Congenital Heart Defects Clinical Trial
Official title:
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.
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.
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