Myocardial Demands of Atrial-Triggered Versus Fixed-Rate Ventricular Pacing in Patients with Complete Heart Block

Hemodynamics, myocardial oxygen consumption, and lactate concentration were determined by cardiac catheterization at rest and during exercise in eight patients treated with AV universal pacemakers (DDD) for high degree AV block. The pulse generator was alternately programmed in ventricular inhibited (VVI) or atrial synchronous (VAT) mode. During VVI pacing, the cardiac output rose between rest and exercise (4.3-7.6 L/min) due to increased stroke volume. VAT pacing gave significantly greater increase (4.5-8.8 L/min) which, as the stroke volume was unchanged, resulted from accelerated heart rate. The myocardial oxygen consumption and the coronary blood flow did not differ between VVI and VAT mode at rest or during exercise, nor did the modes make a difference in arterial systolic and pulmonary wedge pressures. These observations suggested that VAT pacing offers higher cardiac output than VVI pacing, but with similar demands on myocardial oxygen consumption.     

Importance of Heart Rate Response During Exercise in Patients Using Atrioventricular Synchronous and Ventricular Pacemakers

Atrioventricular synchronous pacing offers advantages over fixed-rate ventricular (VVI) pacing both at rest and during exercise. This study compared the hemodynamic effects at rest and exercise of ventricular pacing at a rate of 70 beats/min, ventricular pacing where the rate was increased during exercise and dual chamber pacing. Ten patients, age 63 +/- 8 years, with multiprogrammable DDD pacemakers were studied using supine bicycle radionuclide ventriculography. Radionuclide data during dual chamber pacing was acquired at rest and during a submaximal workload of 200-400 kpm/min. The pacemakers were then programmed to VVI pacing at a rate of 70 beats/min, and 1 week later, studies were repeated in the VVI mode at rest, during exercise at a rate of 70 beats/min, and during exercise with the VVI pacemaker programmed to a rate adapted to the DDD pacing exercise rate. At rest, the cardiac output was lower in the VVI compared with the AV sequential mode (4.1 +/- 1.1 vs 5.7 +/- 1.1 1/min, P less than 0.01). During exercise, the cardiac output increased from resting values in the DDD and VVI pacing modes, however cardiac output in the rate-adapted VVI mode was higher than in the VVI mode with the rate maintained at 70 beats/min (8.1 +/- 1.5 vs 6.3 +/- 1.1 1/min, P = 0.02). Three patients completed lower workloads with VVI pacing at 70 beats/min compared with AV synchronous pacing. At rest, AV sequential pacing was superior to VVI pacing, suggesting the importance of the atrial contribution to ventricular filling. With VVI pacing during exercise, cardiac output was improved with an increased pacemaker rate, suggesting that the heart rate response during exercise was the major determinant of the higher cardiac output.     

AV Pacing and LV Performance

Five patients with impaired left ventricular function (LV) and implanted AV sequential pacemakers underwent serial radionuclide angiograms. The goal was a non-invasive evaluation of the rapid changes in left ventricular performance elicited by rate, pacing mode and AV interval manipulation. End diastolic volume, end systolic volume, stroke volume and cardiac output were increased by AV sequential pacing in comparison with ventricular pacing at 70 beats per minute. No significant change in ejection fraction and blood pressure were noted with changing AV sequential pacing rates at usual pacing rates. Our data suggest that a short A V interval (150 ms) improved LV performance more than a long AV interval (250 ms). A non-invasive technique to optimize left ventricular performance on an acute basis by varying heart rate, AV interval and pacing mode with the implanted AV sequential pacemaker is feasible and may be useful in selective clinical situations.     

