Inger Olson, MD

CASE

14.1

Introduction

Although echocardiography is the definitive diagnostic tool for diagnosing congenital heart disease, electrocardiography can be useful for identifying patients at risk for congenital heart defects.

Right QRS axis deviation can be normal in the newborn and is not strongly associated with any particular cardiac defect. However, left-axis deviation or superior QRS-axis deviation with a counterclockwise frontal plane loop is almost invariably associated with a structural abnormality.

Atrial Septal Defect (ASD)

Children and adults with ASD experience variable degrees of right-sided volume overload, particularly enlargement of the right ventricle. This is generally manifested on the ECG as a terminal right interventricular conduction delay with an rSR′ in lead V₁. Other associated findings include right-axis deviation and right atrial enlargement or right ventricular hypertrophy, especially in cases of long-standing volume overload or pulmonary hypertension.

Figure 14.1.1 This ECG is from a 4-year-old female with a secundum atrial septal defect. There is sinus rhythm with normal P waves and a normal PR interval. She has a borderline right-axis deviation. The most significant finding is the presence of RSR’ in V₁. However, it should be noted that RSR’ can be a normal variant in children.

Figure 14.1.2 This tracing is from a 10-year-old male with a secundum atrial septal defect and pulmonary hypertension. He has sinus rhythm with a normal PR interval, but there is significant right-axis deviation and signs of right ventricular hypertrophy. The RSR’ in lead V₁ includes a very tall secondary R wave. (Note that the precordial leads are recorded at half standard.) The signs of right ventricular hypertrophy in children include: upright T wave in V₁ (note: in children, T waves are normally inverted in leads V₁ and V₂); QR pattern in leads V₁ and V₃; tall R wave in leads V₁ and V₄; and deep S wave in lead V₆.

Endocardial Cushion Defects

Endocardial cushion defects encompass a spectrum of structural abnormalities, which range from isolated ostium primum atrial septal defect to complete atrioventricular canal defects. All patients with endocardial cushion defect share a common ECG finding, namely the presence of a leftward superior QRS axis representative of a counterclockwise frontal plane QRS loop.

Figure 14.1.3 This is an ECG from a 13-month-old male with an ostium primum atrial septal defect. There is sinus rhythm with normal PR and QRS intervals. The QRS axis is leftward with a QR pattern in lead aVL, suggesting a counterclockwise superior loop. In this case, there is also an rSR’ in lead V₁. However, there are no signs of right ventricular hypertrophy.

Figure 14.1.4 This tracing is from a newborn baby with a complete atrioventricular canal defect. The tracing demonstrates sinus rhythm with an extreme rightward QRS axis. In a newborn, the rightward QRS axis can be normal; however, in this case the QRS axis is rightward and superior, suggesting the presence of a structural heart defect. There is also right ventricular hypertrophy, which can also be a normal finding for an infant 1 hour after birth.

Tricuspid Atresia

There are other, less common causes of leftward or superior QRS axis in children. Tricuspid atresia is associated with a leftward QRS axis. Other, less common causes include other forms of single ventricle and anomalous left coronary artery from the pulmonary artery.

Figure 14.1.5 This ECG is from a 2-year-old male born with tricuspid atresia and normally related great arteries. His left ventricle was normal and the right ventricle was hypertrophied but diminutive. The ECG demonstrates sinus rhythm with a leftward QRS axis (–83°). There is also evidence of right ventricular hypertrophy with a biphasic T wave and tall R waves in lead V₁ and deep S waves in lead V₆.

Tetralogy of Fallot

Tetralogy of Fallot (TOF) is one of the more common forms of complex congenital heart disease. The degree of right ventricular outflow obstruction varies along a continuum. Therefore, ECG findings are somewhat nonspecific but usually include right ventricular hypertrophy.

