Mitral valve closure and left ventricular filling time in patients with VDD pacemakers. Assessment of the onset of left ventricular systole and the end of diastole

The Interplay of PR Interval and AV Pacing Delays Used for Cardiac Resynchronization Therapy in Heart Failure Patients: Association with Clinical Response in a Retrospective Analysis of a Large Observational Study

Background. Cardiac resynchronization therapy (CRT) is a treatment for heart failure (HF) patients with prolonged QRS and impaired left ventricular (LV) systolic function. We aim to evaluate how the baseline PR interval is associated with outcomes (all-cause death or HF hospitalizations) and LV reverse remodeling (>15% relative reduction in LV end-systolic volume). Methods. Among 2224 patients with CRT defibrillators, 1718 (77.2%) had a device programmed at out-of-the-box settings (sensed AV delay: 100 ms and paced AV delay: 130 ms). Results. In this cohort of 1718 patients (78.7% men, mean age 66 years, 71.6% in NYHA class III/IV, LVEF = 27 ± 6%), echocardiographic assessment at 6-month follow-up showed that LV reverse remodeling was not constant as a function of the PR interval; in detail, it occurred in 56.4% of all patients but was more frequent (76.6%) in patients with a PR interval of 160 ms. In a median follow-up of 20 months, the endpoint of death or HF hospitalizations occurred in 304/1718 (17.7%) patients; in the multivariable regression analysis it was significantly less frequent when the PR interval was between 150 and 170 ms (hazard ratio = 0.79, 95% confidence interval (CI): 0.63−0.99, p = 0.046). The same PR range was associated with higher probability of CRT response (odds ratio = 2.51, 95% CI: 1.41−4.47, p = 0.002). Conclusions. In a large population of CRT patients, with fixed AV pacing delays, specific PR intervals are associated with significant benefits in terms of LV reverse remodeling and lower morbidity. These observational data suggest the importance of optimizing pacing programming as a function of the PR interval to maximize CRT response and patient outcome.

A randomized controlled trial of cardiac resynchronization therapy in patients with prolonged atrioventricular interval: the REAL-CRT pilot study

Aims

A prolonged PR interval is known to be associated with increased mortality and a higher risk of developing atrial fibrillation (AF). We tested the hypothesis that cardiac resynchronization therapy (CRT) is superior to conventional dual-chamber pacing with algorithms for right ventricular pacing avoidance (DDD-VPA) in preserving systolic and diastolic function and in preventing new-onset AF in patients with normal systolic function, indication for pacing and prolonged atrioventricular conduction (PR interval ≥220 ms).

Methods and results

We randomly assigned 82 patients with ejection fraction >35%, indication for pacing and PR interval ≥220 ms to CRT or to DDD-VPA. On 12-month follow-up examination, the study and control arms did not differ in terms of left ventricular end-systolic volume (44 ± 17 mL vs. 47 ± 16 mL, P = 0.511) or ejection fraction (55 ± 6% vs. 57 ± 8%, P = 0.291). The E to A mitral wave amplitude ratio was higher in the CRT arm (1.3 ± 1.3 vs. 0.8 ± 0.4, P = 0.046) and the E wave deceleration time was longer (262 ± 83 ms vs. 205 ± 51 ms, P = 0.027). Left atrial volume was smaller in the CRT arm (64 ± 17 mL vs. 84 ± 25 mL, P = 0.035). Moreover, the functional class was lower in CRT patients (1.4 ± 0.6 vs. 1.8 ± 0.5, P = 0.010). During follow-up, CRT was associated with a lower risk of new-onset AF [hazard ratio = 0.37 (0.13–0.98), P = 0.046].

Conclusion

Cardiac resynchronization therapy proved superior to DDD-VPA in terms of better diastolic function, less left atrial enlargement and lower risk of new-onset AF, at 12 months. These data need to be confirmed in a larger trial with longer follow-up.

Clinical trial registration

URL: http://clinicaltrials.gov/ Identifier: NCT02150538

Non-invasive determination of the optimized atrioventricular delay in patients with implanted biventricular pacing devices

BACKGROUND

Biventricular (BiV) is extensively used in the treatment of congestive heart failure but so far no recommendations for optimized programming of atrioventricular-delay (AVD) settings have been proposed. Can AVD optimization be performed using a simple formula based on non-invasive doppler-echocardiography?