Left Ventricular Function During Physiological Cardiac Pacing: Relation to Rate, Pacing Mode, and Underlying Myocardial Disease

The hemodynamic effects of cardiac pacing at different rates and in different modes were studied in 21 patients who were candidates for permanent pacemaker implantation. Nine of these had primary conduction disturbances (PCD), ten had ischemic heart disease (IHD), seven with additional cardiac failure (CHF), and two had hypertrophic cardiomyopathy (HCM). In patients with PCD, atrial (AOO) and AV sequential (DVI) pacing did not change systolic blood pressure and pulse pressure but ventricular (VVI) pacing caused a progressive fall in these measurements, especially as heart rate increased. Ventricular volume and stroke volume (counts) derived from radionuclide ventriculography (RVG) decreased progressively with higher pacing rates, especially during VVI pacing. Cardiac output was maintained during VVI pacing by the increase in heart rate; during AOO and DVI pacing, cardiac output increased. Similar but more marked differences were observed in patients with IHD and CHF and the changes were even greater in the patients with HCM. Left ventricular (LV) ejection fraction changed little with increasing heart rate in PCD but decreased progressively with the onset of ischemia in IHD and CHF. There was no difference in ejection fraction in the different pacing modes. Graphs related to LV contractility (end-systolic pressure-volume relations) showed that AOO pacing produced the highest and VVI pacing produced the lowest curves of myocardial contractility in all patient groups, except that at higher rates the AOO curve shifted down again in patients with IHD and CHF, presumably with the onset of myocardial ischemia. This study showed that physiological pacing produced the best hemodynamic results in all patient groups. Higher pacing rates should be avoided in patients with ischemic heart disease while VVI pacing should not be used in patients with HCM. Blood pressure and RVG studies during temporary pacing are useful in selecting the optimal pacing system in an individual patient when the clinical choice is not clear.     

Doppler Echocardiographic Studies in Sequential Atrioventricular Pacing

Six patients with sequential atrioventricular pacemakers were studied by Doppler echocardiography. A commercially available continuous wave system (transcutaneous aortovelography) was used and the transducer was placed in the suprasternal notch and angled to obtain peak aortic arch blood flow velocity. Changes in Doppler peak velocity have been previously shown to correlate closely and reliably with changes in hemodynamically measured stroke volume/cardiac output in the same patients following interventions, In all patients, the pacemaker was programmed from DVI mode to VVI (heart rate was kept constant) and then back to DVI, with the Doppler transducer held in a fixed position all the time, and peak velocities measured after the patient had been in any particular mode for at least 1 minute. Five of 6 patients showed reduction in peak velocities ranging from 13–25% (mean 18.4%) when the pacing mode was switched from DVI to VVI. Doppler peak velocity remained unchanged in 1 patient. Doppler echocardiography represents a simple, noninvasive method for estimating increments in stroke volume/cardiac output obtained with sequential AV pacing.     

Doppler echocardiographic studies in sequential atrioventricular pacing

Six patients with sequential atrioventricular pacemakers were studied by Doppler echocardiography. A commercially available continuous wave system (transcutaneous aortovelography) was used and the transducer was placed in the suprasternal notch and angled to obtain peak aortic arch blood flow velocity. Changes in Doppler peak velocity have been previously shown to correlate closely and reliably with changes in hemodynamically measured stroke volume/cardiac output in the same patients following interventions. In all patients, the pacemaker was programmed from DVI mode to VVI (heart rate was kept constant) and then back to DVI, with the Doppler transducer held in a fixed position all the time, and peak velocities measured after the patient had been in any particular mode for at least 1 minute. Five of 6 patients showed reduction in peak velocities ranging from 13-25% (mean 18.4%) when the pacing mode was switched from DVI to VVI. Doppler peak velocity remained unchanged in 1 patient. Doppler echocardiography represents a simple, noninvasive method for estimating increments in stroke volume/cardiac output obtained with sequential AV pacing.     

