Importance of left atrial timing in the programming of dual-chamber pacemakers

To determine the hemodynamic effect of different programmed atrioventricular (AV) delays and the importance of the actual timing of left atrial (LA) depolarization, 16 patients with dual-chamber pacemakers were studied and all were found to have an optimal programmed AV delay for cardiac function. However, randomly chosen AV delays of 150, 200 or 250 ms actually provided worse stroke volume than VVI pacing in 7 patients. The optimal programmed AV delay was variable between patients and was related to the interatrial conduction delay, measured as the time from right atrial pacing artifact to LA depolarization (mean 144 +/- 82 ms, range 70 to 380.) Patients with short interatrial delays (less than or equal to 90 ms) were served better by shorter programmed AV delays (150 ms), and patients with longer interatrial delays (greater than or equal to 120 ms) were served better by longer programmed AV delays (greater than or equal to 200 ms) (p less than 0.05). Furthermore, as pacing mode changed from dual-chamber sequential pacing (DVI) to atrial synchronous ventricular pacing (VDD), the LA to ventricular sequence increased from 6 +/- 81 ms to 137 +/- 50 ms (p less than 0.001). This change in the LA to ventricular sequence with mode change produced a significant decrease in stroke volume (p less than 0.05). Thus, the optimal programmed AV delay in patients with dual-chamber pacemakers is predicted by the relation of LA and ventricular activation. Because interatrial conduction delays vary widely, optimal programming requires knowledge of the LA to ventricular sequence.(ABSTRACT TRUNCATED AT 250 WORDS)     

Doppler echocardiographic study of hemodynamic changes of double stimulation mode and atrial detection in patients with dual chamber pacemaker. Value of hysteresis of the atrioventricular delay

This Doppler echocardiographic study of patients with a dual chamber pacemaker was undertaken to assess the changes in mitral and aortic flow induced by passing from the double stimulation to the atrial detection mode. Thirteen patients totally dependent on ventricular pacing were examined and mitral and aortic blood flow recorded by pulsed wave Doppler. The chronology of left atrial contraction as assessed by the Doppler mitral A wave was measured with respect to the ventricular stimulation. The A wave was recorded on average 177 ms after the right atrial stimulation artefact. For an average AV delay of 168.8 ms and an identical pacing frequency, the passage from the double stimulation to the atrial detection mode led to left atrial contraction occurring on average 70 ms earlier with respect to ventricular stimulation, reflecting prolongation of the programmed AV delay related to the delay in detection of the sinus atrial wave. This earlier atrial systole shortened the total duration of mitral flow from 363 to 317 ms, decreased the early diastolic mitral flow and increased the atrial end diastolic flow; the stroke volume and cardiac output calculated from the aortic velocity time integral decreased significantly from 73 +/- 11 ml to 67 +/- 10 ml and 5.4 +/- 1.11/mn to 4.9 +/- 1.01/mn respectively. The initial parameters were restored (average 74 +/- 9 ml and 5.5 +/- 1.11/mn respectively) when the AV delay in the atrial detection mode was reduced by a value close to that of the calculated increase.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of Various Measures of Optimum Atrial Timing in Patients with Dual Chamber Pacemakers

Background: In patients with dual chamber pacemakers, the optimal AV delay is highly variable. This study examines the alternative measures of optimum atrial timing and the factors responsible for the marked variability in the optimal AV delay. Methods and results: Twelve patients with dual chamber pacemakers were studied. The AV delay was varied from 25 to 250 ms in 25‐ms increments and at each stage, mitral, tricuspid, and aortic flows were recorded using the Doppler technique. The optimum AV delay varied from 75 to 175 ms (146 ± 37 ms). At optimum AV delay, both the E and A waves of the transmitral flow were partially fused, eliminating diastasis with a fusion velocity of 27 ± 14 cm/s. The stroke distance was lower when the E and A waves were not fused at shorter AVD, despite a longer diastolic filling period, or fully fused at a longer AVD, which also the shortened diastolic filling period. At optimum AV delay, the E/A velocity ratio was 0.74 ± 0.15, reflecting slight atrial predominance of LV filling. The optimum timing of atrial contraction was better defined in terms of its relation to LV ejection (175 ± 31 ms before LV ejection), and this had a smaller coefficient of variation than optimum AV delay. This interval, unlike the AV delay, was not affected by interatrial and interventricular conduction times. Conclusions: In this older population of patients with dual chamber pacemakers without significant valvular heart disease, the effective LA contraction in relation to LV ejection is a better measure of atrial timing than the programmed AV delay which is affected by atrial and ventricular conduction times. A.N.E. 2000;5(1):68–72     