METHODS

25 patients (ejection fraction 30+/-8%) received BiV ICDs. Doppler-echocardiographic evaluation of diastolic and systolic flow was performed for different AVDs (30ms to 150ms) and different stimulation sites (left ventricular (LV), right ventricular and BiV). The optimal atrioventricular delay was calculated applying a simple formula based on systolic and diastolic mechanical delays determined during doppler-echocardiography.

RESULTS

The mean optimal AVD was calculated to be 112+/-29ms (50 to 180ms) for BiV, 95+/-30ms (65 to 150ms) for LV and 75+/-28ms (40 to 125ms) for right ventricular pacing with wide interindividual variations. Compared to suboptimal AVDs diastolic optimization improved preejection and ejection intervals independent to pacing site. Optimization of the AVD significantly increased ejection time during BiV pacing (279ms versus 266ms; p<0.05). Compared to LV or right ventricular pacing BiV pacing produced the shortest mean pre-ejection and longest ejection intervals as parameters of improved systolic ventricular contractile synchrony. Diastolic filling times were longest during BiV pacing compared to LV or RV pacing.

CONCLUSIONS

Individual programming of BiV pacing devices increases hemodynamic benefit when implementing the inter-individually widely varying electromechanical delays. Optimization applying a simple formula not only improves diastolic ventricular filling but also increases systolic functional parameters.

A Fast and Simple Echocardiographic Method of Determination of the Optimal Atrioventricular Delay in Patients After Biventricular Stimulation

The optimization of atrioventricular (AV) delay is known to significantly contribute to maximum cardiac performance. The aim of this study was to validate a new, fast, and simple echocardiographic method of identifying the AV delay that provides the maximum cardiac output (CO). Right heart catheterization and Doppler echocardiography of transmitral filling were performed simultaneously in 18 patients with heart failure and at least minimum functional mitral regurgitation treated with atrial synchronized biventricular pacing. CO derived from catheterization and Doppler filling parameters were measured at the predicted optimal AV delay (oAVD), the short AV delay (oAVD - 50 ms), and the long AV delay (oAVD + 28 ms on average/range, +10 ms to +50 ms) during a constant heart rate. The AV delay was regarded as optimal if the end of atrial contraction (represented by the end of A wave of transmitral filling) coincided with the beginning of ventricular contraction (heralded by the onset of the systolic component of mitral regurgitation). Prediction of the optimal AV delay included the following steps: (1) The maximum AV delay at which full ventricular capture is still preserved was found under electrocardiographic control. (2) This value, decreased by 5 to 10 ms, was designated as "the testing long AV delay," and the time interval from the end of the A wave to the onset of the systolic component of mitral regurgitation (time t1) was measured at this setting. (3) oAVD was simply calculated as "the testing long AV delay"- time t1. The CO measured at the oAVD (4.5 +/- 0.7 1. min-1) significantly exceeded those at the short AV delay (4.3 +/- 0.7 1. min-1, P < 0.01) and the long AV delay (4.4 +/- 0.8 1. min-1, P < 0.01), respectively. The method correctly determined the maximum CO in 78% of the patients. In conclusion, Doppler echocardiography enables very rapid and accurate optimization of AV synchrony in patients after the implantation of a biventricular pacemaker.

Acute effects of cardiac resynchronization therapy on left ventricular Doppler indices in patients with congestive heart failure

BACKGROUND

Patients with heart failure frequently exhibit intraventricular conduction delays, which contribute to asynchronous contraction patterns and impaired hemodynamic performance. Cardiac resynchronization therapy (CRT) with biventricular (BV) and left ventricular (LV) pacing has been shown to improve both hemodynamic and clinical performance. This study investigated the effects of CRT on LV Doppler indices in these patients.

METHODS AND RESULTS

Thirty-two patients with advanced heart failure (New York Heart Association class > or =III, QRS >120 milliseconds, PR interval >150 milliseconds) were studied 4 weeks after implantation of a CRT system. Doppler echocardiography was conducted in 3 separate CRT modes, right ventricular, LV, and BV stimulation at 3 different atrioventricular delays. CRT resulted in significant improvement of Doppler parameters such as filling time (FT, 313 +/- 111 milliseconds at baseline --> 363 +/- 154 milliseconds [BV], P <.05), aortic velocity time integral (AO(VTI) 23.2 +/- 7.4 cm at baseline --> 26.8 +/- 8.8 cm [LV], P <.05), and the myocardial performance index (MPI, 1.21 +/- 0.51 at baseline --> 0.85 +/- 0.34 [BV], P <.05). The most improvement was observed with LV and BV stimulation at short and intermediate atrioventricular delays (80-120 milliseconds), independent of ischemic or idiopathic origin.

