The importance of different atrioventricular delay for left ventricular filling in sequential pacing: clinical implications

The effect of different atrioventricular delays on left atrium and left atrial appendage function in patients with DDD pacemaker

BACKGROUND

Although it has been known that optimization of atrioventricular delay (AVD) has favorable effect on the left ventricular functions in patients with DDD pacemaker, the effect of different AVDs on left atrium (LA) and left atrial appendage (LAA) functions has not been exactly evaluated. The aim of the present study was to assess the effect of different AVDs on LA and LAA functions in DDD pacemaker implanted patients with atrioventricular block.

METHODS

Forty-eight patients with DDD pacemaker were enrolled into the study. Patients were divided into two groups according to the echocardiographic diastolic function: Group I (normal diastolic function) and Group II (diastolic dysfunction). LAA emptying velocity on pulsed wave Doppler and LAA late systolic wave velocity by using tissue Doppler were recorded. Patients were paced for five successive continuous pacing periods of 10 minutes duration using five selective AVDs (80-250 ms).

RESULTS

Significant effect on LA and LAA functions has not been observed by the setting of AVD in Group I. However, when the AVD was gradually shortened form 150 ms to 80 ms, LA and LAA functions gradually decreased in Group II patients. When AVD increased to 200 ms, LA and LAA functions were improved. Further increase in AVD resulted in decreased LA and LAA functions.

CONCLUSION

Setting of AVD has not significant effect on the LA and LAA functions in patients with normal diastolic function, but moderate prolongation of AVD in physiological limits improved LA and LAA functions in DDD pacemaker implanted patients with diastolic dysfunction.

Cardiac Index and Exercise during VDD/DDD versus VVIR Pacing in Children

Twelve children with a VDD/DDD pacemaker during 100, 125, 150, 200 ms atrioventricular delays and VVIR pacing, cardiac index was measured at rest and evaluated by endurance time during exercise stress test. The optimal atrioventricular delay, which provides highest cardiac index, was 100 ms in three, 125 ms in two, and 150 ms in four and 200 ms in three patients. VDD/DDD pacing with different atrioventricular intervals resulted in a significantly higher cardiac index (6.70 +/- 3.06, 6.49 +/- 2.51, 6.15 +/- 2.35, 6.37 +/- 2.69 l/min/m(2), respectively) than VVIR pacing (5.25 +/- 2.39 l/min/m(2)) at the rest. However, endurance times to treadmill exercise were similar in both the optimal atrioventricular delay (21.6 +/- 3.7 min) and VVIR mode (22.4 +/- 3.4 min) (p > 0.05).

Atrioventricular conduction in mammalian species: Hemodynamic and electrical scaling

OBJECTIVES

The purpose of this study was to investigate scaling of the duration of late diastolic left ventricular (LV) filling in relation to AV conduction time (delay) (PR interval on the ECG) in mammals.

BACKGROUND

From mouse to whale, AV delay increases 10-fold, whereas body mass increases one million-fold. The apparent "mismatch" results from scaling of AV delay versus body and heart mass.

METHODS

We measured (1) mitral orifice diameter in 138 postmortem hearts of 48 mammalian species weighing between 17 g and 250 kg and (2) transmitral diastolic flow using magnetic resonance imaging (MRI) recordings of 10 healthy human individuals. (3) We visually inspected early and late diastolic LV filling. (4) We developed two physical models to explain scaling of late diastolic LV filling time.

RESULTS

(1) Diameter of the mitral orifice proportionally relates to heart length (third root of heart mass). (2) Atrial contraction starts at a fixed instant (+/- 80%) of the (normalized) cardiac cycle and contributes 31% +/- 5% to LV filling. (3) MRI shows that during diastole, the left atrium (LA) and LV form a single space. (4) The physical models relate the duration of late diastolic LV filling directly to heart length, the third root of heart mass.

CONCLUSIONS

(1) Late diastolic (LV) filling time scales with heart length (third root of heart mass). (2) No "mismatch" exists between AV delay and heart size. (3) Knowledge of the actual starting time of atrial contraction may contribute to better treatment of patients with heart failure. (4) The findings suggest that in evolution of mammalian species, hemodynamics commands electrical behavior of the heart.