The hemodynamic benefit of differential atrioventricular delay intervals for sensed and paced atrial events during physiologic pacing

The ability to program different atrioventricular (AV) delay intervals for paced and sensed atrial events is incorporated in the design of some newer dual chamber pacemakers. However, little is known regarding the hemodynamic benefit of differential AV delay intervals or the magnitude of difference between optimal AV delay intervals for paced and sensed P waves in individual patients. In this study, Doppler-derived cardiac output was used to examine the optimal timing of paced and sensed atrial events in 24 patients with a permanent dual chamber pacemaker. The hemodynamic effect of utilizing separate optimal delay intervals for sensed and paced events compared with utilizing the same fixed AV delay interval for both was determined. The optimal delay interval during DVI (AV sequential) pacing and VDD (atrial triggered, ventricular inhibited) pacing at similar heart rates was 176 +/- 44 and 144 +/- 48 ms (p less than 0.002), respectively. The mean difference between the optimal AV delay intervals for sensed (VDD) and paced (DVI) P waves was 32 ms and was up to 100 ms in some individuals. The difference between optimal AV delay intervals for sensed and paced atrial events was similar in patients with complete heart block and those with intact AV node conduction. At the respective optimal AV delay intervals for sensed and paced P waves, there was no significant difference in the cardiac output during VDD compared with DVI pacing. However, cardiac output significant declined during VDD pacing at the optimal AV delay interval for a paced event and during DVI pacing at the optimal interval for a sensed event.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ventrikuläre Stimulationsvermeidung bei Patienten mit Sinusknotenerkrankung oder intermittierendem AV-Block

In patients with frequent right ventricular stimulation, worsening of heart failure and atrial fibrillation may occur. Avoidance of unnecessary right ventricular pacing is a major requirement for pacemaker selection and programming in patients with sinus node disease or intermittent AV block. In dual chamber pacemakers this goal can be achieved by programming a long AV delay or an AV delay hysteresis. Algorithms that allow AAI pacing in a dual chamber pacing mode and change to DDD mode in case of high degree AV block are a new attempt to avoid unnecessary right ventricular pacing. The article describes various strategies to avoid unnecessary ventricular pacing and discusses their advantages and disadvantages.     

心房起搏脉冲传导延迟患者AV问期的优化

目的探讨心房起搏至心房除极波时间延迟患者设置起搏的房室间期（PAV）的方法及远期心房起搏的有效性。方法分析2005年1月至2012年12月我院起搏器植入后发生心房起搏至心房除极波时间延迟≥lOOms的患者10例,病窦综合征（SSS）患者的房室间期设置为最大值,并最大限度开启房室问期滞后功能;对房室传导阻滞（AVB）患者设置PAV的值为：140～180ms＋心房起搏至心房除极波延迟时间,不开启AV滞后。结果经1个月至7年随访,5例SSS患者心室起搏比例〈10％,3例SSS患者心室起搏比例30％。50％,Holter显示心室起搏时为假性融合波,l例SSS患者及1例AVB患者为心室起搏心律,起搏比例〉99％,保证了房室问期的生理性。10例患者心房起搏阈值均〈1．5／0．4ms,未发生心房起搏阈值增高及失夺获。结论心房起搏至心房除极波时间延迟患者远期的心房起搏夺获是安全的;设置起搏器PAV间期要将心房起搏至心房除极波延迟时间计算其中,程控随访中应注意观察程控仪中监护图的心房波,房室传导阻滞患者可延长房室间期后观察心房波,部分患者因监护导联显示不清,需要通过12导联心电图进行观察,避免心房起搏至心房除极波延迟病例被遗漏．导致增加心室起搏及非生理性的房室间期。     