Is DDD Pacing Superior to VVI,R? A Study on Cardiac Sympathetic Nerve Activity and Myocardial Oxygen Consumption at Rest and During Exercise

Rate responsive ventricular pacing (VVI,R) has been demonstrated to equal atrial synchronous ventricular pacing (DDD) with regard to hemodynamics and exercise tolerance. Whether the two modes are also comparable, with regard to cardiac metabolic effects, is not yet dear. We assessed central hemodynamics, cardiac sympathetic nerve activity fcardiac norepinephrine overflow), and myocardial oxygen consumption in 16 patients treated with rate responsive atrial synchronous ventricular pacemakers (DDD,R), due to high degree AV block. The study was performed at rest and during supine exercise at two workloads (30 ± 12 and 68 ± 24 watts, respectively) during VDD and rate matched VVI pacing (VVI_m). Ventricular rates at rest and during both workloads were almost identical. Cardiac output at rest tended to be higher in the VDD mode, due to a slightly higher stroke volume. Central pressures including right atrial pressure and pulmonary capillary wedge pressure were similar in the pacing modes. The coronary sinus blood flow, the coronary sinus arteriovenous oxygen difference, and the myocardial oxygen consumption did not differ between the two pacing modes. Cardiac norepinephrine overflow was similar in the two pacing modes, at rest or during exercise. Thus, we found no significant differences between VDD and VVI_m pacing with regard to central hemodynamics, cardiac sympathetic nerve activity (cardiac norepinephrine overflow), or myocardial oxygen consumption either at rest or during moderate exercise.     

Lack of Influence of Atrioventricular Delay on Stroke Volume at Rest in Patients with Complete Atrioventricular Block and Dual Chamber Pacing

Dual chamber pacing (DDD) maintains atrioventricular (AV) sequence; AV delay programmability modifies the relationship between atrial and ventricular contraction. To evaluate the hemodynamic effects of such a modification, ten patients with a DDD unit for complete AV block were studied by time-motion (M-mode) and Doppler echocardiography during inhibited ventricular pacing (VVI), atrial-triggered ventricular pacing (VDD) and atrioventricular sequential pacing (DVI) at different AV delay (90, 140, 190, 240 msec). A significant improvement in stroke volume (SV) (15%-20%, P less than 0.05) was seen during DDD versus VVI pacing; no changes, however, were observed in the same patient with different AV delay or during DVI versus VDD pacing. These data suggest that programming of AV delay does not affect systolic performance at rest; longer diastolic filling times recorded during DDD pacing with "short" AV delay (90-140 msec) do not seem to be a hemodynamically relevant epi-phenomenon of PM programming.     

Evaluation of atrial thrombus formation and atrial appendage function in patients with pacemaker by transesophageal echocardiography

BACKGROUND: Physiologic pacing is claimed to be superior to ventricular pacing in as much as it entails lower risk of atrial fibrillation, stroke, and atrial remodeling. There are few data on the relation between atrioventricular (AV) synchrony and atrial clot formation. Utilizing transesophageal echocardiography (TEE), this study sought to evaluate the effect of AV synchrony loss on left atrial physiology, atrial stasis, and clot formation. METHODS: We conducted a cross-sectional study on patients with both AV and ventricular pacing with left ventricular ejection fraction (LVEF) >30%. TEE enabled us to explore atrial and pacing leads thrombi and measure left atrial appendage (LAA) flow velocity. RESULTS: A total 72 patients (mean age, 65 +/- 11.7) were enrolled in the study. The pacing mode was VVI in 53% and AV sequential in 47% of patients. LVEF (mean +/- SD; %) was 53.3 +/- 6.2% in ventricular pacing mode and 52.2 +/- 6.6 in physiologic pacing mode. Thrombus formation on pacing lead (<10 mm in 97% of patients) was observed in 32% of all the patients (23% in patients with AV sequential pacing mode and 39% with VVI mode). Left atrial appendage flow velocity (LAA-FV) was significantly higher among the patients with AV sequential pacing mode (49.44 +/- 18 cm/s vs 40.94 +/- 19.4 cm/s, P value = 0.02). LAA-FV >40 cm/s was detected in 60% of the patients, 60% of whom were in physiologic mode. Left atrial size was significantly larger among the patients with VVI pacing mode (42.3 +/- 2.3 mm vs 37.79 +/- 4.5 mm, P = 0.001). Multivariate analysis showed no relation between LAA-FV and age, hypertension, diabetes mellitus, left atrial size, and left ventricular function. Only one patient had right atrial clot. There was no thrombus in the ventricles and atrial appendage. CONCLUSION: Long-term loss of AV synchrony induced by VVI pacing is associated with the impairment of LAA contraction. Thrombus formation in the LAA is not increased by VVI pacing in patients with relatively good left ventricular (LV) function and sinus rhythm.     

