Age: 47 years
Gender: Female
Occupation: Secretary
Working diagnosis: Ebstein anomaly
HISTORY
The patient presented with presyncope 14 months earlier, having been asymptomatic and well all her life. She was found to be in complete heart block and a dual chamber DDD pacemaker was placed. Echocardiography, performed to rule out structural heart disease, demonstrated a previously unknown diagnosis of Ebstein anomaly of the tricuspid valve with a small secundum ASD or PFO. Except for some diaphragmatic pacing she was extremely well. However, over the ensuing 5 months she complained of slowly progressive shortness of breath on exertion (one flight of stairs), mild orthopnea, and increasing fatigue. Further investigation was recommended to assess the possibility and severity of right-to-left shunting at rest and the possible role of percutaneous closure of the defect in the interatrial septum.
There was no known maternal exposure to lithium during her gestation. She was followed with uterine fibroids, a mild anxiety syndrome, and a smoking history of 20 pack-years. She had no known allergies.
Comments: Only a small percentage of patients with Ebstein anomaly require pacing.
Maternal lithium use is a risk factor for Ebstein anomaly in the fetus.
PHYSICAL EXAMINATION
Well-developed white female in no apparent distress
BP 110/70 mm Hg, HR 86 bpm and regular, oxygen saturation (upright and recumbent) 93%
Height 162 cm, weight 59.2 kg BSA 1.63 m 2
Surgical scars: None
Neck veins: JVP was elevated to 10 cm with a prominent V-wave.
Lungs/chest: Respiratory excursion was symmetric, and breath sounds were normal.
Heart: The pulse was regular. The apical impulse was normal; there was a left parasternal RV lift. The heart sounds were normal, and there was a soft holosystolic murmur at the lower left sternal border that became louder with inspiration.
Abdomen: The liver was enlarged and mildly pulsatile.
Extremities: There was no lower extremity edema. Peripheral arterial pulses were normal and equal bilaterally.
Comments: RV volume overload caused by tricuspid valve regurgitation is responsible for the RV lift. It is unusual for the JVP to be frankly elevated in patients with Ebstein anomaly.
LABORATORY DATA
| Hemoglobin | 16.3 g/dL (11.5–15.0) |
| Hematocrit/PCV | 45% (36–46) |
| MCV | 97 fL (83–99) |
| MCHC | 34 g/dL (31–35) |
| Platelet count | 157 × 10 9 /L (150–400) |
| Sodium | 139 mmol/L (134–145) |
| Potassium | 4.1 mmol/L (3.5–5.2) |
| Creatinine | 0.9 mg/dL (0.6–1.2) |
| Blood urea nitrogen | 10 mg/dL (6–24) |
Comments: The elevated hemoglobin concentration presumably represents secondary erythrocytosis, and suggests that despite the mildly reduced resting oxygen saturation, the patient presumably desaturates further with exercise.
ELECTROCARDIOGRAM
FINDINGS
Dual chamber pacing (A paced–V paced) with 160 msec AV interval at low rate of 60 bpm.
Comments: In this paced rhythm, there is no AV conduction across a right-sided bypass tract that is present in some patients with Ebstein anomaly.
Pacing is from the RV, with a LBBB conduction pattern.
CHEST X-RAY
FINDINGS
Cardiothoracic ratio: 52%
There is mild cardiomegaly. The mediastinum is unremarkable.
The lungs are clear. A left subclavian transvenous pacemaker is present with tips overlying the RA and RV. The RA is prominent. The left heart border is straight, likely from RV and RVOT dilation.
Comments: The cardiomegaly is mainly due to RA enlargement. The normal appearance of the pulmonary arteries argues against a significant left-to-right shunt, but does not exclude a right-to-left shunt as a cause of her low oxygen saturation.
EXERCISE TESTING
Stress/Echo Study
| Exercise protocol: | Modified Bruce |
|---|---|
| Duration (min : sec): | 8 : 45 |
| Reason for stopping: | Dyspnea |
| ECG changes: | Not diagnostic |
| Rest | Peak | |
|---|---|---|
| Heart rate (bpm): | 86 | 150 |
| Percent of age-predicted max HR: | 87 | |
| O 2 saturation (%): | 93 | 87 |
| Blood pressure (mm Hg): | 110/70 | 166/82 |
| Peak V o 2 (mL/kg/min): | 13.3 | |
| Metabolic equivalents: | 4.6 | |
Resting PA systolic pressure: 30 mm Hg
Peak PA systolic pressure: 60 mm Hg
Comments: This exercise study was done as part of a stress echocardiogram. The major finding of the study was low-normal arterial saturation at rest with mild additional arterial desaturation at peak exercise. The dyspnea that terminated exercise was probably related to the low saturation and to reaching the upper ventricular response rate of the pacemaker.
It is postulated that the normal increase of RV peak pressure during exercise (estimated at 60 mm Hg) results in increased tricuspid valve regurgitation and RA pressure, promoting right-to-left shunting across the atrial septum.
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