CONCLUSIONS

CRT improves hemodynamic performance in patients with heart failure with intraventricular conduction delays. Doppler echocardiography allows noninvasive evaluation of acute CRT effects in patients with heart failure. In particular, FT, AO(VTI), and MPI are useful parameters for noninvasive follow-up and optimization of pacing parameters.

Echocardiographic evidence of hemodynamic and clinical improvement in patients paced for heart failure

Dilated cardiomyopathy is frequently associated with electrical conduction disturbances. Development of left bundle-branch block with discoordinated ventricular contraction pattern further contributes to impaired hemodynamic performance. Biventricular pacing has evolved as a new treatment option for patients with dilated cardiomyopathy and conduction disturbances. The "electrical" approach aims to normalize the disturbed contraction pattern, thereby improving hemodynamic function by simultaneous stimulation at different ventricular sites. Acute hemodynamic improvement with biventricular pacing has been demonstrated in patients with depressed left ventricular function and delayed intraventricular conduction. Due to the variations in optimal pacing site and atrioventricular delay, individual optimization to achieve optimal hemodynamic benefit is necessary. Echocardiography has the potential to provide hemodynamic data by Doppler techniques and combine these with geometric information about ventricular volumes, ejection fraction, and contraction patterns. This article focuses on the use of echocardiographic techniques for noninvasive optimization in cardiac pacing and presents preliminary experience from the initial trials on multisite pacing in heart failure.

Different effects of abnormal activation and myocardial disease on left ventricular ejection and filling times

BACKGROUND

Ventricular activation is often abnormal in patients with dilated cardiomyopathy, but its specific effects on timing remain undetermined.

OBJECTIVE

To investigate the use of the ratio of the sum of left ventricular ejection and filling times to the total RR interval (Z ratio) to dissociate the effects of abnormal activation from those of cavity dilatation.

METHODS

Subjects were 20 normal individuals, 11 patients with isolated left bundle branch block (LBBB, QRS duration > 120 ms), 17 with dilated cardiomyopathy and normal activation, and 23 with dilated cardiomyopathy and LBBB. An additional 30 patients (nine with normal ventricular systolic function and 21 with dilated cardiomyopathy) were studied before and after right ventricular pacing. Left ventricular ejection and filling times were measured by pulsed wave Doppler and cavity size by M mode echocardiography.

RESULTS

Z ratio was independent of RR interval in all groups. Mean (SD) Z ratio was 82 (10)% for normal subjects, 66 (10)% for isolated LBBB (p < 0.01 v normal), 77 (7)% for dilated cardiomyopathy without LBBB (NS v normal), and 61 (7)% for dilated cardiomyopathy with LBBB (p < 0.01 v normal). In the nine patients with normal left ventricular size and QRS duration, Z ratio fell from 88 (6)% in sinus rhythm to 77 (10)% with right ventricular pacing (p = 0.26). In the 21 patients with dilated cardiomyopathy and LBBB, Z ratio rose from 59 (10)% in sinus rhythm to 74 (9)% with right ventricular DDD pacing (p < 0.001).

CONCLUSIONS

Z ratio dissociates the effects of abnormal ventricular activation and systolic disease. It also clearly differentiates right ventricular pacing from LBBB. It may thus be useful in comparing the haemodynamic effects of different pacing modes in patients with or without left ventricular disease.