Surgical repair of TOF includes patch closure of the ventricular septal defect and relief of right ventricular outflow tract obstruction. In the past, virtually all patients who underwent surgery developed complete right bundle branch block pattern on ECG. This was generally due to the fact that surgery was either performed through a right ventriculotomy or included excision of a substantial amount of right ventricular muscle. However, TOF repair is now performed at an earlier age involving less right ventricular muscle resection and with an approach from the atrium obviating the need for a right ventriculotomy. Therefore, there is a variable appearance of the postoperative ECG in patients following repair of TOF.

Figure 14.1.6 This ECG from an 8-year-old male demonstrates a typical pattern in a patient with TOF after complete repair. There is sinus rhythm and a pattern of a complete right bundle branch block (QRS duration = 138 ms) with a deep S wave in lead I and a wide secondary R wave in lead V₁. This pattern will persist throughout his lifetime.

Figure 14.1.7 This is an ECG from a 5-year-old male who underwent neonatal repair of TOF. The QRS axis is somewhat indeterminate. PR and QRS intervals are normal with no conduction delay and no bundle branch block. At the time of the ECG, he had moderate pulmonary stenosis, and the QR pattern in lead V₁ suggests right ventricular hypertrophy.

Ebstein’s Malformation

Ebstein’s malformation is a complex form of congenital heart disease that includes variable displacement and dysplasia of the tricuspid valve. Tricuspid regurgitation is common, and the right atrium is usually significantly enlarged. The ECG frequently demonstrates right atrial enlargement and right ventricular conduction delay. In addition, Ebstein’s malformation is frequently accompanied by accessory bypass tracts, both overt and concealed.

Figure 14.1.8 This is an ECG from a 9-year-old male with severe Ebstein’s malformation of the tricuspid valve. The P waves are gigantic and dwarf the QRS complexes. In addition, the PR interval is prolonged due to intra-atrial conduction delay. The QRS complexes have low voltage and a right bundle branch block pattern. It is worthwhile noting that an individual with Ebstein’s malformation who presents without a conduction delay most frequently has a concealed accessory bypass tract which preexcites the right ventricle, narrowing the QRS complex.

Figure 14.1.9 This is an ECG from a 29-year-old female with moderately severe Ebstein’s malformation of the tricuspid valve. The PR interval is prolonged due to intra-atrial conduction delay. There are low voltage QRS complexes with a rightward QRS axis and complete right bundle branch block pattern.

Dextrocardia

It is not uncommon to encounter an individual with dextrocardia with or without congenital heart disease. In cases of situs inversus with mirror-image dextrocardia, all of the abdominal and thoracic organs are reversed and the cardiac structures are likewise reversed.

Figure 14.1.10 This is an ECG from a 3-year-old female with situs inversus totalis. Note that her P-wave axis is rightward, her QRS axis is inferiorly directed and her T-wave axis is rightward. One might suspect limb lead reversal until one examines the precordial leads. The most striking finding is that the QRS voltage consistently decreases from lead V₁ to V₆, suggesting that the lead placement is moving away from the cardiac mass. It is recommended to perform standard precordial lead placement on all patients, even those with suspected or known dextrocardia or situs inversus.

Figure 14.1.11 This tracing is from the same patient with right chest leads rather than left chest leads. The R-wave voltage increases progressively from V₁R to V₆R. This confirms the presence of dextrocardia. The patient does have a deep S wave in V₁R and a tall R wave in V₆R due to the presence of a ventricular septal defect with resulting left ventricular hypertrophy.

Pulmonary Atresia, Intact Ventricular Septum

Figure 14.1.12 This ECG is from a 20-year-old female with pulmonary atresia and intact ventricular septum who had undergone balloon pulmonary valvuloplasty in infancy and had a subsequent pulmonary valve replacement 5 years ago. She presented with chronic worsening pain, described as ‘stabbing,’ in the mid-sternum over her sternotomy scar. Her ECG shows sinus rhythm with a nonspecific interventricular conduction delay and T-wave inversion in the inferior and lateral leads, which was unchanged from her previous tracings. For patients who have undergone surgical “repair” of congenital heart defects, there may be a range of ECG abnormalities, which makes it crucially important that the patient and all physicians have access to a “baseline” ECG.

