Assessing the Hemodynamic Benefits of Cardiac Resynchronization Therapy in Children Following Open-Heart Surgery

Malformations of the heart (congenital heart disease) are the most common congenital birth defects, occurring in about 1% of children. Each year, between 150-200 children will undergo open heart surgery at British Columbia Children's Hospital (BCCH) to repair the defect(s) in their heart. The abnormal structure of the heart or the open heart surgery may cause damage to the electrical system of the heart which can disturb the rhythm of the heart (arrhythmias), prolong recovery or be life-threatening. For this reason, temporary pacing wires are placed in the heart following surgery to ensure the heart rhythm is as normal as possible during the post-operative period (pacing). In recent years, scientists have recognized that pacing the heart from one area is not necessarily the same as pacing it from a different area. In fact, in some individuals with arrhythmias and poor heart function, pacing the heart from different areas can improve the pumping of the heart, resulting in better heart function. This form of treatment is called Cardiac Resynchronization Therapy (CRT) because it endeavours to optimize the pumping of the heart by changing the electrical activation of the heart. CRT has been used to a very limited extent in children. A few pediatric cardiologists have used CRT to help children who are in heart failure. We would like to determine whether pacing the heart from different areas after open heart surgery improves the child's heart function and aids his or her recovery.

Study Overview

• Status: Completed
• Conditions: Congenital Heart Defects
• Intervention / Treatment: Procedure: Congenital Heart Surgery Patients

Detailed Description

The heart's rhythmic beating or contraction is determined by the flow of an excitatory electrical wave-front along a specialized cardiac conduction system. In the presence of altered conduction, such as a bundle branch block or an intra-ventricular conduction delay, abnormal cardiac contraction or dyssynchrony occurs. The delay can occur in the specialized conduction system (electrical dyssynchrony) or myocardium (mechanical or structural dyssynchrony).1 Techniques to improve both electrical and mechanical synchrony in patients with bundle branch block were initially done on adults. Research in this field began to appear in the last decade when dual chamber pacing was first used as adjunctive therapy for adults with medically refractory heart failure.2 Acute studies showed that atrioventricular (AV) synchronous pacing with a short AV delay improved cardiac output and exercise duration in patients with heart failure and a prolonged PR interval.3 The beneficial effects of AV resynchrony (optimizing AV conduction times with pacing) were shown to be due to increased diastolic filling time, and reduction in mitral or tricuspid valve regurgitation. The results of long-term studies, however, did not demonstrate consistent improvement in ejection fraction or NYHA functional class with DDD pacing.4 Since then, Cardiac Resynchronization Therapy (CRT) has established itself as a proven therapy for congestive heart failure in adults, with patients showing improvement in exercise tolerance, quality of life, and survival.1, 5, 6 More recently, the technique of utilizing CRT to stimulate the heart from novel or multiple sites has been applied to pediatric patients.7-9 Children with chronic heart failure have received CRT successfully as an adjunctive therapy.

One of the major limitations of CRT is the objective assessment of whether cardiac output and ventricular function are improved. As well, the precise location of where to pace the heart in order to optimize hemodynamic function needs to be determined. The objective assessment of successful CRT is a difficult clinical issue and should ideally be performed non-invasively. Traditional two-dimensional echocardiographic and Doppler indices have been used to assess the efficacy of CRT and include measuring cardiac output, looking at ventricular ejection times, visually assessing wall motion, and measuring the length of diastole using the mitral "E" and "A" waves. As most of the existing techniques are limited to assessing global function, more detailed methods of assessment are necessary in order to fully assess and optimize CRT.10, 11 Tissue Doppler Imaging (TDI) offers a more detailed analysis of regional cardiac function and allows quantitative measures to be obtained. TDI operates at high frame rates and can non-invasively map cardiac activation and add information related to the degree and location of cardiac dyssychrony. TDI and its derivatives allow: (1) measurement of myocardial velocities, which is based on the detection of the Doppler shift caused by the motion of myocardial tissue during the cardiac cycle; (2) visualization of tissue tracking, which color-codes tissue segments with similar displacements according to a color map; (3) measurement of regional strain rates, which describes the rate of deformation, or how quickly a segment of tissue shortens or lengthens; and (4) measurement of regional strain, which describes the deformation of an object (in this case, tissue) relative to its original state. 12, 13