Optimizing the AV delay in DDD pacemaker patients with high degree AV block: mitral valve Doppler versus impedance cardiography

In DDD-pacemaker patients with high degree AV block, Doppler echocardiography of transmitral blood flow can be used to find the individually optimal AV delay (AVO) for left heart AV synchronization. This study tried to validate a Doppler method (ECHO) recently proposed to optimize left ventricular filling by comparing it to stroke volume data derived from impedance cardiography (ICG). It should be further elucidated if optimizing the AV delay (AVD) by means of this method is superior to fixed AVD settings and which differential AVD (pace-sense-offset) should be programmed for atrially triggered (ATP) and AV sequential (AVP) pacing, respectively. AVO as measured in 53 patients showed a linear correlation between ECHO and ICG for both ATP (r = 0.66, P < 0.00001) and AVP (r = 0.53; P < 0.005). The mean deviation in AVO between ECHO and ICG was +/- 26 ms (ATP) and +/- 30 ms (AVP), respectively, with a tendency to longer AVDs with the Doppler method. ECHO limitations could mainly be attributed to: (1) restrictions of AVD programming options (which may be compensated for by slight modification of the proposal); and (2) to pathophysiological mechanisms that alter mitral valve dynamics. Optimization of the AVD by Doppler produced a stroke volume that was significantly higher (19%) than with a fixed AVD (150 ms in ATP; 200 ms in AVP). There was a wide scatter in pace-sense-offsets between-7 and 134 ms, which was reflected by both methods. It is concluded that AVO determinations by ECHO are valid provided that methodological pitfalls and limitations caused by the disease are recognized. Tailoring AVD with respect to diastolic filling improves systolic function and is superior to nominal AVD settings. Fixed differential AVDs as offered by some manufacturers are far from being physiological. Thus modern pulse generators should offer free programmability over a wide range of AV delays.

Hemodynamic benefit of optimizing atrioventricular delay after cardiopulmonary bypass

BACKGROUND

Shortening of atrioventricular delay (AVD) by sequential cardiac pacing has been proposed to improve hemodynamics in patients with end-stage heart failure. In addition, optimization of prolonged AVD may be associated with a decrease of presystolic mitral insufficiency. The aim of this study was to explore the incidence of prolonged AVD during the early postcardiopulmonary bypass (CPB) period and to evaluate the hemodynamic benefit of its shortening by using sequential cardiac pacing.

METHODS

Fifty consecutive patients scheduled for coronary artery bypass grafting were prospectively screened. AVD was measured immediately after separation from CPB. Patients presenting with AVD greater than or equal to 200 ms entered the study. Sequential cardiac pacing was introduced with programmed AVD starting at 80 ms and randomly increased by steps of 20 ms until resumption of native anterograde atrioventricular node conduction. Cardiac index (CI) was derived from transesophageal echocardiographic data during each step of this procedure.

RESULTS

Nineteen patients were included. Median native AVD was 220 ms. Median optimal AVD was 140 ms. Mean native CI (CI-nat) was 2.59 +/- 0.42 L/min/m2. Mean optimal CI (CI-opt) was 3.12 +/- 0.45 L/min/m2. CI-opt/CI-nat was 1.20 +/- 0.07. CI-opt/CI-nat was significantly inversely correlated with preoperative left ventricular ejection fraction (r = -0.83).

CONCLUSIONS

Prolonged AVD is a common occurrence after CPB. Its artificial shortening by sequential cardiac pacing is always associated with a significant increase of CI. The magnitude of this hemodynamic improvement is inversely correlated with preoperative left ventricular ejection fraction.

Systolic and diastolic effects of variable atrioventricular delay in patients with complete heart block and normal ventricular function

This study was designed to demonstrate the effects of varying the atrioventricular delay (AVD) on ventricular diastolic filling dynamics and the resultant stroke volume in patients with complete heart block and normal cardiac function. We studied 7 patients with normal cardiac function in whom a dual chamber pacemaker had been implanted because of complete heart block. Doppler and M-mode echocardiography was performed at 70, 100, 140, 180, and 220 ms, AVD with the device in DDD mode at a rate of 80 beats/min. The effects of these variable intervals on the contribution of the E and A waveform to the diastolic filling, on the stroke volume, and on the systolic intervals were evaluated. Optimization of this interval, with a 19% increase in stroke volume was achieved in the group of patients at an AVD of 140 ms. When considered individually, the AVD associated with the largest stroke volume, was 100 ms in 2 patients and 140 ms in the remaining 5. At this individual optimal AVD the ventricular septal contraction occurred 31 +/- 14 ms, before the end of the transmitral flow. The optimal AVD is, therefore, the one which synchronizes the ventricular and atrial systole so that the first ventricular septal contraction occurs after the peak of the A wave, just before the end of the transmitral flow. Because of the different functional cardiovascular status of the single patient, this parameter should be individualized; this can be clinically important as it may lead, in this patient population, to an improvement of the stroke volume up to 42%.

