The Medtronic Chronicle implantable hemodynamic monitor used a specialized RV lead/sensor. The device was able to monitor and telemeter:
- Systolic and diastolic pressure
- Estimated pulmonary artery diastolic pressure
- RV dp/dt (positive & negative)
- Heart rate & activity
- Core body temperature
- Continuous remote monitoring
The device and its use is described in: Steinhaus D, Reynolds DW, Gadler F, Kay GN, Hess MF, Bennett T; Chronicle Investigators, “Implant experience with an implantable hemodynamic monitor for the management of symptomatic heart failure”, Pacing Clin Electrophysiol. 2005 Aug;28(8):747-53. From the paper:
“The lead (Model 4328A, Medtronic, Inc) is implanted transvenously, and utilizes a coaxial design with a tip electrode at the distal end. Electrogram and heart rate sensing is accomplished via a unipolar vector between the tip electrode and the subcutaneous IHM casing. The lead has an IS-1 connector, is 58 cm long with polyurethane insulation and tines for passive fixation. The pressure sensor capsule is located 3 cm proximal to the tip and has a maximum diameter of 3.7 mm. A nickel alloy is utilized as the conductor material while the sensor capsule is constructed of titanium and titanium alloys, which are in turn covered in polyurethane and medical adhesive.
The pressure sensor capsule is hermetically sealed and includes a deflectable titanium diaphragm. Motion of this diaphragm changes capacitance and thereby reflects changes in RV pressure. Digital sampling is used to construct continuous pressure waveforms for storing hemodynamic information. Due to the sensor capsule, the stylet lumen terminates at the proximal side of the sensor capsule 4 cm from the lead tip. Thus, a stylet cannot be advanced to the tip of the lead.
The monitor includes pressure sensing circuitry and a memory to store continuous pressure trends as well as specific triggered events such as bradyarrhythmias, tachyarrhythmias, or patient-activated episodes. The device stores RV systolic, diastolic, and pulse pressure, estimated pulmonary arterial diastolic pressure (ePAD), RV dP/dt, preejection interval, and systolic time interval. In addition, heart rate, patient activity levels, and central venous temperature are also stored.”
In March 2007, FDA’s Circulatory System Devices Panel voted against the approval of Medtronic’s implantable hemodynamic monitor because its use did not significantly improve clinical outcomes in the COMPASS-HF randomized, controlled trial.
In the COMPASS-HF trial, 274 NYHA class 3-4 heart failure patients who were implanted with a Chronicle were randomized to either have their management guided or not guided by the device’s data output. Clinicians had complete access to the data from patients in the first group and were blocked from access to data from the control patients. After six months, Chronicle-led therapy was associated with a 21% drop in the composite rate of the primary end point: HF-related hospitalizations, emergency-department visits, or urgent clinic visits. The difference fell short of significance.
Medtronic’s Website: www.medtronic.com