AV pacing and LV performance

[History of cardiac resynchronization therapy : 30 years of electrotherapeutic management for heart failure]

The first permanent biventricular pacing system was implanted more than 30 years ago. In this article, the historical development of cardiac resynchronization therapy (CRT), starting with the pathophysiological concept, followed by the initial "proof of concept" studies and finally the large prospective-randomized studies that led to the implementation of CRT in heart failure guidelines, is outlined. Since the establishment of CRT, both an expansion of indications, e.g., for patients with mild heart failure and atrial fibrillation, but also the return to patients with broad QRS complex and left bundle branch block who benefit most of CRT has evolved. New techniques such as conduction system pacing will have major influence on pacemaker therapy in heart failure, both as an alternative or adjunct to CRT.

Phase I and Phase II Oxygen Uptake Kinetics During Atrioventricular Dyssynchrony in Chronotropically Competent Pacemaker Patients

OBJECTIVE

To elucidate the effects of atrioventricular (AV) dyssynchrony on phase I and phase II oxygen uptake (V(O2)) kinetics in chronotropically competent pacemaker patients during exercise of an intensity comparable to activities of daily living.

DESIGN

Blinded patients completed sub-ventilatory threshold (VT) work rate (WR) cycle ergometry exercise in random order during asynchronous AV pacing (AV OFF) and synchronous AV pacing.

SETTING

Tertiary care hospital in a major city.

SUBJECTS

Six chronotropically competent male pacemaker patients (mean [+/- SD] age, 68 +/- 10 years) with high-degree AV block and varying cardiac histories.

RESULTS

The phase I and phase II V(O2) amplitude response and gain (deltaV(O2)/WR ratio) were lower (p < 0.05) and the time course of phase II was slower (p < 0.05) during AV OFF; however, the O2 deficit was similar (p > 0.05) across pacing modes. The stroke volume index (SVI) was consistently lower (p < 0.05) during AV OFF pacing and was significantly correlated with the time course of phase II V(O2). A significant compensatory amplitude response in heart rate (HR) was observed in addition to a higher (p < 0.05) deltaHR/V(O2) ratio during AV OFF. Ventilatory responses were consistent with ventilatory-perfusion mismatching and perceived exertion was higher during asynchronous pacing.

CONCLUSION

This study demonstrated that the contribution of SVI affects V(O2) kinetics and underscores the importance of the atrial contribution to ventricular filling and, consequently, to metabolic and hemodynamic responses. This study supports the theory of an O2 transport limitation and further implicates SV as a potential limiting factor during sub-VT exercise intensities that are comparable to those encountered in activities of daily living.

Mechanisms of Optimized Biventricular Pacing in Pulmonary Stenosis:. Effects on Left Ventricular Geometry in Swine

We tested the hypothesis that optimized biventricular pacing (BiVP) enhances cardiac output (CO) during critical pulmonary stenosis (PS) by attenuating distortions in left ventricular (LV) geometry. Following median sternotomy in six anesthetized pigs, heart block was induced by ethanol ablation. During epicardial, DDD BiVP, atrioventricular delay (AVD) was varied from 60 ms to 180 ms in 30 ms increments. At the AVD with the highest CO right-left delay (RLD) was varied from (+) 80 ms (RV first) to (-) 80 ms (LV first) in 20 ms increments. At each pacing setting, aortic flow, ECG, and LV diameter were measured in the control state (CON) and during PS, created by snaring the pulmonary artery until CO decreased 50%. Short axis LV echocardiograms were obtained at (+) and (-) 80 ms. In CON, RLD had no effect on function or geometry. During PS optimum BiVP resulted in significant increases in CO (1.12 L/min +/- 0.13 SEM at RLD =+ 40 ms versus 0.92 +/- 0.12 at RLD = 0 and 0.73 +/- 0.08 at RLD =-80), and LV fractional shortening (8.97%+/- 0.51% at RLD =+ 40 ms versus 7.34%+/- 0.58% at RLD = 0 and 6.21%+/- 0.66% at RLD =-80). In addition, LV eccentricity with (-) RLD was significantly different versus CON at both end-diastole (0.79 +/- 0.07 vs 1.02 +/- 0.03, P = 0.011 Student's t-test) and end-systole (0.83 +/- 0.05 vs 1.00 +/- 0.02, P = 0.017). However, with (+) RLD differences versus CON were not significant at either end-diastole (0.88 +/- 0.06 vs 0.99 +/- 0.03) or end-systole (0.92 +/- 0.03 vs 1.01 +/- 0.03). In swine hearts with PS, optimized BiVP increases CO, fractional shortening, and LV symmetry. BiVP warrants further study as treatment for acute postoperative heart failure.