Dual chamber pacing in the treatment of congestive heart failure

The present work reviews current literature and the authors' experience of dual chamber pacing in the treatment of patients with congestive heart failure (CHF). In these patients, the atrial contribution to ventricular filling may be less than optimal, especially in the presence of first degree atrioventricular block or mitral insufficiency, both of which are common in the elderly subject with CHF. Dual chamber pacing with short atrioventricular delays has proved effective in enhancing ventricular filling and, in selected cases, cardiac output, with improvement in clinical and instrumental parameters of heart failure. However, for an appropriate atrioventricular synchronization of the left chambers during pacing, the interatrial conduction time must be considered, to avoid atrial contraction against a closed mitral valve. Thus, dual chamber pacing may be a treatment option for CHF that fails to respond to medical therapy.

Refractory Heart Failure: A Therapeutic Approach

Optimal “triple therapy” for patients with chronic congestive heart failure (CHF) includes diuretics, digoxin, and either angiotensin-converting enzyme inhibitors or hydralazine plus nitrates. Refractory CHF is defined as symptoms of CHF at rest or repeated exacerbations of CHF despite “optimal” triple-drug therapy. Most patients with refractory CHF require hemodynamic monitoring and treatment in the intensive care unit. If easily reversible causes of refractory CHF cannot be identified, then more aggressive medical and surgical interventions are necessary. The primary goal of intervention is to improve hemodynamics to palliate CHF symptoms and signs (i.e., dyspnea, fatigue, edema). Secondary goals include improved vital organ and tissue perfusion, discharge from the intensive care unit, and, in appropriate patients, bridge to cardiac transplantation. Medical interventions include inotropic resuscitation (e.g., adrenergic agents, phosphodiesterase inhibitors, allied nonglycoside inodilators), load resuscitation (e.g., afterload and preload reduction with nitroprusside or nitroglycerin; preload reduction with diuretics and diuretic facilitators, such as dopaminergic agents or ultrafiltration), and electrical resuscitation (e.g., prevention of sudden death, correction of new or rapid atrial fibrillation, or dual chamber pacing in the setting of relative prolongation of the PR interval and diastolic mitral/tricuspid regurgitation). Surgical interventions are temporizing (e.g., intra-aortic balloon pump and other mechanical assist devices) or definitive (e.g., coronary artery revascularization, valvular surgery, and cardiac transplantation). Although these interventions may improve immediate survival in the short term, only coronary artery revascularization and cardiac transplantation have been shown to improve long-term survival.

Dual-chamber pacing with a short atrioventricular delay in congestive heart failure: a randomized study

OBJECTIVES

This prospective study assessed the initial hemodynamic effects and long-term clinical benefits of dual-chamber pacing with a short atrioventricular (AV) delay in patients with chronic heart failure who had no traditional indication for pacemaker implantation.

BACKGROUND

Dual-chamber pacing with a short AV delay has been proposed as a nonpharmacologic treatment for drug-refractory heart failure. Both initial and long-term hemodynamic as well as functional benefits have been reported. All previous studies have used an AV delay of 100 ms. Despite encouraging results, these previous studies have been anecdotal and uncontrolled.

METHODS

This double-blind, randomized, crossover trial included 12 subjects with chronic congestive heart failure despite optimal medical therapy. Patients were required to be in sinus rhythm with no evidence of significant bradyarrhythmias. On the day after implantation of a dual-chamber pacemaker, invasive hemodynamic measurements were made at varying AV delays between 100 and 200 ms. Patients were then randomized to either dual-chamber pacing with a 100-ms AV delay or backup mode (VVI at 40 beats/min). After 4 to 6 weeks, crossover to the other pacing mode was programmed.

RESULTS

Hemodynamic measurements on the day after pacemaker implantation demonstrated no benefit of pacing with any AV delay compared with intrinsic conduction. At the optimal AV interval for each patient, neither cardiac output (4.5 +/- 1.5 vs 4.7 +/- 1.6 liters/min [mean +/- SD]) nor wedge pressure (16 +/- 10 vs 17 +/- 8 mm Hg) improved significantly from baseline measurements during intrinsic conduction. The long-term pacing protocol was completed in nine patients. Ejection fraction was 16 +/- 6% with dual-chamber (VDD mode) pacing and 18 +/- 4% in backup mode (p = NS). No patient had an increase in ejection fraction by > or = 5% with VDD pacing, nor did any patient improve in New York Heart Association functional class with short AV delay dual-chamber pacing. Also, there were no significant reductions in body weight or diuretic requirements during this pacing period.

