An unusual cause of OptiVol alarm: increased intra-abdominal pressure associated with irritable bowel syndrome.

Monitoring intrathoracic impedance has become an integral part of follow-up of patients with implantable cardioverter defibrillator (ICD) or cardiac resynchronization therapy/defibrillator due to heart failure. However, several noncardiac factors may influence intrathoracic impedance. We report on an unusual cause of decrease in intrathoracic impedance in a 54-year-old male patient following successful implantation of biventricular ICD for heart failure symptoms due to nonischemic dilated cardiomyopathy and severely impaired left ventricular systolic function. During the follow-up period, the patient presented several times with the OptiVol alarm due to an increase in the OptiVol fluid index, in the absence of symptoms or signs of heart failure. Further inquiry into the possible causes of decreased intrathoracic impedance revealed that the patient had frequent episodes of irritable bowel syndrome, which increased intra-abdominal pressure, leading to elevation of diaphragm and subsequent compression of intrathoracic organs, and thus to a decrease in intrathoracic impedance.