The effects of rate responsive pacing on exercise performance in the postoperative univentricular heart

Impact of Atrial Pacing in Fontan Patients with Junctional Rhythm: A Prospective Echocardiographic Study

Sinus node dysfunction (SND) with junctional rhythm (JR) is common after the Fontan operation. Atrial pacing (AP) restores atrioventricular (AV) synchrony, but the placement of a pacemaker carries significant morbidity. To study the impact of AP on echocardiographic parameters of function in Fontan patients with SND and JR. Nine Fontan patients with AP for SND and JR were prospectively studied with echocardiography in the following conditions-baseline paced rhythm, underlying JR and, if possible, slow-paced rhythm below their baseline paced rate (~ 10 bpm faster than their JR rate). Cardiac index was significantly lower in JR (3 ± 1.1 L/min/m2) vs AP (4.2 ± 1.4 L/min/m2; p = 0.002). Diastolic function also significantly worsened with increased ratio of early diastolic systemic AV valve inflow velocity to early diastolic systemic AV valve annulus velocity (E/e' ratio) by tissue Doppler imaging (TDI) in JR (11.6 ± 4.6) vs AP (8.8 ± 2.2, p = 0.016). Pulmonary venous flow reversal was present in 7/9 patients in JR vs 0/9 in AP (p = 0.016). There were no significant differences in these echocardiographic measurements between the paced and slow-paced conditions. When compared to AP, JR was associated with a significant reduction in cardiac output and diastolic function, and an increased prevalence of pulmonary vein flow reversal. There were no differences between paced and slow-paced conditions, suggesting that AV synchrony rather than heart rate was primarily contributing to cardiac output. Further studies are needed to understand the chronic impact of JR on Fontan outcomes.

Late Fontan Circulatory Failure. What Drives Systemic Venous Congestion and Low Cardiac Output in Adult Fontan Patients?

The Fontan circulation provides definite palliation for children born with a single anatomical or functional ventricle by diverting systemic venous blood directly to the pulmonary arteries, effectively rendering systemic venous return into portal vessels to the lung. Although this restores pulmonary blood flow and avoids the mixture of oxygenated and deoxygenated blood, it also results in elevated systemic venous pressures and low cardiac output. These are the two hallmarks of any Fontan circulation and the cause of Fontan circulatory failure later in life. We highlight the determinants of systemic venous return, its changed relationship with the pulmonary circulation, how it affects preload, and the changed role of the heart (myocardium, valves, and heart rate). By critically evaluating the components of the Fontan circulation, we hope to give some clues in how to optimize the Fontan circulation and avenues for future research.

Heart Rate Reserve in Fontan Patients: Chronotropic Incompetence or Hemodynamic Limitation?

Background Patients with a Fontan circulation achieve lower peak heart rates ( HR ) during exercise. Whether this impaired chronotropic response reflects pathology of the sinoatrial node or is a consequence of altered cardiac hemodynamics is uncertain. We evaluated the adequacy of HR acceleration throughout exercise relative to metabolic demand and cardiac output in patients with a Fontan circulation relative to healthy controls. Methods and Results Thirty subjects (20 healthy controls and 10 Fontan patients) underwent cardiac magnetic resonance imaging with simultaneous invasive pressure recording via a pulmonary and radial artery catheter during supine bicycle exercise to near maximal exertion. Adequacy of cardiac index, stroke volume, and HR reserve was assessed by determining the exercise-induced increase (∆) in cardiac index, stroke volume, and HR relative to the increase in oxygen consumption ( VO ₂). HR reserve was lower in Fontan patients compared with controls (71±21 versus 92±15 bpm; P=0.001). In contrast, increases in HR relative to workload and VO ₂ were higher than in controls. The change in cardiac index relative to the change in VO ₂ (∆cardiac index/∆ VO ₂) was similar between groups, but Fontan patients had increased ∆ HR /∆ VO ₂ and reduced ∆ stroke volume/∆ VO ₂ compared with controls. There was an early and marked reduction in stroke volume during exercise in Fontan patients corresponding with a plateau in cardiac output at a low peak HR . Conclusions In Fontan patients, the chronotropic response is appropriate relative to exercise intensity, implying normal sinoatrial function. However, premature reductions in ventricular filling and stroke volume cause an early plateau in cardiac output beyond which further increases in HR would be physiologically implausible. Thus, abnormal cardiac filling rather than sinoatrial node dysfunction explains the diminished HR reserve in Fontan patients.

Sildenafil improves exercise hemodynamics in Fontan patients

BACKGROUND

Patients with Fontan circulation have reduced exercise capacity. The absence of a presystemic pump may limit flow through the pulmonary circulation, restricting ventricular filling and cardiac output. We evaluated exercise hemodynamics and the effect of sildenafil on exercise hemodynamics in Fontan patients.