CONCLUSIONS

Dual-chamber pacing with a short AV delay does not improve hemodynamic and clinical status or ejection fraction measured on the day after pacemaker implantation in patients with chronic congestive heart failure. Routine use of pacemaker therapy with a short AV delay aas a primary treatment of heart failure in patients without standard arrhythmic indications is unwarranted.

Differing effects of right ventricular pacing and left bundle branch block on left ventricular function

OBJECTIVE

To compare the different effects of right ventricular pacing and classic left bundle branch block on left ventricular function.

DESIGN

Retrospective and prospective study of 48 patients by electrocardiography, and M mode, cross sectional, and Doppler echocardiography.

SETTING

A tertiary cardiac referral centre.

PATIENTS

48 patients (age range 21 to 89 years, 15 women), 24 with a VVI pacemaker implanted and 24 with classic left bundle branch block. Functional mitral regurgitation was present in all those with right ventricular pacing and 22 of those with left bundle branch block.

RESULTS

Age, RR interval, and left ventricular size were similar in the two groups, as were conventional measurements of overall systolic function: shortening fraction and pre-ejection and aortic ejection times. In right ventricular pacing, however, QRS duration (p < 0.01) and electromechanical delay were much longer (p < 0.001), whereas the time intervals from onset of mitral regurgitation to aortic opening (contraction time) and from A 2 to the end of mitral regurgitation (relaxation time) were consistently shorter (p < 0.01) than corresponding values in patients with left bundle branch block. Reversed splitting of the second heart sound was much commoner in left bundle branch block (p < 0.02), and only these patients showed an early systolic ventricular septal contraction. Its onset followed the initial deflection of the QRS complex by 40(15) ms and preceded mitral regurgitation by a small but consistent interval of 10 ms (p < 0.01). The onset of posterior wall thickening was synchronous with the onset of mitral regurgitation in right ventricular pacing but much later (p < 0.01) in patients with left bundle branch block. The extent of incoordinate wall motion measure as relative dimension change during pre-ejection and isovolumic relaxation period was much greater (p < 0.01) in left bundle branch block. These major differences were not altered by left ventricular cavity size in either group, nor by the presence of previous left bundle branch block in patients who were subsequently paced.

CONCLUSIONS

The left ventricle seems to be activated much more rapidly with right ventricular pacing than with left bundle branch block. This applies even when left bundle branch block is present before pacing. Electromechanical delay, contraction and relaxation times, and extent of incoordinate ventricular wall motion differ strikingly between the two conditions. The use of right ventricular pacing as an experimental model of left bundle branch block in humans must be re-examined.

Right ventricular pacing and left ventricular filling pattern. An echo-Doppler study

The influence of right ventricular pacing on left ventricular filling has not been completely clarified. The aim of the study was to analyze the possible alteration in and effects on left ventricular filling resulting from right ventricular pacing. The study population consisted of two groups; group A was comprised of 12 patients with a spontaneous left bundle branch block, and group B had 12 patients without left bundle branch block. All the patients underwent an interrogation of the mitral valve inflow by Doppler echocardiography, in order to measure isovolumic relaxation time, early and late peak velocity (E and A wave), E/A ratio and deceleration time. The study was performed at spontaneous rhythm and after, inhibition of the pacemaker. In group A, there were no changes in the Doppler parameters when passing from a spontaneous to an 80/min electrically induced rhythm. Analysis of group B revealed a statistically significant lengthening of IVR and Dec t with electrical stimulation. No statistically significant differences were found when we compared the Doppler parameters of the two populations at the same pacing frequency. Right ventricular pacing causes interventricular asynchrony and abnormalities in diastolic filling times, which resulted in a lengthening of either IVR and Dec t, simulating a pattern of abnormal relaxation.

Applications of Doppler echocardiography in cardiac pacing

The purpose of this article is to review the use of Doppler echocardiography for assessing responses during cardiac pacing. Doppler techniques allow the physician to select the optimal mode pacemaker and pacemaker settings with regard to heart rate and atrioventricular delay, at rest and during exercise. Doppler parameters can be used to predict the relative hemodynamic advantage of dual chamber or rate adaptive pacing over fixed rate pacing. This valuable noninvasive modality may enhance the benefit of pacemaker therapy.

