人起搏节律和自身窦性节律时的心动周期各时相的左室容量、心功能及左室壁活动之变化:起搏节律时,收缩期各时相左室容量高于窦性节律时,舒张期各时相左室容量低于窦性节律时,心搏量和左室喷血分数均明显低于窦性节律时(P<0.01);起搏节律时,左室壁节段收缩率弱的心肌面积增加,节段收缩率强的心肌面积减少及心室肌各部收缩程度的不协调。其原因是右室起搏不同于正常生理状态下的心脏兴奋收缩。     

Chronic right ventricular apical pacing: Adverse effects and current therapeutic strategies to minimize them

The permanent cardiac pacemaker is the only effective therapy for patients with symptomatic bradycardia and hundreds of millions are implanted worldwide every year. Despite its undisputed clinical benefits, the last two decades have drawn much attention to the negative effects associated with long-term pacing of the right ventricle (RV). Experimental and clinical studies have shown that RV pacing produces ventricular dyssynchrony, similar to that of left bundle branch block, with consequent detrimental effects on cardiac structure and function, with adverse clinical outcomes such as atrial fibrillation, heart failure and death. Although clinical evidence largely comes from subanalyses of pacemaker and implantable cardiac defibrillator studies, there is strong evidence that patients with reduced left ventricular function are at high risk of suffering from the detrimental effects of long-term RV pacing. Biventricular pacing in cardiac resynchronization therapy devices can prevent ventricular dyssynchrony and has emerged as an attractive option in this patient group with promising results and more clinical studies underway. Moreover, there is evidence that specific pacemaker algorithms that minimize RV pacing can reduce the negative effects of RV stimulation on cardiac function and may also prevent clinical deterioration. The extent of the long-term clinical effects of RV pacing in patients with normal ventricular function and how to prevent this are less clear and subject to future investigation.     

Echocardiographic tools for pacemaker optimization of ventricular function in an infant following surgical repair for double outlet right ventricle

A case of an infant, following surgical repair for double outlet right ventricle, who developed low cardiac output syndrome and complete heart block that required insertion of a pacemaker is presented. The infant underwent optimization of his ventricular function to determine whether pacing the right ventricle or left ventricle or both would improve cardiac function. Using standard two-dimensional echocardiography and Doppler imaging, tissue synchronization imaging, and two-dimensional speckle-tracking strain analysis, improvement in cardiac output and function was demonstrated. The present case highlights the usefulness of newer echocardiographic techniques in pacemaker optimization in the acute postoperative setting.     

Radionuclide analysis of right and left ventricular response to exercise in patients with atrial and ventricular septal defects

In patients with ventricular or atrial septal defect, the ventricle which is chronically volume overloaded might not appropriately respond to increased demand for an augmentation in output and thereby might limit total cardiac function. In this study we simultaneously measured right and left ventricular response to exercise in 10 normal individuals, 10 patients with ventricular septal defect (VSD), and 10 patients with atrial septal defect (ASD). The normal subjects increased both right and left ventricular ejection fraction, end-diastolic volume, and stroke volume to achieve a higher cardiac output during exercise. Patients with VSD failed to increase right ventricular ejection fraction, but increased right ventricular end-diastolic volume and stroke volume. Left ventricular end-diastolic volume did not increase in these patients but ejection fraction, stroke volume, and forward left ventricular output achieved during exercise were comparable to the response observed in healthy subjects. In the patients with ASD, no rest-to-exercise change occurred in either right ventricular ejection fraction, end-diastolic volume, or stroke volume. In addition, left ventricular end-diastolic volume failed to increase, and despite an increase in ejection fraction, left ventricular stroke volume remained unchanged from rest to exercise. Therefore, cardiac output was augmented only by the heart rate increase in these patients. Right ventricular function appeared to be the major determinant of total cardiac output during exercise in patients with cardiac septal defects and left-to-right shunt.     

Effect of afterload reduction in patients with ventricular and physiological pacing.

