Load dependence of cardiac output in biventricular pacing: right ventricular pressure overload in pigs

BACKGROUND: The effect of biventricular pacing on stroke volume is believed to be dependent on right ventricular/left ventricular delay, but effects in individual patients are unpredictable. This variability may reflect relative right and left ventricular volume and/or pressure overloads. Accordingly, we tested the hypothesis that the relation of cardiac output to right ventricular/left ventricular delay is load dependent in a pig model of pulmonary stenosis. METHODS: After median sternotomy in 6 anesthetized, domestic pigs, complete heart block was induced by ethanol ablation. During epicardial, atrial tracking DDD biventricular pacing, atrioventricular delay was varied between 60 and 180 ms in 30-ms increments. Right ventricular/left ventricular delay was varied at each atrioventricular delay from +80 ms (right ventricle first) to -80 ms (left ventricle first) in 20-ms increments. Aortic flow, right ventricular pressure, peripheral arterial pressure, and electrocardiogram were measured in the control state and during pulmonary stenosis, created by tightening a snare around the pulmonary artery until cardiac output decreased by 50%. RESULTS: Atrioventricular and right ventricular/left ventricular delay had no effect on cardiac output during the control state, but during pulmonary stenosis there was a statistically significant (P =.0001, repeated-measures analysis of variance) right ventricular/left ventricular delay-related trend toward higher cardiac output with right ventricular pacing first. This effect was more pronounced when the optimal atrioventricular delay was determined first, resulting in a 20% increase in cardiac output when the optimal right ventricular/left ventricular delay was compared with simultaneous biventricular pacing. CONCLUSIONS: Optimized biventricular pacing in swine is associated with increased cardiac output during acute pulmonary stenosis, but not during the control state. Further studies are needed to determine whether specific types of right ventricular and left ventricular overload predictably affect the relation between right ventricular/left ventricular delay and cardiac output.     

Impact of biventricular and left ventricular pacing on hemodynamics and left ventricular dyssynchrony compared with right ventricular pacing in the early postoperative period following cardiac surgery

Objectives

The aims of this study were to test the hypotheses that in the postoperative period following corrective surgery for congenital heart defects: (i) atrio-right ventricular (RA-RV) pacing decreases cardiac output (CO) compared with right atrial (RA) pacing, (ii) atrio-biventricular (RA-BiV) and left ventricular (RA-LV) pacing improves CO compared with RA-RV pacing.

Study design

Prospective observational study.

Patients

Children 0-2 years of age referred for surgery of congenital heart defects were studied during intrinsic rhythm and atrial, atrio-right ventricular, atrio-left ventricular and atrio-biventricular pacing. CO, extrapolated from mean systolic aortic velocity (MSAV), and left ventricular dyssynchrony were assessed using transthoracic echocardiography.

Results

RA-RV pacing induced a significant decrease in CO (MSAV 0.52 ± 0.19 m/s to 0.46 ± 0.16 m/s, p = 0.01) and a significant increase in LV dyssynchrony (8.7 ± 7.9 ms to 33 ± 21 ms, p = 0.001). RA-BiV pacing induced a significant increase in CO (MSAV 0.46 ± 0.16 m/s to 0.52 ± 0.18 m/s, p = 0.01) and a significant decrease in LV dyssynchrony (33 ± 21 ms to 7 ± 4 ms, p = 0.0003) compared with RA-RV pacing. RA-LV pacing induced a significant decrease in LV dyssynchrony (33 ± 21 ms to 9 ± 7 ms, p = 0.0007) without a significant improvement of CO compared with RA-RV pacing.

Conclusions

RA-BiV pacing improves CO compared with RA-RV pacing in the early postoperative period following pediatric cardiac surgery. This improvement is related to a reduction in left ventricular dyssynchrony.     

Corrected right ventricular end-diastolic volume and initial distribution volume of glucose correlate with cardiac output after cardiac surgery

Purpose

Appropriate adjustment of cardiac preload is essential to maintain cardiac output (CO), especially in patients after cardiac surgery. This study was intended to determine whether index of right ventricular end-diastolic volume (RVEDVI), corrected RVEDVI using ejection fraction (cRVEDVI), index of initial distribution volume of glucose (IDVGI), or cardiac filling pressures are correlated with cardiac index (CI) following cardiac surgery in the presence or absence of arrhythmias.