Cardiac pacing in children is done most often following cardiac surgery for congenital heart disease (CHD). This pacing is usually temporary. Following open heart surgery children frequently exhibit cardiac dyssynchrony secondary to conduction abnormalities or regional wall motion abnormalities. Often, damage to the conduction system is an unavoidable result of the operation itself. Regardless of the extent of the conduction abnormality, most patients operated on for congenital heart disease undergo a period of decreased cardiac function related to several factors, including: pre-existing myocardial disease; cardiopulmonary bypass; and residual cardiac lesions.7, 14 The decrease in cardiac performance and, therefore, the risk to the patient's life, can be aggravated by the presence of cardiac dyssynchrony. The benefits of CRT are just beginning to receive attention in the setting of pediatric post-operative cardiac care. 15

We hope to demonstrate that CRT is beneficial in the care of post-operative patients undergoing open-heart surgery for repair of congenital heart defects. We will be using state-of-the-art TDI for assessing cardiac dyssynchrony, and using it as a tool for monitoring therapy. This study has tremendous potential for application to all patients undergoing open-heart surgery for repair of congenital heart defects. If it can be demonstrated that CRT can improve post-operative outcomes in this population, significant morbidity and mortality can be avoided, Intensive Care Unit (ICU) and hospital stays shortened, and the associated health care costs reduced.

• Study Type: Observational
• Enrollment (Actual): 34

Contacts and Locations

Study Locations

• Canada
  • British Columbia
    • Vancouver, British Columbia, Canada, V6H 3V4
      • Children's Heart Centre, British Columbia's Children's Hospital

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 1 week to 18 years (Child, Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: All

• Sampling Method: Non-Probability Sample

Study Population

The study cohort will consist of infants, children, and adolescents (<18 years) who are scheduled to undergo open-heart surgery for CHD. Each year approximately 150-200 patients undergo surgery to repair their CHD (see Section 6.4 for sample size estimates).

Description

Inclusion Criteria:

Subjects will be eligible for enrollment in this study if they are undergoing cardiopulmonary bypass surgery for right or left ventricular surgery or biventricular surgery and (1) have intra-cardiac conduction delay or bundle branch block post-surgery; (2) have echocardiographic evidence of ventricular dyssynchrony; (3) have pre-existing conduction disease or bundle branch block; or (4) have pre-existing ventricular dyssynchrony.

Exclusion Criteria:

Subjects will be excluded if they: (1) have single ventricle morphology; (2) require post-operative ECMO; (3) have sustained atrial or ventricular arrhythmias that may complicate ventricular pacing; (4) are not able to have functioning epicardial pacemaker leads; (5) are, in the opinion of the intensivist, cardiologist or surgeon, not stable enough medically to participate in the study; or (6) are unwilling to provide informed consent or assent.

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Congenital Heart Surgery Patients; Pacing protocol prior to patient's extubation with 20 min. of either conventional right ventricular (RV) or biventricular (BiV) pacing, preceded and followed by 10 min. of recovery time.	Procedure: Congenital Heart Surgery Patients; undergoing either Biventricular (BiV) pacing or Right Ventricular (RV) Pacing

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Time Frame
Cardiac Index	Baseline and after 20 minutes of pacing

Secondary Outcome Measures

Outcome Measure	Time Frame
Systolic Blood Pressure
Incidence of Low Output Syndrome
TDI Indices (Tissue Velocities, Tissue Tracking, Regional Strain, and Regional Strain Rates)
Inotropic Support
Ventilatory Support
QRS Duration	Baseline and after 20 minutes of pacing
Cardio-pulmonary Bypass Time	Baseline and after 20 minutes

Collaborators and Investigators

• Sponsor: University of British Columbia
• Investigators: Principal Investigator: Shubhayan Sanatani, MD, Provincial Health Services Authority

Study record dates

Study Major Dates

• Study Start: October 1, 2006
• Primary Completion (Actual): November 1, 2009
• Study Completion (Actual): November 1, 2009

Study Registration Dates

• First Submitted: November 7, 2006
• First Submitted That Met QC Criteria: November 8, 2006
• First Posted (Estimate): November 9, 2006

Study Record Updates

• Last Update Posted (Actual): December 18, 2017
• Last Update Submitted That Met QC Criteria: November 16, 2017
• Last Verified: November 1, 2017

More Information

Terms related to this study

• Keywords: Congenital heart disease; Biventricular pacing; Tissue Doppler echocardiography
• Additional Relevant MeSH Terms: Heart Diseases; Cardiovascular Diseases; Congenital Abnormalities; Cardiovascular Abnormalities; Heart Defects, Congenital
• Other Study ID Numbers: H03-70642 (Other Identifier: UBC)