By Dr. Anthony C. Pearson, MD, FACC

The Centers for Disease Control and Prevention estimates that there are approximately 1.4 million adults with congenital heart defects (CHD) in the United States, and thanks to modern medical techniques, more children with CHD are surviving to adulthood.

Twelve-lead ECG is an invaluable tool for clinical assessment in these diverse and complex patient cases, as it contains important prognostic and diagnostic information. Anatomic changes from a primary CHD or surgery intended to correct a CHD can influence all aspects of an ECG, from P waves to T waves to QRS complexes, and having these figures in hand is critical to ensuring that any changes that could put the patient at greater risk are identified and addressed in due time.

QRS Patterns Associated with Congenital Heart Defects

The QRS complex, which represents electrical activation of the right and left ventricles, carries a wealth of information that is particularly useful to cardiologists taking care of CHD patients with issues ranging from simple atrial septal defects (ASDs) to complex atrium, ventricle, or atrioventricular valve defects.

Atrial Septal Defects

It has been established in medical research that most patients with significant ASDs have an rsr' or rsR' pattern in leads V1 and V2, which is thought to be related to right ventricular volume overload rather than a true disturbance in conduction.

A recent study in the Annals of Pediatric Cardiology involving 141 children with secundum ASD—which was asymptomatic in the majority of cases—found a prevalent rSR' pattern of 26%, which increased to 54% in the large ASD group. In patients with moderate to large ASDs, the rsR' pattern was predictive of the need for surgical closure.

A so-called "crochetage," which is a notch near the apex of the R wave in the inferior ECG leads, is highly associated with ASD in 73% of diagnosed adults and adolescents, as a study in the Journal of the American College of Cardiology shows. The specificity of the crochetage for the presence of ASD is greater than 90% if it is found in all inferior leads.

In addition, the crochetage has been found to correlate positively with both left-to-right shunt severity and larger shunt size, according to a Circulation report.

D-Transposition of the Great Arteries

Almost 5% of CHD is due to D-transposition of the great arteries (D-TGA), wherein the aorta originates from the right ventricle (RV) and the pulmonary arteries from the left ventricle, as a recent JAMA Cardiology review notes. This defect is incompatible with life unless there is some communication between the systemic and pulmonary circuits.

The current surgery to treat this condition consists of an arterial switch in the first days of life, but prior to the mid-1980s, the condition was treated by surgically creating an interatrial baffle or through atrial switch surgical procedures (Senning or Mustard procedures), which corrected the circulation to physiologic but left the RV facing a systemic load.

Thus, the ECG QRS after atrial switch for D-TGA manifests evidence of RV hypertrophy, including right axis deviation and right bundle branch block (RBBB). RV overload manifests in right precordial leads with high voltage small R waves and in left precordial leads with a deep S wave due to an underdeveloped left ventricle (LV) facing the lower pressure pulmonary circuit.

Congenitally Corrected Transposition of the Great Arteries

Congenitally corrected transposition of the great arteries (CCTGA or L-transposition) is rare. In such cases, both the LV and RV and their respective atrioventricular valves are reversed. The RV therefore faces a systemic arterial circulation and becomes hypertrophied as the patient ages.

As the right and left bundle branches are reversed, septal activation occurs from right to left, according to the JAMA Cardiology review. A pathognomonic CCTGA ECG pattern is the result: Q waves are noted in the right precordial leads, whereas no Q waves are noted in the left precordial leads. The duration of the QRS is typically normal until advanced systemic RV dilatation and dysfunction develop.

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Tetralogy of Fallot

Tetralogy of Fallot (TOF) is the most common cyanotic heart defect. It consists of right ventricular outflow tract obstruction, a ventricular septal defect, an overriding aortic root, and RV hypertrophy. Various surgical approaches are utilized for TOF, typically within the first year of life. The ECG changes seen with TOF reflect both the initial pathology and the results of surgical intervention.

The JAMA Cardiology review notes that with TOF, RBBB is near-universal and may reflect RV hypertrophy and dilatation as well as surgical injury to the right bundle branch. An atypical appearance is common with variable QRS duration, depending on specific leads. Often the maximal QRS duration is in right-sided precordial leads, reflecting interference from RV surgical incisions or patches.

Given that ECG diagnosis of RV hypertrophy in the presence of RBBB is problematic in cases of TOF, multimodality cardiac imaging should be considered for precise estimation of RV size and function in these patients.

A recent review in the Journal of Innovations in Cardiac Rhythm Management evaluated implantable cardioverter-defibrillator (ICD) usage for CHD and found that, among patients with common CHDs, those with TOF, TGA with a systemic right ventricle, or univentricular heart have the highest risk of sudden cardiac death (SCD).

"[TOF] carries a significant risk of SCD, particularly increasing at the point beginning 20 years after repair, from 2% at 20 years to 4% at 25 years and 6% at 30 years, respectively. SCD represents approximately half of all late deaths (i.e., deaths occurring at a time more than 30 days after operation) in patients with TOF."

The review also notes that recent American and European guidelines recognize QRS duration >180 ms as a key factor in predicting SCD in TOF patients. Guidelines from the European Society of Cardiology state that ICD implantation should be considered for select patients with TOF and multiple risk factors for SCD, including:

Left ventricular dysfunction
Nonsustained VT
QRS duration >180 ms
Inducible sustained VT on programmed ventricular stimulation

Ebstein Anomaly

Ebstein anomaly (EA) is characterized by an apically displaced and malformed tricuspid valve (TV). With EA, there is a wide range of TV displacement/malformation, resulting in a wide range of tricuspid regurgitation. Milder forms tend to be without any signs or symptoms and can remain undiagnosed late into adulthood. These cases are often diagnosed by an incidentally performed ECG.

The major ECG manifestations in EA are related to the right atrial enlargement caused by variable amounts of tricuspid regurgitation, as noted in the JAMA Cardiology review. The QRS axis reflects abnormal activation of the atrialized RV, resulting in an incomplete or complete but atypical RBBB.

Atrioventricular Septal Defect

Atrioventricular septal defect (AVSD) is strongly associated with Down's syndrome. Partial AVSD is characterized by the presence of an ostium primum ASD and a cleft mitral valve.

A characteristic ECG pattern with AVSD consists of a superior QRS axis with R waves in aVl and aVr and predominant S waves in the inferior leads, as the JAMA Cardiology review explains. This is thought to represent early impulse propagation to posterior aspects of the LV due to hypoplasia of the left anterior fascicle and the posterior displacement of the AV node.

The Role of 12-Lead ECG

The 12-lead ECG remains a crucial tool for cardiologists in their clinical evaluation of adult patients with CHD. Distinctive and sometimes unique ECG patterns of ventricular activation can often be found in the QRS of these patients. Knowledge of these QRS changes may allow diagnosis of heretofore unknown CHD, and it could also provide additional prognostic information in patients with known CHD before and after surgical intervention.

Dr. Anthony C. Pearson, MD, FACC is a Professor of Medicine at the St. Louis University School of Medicine Division of Cardiology and specializes in general and noninvasive cardiology.

The opinions, beliefs and viewpoints expressed in this article are solely those of the author and do not necessarily reflect the opinions, beliefs and viewpoints of GE Healthcare. The author is a paid consultant for GE Healthcare and was compensated for creation of this article.

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