Methods

Eighty-six consecutive cardiac surgical patients were studied. Patients were divided into two groups: the non-arrhythmia (NA) group (n = 72) and the arrhythmia (A) group (n = 14). Three sets of measurements were performed: on admission to the ICU and daily on the first 2 postoperative days. The relationship between each cardiac preload variable and cardiac index (CI) was evaluated. A p value less than 0.05 indicated statistically significant differences.

Results

Each studied variable was not different between the two groups immediately after admission to the ICU. cRVEDVI had a linear correlation with CI in both group (NA group: r = 0.67, n = 216, p < 0.001; A group: r = 0.77, n = 42, p < 0.001), but RVEDVI had a poor correlation with CI (NA group: r = 0.27, n = 216, p < 0.001; A group: r = 0.19, n = 42, p = 0.036). IDVGI had a linear correlation with CI (NA group: r = 0.49, n = 216, p < 0.001; A group: r = 0.61, n = 42, p < 0.001), Cardiac filling pressures had no correlation with CI.

Conclusion

Our results demonstrated that cRVEDVI and IDVGI were correlated with CI in the presence or absence of arrhythmias. cRVEDVI and IDVGI have potential as indirect cardiac preload markers following cardiac surgery.     

Impact of pacing modality and biventricular pacing on cardiac output and coronary conduit flow in the post-cardiotomy patient

We have previously demonstrated the role of univentricular pacing modalities in influencing coronary conduit flow in the immediate post-operative period in the cardiac surgery patient. We wanted to determine the mechanism of this improved coronary conduit and, in addition, to explore the possible benefits with biventricular pacing. Sixteen patients undergoing first time elective coronary artery bypass grafting who required pacing following surgery were recruited. Comparison of cardiac output and coronary conduit flow was performed between VVI and DDD pacing with a single right ventricular lead and biventricular pacing lead placement. Cardiac output was measured using arterial pulse waveform analysis while conduit flow was measured using ultrasonic transit time methodology. Cardiac output was greatest with DDD pacing using right ventricular lead placement only [DDD-univentricular 5.42 l (0.7), DDD-biventricular 5.33 l (0.8), VVI-univentricular 4.71 l (0.8), VVI-biventricular 4.68 l (0.6)]. DDD-univentricular pacing was significantly better than VVI-univentricular (P=0.023) and VVI-biventricular pacing (P=0.001) but there was no significant advantage to DDD-biventricular pacing (P=0.45). In relation to coronary conduit flow, DDD pacing again had the highest flow [DDD-univentricular 55 ml/min (24), DDD-biventricular 52 ml/min (25), VVI-univentricular 47 ml/min (23), VVI-biventricular 50 ml/min (26)]. DDD-univentricular pacing was significantly better than VVI-univentricular (P=0.006) pacing but not significantly different to VVI-biventricular pacing (P=0.109) or DDD-biventricular pacing (P=0.171). Pacing with a DDD modality offers the optimal coronary conduit flow by maximising cardiac output. Biventricular lead placement offered no significant benefit to coronary conduit flow or cardiac output.     

Early effects of right ventricular volume overload on ventricular performance and beta-adrenergic signaling

OBJECTIVE: Right ventricular dysfunction is a poorly understood but persistent clinical problem. This study was undertaken to evaluate ventricular performance and beta-adrenergic receptor signaling in a tricuspid regurgitation model of right ventricular overload. METHODS: Seventeen dogs were chronically instrumented with epicardial dimension transducers. By means of the shell-subtraction model, right ventricular pressure-volume relationships were evaluated in normal and right ventricular overload states. Right ventricular chamber performance was quantified by the stroke work at an end-diastolic volume relationship. RESULTS: Right ventricular volume overload caused a 28% +/- 11% and 31% +/- 9% decline in chamber performance acutely and at 1 week, respectively, whereas end-diastolic volume increased from 45 +/- 21 to 60 +/- 30 mL (P =. 019). beta-Adrenergic receptor signaling in myocardial samples was assessed, examining adenylyl cyclase and G-protein-coupled receptor kinase activity. Stimulated adenylyl cyclase activity significantly decreased, and G-protein-coupled receptor kinase activity significantly increased in both left and right ventricular samples caused by increased levels of beta-adrenergic receptor kinase 1. No change in beta-adrenergic receptor density was seen at 1 week. CONCLUSIONS: Early right ventricular overload is associated with impaired right ventricular chamber contractility, dilation, and, importantly, a biventricular alteration of beta-adrenergic receptor signaling.     