QUESTION

What congenital lesions are commonly associated with an extreme leftward QRS axis? (Circle all that apply.)

1. Endocardial cushion defects

2. Truncus arteriosus

3. Ebstein’s anomaly

4. Tricuspid atresia

5. Coarctation of the aorta

ANSWER

1 and 4: Endocardial cushion defects and tricuspid atresia are almost always associated with extreme leftward deviation of the QRS axis. Ebstein’s anomaly has a common association with Wolff-Parkinson-White syndrome, and the accessory pathway can occasionally cause the QRS axis to have an extreme leftward deviation. Truncus arteriosus and coarctation are not associated with extreme axis deviation.

QUESTION

What findings may be present on the ECG of a patient with repaired Tetralogy of Fallot? (Circle all that apply.)

1. Right ventricular hypertrophy

2. Left ventricular hypertrophy

3. Right bundle branch block

4. Normal ECG

ANSWER

1, 3, and 4: Right ventricular hypertrophy or right bundle branch block may be seen on the ECG after repair of TOF. Patients may also have a normal ECG. Left ventricular hypertrophy is not seen in this lesion. Left bundle branch block occurs in children after surgical manipulation of the left ventricle, such as left ventricular myectomy for outflow tract obstruction. Ventricular septal defects are repaired by placing the patch and sutures on the right side of the interventricular septum, so left bundle branch block is not seen after this repair.

Patient History

A 27-year-old male presents with dyspnea on walking up an incline. He had corrective cardiac surgery for congenital heart disease at age 6. His ECG is shown in Figure 14.2.1.

Figure 14.2.1

Question

What cardiac anatomical information does this ECG reveal?

Discussion, Interpretation, and Answer

This ECG shows sinus rhythm with prolongation of the PR interval, left atrial abnormality, and an unusual right bundle branch block (RBBB). This patient was born with tetralogy of Fallot (TOF) and had pulmonary atresia, ventricular septal defect (VSD), overriding aorta, and right ventricular hypertrophy. He received a Blalock-Taussig shunt (subclavian artery to pulmonary artery) at age 5, and subsequently at age 6 had a complete repair with VSD patch closure and conduit placement from right ventricular outflow tract (RVOT) to pulmonary artery. He has now developed stenosis in the conduit to the pulmonary artery with severe enlargement and hypertrophy of the right ventricle.

The conducted QRS in this ECG has a normal appearing initial sharp component (Figure 14.2.2, red arrows) from activation of the left bundle branch. However, the subsequent component (R′ in lead V₁) is of large amplitude, has multiple notches (blue arrows), and the QRS is quite wide (188 ms). The large amplitude of R′ in V₁ (>1 mV or >10 mm) suggests severe right ventricular hypertrophy. The notches and fractionation in R′ suggest regions of conduction block in the interventricular septum and right ventricle (scarring from surgical intervention and cardiomyopathy). The delayed terminal component of the QRS signifies the delay in activating the right ventricular free wall (conduction block and slowed conduction from ventriculotomy scar and myocardial fibrosis).

Figure 14.2.2

The findings on this ECG are typical for patients with surgically corrected TOF, who have right ventricular hypertrophy and a high incidence of RBBB.¹ The right ventricular free wall and outflow tract predictably has myocardial scarring subsequent to corrective surgery. Widening of the QRS beyond 180 ms has been identified as a marker of sudden arrhythmic death.