METHODS AND RESULTS

Ten Fontan patients (6 men, 20±4 years) underwent cardiac magnetic resonance imaging at rest and during supine bicycle exercise before and after sildenafil. Systemic ventricular volumes were obtained at rest and during low- (34±15 W), moderate- (69±29 W), and high-intensity (97±36 W) exercise using an ungated, free-breathing cardiac magnetic resonance sequence and analyzed correcting for cardiac phase and respiratory translation. Radial and pulmonary artery pressures and cGMP were measured. Before sildenafil, cardiac index increased throughout exercise (4.0±0.9, 5.9±1.1, 7.0±1.6, 7.4±1.7 L/(min·m(2)); P<0.0001) with 106±49% increase in heart rate. Stroke volume index (P=0.015) and end-diastolic volume index (P=0.001) decreased during exercise. End-systolic volume index remained unchanged (P=0.8). Total pulmonary resistance index (P=0.005) increased, whereas systemic vascular resistance index decreased during exercise (P<0.0001). Sildenafil increased cardiac index (P<0.0001) and stroke volume index (P=0.003), especially at high-intensity exercise (interaction P=0.004 and P=0.003, respectively). Systemic vascular resistance index was reduced (P<0.0001-interaction P=0.1), whereas total pulmonary resistance index was reduced at rest and reduced further during exercise (P=0.008-interaction P=0.029). cGMP remained unchanged before sildenafil (P=0.9), whereas it increased significantly after sildenafil (P=0.019).

CONCLUSIONS

In Fontan patients, sildenafil improved cardiac index during exercise with a decrease in total pulmonary resistance index and an increase in stroke volume index. This implies that pulmonary vasculature represents a physiological limitation, which can be attenuated by sildenafil, the clinical significance of which warrants further study.

Prognostic significance and correlations of neurohumoral factors in early and late postoperative period after Fontan procedure

We focused on neurohumoral activity and its clinical correlates early and late after fenestrated, lateral intra-atrial total cavopulmonary connection (TCPC). Between 2007 and 2010, we prospectively studied 28 early and 48 late postoperative TCPC patients. Plasma concentrations of vasopressin, endothelin-1, proBNP, proANP were determined. We reviewed clinical data to determine relationship between neurohumoral activation and clinical status after TCPC. There was a significant influence of preoperative ventricular end-diastolic pressure (VEDP) (P=0.008) and vasopressin concentration (P=0.02) on the appearance of prolonged pleural effusions. A significant correlation between a combined predictor (a product of preoperative vasopressin concentration and VEDP) and time of effusions (r=0.59, P=0.006) was found. The mean respiratory equivalent of carbon dioxide at peak exercise (VE/VCO(2peak)) was significantly lower in patients operated before the second year of life compared to patients operated after two years of age (27.5±1.39 vs. 48.6±3.86; P=0.039). There was a significant correlation of endothelin-1 (r=0.84; P=0.008) and proBNP (r=0.88; P=0.02) concentrations with VE/VCO(2peak). The prolonged postoperative pleural effusions can be predicted based on the product of preoperative vasopressin concentration and VEDP. Exercise performance is related to the age at TCPC. Endothelin-1 and proBNP can be useful for identification of high-risk Fontan patients.

Acute Hemodynamic Effects of Pacing in Patients With Fontan Physiology

OBJECTIVES

The purpose of this research was to assess the hemodynamic response to atrial, ventricular, and dual-chamber pacing in patients with Fontan physiology.

BACKGROUND

Bradycardia, due to sinus node dysfunction or atrioventricular (AV) block, with need for pacing, is common after the Fontan operation. The optimal pacing mode for Fontan patients is unknown, but is critical, as hemodynamic aberrancies may cause severe clinical deterioration. We hypothesized that AV synchrony is vital for maximizing Fontan hemodynamics.

METHODS

A cross-over trial was conducted with 21 patients (age 2 to 18 years, median 4 years; male patients = 13) in the intensive care unit after a Fontan operation. Hemodynamic parameters, including mean left atrial pressure (LAP, in mm Hg), mean pulmonary artery pressure (PAP, in mm Hg), mean arterial blood pressure (MAP, in mm Hg), and indexed cardiac output via Fick (Qs, in l/min/m2) were measured with atrial, ventricular, and dual-chamber pacing. Measurements were made after pacing for 10 min in each mode, and a 10-min rest was given between each pacing maneuver.

RESULTS

Asynchronous ventricular (VOO) pacing resulted in significantly worse hemodynamics when compared to dual-chamber (DOO) and atrial (AOO) pacing with a higher LAP (9.4 VOO; 6.8 DOO; 5.4 AOO) and PAP (15.2 VOO; 13.5 DOO; 12.7 AOO) and lower Qs (3.0 VOO; 3.5 DOO; 3.9 AOO) and MAP (60.1 VOO; 66.5 DOO; 67.2 AOO).

CONCLUSIONS

Asynchronous ventricular pacing, after the Fontan procedure, has acute, adverse hemodynamic consequences (elevated LAP and PAP and decreased Qs and MAP).