The effect of afterload reduction was studied in a group of patients who remained breathless or tired after permanent ventricular pacing. Haemodynamic measurements were made before and after giving hydralazine 20 mg intravenously using a triple lumen thermodilution catheter and cuff blood pressure recordings during ventricular pacing at the standard rate of 71/min or an increased rate of 88/min and physiological pacing. Increasing the ventricular pacing rate had no effect on cardiac output as stroke volume fell. Hydralazine produced a greater rise in cardiac output than physiological pacing alone, although peak values were obtained by combining the two. Ventricular pacing produced intermittent large left and right atrial pressure peaks. Physiological pacing produced no such peaks, and mean right and left atrial pressures fell. Hydralazine did not significantly alter atrial pressures. These findings show that in these patients, most of whom had a low cardiac output, afterload reduction with ventricular pacing increased resting cardiac output more than physiological pacing alone. Nevertheless, persistence of high filling pressures despite afterload reduction may limit the potential therapeutic benefit. Care should be taken in extrapolating these data to other patient groups.     

Cardiac resynchronisation therapy

Left ventricular dysfunction is often associated with myocardial conduction slowing which is usually seen clinically as left bundle branch block on the surface ECG. Left bundle branch block causes asynchronous contraction of the left ventricle with the ventricular septum contracting early and the lateral left ventricular wall contracting late. This leads to a reduction in cardiac output and myocardial contraction efficiency and systolic mitral regurgitation worsens. Patients with this combination of findings may benefit from the implantation of a pacing system that aims to normalise conduction and "resynchronise" the ventricles. This mode of cardiac stimulation is referred to as "biventricular" pacing and relies on the implantation of an additional pacing lead on the epicardial surface of the left ventricle. This is achieved by selectively cannulating the coronary sinus and passing a pacing lead via a posterolateral coronary sinus tributary to an appropriate location. This lead, as well as the two conventional right atrial and right ventricular leads, is then attached to a specialised pacemaker. The procedure may be challenging and usually takes 1-2h depending on the operator's experience. The QRS complex shortens as the lateral wall of the left ventricle becomes "pre-excited" and contracts in concert with the ventricular septum. Improved haemodynamics result immediately and favourable reverse left ventricular remodelling occurs over subsequent weeks. Recently, these physiologic advantages have been translated into real clinical gains for patients with biventricular pacemakers where improvements in exercise tolerance and quality of life and reduced hospitalisations for recurrent heart failure have been conclusively demonstrated.     

Pacing with capture verification in candidates for resynchronisation therapy: a feasibility study.

BACKGROUND: Devices for cardiac resynchronisation therapy (CRT) deliver energy into 3 output channels. Such a burden can significantly reduce device longevity. Autocapture has been shown to improve pacemaker longevity and safety of right ventricular pacing in clinical studies. The aim of this study was to investigate the application of Autocapture during biventricular pacing (BIV) to decrease the energy cost of CRT. METHODS: During implantation of BIV devices, an acute study was performed to test the hypothesis that the evoked response (ER) elicited by each delivered stimulus is correctly detected and measured either on the right ventricular (RV) channel during BIV pacing with the left ventricular (LV) channel pacing first, or in the LV channel with the RV channel pacing first. A reliable measurement of ER is the critical requirement for the correct performance of Autocapture. RESULTS: ER amplitude in the right ventricle during BIV pacing was not significantly decreased compared with RV pacing in the VVI mode (16.36+/-5.27 mV vs 17.09+/-6.12 mV). ER amplitude in the left ventricle during BIV pacing was not significantly decreased compared with LV pacing in the VVI mode (12.4+/-8.95 mV vs 12.25+/-8.97 mV). Three patients in atrial fibrillation had a DDDR pacemaker with the LV lead connected to the atrial port, and received BIV pacing with Autocapture turned on in the RV channel. Autocapture performance in the long term, as assessed by the trend of RV threshold over 20+/-8 months, showed that LV depolarisation was never sensed as an ER on the RV channel. CONCLUSIONS: Our observations support the feasibility and safety of capture verification during BIV pacing on the ventricular channel paced secondly, which could increase the longevity of CRT devices, and decrease the costs of this new therapy for heart failure patients.     