Importance of maintained atrio-ventricular synchrony in patients with pacemarkers

The effect of atrial contraction on cardiac function is reviewedin patients with dual chamber and rate-responsive ventricularpacemakers. The question posed was is there any haemodynamic,clinical or prognostic advantage of AV synchrony in dual chamberpacemakers in comparison to rate-responsive ventricular pacemakers?Optimal A V delay in dual chamber pacing favours cardiac performanceat rest, while during exercise the increase in heart rate ratherthan A V synchrony influences cardiac performance and workingcapacity. However, there is little information on the benefitof maintained A V synchrony in patients' daily activities. Patientswith pacemakers which maintain AV synchrony seem to have lessmorbidity and mortality than patients with ventricular stimulationalone, and there are comparable rates of complication in carriersof single and dual chamber pacemakers, the former showing problemswith the pacemaker syndrome and the latter with atrial sensingand pacemaker-induced tachycardias. The disadvantage of dualchamber pacemakers are higher costs and time-consuming controls.     

Evaluation by pulsed Doppler echocardiography of the atrial contribution to left ventricular filling in patients with DDD pacemakers

To evaluate the significance of the left atrial (LA) contribution to left ventricular (LV) filling in cardiac pacing, LV inflow velocity was recorded with pulsed Doppler echocardiography in 20 patients with a DDD pacemaker. The pacemaker was programmed to atrioventricular (AV) sequential pacing with AV intervals of 50, 100, 150, 200 and 250 ms, and then to VVI pacing at a fixed rate of 70 beats/min. To evaluate the relative changes of LV filling volume in individual patients, the percent change in time-velocity integral of LV inflow velocity in each pacing mode was calculated as the ratio to that of AV sequential pacing with an AV interval of 150 ms. To estimate the degree of LA contribution to LV filling, the ratio of time-velocity integral during LA ejection phase to that during total LV filling phase was measured at the optimal AV interval. The percent LV inflow volume in AV sequential pacing was 74% for an AV interval of 50 ms, 87% for 100 ms, 98% for 200 ms and 90% for 250 ms. The percent LV inflow volume in VVI pacing was 72%. The percent LV inflow volume at AV intervals of 150 ms was significantly greater than that at an AV interval of 50, 100 and 250 ms, and in VVI pacing (p less than 0.05). The degree of LA contribution to LV filling showed a positive correlation with the percent increase of LV inflow volume with mode conversion from VVI to AV sequential pacing (p less than 0.005) and also with age (p less than 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)     

不同房室间期对双腔起搏左室收缩功能的影响

为探讨双腔起搏不同房室间期对左室收缩功能的影响及最佳房室间期 ,选择 18例置入DDD起搏器的病窦综合征患者 ,在DOO起搏方式下随机将房室 (AV)间期程控为 10 0 ,130 ,15 0 ,170 ,2 0 0ms,在超声心动图下观察左室收缩功能指标 ,每次测量间隔 5min以上。结果 :AV间期为 15 0ms时左室收缩功能最好 ,与AV间期为 10 0ms时相比 ,左室收缩功能明显改善。以心输出量 (CO)为标准 ,18例中有 9例AV间期在 15 0ms时CO最佳 ,5例在 2 0 0ms时CO最佳 ,3例在 170ms时CO最佳 ,1例在 130ms时CO最佳 ;以CO为标准 ,DOO起搏方式最佳AV间期为 16 6±2 4ms。结论 :双腔起搏的AV间期对左室收缩功能有重要的影响 ,以CO为标准 ,个体化地选择双腔起搏的最佳AV间期对改善患者的心脏功能有重要的意义。     

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)     

Doppler echocardiographic study of mitral and aortic flow at various rates and atrioventricular intervals in patients with dual chamber pacemakers

The aim of this study was to measure the changes in mitral and aortic blood flow induced by rate changes and different atrioventricular intervals in dual chamber pacemaker patients. Ten totally pacemaker dependant patients were studied under basal conditions, in double atrial and ventricular stimulation mode, by pulsed Doppler recordings of mitral and aortic flow, at three different pacing rates (80, 100 and 120/mn) and with three different atrioventricular intervals at each rate (short, 90 or 115 ms; medium, 165 or 190 ms; and long, 240 ms). The increase in pacing rate and prolongation of the atrioventricular interval significantly shortened the duration of mitral flow. Increasing the pacing rate induced a significant fall in stroke volume measured from the aortic flow. The optimal atrioventricular interval tended to shorten when the pacing rate was increased; a long atrioventricular interval had a deleterious effect on stroke volume compared with medium and short atrioventricular intervals; however, the difference between the short and medium atrioventricular intervals was not statistically significant even at 120 mn. These observations emphasise the hemodynamic advantages of shortening of the atrioventricular interval of dual chamber pacemakers when the pacing rate increases.     

