Assessing the Hemodynamic Benefits of Cardiac Resynchronization Therapy in Children Following Open-Heart Surgery
Condition: Congenital Heart Defects
MeSH terms: Heart Defects, Congenital
Study type: Observational

Summary: 
      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.
    

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.
    

Intervention name(s): Congenital Heart Surgery Patients
Intervention type(s): Procedure
Intervention description(s): undergoing either Biventricular (BiV) pacing or Right Ventricular (RV) Pacing
Observational model: Cohort
Time perspective: Cross-Sectional
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).
      
Keywords: Biventricular pacing; Congenital heart disease; Tissue Doppler echocardiography