Intermittent Pacemaker Syndrome: Revision of VVI Pacemaker to a New Cardiac Pacing Mode for Tachy-Brady Syndrome

A patient with tachy-brady syndrome manifested by paroxysmal atrial fibrillation and symptomatic sinus bradycardia and treated by VVI pacing developed pacemaker syndrome during episodes of ventricular pacing. His cardiac pacemaker was revised to a dual chamber system utilizing the new AV sequential DDI pacing mode which eliminated pacemaker-related tachycardias and totally abolished the pacemaker syndrome symptoms. There have been no further episodes of atrial fibrillation, possibly due to elimination of temporal dispersion of refractory periods during bradycardia. The propensity for atrial fibrillation has also been minimized by excluding competitive atrial stimulation during DVI pacing. The DDI mode provides the clinician increased utility and flexibility in the use of AV sequential pacing therapy.     

Hemodynamically optimized temporary cardiac pacing after surgery for congenital heart defects

Disturbance of normal AV synchrony and dyssynchronous ventricular contraction may be deleterious in patients with otherwise compromised hemodynamics. This study evaluated the effect of hemodynamically optimized temporary dual chamber pacing in patients after surgery for congenital heart disease. Pacing was performed in 23 children aged 5 days to 7.7 years (median 7.3 months) with various postoperative dysrhythmias, low cardiac output, and/or high inotropic support and optimized to achieve the highest systolic and mean arterial pressures. The following four pacing modes were used: (1) AV synchronous or AV sequential pacing with individually optimized AV delay in 11 patients with first- to third-degree AV block; (2) AV sequential pacing using transesophageal atrial pacing in combination with a temporary DDD pacemaker for atrial tracking and ventricular pacing in three patients with third-degree AV block and junctional ectopic tachycardia, respectively, who had poor signal and exit block on atrial epicardial pacing wires; (3) R wave synchronized atrial pacing in eight patients with junctional ectopic tachycardia and impaired antegrade AV conduction precluding the use of atrial overdrive pacing; (4) Atrio-biventricular sequential pacing in two patients. Pressures measured during optimized pacing were compared to baseline values at underlying rhythm (13 patients with first-degree AV block or junctional ectopic tachycardia) or during pacing modes commonly used in the given clinical situation: AAI pacing (1 patient with slow junctional rhythm and first-degree AV block during atrial pacing), VVI pacing (2 patients with third-degree AV block and exit block and poor sensing on epicardial atrial pacing wires) and dual-chamber pacing with AV delays set to 100 ms (atrial tracking) or 150 ms (AV sequential pacing) in 7 patients with second- to third-degree AV block and functional atrial pacing wires. Optimized pacing led to a significant increase in arterial systolic (mean) pressure from 71.5 +/- 12.5 (52.3 +/- 9.0) to 80.5 +/- 12.2 (59.7 +/- 9.1) mmHg (P < 0.001 for both) and a decrease in central venous (left atrial) pressure from 12.3 +/- 3.4 (10.5 +/- 3.2) to 11.0 +/- 3.0 (9.2 +/- 2.7) mmHg (P < 0.001 and < 0.005, respectively). In conclusion, several techniques of individually optimized temporary dual chamber pacing leading to optimal AV synchrony and/or synchronous ventricular contraction were successfully used to improve hemodynamics in patients with heart failure and selected dysrhythmias after congenital heart surgery.     

