Age: 19 years old
Gender: Male
Occupation: College student
Working diagnosis: Ebstein malformation and tachyarrhythmia
HISTORY
Soon after birth, the patient developed paroxysmal supraventricular tachycardia, which was controlled reasonably well with digoxin. The diagnosis of Wolff-Parkinson-White (WPW) syndrome was made by the presence of ventricular pre-excitation noted on his ECG.
At the age of 8 months, echocardiography confirmed the coexistence of Ebstein anomaly of the tricuspid valve and an ASD of the secundum type. He never had clinical cyanosis.
When he was 6 years old, digoxin was discontinued, and he had no further episodes of tachycardia.
Recent routine echocardiography at a local hospital demonstrated an enlarged RV, worsening tricuspid regurgitation, and a left-to-right shunt between the atria. Therefore, he was referred for further evaluation.
Comments: Digoxin and its relatives were chosen in the past to control supraventricular tachycardia even in infants. Its positive inotropic effects were believed to work synergistically with its blockade of AV conduction. The actual mechanism of action was not clearly understood, however, and the narrow therapeutic window made appropriate dosing troublesome. Serum digoxin levels above the therapeutic range could be arrhythmogenic. More recently, other drugs have replaced digoxin in this role.
Ventricular pre-excitation via one or more accessory AV conduction pathway(s) is the hallmark of WPW syndrome. Such pathways, often manifest by a delta wave on the resting ECG, may conduct antegrade or retrograde, enabling AV reentrant tachycardia under certain circumstances. According to the location of the accessory pathways, several types of clinical arrhythmias may be seen. In some patients, the pre-excitation pattern is not seen on the ECG, which is called a concealed type of WPW syndrome.
Ebstein anomaly is a malformation of the tricuspid valve and RV involving incomplete separation (delamination) of portions of the valve leaflet and the endocardium. An ASD or stretched patent foramen ovale is the most common associated lesion.
The common association between Ebstein anomaly and WPW syndrome (in approximately 25% of cases) is well known. Not surprisingly, incomplete formation of the annular attachment of the tricuspid valve results in less than perfect AV orientation. Some muscle fibers bridging the atrium and the ventricle may persist and allow accessory conduction; hence multiple pathways are often found between the right atrium and the RV in Ebstein patients.
PHYSICAL EXAMINATION
BP 90/60 mm Hg, HR 82 bpm regular rhythm, oxygen saturation 97%
Height 171 cm, weight 66 kg, BSA 1.77 m 2
Surgical scars: None
Neck veins: The venous waveform was normal.
Lungs/chest: Lung sounds were clear with no rales.
Heart: The rhythm was regular. There was no RV lift. The second heart sound had a normal pulmonary component, and there was persistent splitting. A blowing 3/6 systolic murmur was heard at the fourth left intercostal space.
Abdomen: The abdomen was soft and flat, with no organomegaly.
Extremities: No edema was present, there was no clubbing.
Comments: The JVP is often normal in Ebstein patients.
Typically, a secundum ASD will cause fixed splitting of the second heart sound if there is a significant left-to-right shunt. Severe tricuspid regurgitation will cause closure of the pulmonary valve to occur earlier. Hence splitting may be variable.
ELECTROCARDIOGRAM
FINDINGS
Heart rate: 79 bpm
QRS axis: Left axis deviation to −50°
QRS duration: 160 msec
Normal sinus rhythm with a shortened PR interval and widened QRS complex with evidence of pre-excitation. Nonspecific ST- and T-wave inversions. Voltage evidence of possible LV hypertrophy is not reliable in the context of WPW. RA overload is likely in V1–2.
24-hour Holter ECG
Repeated 24-hour ECGs showed no tachyarrhythmia.
Comments: The short PR interval, slurred upstroke of the QRS complex (delta wave), and wide QRS complex make up a typical ECG pattern of WPW syndrome.
Abnormalities of repolarization (ST-T waves) are often present with abnormal depolarization and are not indicative of specific pathology.
The 24-hour ECG is helpful to exclude asymptomatic tachyarrhythmias.
CHEST X-RAY
FINDINGS
Cardiothoracic ratio: 55%
Enlarged cardiac silhouette, RA enlargement, and normal pulmonary vascular markings.
Comments: Patients with Ebstein anomaly have variable but sometimes severe enlargement of the cardiac silhouette on CXR because of severe enlargement of the right heart chambers. Here, the degree of cardiomegaly is modest. The aortic knuckle is small, in keeping with chronic/lifelong low systemic cardiac output.
EXERCISE TESTING
| Exercise protocol: | Modified Bruce |
|---|---|
| Duration (min:sec): | 10:00 |
| Reason for stopping: | Leg fatigue |
| ECG changes: | Persistent ST abnormality |
| Rest | Peak | |
|---|---|---|
| Heart rate (bpm): | 82 | 184 |
| Percent of age-predicted max HR: | 92 | |
| O 2 saturation (%): | 97 | 94 |
| Blood pressure (mm Hg): | 90/60 | 176/80 |
| Peak V o 2 (mL/kg/min): | 36.4 | |
| Percent predicted (%): | 68 | |
| Metabolic equivalents: | 10.0 |
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