Assessment of regional wall motion using strain Doppler imaging during right ventricular bifocal pacing in a patient with severe congestive heart failure: a case report

A 79-year-old man presented with dilated cardiomyopathy and chronic atrial fibrillation. A DDD pacemaker was implanted due to sick sinus syndrome. His left ventricular ejection fraction was 23%. He was repeatedly admitted with congestive heart failure. Although cardiac resynchronization therapy was attempted, insertion of a pacing lead into the coronary sinus failed. Right ventricular bifocal pacing was done. The QRS width was shortened to 155 msec during bifocal pacing and 157 msec during right ventricular outflow pacing from 221 msec during right ventricular apical pacing. Heart failure was improved from New York Heart Association class III to II. Regional wall motion was assessed by strain of the myocardium. Bifocal pacing increased stroke volume due to improvement of longitudinal dyssynchrony of the septal and lateral walls. Bifocal pacing is effective for patients with severe congestive heart failure in whom biventricular pacing therapy has failed. Strain Doppler imaging is useful for the assessment of regional wall motion during cardiac pacing.     

Volume loading improves low cardiac output in experimental right ventricular infarction

To evaluate the effect of volume loading in the low output state associated with right ventricular infarction, isolated right ventricular infarction was produced in seven dogs with the pericardium intact. Volume loading and pericardiotomy were then sequentially performed. After the production of right ventricular infarction, right ventricular systolic pressure decreased by 25%, aortic pressure by 36% and cardiac output by 32%. Right ventricular ejection fraction decreased by 57%, but left ventricular ejection fraction did not change significantly. Left ventricular transmural pressure and diastolic size decreased, and right ventricular diastolic size increased. Intrapericardial pressure increased and equalization of diastolic pressures was noted. Volume loading resulted in increased right ventricular systolic pressure and stroke work, increased aortic pressure and cardiac output and increased transmural pressure and diastolic size in both ventricles. Pericardiotomy resulted in further increases in right and left ventricular filling, stroke work and cardiac output, as well as resolution of equalized diastolic pressures. These results indicate that cardiac output in experimental right ventricular infarction increases with volume loading, which enhances left ventricular preload by augmenting right ventricular output. Elevated intrapericardial pressure affects filling of both ventricles and may play a role in the pathophysiology of low cardiac output in right ventricular infarction.     

左室功能和结构改变与心脏起搏器起搏比例的关系

目的:探讨心脏起搏器起搏比例与左室功能和结构改变的相关性。方法:选择我院2008年2月至2009年2月收治的永久性心脏起搏器植入患者40例,回顾分析相关临床资料。结果:起搏器植入后远期(3～4年)左室射血分数(LVEF)呈下降趋势,左室收缩末容积(LVESV)、左室舒张末容积(LVEDV)呈增大趋势,各参数在置入前与远期比较无显著差异(P>0.05)。将起搏心搏数/总心搏数界值定为60%,按起搏心搏数比例高组(≥60%)及低组(<60%)两个组划分,起搏心搏数比例高组较低组LVEF[(49.2±14.1)%比(63.1±7.3)%]有明显降低,LVEDV[(120.7±69.8)ml比(65.4±10.9)ml]明显增大(P<0.05)。结论:心脏起搏器植入3～4年,左室出现功能和结构重塑,起搏心搏数比例越大,左室射血分数越低,左室越大。     

An update on clinical trials in pacing: is dual chamber pacing better?

PURPOSE OF REVIEW: As pacemaker technology has increased in complexity and now offers a variety of additional capabilities, there is uncertainty as to which pacing mode offers more benefit-dual-chamber or single-chamber. RECENT FINDINGS: Two large-scale randomized trials, the Canadian Trial of Physiologic Pacing and the Mode Selection Trial, demonstrated that dual-chamber pacing does not reduce the incidence of stroke or improve survival when compared with ventricular pacing. However, dual-chamber pacing does reduce the incidence of atrial fibrillation and in patients with sinus node dysfunction, reduces heart failure symptoms when compared with ventricular pacing. The modest results of these trials were unexpected when viewed in the context of the very favorable retrospective studies. SUMMARY: A rethinking of the physiology of cardiac pacing has led to the concept that although atrioventricular synchrony supports an improvement in cardiac output and ventricular pressures, these favorable hemodynamics may be attenuated by ventricular dyssynchrony from right ventricular apical pacing. In patients with a reduced ejection fraction, this dyssynchrony may be especially detrimental. Two trials (DANPACE and SAVE-PACE) are currently underway that will clarify the clinical significance of reducing forced ventricular desynchronization. The results of these trials may direct pacemaker physicians away from the right ventricular apical lead toward a new imperative of atrioventricular and right ventricular-left ventricular synchrony.     