多普勒超声心动图（PDE）评价不同起搏方式对右心功能的影响

对17例安装永久性起搏器者应用脉冲多普勒记录肺动脉血流频谱,对比分析不同方式起搏器植入前后其右心功能的变化。结果显示:DDD起搏较VVI起搏的右室每搏量(SV)、心输出量(CO)增加(P<0.05、P<0.02),肺动脉峰值流速(PPFV)显著增加(P<0.01)。两组舒张早、晚期右室充盈指标均增加,DDD组舒张早期峰值流速(PFVE)显著增加(P<0.01)。表明:房室同步起搏较单纯心室起搏有更好的血液动力学效应,肺动脉血流参数可用于估价右室功能。     

Hemodynamic Findings During Sinus Rhythm, Atrial and AV Sequential Pacing Compared to Ventricular Pacing In a Dog Model

The hemodynamic responses of atrial lAF], atrioventricu-lar sequential (AVP) and ventricuJar pacing (VP) were compared to sinus rhythm (SfiJ in seventeen anesthetized dogs with intact AV conduction. The atrium and/or ventricle were paced at fixed rates above the control sinus rate. An AV interval shorter than normal conduction was selected to capture the ventricle. The changes of pulmonary capillary wedge pressure (PCWP, mmHg). mean aortic pressure (MAP, mmHg), cardiac output (CO, L/min), systemic vascular resistance (SVR, dynes/s/cm⁻⁵), left ventricular stroke work index (SWI) and mean systolic ejection rate (MSER, ml/s) during sinus rhythm, atrial pacing and atrio-ventricular sequential pacing (expressed in percentages of the individual values during ventricular pacing) were:
The importance of atrial systole for cardiac performance was clearly demonstrated in dogs with normally compliant hearts. In both atrial and atrioventricular sequential pacing compared to ventricular pacing there was a reduction of pulmonary capillary wedge pressure (PCWP) (p < 0.01) and systemic vascular resistance (SVR) (p < 0.01) despite an increase in cardiac output (CO). The lesser mean systolic ejection rate (MSER) found during atrioventricular sequential pacing compared to sinus rhythm and atrial pacing may be explained by the abnormal ventricular depolarization in this pacing mode; nevertheless, the mean systolic ejection rate was still greater than that found during ventricular pacing (p < 0.05).     

The Effect of Posture on the Response to Atrioventricular Synchronous Pacing in Patients with Underlying Cardiovascular Disease

In order to determine whether the hemodynamic benefit of atrioventricular synchronous pacing is maintained in the upright position, 14 patients with dual chamber pacemakers were paced in VVI mode and DDD mode in both the supine and standing position. The hemodynamic response was assessed by measuring the velocity time integral derived from the pulsed-wave Doppler signal in the left ventricular outflow tract during VVI pacing and dual chamber pacing at three different AV delays (125, 200, 250 ms). In the supine position, the velocity time integral during VVI pacing was 14.6 ± 3.0 cm and this increased during DDD pacing at all three AV delays (17.7 ± 3.3, 17.9 ± 3,0, 17.5 ± 3.5 cm). In the upright position, the velocity time integral during VVI pacing was 12.9 ± 3.5 cm and this increased with DDD pacing (15.5 ± 3.3, 15. 1 ± 4.0, 15.1 ± 3.9 cm). It was concluded that although stroke volume decreases when assuming the upright position, the beneficial response to dual chamber pacing is maintained and equals that observed in the supine position.     

Radionuclide Evaluation of Dual Chamber Pacing: Comparison Between Variable AV Intervals and Ventricular Pacing

We prospectively evaluated changes in left ventricular ejection fraction, end diastolic volume, and stroke volume via radionuclide multigated acquisition study, Comparison was made between ventricular pacing and dual chamber pacing with varying AV intervals. The volumes and changes in ejection fraction were determined at rest, at set increased pacing rates, and during physiological stress. AV sequential pacing shows overall improvement in cardiac function in the majority of patients regardless of left ventricular function. The shorter AV interval would be appropriate for the majority of patients who have an atrial tracking mechanism (adequate intrinsic sensed atrial activity followed by ventricular pacing) and who undergo significant physiological stress.     

