Case
A 68-yr-old lady underwent a VVI pacemaker [Verity ADx XL SR]
implantation 10 years back for baseline bifascicular block with
intermittent complete heart block. She was doing well with annual follow
up. Now, she presents with 3 episodes of syncope within the last 2
months. Detailed evaluation of pacemaker and extensive neurological work
was unremarkable during one of the prior hospital admissions. Device did
not show any alert. It neither detected any high ventricular rate (HVR)
episode. Her blood biochemistry (K, Mg, Ionised Calcium levels) was
normal. Echocardiography revealed good biventricular systolic function.
A coronary angiogram done in last admission was also normal. After
another recent recurrence she visited the outpatient department. ECG
showed adequate VVI pacing (Fig 1A). This time, during a repeat device
interrogation, as soon as her lower rate was made 45 bpm, she developed
a presyncope in front of us. The real time electrograms are shown in Fig
1B. What could be the mechanism of syncope and how to troubleshoot?