Left ventricular volumes and function during atrial pacing in coronary artery disease: A radionuclide angiographic study

This study set out to determine the pathophysiologic changes in the left ventricle during atrial pacing in 22 patients with coronary artery disease. Graduated right atrial pacing to a rate of 160 beats/min, or the induction of angina pectoris or significant ST depression was undertaken. Ventricular volumes were measured at rest and at rates of 100, 120, 140 and 160 beats/min using radionuclide angiography. The volumes at a pacing rate of 100 beats/min were used as a reference standard (100%). In the 22 patients with coronary artery disease, left ventricular end-diastolic volume decreased from 118 ± 3% at rest to 80 ± 5% at a rate of 160 beats/min; stroke volume from 121 ± 3% to 54 ± 5%; and ejection fraction (EF) from 49 ± 3% to 37 ±5%. End-systolic volume decreased from 118 ± 4% at rest, reached its minimal value of 94 ± 5% at a rate of 120 beats/min and then increased slightly to 106 ± 9% at 160 beats/min. Cardiac output and blood pressure did not change significantly. Compared to the control group of 10 normal subjects, the patients had a significantly smaller decrease in end-diastolic volume and end-systolic volume than in normal control subjects. EF in the normal subjects did not change. Blood pressure, cardiac output and stroke volume were similar in both groups. Atrial pacing tachycardia induced reversible ventricular dysfunction with a decrease in EF. Stroke volume was maintained because of relative ventricular dilatation.     

组织运动瓣环位移技术评价老年双腔起搏器患者不同部位起搏与预后关系

目的 探讨右心室中位间隔面及心尖部起搏下组织运动瓣环位移（TMAD）及N末端B型利钠肽（NT-proBNP）水平与患者预后的关系.方法 2009年3月至2012年1月植入DDD起搏器老年患者148例为研究对象,选择右心室中位间隔部起搏患者（RVMSP组）56例、右心室心尖部起搏患者（RVAP组）42例,观察2组患者术前、术后6、18个月心电图QRS时限,采用TMAD技术检测二尖瓣环六个位点二尖瓣环位移（MADseg）、整体位移（MADglobal）,采用M型超声检测左心室收缩期同步性指标TAS-POST以及双平面法测量左心室射血分数（LVEF）,实验室检查NT-proBNP、测量左心室舒张末期容积（LVEDV）以及出现心血管事件包括心室高频事件（VHR）等指标.结果 所有患者均顺利完成手术,按期随访.2组心血管事件发生率比较,RVAP组最高（P＜0.05）,2组VHR差异无统计学意义（P＞0.05）;与术前比较,RVMSP组患者术后6、18个月NT-proBNP、LVEF、LVEDV等均无变化,RVAP组NT-proB-NP、LVEF、LVEDV无变化,二尖瓣环各位点MAD以及二尖瓣环MADgloba降低,TAS-POST增加（P＜0.05）.术后18个月RVAP组NT-proBNP增加,LVEDV值增加（P＜0.05）,差异有统计学意义（P＜0.05）,LVEF无变化.结论 RVMSP心血管事件发生率较低,不影响患者心功能,为较理想起搏部位,TMAD可早期监测心功能受损,为起搏器患者早期心功能异常的检测提供新的方法.     

Hemodynamic benefit of atrioventricular synchrony: prediction from baseline Doppler-echocardiographic variables

The purpose of this study was to determine if baseline Doppler-echocardiographic variables of systolic or diastolic function could predict the hemodynamic benefit of atrioventricular (AV) synchronous pacing. Twenty-four patients with a dual chamber pacemaker were studied. Baseline M-mode and two-dimensional echocardiograms were obtained and Doppler-echocardiographic measurements of mitral inflow and left ventricular outflow were made in VVI mode (single rate demand) and in VDD (atrial synchronous, ventricular inhibited) and DVI (AV sequentially paced) modes at AV intervals ranging from 50 to 300 ms. Forward stroke volume and cardiac output were determined in each mode at each AV interval from the left ventricular outflow tract flow velocities, and the percent increase in cardiac output over VVI mode was determined. M-mode measurements, including left ventricular end-diastolic dimension, shortening fraction and left atrial size and Doppler measurement of diastolic filling, including peak early velocity and percent atrial contribution, did not correlate with the percent increase in cardiac output during physiologic pacing. The stroke volume in VVI mode correlated significantly with the percent increase in cardiac output during physiologic pacing (r = -0.61, p less than 0.005 for VDD mode and r = -0.55, p less than 0.05 for DVI mode). Five of the 15 patients with VVI stroke volume less than 50 ml but none of the 9 patients with stroke volume greater than 50 ml had ventriculoatrial (VA) conduction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Simultaneous assessment of left ventricular systolic and diastolic dysfunction during pacing-induced ischemia