DDI Pacing: Indications, Expectations, and Follow-Up

The DDI mode of pacing that permits noncompetitive atrioventricular sequential bradycardia support was chosen in 65 of 480 (14%) patients selected for dual chamber pacing between February 1985 and March 1990. All patients were implanted with Pacesetter 283 or 285 pulse generators and programmed to DDI. The indications for pacing were sick sinus syndrome (n = 52), combined sinus node dysfunction and AV block (n = 13). Forty-two of these patients had a history of paroxysmal atrial arrhythmias. All patients received passive fixation atrial and ventricular leads. Follow-up thereafter was performed predischarge, and at 6 weeks, 3 and 6 months after discharge. The duration of follow-up ranged from 1-61 months (mean 31 months). Fifty-four of 65 (83%) patients chosen for DDI remain programmed in the DDI mode. Three patients were reprogrammed to VVI and eight to DDD. During the course of follow-up, six patients presented with effective VVI pacing with consistent ventriculoatrial conduction that was appropriately sensed by the atrial circuit with atrial output inhibition. A further four patients presented with "functional undersensing" due to ventricular blanking period (VBP) characteristics in these pulse generators and in this mode. Functional undersensing was eliminated in all but one patient by reprogramming the VBP to 13 msec with no subsequent episodes of provoked crosstalk inhibition. Effective VVI pacing was observed in patients with AV block during times of sinus acceleration. While DDI mode is an effective form of pacing, permitting non-competitive atrioventricular sequential pacing, potential limitations include: effective VVI pacing during intact ventriculoatrial conduction, functional undersensing when long VBP are programmed, and effective VI pacing with sinus node acceleration during AV block.     

VDD Pacing at Short Atrioventricular Intervals Does Not Improve Cardiac Output in Patients with Dilated Heart Failure

Atrial synchronous pacing with short, nonphysiologicai atrioventricular (AV) intervals has been reported to increase cardiac output in selected patients with severe dilated heart failure. The aim of this study was to determine the acute effect of atrial synchronous pacing with short AV intervals in a consecutive series of patients with dilated heart failure. Twelve patients with a mean ejection fraction of 21 %± standard error 2.5% were studied. Pacing catheters were placed in the high right atrium and right ventricular apex and a balloon flotation catheter in the pulmonary artery for measurement of cardiac output. Simultaneous transthoracic echocardiography was performed for measurement of left ventricular filling time and mitral regurgitation. In a randomized crossover design, measurements were made during VDD pacing at programmed AV intervals of 100 and 60 msec and during a control period in sinus rhythm. Left ventricular filling time increased at AV intervals of 100 and 60 msec (mean difference 37 ± 9 and 34 ± 11 msec, respectively, both P < 0.01 compared to control). Despite increases in ventricular filling time, stroke, and cardiac index declined with short atrioventricular intervals (at an AV interval of 60 msec, stroke index fell by 2.1 ± 0.5 mL/m², P < 0.05 and cardiac index by 125 ± 45 mL/m²; P = NS). Heart rate was unchanged at both AV intervals (78 ± 4.9 at control, 78 ± 5.2 at 100 msec and 79 ± 4.9 beats/min at 60 msec; P = NS). The decrease in stroke index at an AV Interval of 60 msec was inversely related to control left ventricular filling time (r = 0.74; P = 0.01) and ejection fraction (r = 0.69; P = 0.02) and directly related to heart rate (r = 0.77; P < 0.01). The change in stroke index at an AV delay of 60 msec was also inversely related to the change in mitral regurgitation induced by pacing (r = 0.84; P = 0.01). Thus, in a group of patients with stable dilated heart failure, atrial synchronous pacing with short AV intervals did not improve cardiac output. The change in cardiac output with pacing was inversely related to baseline left ventricular function and to the change in mitral regurgitation induced by pacing.     