Noninvasive beat-to-beat arterial blood pressure measurement during VVI and DDD pacing: relationship to symptomatic benefit from DDD pacing

To noninvasively assess the hemodynamic effects of VVI and DDD pacing modes we measured beat-to-beat arterial blood pressure during VVI and DDD pacing in 30 patients with complete heart block (CHB), using fingertip photoplethysmography. Of these patients, 15 undertook a double-blind cross-over comparison of the symptomatic effects of VVI versus DDD pacing to determine the relationship between blood pressure changes and the occurrence of symptoms suggestive of the pacemaker syndrome during ventricular pacing. Mean (SD) systolic blood pressure was 11.7 (15.4) mmHg lower during VVI pacing compared to DDD pacing (P < 0.0005). The mean (SD) beat-to-beat variability of systolic blood pressure was 5.20 (2.87%) in VVI mode versus 2.12 (1.07%) in DDD mode (P < 0.0000005). In comparison with DDD pacing, the excess of symptoms experienced by patients during VVI pacing did not correlate with the change in mean systolic blood pressure, but was significantly correlated with the increase in beat-to-beat systolic blood pressure variation during VVI pacing (r = 0.58, P = 0.024). We conclude that noninvasive measurement of fingertip arterial beat-to-beat blood pressure is a rapid and simple method of assessing the hemodynamic effect of VVI pacing. Beat-to-beat blood pressure variability was related to symptomatic intolerance of VVI pacing and may have potential utility as an aid to diagnosis or as a predictor of pacemaker syndrome.

Preimplantation echo Doppler evaluation of VVI versus DDD pacing

This study was carried out to select before permanent pacemaker implantation patients with complete atrioventricular block (CHB) who would benefit best from DDD pacing, and to determine the optimal atrioventricular delay (AVD) for each of those patients. This was achieved with the aid of Doppler echocardiography. The effect of different AVDs on both the systolic and diastolic function of the normal and failing heart was also delineated in this study.

METHODS

Thirty patients with CHB and normal sinoatrial function were selected, with no age or sex predilection. These patients were categorized into three equal groups: groups A, B, and C with normal left ventricular (LV) systolic and diastolic function, LV diastolic dysfunction, and LV systolic dysfunction, respectively. For each patient, systolic and diastolic function was calculated utilizing echo Doppler during CHB, temporary VDD pacing with different AVDs, and temporary VVI pacing with a rate matching that during VDD mode. Temporary VDD mode of pacing was performed utilizing a temporary bipolar ventricular lead for ventricular pacing and an esophageal lead for atrial sensing to trigger ventricular pacing.