Optimal Maximum Tracking Rate of Dual-Chamber Pacemakers Required by Children and Young Adults for a Maximal Cardiorespiratory Performance

INTRODUCTION

Children and young adults require a higher maximum tracking rate (MTR) for physical activity. The objective of the present study was to observe whether higher MTR of 170 or 190 beats per minute (bpm) have a positive impact on the maximal cardiorespiratory capacity of children and young adults in comparison with a lower MTR of 140 bpm.

METHODS

Fifteen patients with atrioventricular block and normal sinus-node chronotropic function (age 7-24 years) with DDD- (14) or VDD-pacemakers (PM) (1) were enrolled. First, the MTR was adjusted to 140 bpm for 6 weeks and elevated in a second step to 170 or 190 bpm. At the end of each period two cardiopulmonary exercise tests, a 24-hour ECG and a PM test were performed.

RESULTS

All patients increased their maximal heart rate (139.0 +/- 1.0 vs 177.0 +/- 10.0 bpm, P < 0.001), peak cardiorespiratory capacity (2.4 +/- 0.6 vs 2.8 +/- 0.7 W/kg, P < 0.001), peak oxygen uptake (28.3 +/- 7.0 vs 35.7 +/- 9.5 mL/kg/min, P < 0.005), and oxygen uptake (23.7 +/- 7.4 vs 29.3 +/- 8.4 mL/kg/min, P < 0.02) at the anaerobic threshold. There were no evident heart rhythm disturbances with elevated MTR. Patients with a Wenckebach behavior of the PM had an attenuated increase of maximal cardiorespiratory performance.

CONCLUSION

Children and young adults with DDD-/VDD-PM benefit from an elevated MTR by an increased cardiorespiratory capacity, without having more heart rhythm disturbances. A Wenckebach behavior of the PM should be avoided.

Exercise testing in pediatrics

This article discusses exercise physiology and its application in the pediatric population. This article discusses exercise physiology and its application in the pediatric population. The authors briefly review the normal physiologic response to exercise. They then discuss populations in which exercise testing is most useful, the indications and contraindications for graded exercise, and the usual parameters that are measured during testing. Finally, the authors review some of the recent data on exercise performance in specific pediatric populations.

Atrial arrhythmias during chronic follow-up of surgery for complex congenital heart disease

After surgery for complex congenital heart disease, clinically important atrial tachyarrhythmias have a higher than normal incidence if sufficiently large regions of conduction block occur within the atria, especially in the presence of hemodynamic alterations. Sinus bradycardia may result from direct damage to sinus node and its blood supply. Historical data have identified patients who have undergone the Mustard or Senning operations for dextrotransposition of the great vessels and the Fontan operation in cases of functional single ventricle as being at great risk for atrial tachyarrhythmias. These arrhythmias are especially poorly tolerated when there are co-existing hemodynamic alterations and are an important source of morbidity and mortality. Until recently, treatment strategies have been limited to antiarrhythmic drugs, bradycardia pacing, and--in suitable patients--antitachycardia pacing, often in combination. Amiodarone has been the most efficacious drug, but has only been of moderate value because of extracardiac side effects. Radiofrequency ablation of the atrial regions critical to reentrant circuits, which was discovered to be of value in patients with atrial flutter and a normal heart is being applied to this diverse group of patients. Early results are promising, but the Fontan operation patients are especially challenging because of early recurrences of apparently new reentrant circuits. Progress in this area will likely come from newer surgical techniques that prevent the milieu for atrial reentry and from multidimensional mapping systems for our current patients.

Improved epimyocardial pacing: initial experience with a new bipolar, steroid-eluting, high impedance lead design

Epicardial pacing typically is associated with decreased pacing and sensing capabilities compared with the endocardial approach. Since endocardial pacing is neither appropriate nor possible in all instances, this study was conducted to evaluate a new concept in a chronic epimyocardial lead design in six 3-month-old growing dogs. The new bifurcated lead (Medtronic model 10401) is a low current drain, high impedance, steroid-eluting, bipolar design. The implant is facilitated by a suture attached with an atraumatic needle. Twelve ventricular leads were implanted (2 per animal) and followed for 6 months with weekly analysis of pacing and sensing capabilities. Results at explant were compared with implant values. There were no significant differences between implant and explant in sensed R waves, or in the slew rate of the R wave in unipolar or bipolar modes. Lead impedances at explant remained high in both modes: bipolar, 1550 +/- 223; unipolar, 1234 +/- 262 omega (P < 0.05). Chronic voltage (v) threshold at 0.5 msec showed no significant change from implant values during the study: unipolar, 0.4 +/- 0.2 vs 0.7 +/- 0.3; bipolar, 0.5 +/- 0.4 vs 1 +/- 0.5. Histologic evaluations of the electrode tissue interface demonstrated negligible fibrotic capsule formation. This study introduces a new, easily implanted, high impedance, low threshold, bipolar epimyocardial pacing lead design with excellent chronic pacing and sensing characteristics.