Learn about Cardiac Electrophysiology
Although relatively new, Cardiac Electrophysiology is one of the fastest progressing fields in medicine. Cardiac Electrophysiology (EP) is the study of the heart’s electrical system; aimed at analyzing, diagnosing, and treating its electrical activities. The human heart pumps blood through the body’s intricate vascular network and although displacement of blood is its principal function, the heart instigates and finely regulates electrical impulses to create the beats.
How does it work?
Cardiac EP studies this phenomenon by recording the electrical activity of the heart using an invasive catheter. These studies help assess complex Heart Rhythm Disorders. These procedures include therapeutic methods (typically RF Ablation) along with other diagnostic and prognostic procedures. Cardiac EP also includes Implantation of pacemakers and Implantable Cardioverter-Defibrillators (ICDs).
Electrophysiology Study Basis (EP Study)
The electricity that flows throughout the heart in a regular pattern causes heart muscle contractions; any disruption in the electrical pathway disturbs the heart rhythm. An EP study involves the precise diagnosis and treatment of such heart rhythm disorders.
Arrhythmias or Heart Rhythm Disorders are unpredictable and irregular and hence may not be picked by tests like ECG and Holter. A trained Electrophysiologist can provoke Arrhythmia events and gather data about the flow of electricity. Such EP studies help locate the precise heart tissue that causes the abnormal electrical impulses resulting in Arrhythmias.
Purpose of EP Study
Diagnose the source of Arrhythmia Symptoms
Assess the efficiency of certain medications used to control Heart Rhythm Disorders
Forecast the risk of a future cardiac event (a sudden cardiac arrest)
Check for the need for pacemakers or other treatments like RF Ablation
Procedure of EP Study
EP study is an invasive test similar to angiography and is performed in a Cath-lab. After the patient is administered with local anesthesia (or in some cases, general anesthesia) a catheter is inserted into a blood vessel through a site in the groin or neck and the catheter is guided by fluoroscope images of the catheter and the heart muscles. Once the catheter reaches the heart, electrodes at its tip gather data and a variety of electrical measurements are made. This “electrical mapping” helps the cardiac arrhythmia specialist identify the location of the area disrupting the electrical flow.
The Electrophysiologist then administers different medications or electrical impulses to determine their ability to terminate the arrhythmia and restore normal heart rhythm. Sometimes the specialist will perform cardiac ablation or place an Implantable Cardioverter Device (ICD) or a pacemaker. The procedure usually lasts for about two hours.
Cardiac arrhythmias remain a major source of morbidity and mortality for patients with congenital heart defects (CHD). This is especially true for those who underwent successful treatment for Congenital Heart Defects or palliation during childhood, only to present decades later with a complex arrhythmogenic substrate caused by their abnormal anatomy, surgical scars, and suboptimal hemodynamics of long duration. Surgical advances are attenuating some of the hemodynamic and suture-related proarrhythmic factors; however, they cannot be eliminated totally and are only part of the puzzle. Inherent preoperative abnormalities and chronic remodeling continue to affect conduction properties of the myocardium, despite many intelligent modifications in surgical approach.
Although antiarrhythmic medications retain a role under certain circumstances, there is growing reliance on interventional procedures to address rhythm disturbances in children and adults with treatment for Congenital Heart Defects.
Atrial tachycardias are the most common arrhythmias observed in patients with CHD. They are a major cause of symptomatology, and in some cases, they can contribute to sudden cardiac death (SCD). Bouchardy et al found in a large cohort of adults with CHD that the prevalence of some type of atrial tachycardia was 15%, with a lifetime risk of ≈50% regardless of severity of the CHD lesion. Atrial arrhythmias were associated with a 50% increase in mortality, a 2-fold increased risk of heart failure or stroke, and a 3-fold higher risk of requiring some major cardiac intervention. Single ventricle patients with a Fontan circulation and those with transposition of the great arteries after Mustard or Senning operations have the highest burden of atrial tachycardia, but even simple atrial septal defect closure can be associated with atrial rhythm disturbances.
Most atrial tachycardias in patients with CHD involve macro reentrant circuits localized to the right atrium (RA). These can include classic atrial flutter through the Cavo tricuspid isthmus, as well as atypical circuits related to atriotomy incisions and other scars. The general term intra-atrial reentrant tachycardia (IART) has been used to describe all these circuits in CHD. Focal atrial tachycardia can also be observed in a small number of patients, usually arising from locations mapped near a scar zone.
Atrial fibrillation (AF) is also being reported with increasing regularity in patients with CHD, particularly those with left heart obstructive lesions, chronic left atrial dilation, and advanced age. There are some disturbing trends being recognized in this regard. It was recently reported that nearly a quarter of patients will develop AF many years after straightforward atrial septal defect closure. In addition, it has been noted that as many as 30% of patients with CHD who have undergone prior successful IART ablation may present with AF at some later time. Clearly, AF is emerging as a growing concern as more patients with CHD survive to older ages.
Cardiac Electrophysiology with regards to Congneital Heart Defects (CHD) is still an evolving field and lot of research is continuing.
-Contributed by R. Srivatsan