Superior cardiac hemodynamics of atrioventricular synchrony over rate responsive pacing at submaximal exercise: observations in activity sensing DDDR pacemakers

The relative hemodynamic profile between dual chamber pacing (DDD) and activity sensing rate responsive pacing (VVIR) was compared in ten patients with dual chamber rate responsive pacemakers (Synergist II). With a double blind, randomized exercise protocol, DDDR pacemakers were programmed into VVI, VVIR, and DDD (AV interval 150 msec) modes and in seven patients the test in the DDD mode was repeated with the AV interval programmed at 75 msec. A treadmill exercise test of 6-minutes duration (2 stages, Stage I at 2 mph, 0% gradient and Stage II at 2 mph, 15% gradient) was performed at each of the programmed settings, with a rest period of 30 minutes in between tests. Cardiac output was assessed using continuous-wave Doppler sampling ascending aortic flow and expressed as a percentage of the value achieved during VVI pacing. During exercise, pacing rate between DDD and VVIR pacing was similar but was higher with DDD at the first minute of recovery (91 +/- 4 vs 81 +/- 3 beats/min, respectively). Cardiac output was significantly higher at rest, during low level exercise, and recovery with DDD pacing compared with VVIR pacing (resting: 21 +/- 14 vs -2 +/- 7%; Stage I: 36 +/- 6 vs 16 +/- 7%; Stage II: 25 +/- 15 vs 10 +/- 8%; recovery: 26 +/- 12 vs 4 +/- 9%; P less than 0.05 in all cases). Systolic blood pressure was significantly higher during low level of exercise in the DDD mode. Shortening of the AV interval to 75 msec did not significantly affect cardiac output during exercise, but cardiac output after exercise was reduced (2 +/- 6 vs 23 +/- 6% at an AV interval of 150 msec, P less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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)

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.

Physiological importance of different atrioventricular intervals to improved exercise performance in patients with dual chamber pacemakers

To determine the importance of different atrioventricular intervals during exercise in patients with dual chamber pacemakers, seven patients with complete heart block and sinus rhythm were exercised in different pacing modes and atrioventricular intervals: (a) ventricular inhibited (VVI) pacing with no synchronous atrial augmentation or rate responsiveness; (b) atrial synchronous ventricular or DDD pacing with a short mean (SD) atrioventricular interval of 66 (4) ms; and (c) DDD pacing with a long atrioventricular interval of 168 (12) ms. Pacing with a short or long atrioventricular interval gave similar maximum heart rates, oxygen uptake at the anaerobic threshold, end tidal pressure of carbon dioxide or oxygen pulse (a measure of stroke volume). Pacing with either a short or long atrioventricular interval produced a significantly higher oxygen consumption and anaerobic threshold and less lactate production than VVI pacing. During exercise a short atrioventricular interval does not provide a better cardiopulmonary performance than a long atrioventricular interval.

Physiological benefits of a pacemaker with dual chamber pacing at low heart rates and single chamber rate responsive pacing during exercise

Dual chamber rate responsive pacing may be an ideal mode but may result in high current drain and premature battery depletion. To minimize battery drain during exercise, this study compared a combination pacing mode of DDD and ventricular rate responsive pacing (VVIR). Nine patients were studied who had complete heart block, sinus rhythm, DDD pacemakers, and a reduced mean left ventricular ejection fraction of 44%. Patients were exercised in DDD, VVIR, and a combination of DDD at low heart rates and VVIR at mean heart rates over 89 bpm. Blood pressure, heart rate, exercise duration, work rate, oxygen uptake, anaerobic threshold, and oxygen pulse were measured. There was no difference in symptoms or in mean cardiopulmonary function indices including exercise duration 10.7, 10.3, 10.3 minutes; heart rate 127, 133, 136 bpm; oxygen uptake 1.4, 1.5, 1.5 L/minute; or anaerobic threshold 5.6, 5.5, 5.7 minutes (p greater than 0.05) in any mode. A pacemaker that provides atrioventricular synchrony at low heart rates with ventricular rate responsiveness at high heart rates may be an alternative mode for some patients.