Studies of cardiovascular signals continuously sensed by implantable devices provide
unique insight into detailed pathophysiology as patients progress from stable to congested
states. These data suggest that volume expansion, autonomic adaptation, and pulmonary
interstitial edema begin several weeks before patients develop symptoms or demonstrate
changes in daily weight. Monitoring physiologic signals from implanted devices may
provide earlier warning of impending decompensation, thereby allowing changes in medical
therapy to prevent worsening heart failure.