Changes in Ventilation Associated with Worsening Heart Failure in Ambulatory Patients

Breathlessness is a cardinal symptom of heart failure (HF) and reflects abnormal ventilation, particularly during exercise. Cardiopulmonary exercise testing provides only a snapshot of ventilatory physiology and cannot capture longitudinal changes associated with deterioration. Continuous physiologic monitoring from implantable devices offers an opportunity to characterize ventilatory trends preceding HF events in ambulatory patients. The MultiSENSE study followed 900 patients with a cardiac resynchronization therapy defibrillator (CRT-D) modified to record high fidelity physiologic data. Ventilatory variables derived from thoracic impedance were examined before adjudicated HF events (hospitalization for HF or outpatient visit requiring IV diuretics) and between clinic visits associated with worsening dyspnea. Variables included respiratory rate (RR), tidal volume (TV), minute ventilation (MV) and Rapid Shallow Breathing Index (RSBI; RR/TV). Patient activity was assessed using a device-embedded accelerometer. A total of 130 HF events from 92 patients were analyzed. In the 3 days preceding HF events, mean daily RR increased (adjusted mean change: 0.59 [95% CI: 0.31, 0.86], relative change: 3.56%, p<0.0001) and mean daily TV decreased (-0.07 [-0.10, -0.04], -7.4%, p<0.0001), resulting in a significant increase in RSBI (2.34 [1.56, 3.12], 10.5%, p<0.0001). Daily MV decreased (-0.72 [-1.2, -.23], -4.4%, p=0.0042), largely reflecting reduced activity. When accounting only for resting periods, a similar increase in RSBI was observed in the 3 days preceding HF events (1.98 [1.10, 2.86], 7.32%, p<0.0001) relative to baseline, whereas MV showed no significant change. In patients with worsening dyspnea between clinic visits, mean daily RR and RSBI increased significantly without a significant change in TV or MV. Worsening HF in ambulatory patients is characterized by a shift toward rapid shallow breathing. RSBI significantly increased prior to HF events and with worsening dyspnea.. These findings suggest that RSBI may be a sensitive marker for worsening HF and may provide clinically relevant insight for monitoring ambulatory patients.