A Slow Problem
Dr James Gamble BM BCh MRCP (Clinical Research Fellow, Oxford University Hospitals NHS Trust)
We were referred a 68 year old man for LV lead revision. He had an ischaemic cardiomyopathy, anda primary prevention ICD had been implanted in 2006. By 2014 his QRS had broadened and he was upgraded to CRTD. The implant was reportedly difficult, and after a challenging procedure he ended up with a Medtronic Starfix (a unipolar LV lead with fixation tines) in a lateral vein. He had a clear response to CRT and felt much improved. A few months later he developed troublesome palpatations and required an AV node ablation for paroxysmal atrial fibrillation.
About a year after implant, he re-presented to the implanting centre with recurrent symptoms of heart failure. ECGs and a device check were reported as showing no LV lead capture, and he was referred to us for extraction and replacement of the LV lead.
He was seen in our centre before the procedure. He was highly symptomatic with NYHA class 3 symptoms. We rechecked the device, and recorded ECGs in several pacing modes. Of note, he was in permanent AF with VVIR pacing after the AVN ablation. The unipolar LV lead was set up to pace tip-can, so there should be no risk of RV anodal capture.
Figure 1 – RV only pacing
Figure 2- Biventricular (BiV) pacing, with high LV lead output (5V @ 1.0ms), showing an identical ECG to RV only pacing above, and apparently confirming no LV capture.
Figure 3 – LV only pacing, high LV lead output (5V @ 1.0ms).
Surprisingly, LV only pacing revealed LV capture, and in fact the LV threshold was only 0.8V @ 1ms.
At this point I would ask the reader to
1. Identify the problem
2. Determine how it might be solved
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