Case report
A 74-year-old man presented with frequent palpitations, described as
“the heart beating on the neck.” He also had a history of two syncope
episodes; the most recent was more than six months before his admission.
By careful history taking, we found that the syncope episodes did not
seem to occur as a result of vasovagal reflex. The patient’s resting
electrocardiogram (ECG) showed a right bundle branch block (RBBB)
pattern (Figure 1 ). Holter monitoring and exercise tests
revealed a bundle branch block alternating between the right and left
bundles. His echocardiogram was normal with preserved ejection fraction
(EF) (66%).
After this initial evaluation, he was subjected to an
electrophysiological study (EPS) and the basic intervals measured were
as follows: PR, 186 ms; QRS, 153 ms (RBBB); AH, 86 ms (basal); and HV,
60 ms. Atrial electrical stimulation (AES) induced a wide QRS complex
tachycardia (Figure 2A ), with predominantly RBBB morphology,
some of the QRS having a left bundle branch block (LBBB) pattern, and
some atrial beats being blocked to the ventricles below the bundle of
His (Figure 2B ).