Temporary and permanent biventricular pacing via left ventricular epicardial leads implanted during primary cardiac surgery

OBJECTIVES: Biventricular pacing (BVP) is a new strategy for treating patients with severe congestive heart failure (CHF) and intraventricular conduction delay, but its full potential and technicalities of BVP require further evaluation. We evaluated BVP benefits in 4 patients in whom we implanted a left ventricular lead during primary cardiac surgery. METHODS: Four CHF patients treated surgically between October 2000 and August 2001 underwent, at primary surgery, the implantation of leads in the right atrium, right ventricle, and left ventricle (LV) for postsurgical BVP. All patients had severe LV dysfunction and dilatation with intraventricular conduction delay. Surgeries involved CABG alone (n = 1), CABG + Dor's operation (n = 2), and tricuspid valve replacement + Maze procedure (n = 1). BVP was begun immediately after surgery in all 4 patients. Hemodynamic variables with BVP were compared to those without BVP for each patient, and the utility and technical aspects of implantation were evaluated. RESULTS: BVP increased mean systemic blood pressure by 11% and mean LV stroke work index by 19% in the acute postsurgery period, and reduced mitral regurgitation. Two of the patients were implanted with a generator for permanent BVP, one at 1 month and the other at 6 months after surgery. The threshold of the LV epicardial lead of these 2 patients was below 2 V during follow-up, and BVP was successful. CONCLUSIONS: Temporary BVP during the short-term after cardiac surgery improved cardiac function and decreased mitral regurgitation in all 4 of our patients. Epicardial lead implantation may thus be a useful option during surgical treatment of patients with CHF and intraventricular conduction delay if long-term permanent BVP is indicated.     

Concurrent left and right ventricular hypertrophy in dog models of right ventricular overload

In two pressure and volume overload models of canine right ventricular hypertrophy, we have demonstrated significant hypertrophy of both the left and the right ventricles. The extent of hypertrophy was correlated positively to the extent of the increase in plasma epinephrine in both volume and pressure overload models. Attenuation or ablation of plasma epinephrine through the administration of propranolol, a beta-adrenergic blocker, or by denervation of the adrenal medulla prevented the hypertrophy process. No hemodynamic parameter was altered consistently in a parallel manner to hypertrophy. This is the first report of concurrent right and left ventricular hypertrophy in response to pressure or volume overload of the right ventricle. These studies further implicate epinephrine as a major trophic hormone of the heart.     

Heart failure due to rapid right ventricular volume overload in patients with pulmonary hypertension

We have described three cases of pulmonary artery hypertension (PAH). Two of them developed severe systemic hypotension and cardiac arrest following cardiopulmonary bypass (CPB). Imminent pre-operative right ventricular (RV) failure and subsequent myocardial injury during CPB may have contributed to the insult following CPB. In these cases, RV failure is presumably due to rapid volume overloading, since left atrial pressure (LAP) was essentially unchanged while right atrial pressure (RAP) was markedly elevated during the period of severe hypotension. Furthermore, these events may be attributed to protamine, since the circulatory derangement coincides with its administration. Thus, in these patients with severe PAH, blood transfusion should be carefully titrated under the strict evaluation of both LAP and RAP. Additionally, protamine should be infused at a rate slow enough to avoid concomitant hemodynamic changes. We have also reported a case of over-systemic PAH who was successfully managed intraoperatively by careful monitoring and discreet administration of protamine.     

Rapid ventricular pacing: a novel technique to decrease cardiac output for giant basilar aneurysm surgery

A case of a 49 year old man with a giant basilar artery aneurysm requiring rapid ventricular pacing is presented. Rapid ventricular pacing decreased aneurysm size and increased operative exposure, which aided surgical decision making. It also provided decreased wall tension in the aneurysm.     

Robotically assisted left ventricular epicardial lead implantation for biventricular pacing: the posterior approach

Patients with congestive heart failure and altered interventricular conduction enjoy improvements in quality of life and ventricular function after successful resynchronization therapy with biventricular pacing. Technical limitations owing to individual coronary sinus and coronary venous anatomy result in a 10% to 15% failure rate of left ventricular (LV) lead placement through percutaneous approaches. To provide a minimally invasive option for these patients with LV lead failures, we developed a technique of endoscopic, epicardial LV lead implantation with the use of the da Vinci robotic system. The surgical approach targets the posterolateral wall through a novel posterior approach.     

