Title : Intermittent loss of cardiac resynchronization: Guess why!
Abstract:
Introduction:
Many studies have demonstrated that biventricular pacing in patients with advanced chronic heart failure significantly improves ventricular hemodynamic, exercise capacity, and reduces mortality and hospitalization rates. Biventricular pacing less than 90% is considered as insufficient and may lead to bad response to cardiac resynchronization and worsening congestive heart failure.
Case Summary:
A 58-year-old man with past history of ischaemic cardiomyopathy, LBBB and LVEF of 30% presented with worsening dyspnoea on exertion three mounths after successful Cardiac Resynchronization Therapy-Defibrillator ( CRT-D ) implantation (Claria MRI Quad , MEDTRONIC). Medical treatment was optimal and uninterrupted. On examination, his heart rate was 79 bpm, fine crackles in the base of both lungs. The 12-lead ECG showed sinus rhythm with regular intermittent biventricular stimulation with affined QRS (120 ms) and spontaneous ventricular rhythm with baseline LBBB (160 ms).
The interrogation of the defibrillator showed that the device was programmed in DDDR 50-130 bpm. Over sensing of T wave with double counting leaded to a ventricular rate higher than the upper synchronized ventricular tracking rate (130 bpm in this case) witch inhibits the following sensed atrial activity to generate a paced atrio-ventricular delay and programmed biventricular stimulation. This phenomenon explains the emergence of intrinsic ventricular beat one time in two.
The problem was resolved by reprogramming the ventricular sensing vector from distal-spire to bipolar with total disappearance of T wave and permanent biventricular pacing. The patient was a good responder to cardiac resynchronization with improvement of LVEF to 45% (echocardiography 6 mounths later) with controlled heart failure symptoms during following up.
Conclusion:
Reprogramming devices to optimize the delivery of CRT is an important step which shoudn’t be neglected. Like our case witnesses, simple intervention can avoid loss of cardiac resynchronization with clinical and echocardiographic benefits during following up.