Acute hemodynamic effects of different atrioventricular intervals in dual chamber pacemakers: is there an optimum atrioventricular delay.

Conflicting data have been reported regarding adjustment of atrioventricular (AV) interval to maximise hemodynamic performance of dual chamber pacemakers. Eleven consecutive patients with complete heart block and dual chamber pacemakers were paced at three AV intervals (150, 200, 250 msec) and free running rates (60-93 bpm, mean 73 +/- 12 bpm) with simultaneous measurements of cardiac output, atrial contribution to left ventricular filling, left ventricular ejection fraction, and peak aortic velocity and acceleration by echo-Doppler techniques to define the optimum AV delay. At all the three AV intervals tested there was no difference in cardiac output (4.7 +/- 0.96, 4.83 +/- 1.12, 4.77 +/- 1.19 litres/min respectively, p = NS), left ventricular ejection fraction (60.2 +/- 10.6%, 61.2 +/- 9.9% and 64 +/- 8.3%, p = NS), atrial contribution to left ventricular filling (0.37 +/- 0.10, 0.38 +/- 0.09, 0.36 +/- 0.16, n = 8, p = NS), peak aortic velocity (104 +/- 8, 105 +/- 12, 104 +/- 13 cm/sec, p = NS) and aortic acceleration (19.68 +/- 4.26, 20.4 +/- 5.58 and 19.0 +/- 4.54 m/sec2, p = NS). Compared to AV delay of 150 msec an increase in cardiac output of 0.5 L/minute was observed in three patients at an AV delay of 200 msec and in one patient at the AV delay of 250 msec. These data suggest that it is difficult to generalize an optimum AV delay in patients with dual chamber pacemakers. With the AV interval in the range of 150-250 msec, only a minority of patients could improve their haemodynamics at rest by adjusting this interval if the baseline cardiac function was normal.     

Preventricular Far-Field Sensing in the Atrial Channel of Dual Chamber Pacemakers—An Occasional Cause of Inappropriate Mode Switch

INTRODUCTION AND AIMS OF THE STUDY: Atrial oversensing may trigger false positive mode switch to an asynchronous mode in dual chamber pacemakers. While myopotential oversensing and far-field R wave sensing within the postventricular atrial refractory period are well characterized, data about oversensing (near-field P wave or far-field R wave) within the atrioventricular delay is limited. Aim of the study was to determine the incidence of preventricular oversensing in the atrial channel of current dual chamber pacemakers. METHODS: Consecutive patients with dual chamber pacemakers who were in sinus rhythm and who showed no myopotential oversensing were included in the study. Atrial sensitivity was programmed to the maximal available value and atrioventricular delay was prolonged when necessary for intrinsic atrioventricular conduction. RESULTS: Ten out of 100 (10%) patients showed oversensing within the atrioventricular delay at highest levels of atrial sensitivity, median sensing threshold for the signals was 0.35 mV, and the median coupling interval between preventricular atrial oversensing and the ventricular sensed event was 20 ms. CONCLUSION: The incidence of inappropriate mode switch caused by atrial preventricular oversensing related to near-field P wave or far-field R wave oversensing in dual chamber pacemakers is up to 10%. Interpretation of pacemaker Holters should consider oversensing within the atrioventricular delay as a differential diagnosis to true episodes of atrial tachyarrhythmias.     