A Time-Related Study of the Hemodynamic Benefit of Atrioventricular Synchronous Pacing Evaluated by Doppler Echocardiography

We have used Doppler echocardiography to estimate the stroke volume (SV) in a study of 13 patients equipped with DDD pacemakers. SV was measured both during DDD and VVI pacing after observation times of 1,3,6, and 12 months of DDD pacing. SV was also measured at seven atrioventricular (AV) intervals (75-250 ms) in the search for optimal AV intervals. Mitral flow velocity was investigated to see if DDD pacing resulted in synchronous atrial contraction, and if mitral insufficiency existed at any of the pacing modes. Compared with the VVI mode, DDD pacing resulted in a mean increase in SV of 21 +/- 2% for the four observation periods. Two patients with severe left ventricular failure had no significant increase in SV during DDD vs VVI pacing. In each patient, an optimal AV interval ranging between 100-250 ms for the SV was found. Velocity profiles of mitral flow showed synchronous atrial contraction during DDD pacing, but not during VVI pacing. Mitral insufficiency was not seen in any pacing mode. DDD pacing resulted in a reduction in SV during the first 6 months, and was constant thereafter. Doppler echocardiography can be used repeatedly to evaluate the hemodynamic response of DDD pacing vs VVI pacing, and to find which AV interval gives the highest SV in the individual patient. Our study further shows that the hemodynamic benefit of DDD pacing is present after short-term as well as after long-term DDD pacing.     

Usefulness of Doppler Echocardiography in Cardiac Pacing: Assessment of Mitral Regurgitation,Peak Aortic Flow Velocity and Atrial Capture

Doppler echocardiographic studies were performed in 14 patients with dual chamber pacemakers. Transmitral flow studies (12 patients) revealed absence of mitral regurgitation (MR) or no change in MR severity in 6, new development or increased MR during VVI and/or short or long A V interval lengths compared to more normal AVintervals(150–160 ms) in 5, and appearance of MR when the pacing mode was changed from VVI to DVI with a fixed AV interval of 250 ms in 1 patient. Aortic peak flow velocity measurements (7 patients) showed significant increases in stroke volume(range9 to 25%. mean 19.5%) in all patients with DVI/VDD pacing compared to VVI pacing (4 patients) or to shortest available AV interval (3 patients). Presence of Doppler left atrial systolic flow correlated with evidence of atrial depolarization in all 7 patients in whom high quality 12-lead surface electrocardiograms were obtained. Our preliminary study demonstrates the value of Doppler echocardiography in the “fine tuning” of cardiac pacemaker parameters by assessment of presence, absence, or change in severity of MR, estimation of relative changes in stroke volume, and determination of atrial capture in different pacing modes and at various AV intervals.     

Comparison of Intrinsic Versus Paced Ventricular Function

There is increasing evidence supporting the benefits of providing optimum AV delay in cardiac pacing, though controversy exists regarding its value and the benefits of intrinsic versus paced ventricular activation. This study compared various AV delays at rest in patients whose native AV delays were 200 msec. Only patients with DDD pacemakers who had intact AV conduction and normal ventricular activation were included in the study. Nine patients were studied. Methods: Ten studies were performed. Evaluation was done in AAI and DDD modes at paced heart rates of 60/min or as close as possible to the intrinsic heart rate if this was > 60/min. Stroke volume (SV) and cardiac output (COJ were measured. Results: When AV sequential pacing in the DDD mode with an optimum AV delay was compared to AAI pacing with a prolonged AV interval, the average optimum AV delay in the DDD mode was 157 msec and ranged from 125 to 175 msec. The average AV interval in the AAI mode was 245 msec and ranged from 212 to 300 msec. In the DDD mode, there was an overall significant improvement in CO of 11% and SV of 9%. Patients with intrinsic AV conduction times of > 220 msec showed an overall significant improvement in CO of 13% and SV of 11%. In patients with intrinsic AV conduction times of < 220 msec, an improvement in CO of 6% and SV of 4% was seen. Conclusions: (1) An optimum AV delay is an important component of hemodynamic performance; and (2) AV sequential pacing at rest with an optimum AV delay may provide better hemodynamic performance than atrial pacing with intrinsic ventricular conduction when native AV conduction is prolonged > 220 msec.