Similar findings can be observed after surgical correction of other forms of conotruncal anomalies, or isolated VSD. Before surgery, patients with VSD with intact bundle branches demonstrate large equiphasic RS complexes (≥5 mV or ≥50 mm) in mid precordial leads (V₂–V₅) due to biventricular hypertrophy (Katz-Wachtel phenomenon). The bundle of His and proximal bundle branches course along the inferior margin of a membranous VSD (with the exception of congenitally corrected transposition of great arteries and double inlet left ventricle when the conduction axis can be anterior to the VSD^2,3). RBBB can occur in patients with VSD, either spontaneously, with progressive right ventricle cardiomyopathy, or related to surgical intervention with right ventriculotomy and repair of the VSD.¹

RBBB also occurs frequently in patients with Ebstein’s anomaly. These patients have severe right atrial enlargement with tall, peaked P waves in inferior leads. There is a high incidence of right-sided accessory pathways, and absence of a RBBB pattern might reflect accessory pathway conduction, compensating for the delay in right ventricular activation from the RBBB. The RBBB morphology in Ebstein’s anomaly is distinctly different from TOF. Though the right ventricular activation (R′) is delayed, the degree of ventricular scarring and notches in the R′ are limited. The anatomic right ventricle is often diminutive, and the amplitude of the R′ in lead V₁ is generally small in contrast to the large R′ with RBBB in TOF.¹ An example of RBBB in a 43-year-old female with Ebstein’s anomaly following surgical tricuspid valve repair is shown in Figure 14.2.3. The peaked P waves are lacking as she had reduction right atrioplasty during surgery.

Figure 14.2.3

In an ECG with right ventricular hypertrophy, it is important to recognize the initial r wave (rsR′ pattern) in lead V₁ (red arrows in Figure 14.2.2 and 14.2.3). Absence of the V₁ r wave (qR pattern) signifies severe pulmonary hypertension with suprasystemic right ventricular pressures (e.g., Eisenmenger’s syndrome), resulting in simultaneous right ventricular hypertrophy and rotation of the heart to create an initial vector away from lead V₁.⁴

References

1. Khairy P, Marelli AJ. Clinical use of electrocardiography in adults with congenital heart disease. Circulation. 2007;116(23):2734–2746.

2. Anderson RH, Becker AE, Arnold R, et al. The conducting tissues in congenitally corrected transposition. Circulation. 1974;50(5):911–923.

3. Anderson RH, Arnold R, Thapar MK, et al. Cardiac specialized tissue in hearts with an apparently single ventricular chamber (double inlet left ventricle). Am. J. Cardiol. 1974;33(1):95–106.

4. Surawicz B, Knilans TK. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric. 6th ed. Philadelphia, PA: Saunders. 2008:62.

Patient History

A 34-year-old male with a complex cardiac history [situs inversus, congenitally corrected transposition of the great arteries (L-TGA), ASD/VSD and subpulmonic stenosis status post repair and subpulmonary muscle resection (1985), severe tricuspid, pulmonic and mitral regurgitation status post mechanical tricuspid valve, biprosthetic pulmonary valve, and mitral valve repair (10/21014)] presents with recurrent atrial flutter.

Figure 14.3.1

The flutter wave morphology was negative in the inferior leads, positive in V₁ with an early precordial transition (lead V₃ is isoelectric), which is consistent with counterclockwise flutter in the anterior atrium. Even though the anterior (morphologic right) atrium was on the left side of his chest (accounting for the negative flutter wave in lead I), the logic of the ECG still made this an easy diagnosis despite the complexity of the situation.

Figure 14.3.2

Patient History

Transposition of the great arteries with Mustard repair after balloon septostomy.

While reentry around the tricuspid annulus is the most common atrial tachycardia in these patients, other reentrant or focal substrates may also be present. Typical hints from 12-lead ECGs may be misleading as these patients have a complex pattern of surgical patches and scars that make the interpretation of the activation sequence difficult.

Figure 14.4.1 Sustained atrial tachycardia after successful deployment of a linear lesion on the floor of the right atrial (RA) compartment of the pulmonary venous atrium (PVA) which, on the first glance, presents as an atrial tachycardia with 2:1 atrioventricular (AV) nodal conduction (doubled amplitude to depict the P-wave morphology (fused at the end of the T wave).

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