Improved method for evaluating ventriculoatrial conduction before implantation of atrial-sensing dual chamber pacemakers

Pacemaker-mediated tachycardia may occur when a spontaneous ventricular premature depolarization is retrogradely conducted to the atrium with a ventriculoatrial (VA) interval that exceeds the atrial refractory period of an atrial-sensing dual chamber pacemaker. Previous methods for evaluating VA conduction have failed to predict clinical occurrences of pacemaker-mediated tachycardia. In this study, maximal VA intervals after ventricular extrastimuli during atrial or atrioventricular (AV) sequential pacing were compared with intervals measured by the standard method of ventricular pacing. VA intervals were 201 +/- 53 ms during ventricular pacing and 224 +/- 52 ms after ventricular extrastimuli during atrial pacing (p = NS). VA intervals were 305 +/- 77 ms after ventricular extrastimuli during AV sequential pacing and were longer than VA intervals during ventricular pacing (p less than 0.001) or after ventricular extrastimuli during atrial pacing (p less than 0.01). Thus, the ventricular extrastimulus technique during AV sequential pacing reveals substantially longer VA intervals than does ventricular pacing and explains why pacemaker-mediated tachycardia might occur when pacemaker atrial refractory periods are designed or programmed according to VA intervals measured only during ventricular pacing.     

Optimal atrioventricular delay at rest and during exercise in patients with dual chamber pacemakers: a non-invasive assessment by continuous wave Doppler.

The optimal atrioventricular delay at rest and during exercise was investigated in nine patients with heart block and implanted dual chamber pacemakers. All patients studied had normal left ventricular function and a normal sinus node rate response to exercise. Cardiac output was measured by continuous wave Doppler and was calculated as the product of stroke distance measured by Doppler at the left ventricular outflow, aortic root area measured by M mode echocardiography, and heart rate. Pacemakers were programmed in the DDD mode. Cardiac output was measured with the patient at rest while supine and while erect and at the peak of submaximal exercise (the end of stage 1 of the Bruce protocol) with the pacemakers programmed to the following atrioventricular intervals: 75-80 ms, 100-110 ms, 140-150 ms, and 200 ms. During exercise the basic pacing rate was programmed to 70 beats/min. Cardiac output at rest while supine and erect was greatest with an atrioventricular delay of 140-150 ms and it was significantly higher than that with an atrioventricular delay of 75-80 ms. On average there was a 31% decrease in cardiac output when patients stood up. During treadmill exercise, however, cardiac output was greatest when the atrioventricular delay was 75-80 ms, and this was significantly higher than the cardiac output with atrioventricular delays of 150 and 200 ms. During exercise 1:1 atrioventricular relations were maintained in patients at all atrioventricular intervals. In patients with atrioventricular sequential pacemakers cardiac output at rest is greatest with an atrioventricular delay of 140-150 ms but during exercise the optimal atrioventricular delay is shorter. Rate modulation of the atrioventricular interval may improve the haemodynamic response and possibly exercise tolerance in patients with dual chamber pacemakers.     

Optimal atrioventricular delay at rest and during exercise in patients with dual chamber pacemakers: a non-invasive assessment by continuous wave Doppler

The optimal atrioventricular delay at rest and during exercise was investigated in nine patients with heart block and implanted dual chamber pacemakers. All patients studied had normal left ventricular function and a normal sinus node rate response to exercise. Cardiac output was measured by continuous wave Doppler and was calculated as the product of stroke distance measured by Doppler at the left ventricular outflow, aortic root area measured by M mode echocardiography, and heart rate. Pacemakers were programmed in the DDD mode. Cardiac output was measured with the patient at rest while supine and while erect and at the peak of submaximal exercise (the end of stage 1 of the Bruce protocol) with the pacemakers programmed to the following atrioventricular intervals: 75-80 ms, 100-110 ms, 140-150 ms, and 200 ms. During exercise the basic pacing rate was programmed to 70 beats/min. Cardiac output at rest while supine and erect was greatest with an atrioventricular delay of 140-150 ms and it was significantly higher than that with an atrioventricular delay of 75-80 ms. On average there was a 31% decrease in cardiac output when patients stood up. During treadmill exercise, however, cardiac output was greatest when the atrioventricular delay was 75-80 ms, and this was significantly higher than the cardiac output with atrioventricular delays of 150 and 200 ms. During exercise 1:1 atrioventricular relations were maintained in patients at all atrioventricular intervals. In patients with atrioventricular sequential pacemakers cardiac output at rest is greatest with an atrioventricular delay of 140-150 ms but during exercise the optimal atrioventricular delay is shorter. Rate modulation of the atrioventricular interval may improve the haemodynamic response and possibly exercise tolerance in patients with dual chamber pacemakers.     

