Rise in left ventricular capture threshold
Tracing
Manufacturer Boston Scientific
Device CRT
Field Left ventricular pacing
N° 5
Patient
This 67-year-old man suffering from dilated cardiomyopathy with left bundle branch block received a Boston Scientific Cognis triple chamber defibrillator. At 6 months after the implant, the patient had not responded to therapy and continued to suffer from dyspnea during routine daily activities. Interrogation of the defibrillator revealed 100% BiV stimulation.
Graph and trace
Tracings recorded in the ambulatory department.
- spontaneous atrial rhythm and BiV stimulation
Tracing recorded without changing the programming; pulse amplitude for LV stimulation = 2.5 V/0.4 ms.
- same QRS morphology as on previous tracing
- different QRS morphology; alternans between both morphologies.
LV stimulation threshold measurement = 2.5 V/0.4 ms.
Tracing recorded after reprogramming of LV stimulation pulse strength to 3.5 V/0.4 ms without change in configuration.
- morphology of BiV capture (on the first tracing, morphology consistent with RV capture only).
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This patient’s LV lead threshold rose. The chest radiograph showed no macro-dislodgement. The rise in threshold may have been due to a micro-dislodgement invisible on X-ray or to local changes in the myocardium. This unexpected non-response in a patient with left bundle branch block was, therefore, probably due to a consistent failure of BiV capture despite a BiV stimulation rate near 100%. After the measurement of the bipolar lead threshold at various LV stimulation configurations, we selected the lowest that was not associated with phrenic nerve stimulation.