Influence of right ventricular stimulation site on left ventricular function in atrial synchronous ventricular pacing

OBJECTIVES

The study investigates the correlation between left ventricular function and QRS duration obtained by alternate right ventricular pacing sites.

BACKGROUND

1. Right ventricular apical pacing is associated with alterations of left ventricular contraction sequence. 2. A stimulation producing narrow QRS complexes is supposed to provide for better left ventricular contraction patterns.

METHODS

Fourteen patients with third degree AV block received one ventricular pacing lead in apical position. The alternate lead was attached to that site on the septum that produced the smallest QRS complex as measured from the earliest to the last deflection in any of the orthogonal Frank leads (xyz). During atrial synchronous ventricular pacing, the AV delay was optimized individually and for each stimulation site using mitral valve doppler or impedance cardiography. By radionuclide ventriculography, the phase distribution histogram of left ventricular contraction was evaluated as area under the curve (AuC); systolic function was determined as ejection fraction (EF) and as absolute ejected counts (EC) in random order. The difference (delta) in QRS duration between apical and septal stimulation (deltaxyz) was correlated with the difference in phase distribution (deltaAuC) and ejection parameters (deltaEF, deltaEC).

RESULTS

QRS duration was shorter with septal than with apical pacing in 9 out of 14 patients (64%); it was longer in 4 (29%), and no difference was seen in 1 patient. There was a significant positive correlation between the change in QRS duration (deltaxvz) and phase distribution (deltaAuC: r = 0.66393, p = 0.010) and a significant negative correlation to systolic function (deltaEF: r = 0.70931, p = 0.004; deltaEC: r = 0.74368, p = 0.002).

CONCLUSIONS

In atrial synchronous right ventricular pacing, if the AV delay is adapted individually, decreased QRS duration obtained by alternate pacing sites is significantly correlated with homogenization of left ventricular contraction and with increased systolic function in acute tests.

Short atrioventricular delay dual-chamber pacing early after coronary artery bypass grafting in patients with poor left ventricular function

OBJECTIVE

To investigate the effect of short atrioventricular (AV) delay dual-chamber pacing on mean arterial pressure (MAP) and stroke volume index (SVI) in patients with poor left ventricular (LV) function after cardiac surgery.

DESIGN

A prospective study.

SETTING

A university hospital, single-center study.

PARTICIPANTS

The study group consisted of 20 patients aged 63 +/- 9 years with a left ventricular ejection fraction (LVEF) less than 30%. The control group consisted of 20 patients aged 61 +/- 10 years, with an LVEF greater than 50%.

INTERVENTIONS

Immediately after routine coronary artery bypass grafting (CABG) the AV delay was shortened from 160 to 40 milliseconds in atrial-paced (DDD) mode and from 100 to 40 milliseconds in atrial-sensed ventricular stimulation (VDD) mode. MAP was on-line monitored and SVI was calculated by thermodilution. In one patient with an LVEF of 18% (case study), transmitral flow velocity and LV isovolumetric relaxation time were assessed using Doppler echocardiography during VDD pacing at 40-, 80-, and 120-millisecond AV delay.

RESULTS

Short-AV delay DDD pacing decreased MAP in the control group (84.3 +/- 9 v 75.7 +/- 9 mmHg; p < 0.05) and SVI in both groups (study group, 35.9 +/- 7 v 31.7 +/- 7 mL/m2; control group, 35.3 +/- 6 v 31.0 +/- 6 mL/m2; p < 0.05). Shortening the AV delay had no influence on MAP and SVI during VDD pacing. During the echocardiographic case study, AV delay shortening distinctly modified ventricular filling patterns. Optimal LV filling and transmitral flow were achieved with an intermediate AV delay of 80 milliseconds.

CONCLUSION

Dual-chamber pacing with nonphysiologic short AV delay failed to improve acute hemodynamics in patients with poor LV function after CABG. Short AV delay VDD pacing was superior to DDD pacing in both normal and impaired LV function. The use of Doppler echocardiography enabled optimization of the AV delay on the basis of LV filling patterns.