Endless loop tachycardia started by an atrial premature complex in a patient with a dual chamber pacemaker

In a patient with a dual chamber pacemaker that senses in both the atrium and ventricle (VDD, DDD), a ventricular depolarization temporally displaced from a P wave can cause retrograde atrial activation and initiate an endless loop pacemaker-mediated tachycardia. A case in which an endless loop tachycardia was initiated by an end-diastolic atrial premature complex is reviewed. Retrograde conduction occurred because of the change in the temporal relation of atrial sensing and atrioventricular (AV) node depolarization. The implanted pacemaker did not have the capability of atrial refractory programmability. Atrial refractory interval extension, which occurs in this model after a ventricular premature complex to protect against a retrograde P wave, was not invoked since the tachycardia was begun by an atrial rather than a ventricular premature complex. The tachycardia was controlled by shortening the programmable AV delay. The mechanism of tachycardia induction and its management are outlined. Atrial refractory programmability is required in all VDD or DDD pacemakers.     

不同起搏方式对心房电机械延迟影响的对比研究

了解双腔起搏 (DDD)患者右心耳起搏 (RAA)方式对心房电机械延迟 (AEMD)的影响。对 2 1例置入DDD的患者 ,用M型超声心动图结合同步心电图分别测量DDD方式及心房感知心室起搏 (VDD)方式下的AEMD。结果 :RAA起搏与窦性节律比较 ,AEMD明显增加 ,其中P波起始至中央纤维体 (CFB)运动发生的时间增加 2 8± 4ms、至CFB最大收缩振幅出现的时间增加 42± 3ms、至左房侧壁 (LLA)运动发生的时间增加 35± 5ms、至LLA最大收缩振幅出现的时间增加 34± 4ms (所有P <0 .0 0 1)。结论 :DDD患者右心耳起搏能明显增加AEMD     

Physiological cardiac pacing: Current status

Adverse hemodynamics of right ventricular (RV) pacing is a well-known fact. It was believed to be the result of atrio-ventricular (AV) dyssynchrony and sequential pacing of the atrium and ventricle may solve these problems. However, despite maintenance of AV synchrony, the dual chamber pacemakers in different trials have failed to show its superiority over single chamber RV apical pacing in terms of death, progression of heart failure, and atrial fibrillation (AF). As a consequence, investigators searched for alternate pacing sites with a more physiological activation pattern and better hemodynamics. Direct His bundle pacing and Para-Hisian pacing are the most physiological ventricular pacing sites. But, this is technically difficult. Ventricular septal pacing compared to apical pacing results in a shorter electrical activation delay and consequently less mechanical dyssynchrony. But, the study results are heterogeneous. Selective site atria pacing (atrial septal) is useful for patients with atrial conduction disorders in prevention of AF.     

Assessment of the optimal atrio-ventricular delay in DDD paced patients by impedance plethysmography

The beneficial haemodynamic effects of sequential atrioventricular(AV) pacing have been clearly established and are dependenton the AV delay and pacing rate. However, the optimal AV delayis difficult to determine in each particular patient. We useda modified impedance plethysmographic method to assess variationsin stroke volume for different AV delay and pacing rate settings.Impedance measurements showed a good correlation with CO₂ rebreathingstroke volume measurements in VVI patients. Impedance variationswere then used to set the optimal AV delay at different pacingrates in DDD patients. The inverse relationship between theoptimal AV delay and the pacing rate has been accurately identifiedin most of the patients but is not predictable. In all cases,the cardiac output was higher in DDD mode at the optimal AVdelay than in VVI mode. In some patients with a damaged myocardium,the stroke volume appeared to be highly sensitive to multipleA V delay settings. Impedance plethysmography can permit suchrepetitive non-invasive quick measurements, increasing the accuracyof optimal A V delay determination and is well suited for routineexamination of patients with cardiac dual chamber pacemakers