Implantable Loop Detector Placement
Student: Chris Tedder, Vanderbilt University 2011
Advisor: Blair Anderson, St. Jude Medical
Abstract
My project addresses the challenge in finding a convenient implant site that obtains an accurate cardiac electrical signal reading through an Implantable Loop Recorder (ILR). This procedure is to be done non-invasively without patient prep and should be applicable to all patients, regardless of size, age, gender, etc. My device must fulfill the requirements to determine where the maximum signal occurs and at what angle in relation to the major axis the ILR should be oriented. The nurse or tech that will be operating my device must know how to manually arrange the device to locate this optimal implant site. To achieve the most thorough analysis of the electrical activity on the chest, my device will be arranged in a pattern that mimics Einthoven’s Triangle.
· Identify the ideal implant site for an ILR. If R-wave amplitudes are undersensed, patients can be falsely diagnosed with asystole. On the contrary, if R-waves are oversensed, doctors may falsely diagnose tachyarrhythmias. The anatomical location must be consistent for all patients, so physicians are only required to make one incision. Multiple trials increase the patient’s risk of infection, discomfort, and scarring.
· Include electrode specifications consistent with those of the ILR manufacturing to ensure values obtained with the mapping device will translate to the implanted ILR
· Digital read-out of P and R-wave in a format that is displayable on a laptop computer in millivolts with a range of 0-2 mV in 0.01 mV increments.
Introduction
Implantable loop recorders (ILRs) are instruments implanted subcutaneously that assist physicians in identifying whether or not patient symptoms are related to or caused by abnormal cardiac rhythms. These devices are often implanted in patients who complain of syncope, palpitations, or other significant symptoms in which an electrophysiology study has deemed inconclusive. The ILR continuously monitors the patient’s rhythm and can record snapshots called electrograms, based on specific programmable parameters – for example, the device will record when the heart rate drops below 40 bpm or when the rate exceeds 150 bpm. Additionally, most ILRs come with a patient activator that will allow the patient to manually record when they start to feel symptoms. The ILRs remain implanted for up to three years or until the physician can conclude the source of the patient’s symptoms based upon the electrograms.
History and Context
I have met with Blair Anderson at the Eskind Biomedical Library on the Vanderbilt University campus. She provided me with several resources for the project, including a dummy St. Jude Medical (SJM) ILR (seen in Figure 1), a Dubin’s “Rapid Interpretation of EKGs,” and a SJM Confirm Implant Guide, both of which I have begun reading. As a nurse practitioner by trade, Blair would like me to meet with one of her BME colleagues, Sarah Whittam, to discuss the issues in engineering terms.
Team
I am pursuing a career in the cardiac rhythm disease management industry, so I was excited to see the design project posted. My knowledge of this discipline and passion for helping patients overcome abnormal heart rhythms will allow me to positively contribute to St. Jude Medical’s initiative. As mentioned previous, I am working under the direction of Blair Anderson and her colleague(s).
Work Plan and Outcomes
I pan to determine the optimal device implant site and orientation using standard surface ECG electrodes and an ECG measurement system. In this determination, I will focus on wave amplitudes, site movement/proximity to midline, and patient comfort.
Evaluation and Sustainability Plan
Success will be primarily determined by my advisor. With my current understanding, success will be defined by determining the optimum location within the body to implant the device and the best location on the device to place the electrodes without violating any patents to acquire optimum P-, R-, and T-waves.