RESULTS

Qualitatively the most obvious change in the pattern of LV filling as AVD is increased in the three groups, is the earlier occurrence of active atrial filling A wave due to progressive approximation of the ECG P wave toward the previous QRS. As the AV interval is increased, the following changes occur: (a) A wave occurs progressively earlier with superimposition onto the early filling E wave resulting in a progressive increase in its velocity (VA), its FVI, and its percent atrial contribution (%AC); (b) the three times diastolic filling time (DFT), mitral valve opening to Q wave (MVO-Q), and closure (Q-MVC) progressively shorten; (c) since DFT decreases, less passive filling occurs early during diastole, thus E.FVI decrease with longer AV intervals; (d) the ratios VE/VA and FVI E/A decrease subsequently to the previous described changes. Compared to CHB, percent ejection fraction (% EF) was not significantly changed during VVI pacing. Percent EF increased significantly during VDD in comparison to VVI pacing modes. Percent EF was highest at optimal AVD and decreased as this AVD increased or decreased. The cardiac output (CO) increment during VDD in comparison to VVI pacing modes differed much among the three groups. In group A, a 10.29% increase in CO was seen when comparing VDD pacing (with optimal AVD) with that of VII one; in group B, this increment was much greater and reached 29.48%; in group C it reached 23.68%.(ABSTRACT TRUNCATED AT 400 WORDS)

Importance of an individually programmed atrioventricular delay at rest and on work capacity in patients with dual chamber pacemakers

Despite higher costs, expenditure, and the necessity of repeatedly reprogramming of dual chamber pacemakers, they are increasingly implanted to achieve an optimal work capacity. The influence of an individually programmed atrioventricular (AV) delay between 100-250 msec on physical work capacity in 12 patients (68 +/- 16 years) with dual chamber pacemakers implanted for high degree AV block was studied. During radionuclide ventriculography at rest the "optimal AV delay" with the maximal achieved left ventricular ejection fraction and the "most unfavorable AV delay" with the least achieved ejection fraction were determined. The ejection fraction at rest with the "optimal AV delay" was 51 +/- 14% and with the "most unfavorable AV delay" 45 +/- 15% (P < 0.001). In random order each patient was assigned to either AV delay and a spiroergometry was performed to determine maximum oxygen uptake (max VO2), which correlates best with work capacity, at a respiratory quotient of 1.1. The results show neither a difference in maximum oxygen uptake (1,262 +/- 446 mL/min with the optimal AV delay, 1,248 +/- 400 mL/min with the most unfavorable AV delay, respectively) nor in heart rate, blood pressure, exercise duration, maximal workload, and minute ventilation. Thus, an individually programmed AV delay affects left ventricular ejection fraction at rest. In contrast, an individually programmed AV delay has no influence on physical work capacity in patients with a dual chamber pacemaker.

Comparative evaluation of rate modulated dual chamber and VVIR pacing

While dual chamber pacing is considered superior to VVI pacing at rest, there is a continuing debate as to the relative benefit of AV synchrony versus rate increase with exercise. To evaluate this question and to correlate different methods of evaluation, 14 patients with DDDR pacemakers were studied using serial treadmill exercise test with a CAEP protocol. Patients were exercised in DDD, DDDR, and VVIR modes. Echo-Doppler cardiac outputs were determined and pulmonary gas exchange was measured during exercise. There was a significant improvement in cardiac output with exercise in the DDDR versus VVIR modes, and in DDDR versus DDD modes in patients with chronotropic incompetence. There were small increases in exercise duration in DDDR versus VVIR modes, and small but consistent increases in VO2 at all levels of exercise, though not statistically significant. In this group of patients, DDDR pacing was superior to VVIR pacing, and superior to DDD pacing when chronotropic incompetence was present.

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)

M-mode echocardiograms for determination of optimal left atrial timing in patients with dual chamber pacemakers

To determine if the A wave of the mitral valve echocardiogram can be used as a marker for left atrial (LA) activity and assist in the programming of dual chamber pacemakers, 156 echocardiograms with the mitral A wave present were obtained from 23 patients with dual chamber pacemakers, all of whom had bipolar esophageal recordings of LA depolarization. Twelve of these patients also underwent hemodynamic study with cardiac function determined at 5 different pacemaker settings: ventricular demand pacing and dual chamber sequential pacing at 0 or 25, 150, 200 and 250 ms programming atrioventricular (AV) delay. The time delay from right atrial pacing artifact to onset and peak of mitral A wave was linearly related to the time from atrial pacing artifact to LA depolarization on the esophageal lead (p less than 0.001). As pacing mode changed from dual chamber sequential pacing (DVI) mode to atrial synchronous-ventricular pacing (VDD), the A wave came earlier relative to the ventricular pacing spike, linearly related to the LA to ventricular extension with mode change determined with the esophageal lead (r = 0.94, p less than 0.001). The time from atrial pacing to peak of A wave was shorter in patients whose optimal programmed AV delay was 150 ms compared with those whose optimal AV delay was 200 or 250 ms (p less than 0.02). At the optimal programmed delay for cardiac output, the peak of the A wave was an average of 13 +/- 36 ms after the ventricular pacing spike.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Influence of recipient atrial contraction on left ventricular filling dynamics of the transplanted heart assessed by Doppler echocardiography