Both systolic and diastolic dysfunction have been described during pacing-induced ischemia, but the temporal sequence of systolic and diastolic impairment has not been established. Accordingly, 22 patients with coronary artery disease were paced at increasing heart rates and studied with simultaneous hemodynamic monitoring, electrocardiographic recording, and radionuclide ventriculography. In addition, with synchronized left ventricular pressure tracings and radionuclide volume curves, three sequential pressure-volume diagrams were constructed for each patient corresponding to baseline, intermediate, and maximum pacing levels. Eleven patients (group I) demonstrated a nonischemic response to pacing tachycardia without chest pain, significant electrocardiographic changes, or significant rise in left ventricular end-diastolic pressure (LVEDP) in the immediate postpacing period. These patients demonstrated a progressive decrease in LVEDP, end-diastolic volume, and end-systolic volume, no change in cardiac output or left ventricular ejection fraction, and a progressive increase in left ventricular diastolic peak filling rate and the end-systolic pressure-volume ratio. Pressure-volume diagrams shifted progressively leftward and slightly downward, suggesting both an increase in contractility and a mild increase in left ventricular distensibility. The remaining 11 patients (group II) exhibited an ischemic response to pacing tachycardia, with each patient experiencing angina pectoris, demonstrating greater than 1 mm ST segment depression on the electrocardiogram, and exhibiting greater than 5 mm Hg rise in LVEDP immediately after pacing. LVEDP, end-diastolic volume, and end-systolic volume in these patients initially decreased and then subsequently increased during angina, with no change in cardiac output but a decrease in ejection fraction. Left ventricular peak diastolic filling rate and the left ventricular end-systolic pressure-volume ratio both increased at the intermediate pacing rate but fell at maximum pacing. Pressure-volume diagrams for these patients shifted leftward initially, then back to the right, during intermediate and peak pacing levels, often with an upward shift in the diastolic pressure-volume relationship. LVEDP in group II was significantly higher than that in group I at the intermediate pacing level with no difference in end-diastolic or end-systolic volumes, suggesting decreased left ventricular distensibility in these patients before the onset of systolic dysfunction at the maximum pacing level.(ABSTRACT TRUNCATED AT 400 WORDS)     

不同部位起搏对心脏收缩功能的影响

通过不同部位起搏 ,观察房室同步和心室激动顺序对人体心脏收缩功能的影响及起搏体表心电图QRS波时限与心输出量 (CO)的关系。 1 5例射频消融术后的病人分别按顺序进行右房、右室心尖部和室间隔起搏 ,采用心导管法分别测定右房压 (RAP)、肺动脉压 (PAP)、肺毛细血管楔压 (PCWP)和CO ,并计算心脏指数 ,记录心电图。结果 :右室心尖部起搏和室间隔起搏较右房起搏时RAP、PAP升高。心尖部起搏时CO较右房起搏降低 1 9.1 5 % (P <0 .0 1 ) ,室间隔起搏时CO较右房起搏降低 7.86% (P <0 .0 5 ) ,而较心尖部起搏提高 1 2 .2 4 % (P <0 .0 5 )。心尖部起搏和室间隔起搏较右房起搏体表心电图QRS波时限明显延长 ,而室间隔起搏体表心电图QRS波时限比心尖部起搏平均缩短 1 8.6ms(P <0 .0 0 1 )。CO和△QRS波时限的相关性分析表明两者呈负相关关系 (r=- 0 .30 ,P <0 .0 5 )。结论 :起搏体表心电图△QRS波时限与CO呈负相关 ,不同部位起搏对心脏收缩功能的影响不同 ,其中室间隔起搏较心尖部起搏更符合生理性起搏