Case 1
A 56-year-old male with mild preexcitation was referred for EP study who
had several episodes of palpitation recently. All recorded ECGs during
tachycardia were in left bundle branch block type. Maximal preexcitation
pattern was consistent with a left AP. Retrograde conduction was over
distal coronary sinus (CS) when pacing from right ventricle (RV).
Tachycardia was induced by an atrial extrastimulus blocked in the AP,
conducting over the AV node and causing left bundle branch block.
A late-delivered premature ventricular contraction (PVC) was able to
advance the next A and reset the tachycardia, which was diagnostic for
ORT with aberrancy. In the meantime, left bundle branch conduction was
restored which narrowed the next QRS complex. Tachycardia was then
terminated by the advanced wavefront reaching the ventricular insertion
site of AP which was refractory (Figure 1). Mapping of the AP was
performed using transseptal approach during RV pacing. The earliest
atrial activation site was located at anterolateral mitral annulus (MA)
with a sharp potential, where radiofrequency application successfully
blocked the AP. The patient has been free from the tachycardia for 1
year.
Case 2
A 64-year-old gentleman presented with very frequent tachycardia which
always terminated spontaneously within minutes. The only ECG from
emergency room showed tachycardia with left bundle branch block type.
His tortuous femoral veins made it difficult for catheterization,
therefore only an RV catheter was inserted with CS catheter placed from
jugular vein for EP study. The earliest atrial activation site was CS3-4
during RV pacing, indicating a left lateral AP. Atrial pacing and
extrastimulus showed no preexcitation or intraventricular block.
The clinical tachycardia could only be induced by RV extrastimulus with
isoproterenol, which could not sustain for more than 10 beats,
compatible with ORT with aberrancy. Termination of the tachycardia was
always preceded by a narrow QRS complex, with the V and subsequent A at
MA advanced, suggesting anterograde block in the AV junction (Figure 2).
The pathway was ablated at anterolateral MA with retrograde approach,
after which no tachycardia could be induced. The patient has been free
from the symptom for more than 3 years.