Quantification of right ventricular extracellular volume in pulmonary hypertension using cardiac magnetic resonance imaging

PurposeThe purpose of this prospective study was to assess the value of biventricular extracellular volume (ECV) in pre-capillary pulmonary hypertension (PH) obtained using cardiac magnetic resonance imaging (CMR) and to correlate ECV with markers of prognosis such as strain echocardiography and blood biomarkers of fibrosis.Materials and methodsTwelve patients with PH (6 men, 6 women; mean age = 50 ± 16 [SD] years; age range: 22–73 years) underwent the same day: (i), transthoracic echocardiography including measurement of right ventricular (RV) fractional shortening (RVfs), tricuspid annular plane systolic excursion (TAPSE), maximal tricuspid annular velocity, RV global and segmental deformation; (ii), right heart catheterization measuring pulmonary arterial pressures (in mmHg) and cardiac output (in L/min); (iii), CMR at 1.5-T measuring RV volumes and ejection fraction; (iv), native and 15 min post-contrast T1 mapping using modified look-locker inversion-recovery sequence; and (v), serum quantification of two biomarkers of collagen turnover and hematocrit. Non-parametric Mann-Whitney tests were used to search for differences between categorical variables. Spearman correlation test was used for search for correlation between quantitative values.ResultsGlobal RV ECV was 34% ± 4.2 (SD) for our entire population. A significant correlation was found between RV ECV and RVfs (r = 0.6; P = 0.026), S wave velocity (r = 0.7; P = 0.009), TAPSE (r = 0.6; P = 0.040) and RV systolic ejection fraction on CMR (r = 0.6; P = 0.04). There were no correlations between the ECV values in the lateral wall of the RV and in the septum (r = 0.4; P = 0.206). A significant correlation was found between septal ECV and 2D septal strain (r = 0.7; P = 0.013).ConclusionECV in PH as obtained using CMR appears to correlate with known echocardiographic prognostic markers and more specifically with the markers, which assess RV systolic function.     

Surgical epicardial left ventricular lead versus coronary sinus lead placement in biventricular pacing.

OBJECTIVE: Biventricular pacing has demonstrated improvement in cardiac function in treating congestive heart failure (CHF). Two different operative strategies (coronary sinus vs. epicardial stimulation) for left ventricular (LV) pacing were compared. METHODS: Since April 1999, a total of 86 patients (pts, age: 63+/-10 years) with depressed systolic LV function (mean ejection fraction 24+/-9%), left bundle-branch-block (mean QRS 182+/-22 ms) and congestive heart failure NYHA III or higher were enrolled. For biventricular stimulation coronary sinus (CS) leads were placed in 79 pts. Nine of these devices were converted to surgical epicardial LV-leads, because of CS-lead failure. In 7 patients epicardial LV-leads were initially implanted surgically, accounting for a total of 16 pts with surgical placed epicardial steroid-eluting LV-leads. For these, a limited left-lateral thoracotomy (7+/-4 cm) was used. Thirty-three (38%) pts had an indication for a defibrillator. The mean follow-up time was 16.4+/-15.4 months (0.1-45 months), representing 107.1 patient-years. RESULTS: In the biventricular pacing mode, QRS duration decreased to 143+/-16 ms (P<0.001). Threshold capture of the CS-leads increased significantly compared to surgically placed epicardial leads (18 month control: 2.2+/-1.4V/0.5 ms vs. 0.7+/-0.3V/0.5 ms), which had no increase in threshold (P<0.001). At the 18 month follow-up 7 CS-leads had a threshold of >4V/0.5 ms vs. epicardial leads which were under 1.1V/0.5 ms, except for one (1.8V/0.5 ms). After CS-lead implantation 25 LV-lead related complications occurred, (failed implantation, CS-dissection, loss of pacing capture, diaphragm stimulation or lead dislodgment), vs. one dislodgement after surgical epicardial lead placement (P<0.05). Correct lead positioning (obtuse marginal branch area) was achieved in all surgical epicardial placements but only in 70% with CS-leads (P<0.03). In the follow up period, 9 pts died (4 cardiac related). Heart transplantation was necessary in 4 pts due to deterioration of the cardiomyopathy. CONCLUSIONS: Surgical epicardial lead placement revealed excellent long-term results and a lower LV-related complication rate compared to CS-leads. Although, the approach via limited thoracotomy for biventricular pacing is associated with 'more surgery', it is a safe and reliable technique and should be considered as an equal alternative.