Recipient atrial remnants retain electrical and mechanical activity after orthotopic cardiac transplantation. This study investigated the influence of recipient atrial contraction timing on Doppler ultrasound mitral flow velocity curves, isovolumic relaxation time, peak early mitral flow velocity (M1), mitral valve pressure half-time and peak mitral flow velocity due to atrial systole (M2). Clearly identifiable recipient atrial electrical activity (P waves) was present in 7 of 10 patients studied early postoperatively 2 to 6 months (mean 2.5) (early group) and in 20 of 24 patients seen 1 to 11 years (mean 3) after transplantation (late group). Median age and gender distribution were similar in both groups. For analysis of its influence on isovolumic relaxation time, pressure half-time and M1, recipient atrial contraction was classified by its position in the cardiac cycle as early systole, late systole or diastole. For analysis of M2, it was classified as early diastole, late diastole or systole. Compared with its occurrence in diastole, recipient atrial contraction in late systole was associated with a shorter isovolumic relaxation time, shorter pressure half-time and higher M1. In early systole it was associated with a longer pressure half-time and lower M1 than in diastole; isovolumic relaxation time was unchanged. Recipient atrial contraction in early diastole resulted in a lower M2 than in systole, whereas simultaneous contraction of recipient and donor atria in late diastole resulted in an increase in M2. These results indicate that the timing of recipient atrial contraction and relaxation significantly influences left ventricular filling dynamics.

Effect of variation in PQ interval on patterns of atrioventricular valve motion and flow in patients with normal ventricular function

M-mode echocardiography and Doppler ultrasonography were used to study patterns of atrioventricular (AV) valve motion and flow in five patients with complete heart block, normal ventricular function and an implanted dual chamber pacemaker with programmable PQ intervals. Changes in AV valve motion and flow patterns resulting from steady state changes in PQ interval over the range studied (75 to 250 ms) were similar in all patients. Events reflecting AV valve opening and rapid ventricular filling bore a constant temporal relation to the Q wave and were unaffected by changes in PQ interval. Events reflecting atrial contraction occurred progressively earlier in diastole with lengthening of the PQ interval, until superimposition of atrial contraction on rapid ventricular filling at a PQ interval of 250 ms. The duration of mid-diastolic slow ventricular filling and overall diastole, defined with respect to an open valve, decreased with lengthening of the PQ interval. The onset of AV valve closure (A point) bore a constant temporal relation to the P wave, indicating that atrial systole initiated valve closure. However, completion of AV valve closure occurred progressively earlier with respect to the P wave as the PQ interval was decreased. This suggests an increasing contribution of ventricular systole to completion of AV valve closure with decreasing PQ interval. End-diastolic and end-systolic ventricular and atrial dimensions were independent of the PQ interval.

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.

Programmability in DDD pacing

Safe and reliable DDD pacemakers with multiple programming capabilities have now been developed. Certain programmable parameters are basic, including mode, voltage (or current) output, pulse width, sensitivity and refractory periods in each chamber. Upper rate response as well as low rate settings and A-V delays are equally important. In certain models, the ability to program the blanking period has proven quite useful. The interrelationship between all these functions will assure the smooth overall performance of these sophisticated devices.

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 AV interval lengths compared to more normal AV intervals (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 (range 9 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.