Date on Master's Thesis/Doctoral Dissertation

7-2011

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Bioengineering

Committee Chair

Koenig, Steven Christopher

Author's Keywords

Subcutaneous ECG; QRS detection; Counterpulsation; Circulatory support; Electrocardiogram

Subject

Cardiac pacemakers; Electrocardiography

Abstract

Background: Emerging circulatory support devices that operate in counterpulsation to the native heart require synchronized timing of device ejection and filling on a beat-to-beat basis with the native heart using a patient's ECG. Surface leads are commonly used for short-term patient monitoring but not appropriate for long-term use, and epicardial and non-thoracotomy leads increase the complexity of the device implant/explant procedures. Subcutaneous leads have been shown to be less susceptible to artifacts than surface leads, require less invasive surgery, and have recently been used successfully with a long-term subcutaneous implantable cardioverter-defibrillator. The objective of this study was to develop subcutaneous ECG leads for synchronized timing (filling and ejection cycles) of the Symphony device and wearable pneumatic driver for chronic counterpulsation therapy. To demonstrate feasibility, we tested the hypothesis that subcutaneous ECG leads provide equivalent QRS detection, lead migration, and durability as clinical-standard epicardial leads. Methods: Two epicardial and six subcutaneous leads were implanted in bovine (7 days, n=4 and 14 days, n=2). Epicardial and subcutaneous ECGs were recorded simultaneously in 30 second epochs every hour and in 20 minute epochs during daily treadmill exercise. Landmark features and R-wave triggering detection rates for each lead configuration were calculated and compared. Lead placement, migration, and durability were quantified using fluoroscopy and evaluated at necropsy. Results: There were 2,818 data epochs recorded at rest and 24 data epochs recorded during treadmill exercise. Using a simple adaptive-thresholding R-wave detection algorithm with the epicardial signal as the control, the triggering rate for the subcutaneous ECG leads demonstrated 99.1±0.4% positive predictive value and 96.8±1.5% sensitivity during normal daily activity, and 98.0±10.2% positive predictive value and 93.3±5.6% sensitivity during treadmill exercise. The average QRS voltage was 818±99 µV with a T/R ratio of 0.44±0.05. There was no significant waveform distortion or artifacts observed in ECG waveforms measured with the subcutaneous leads. Upon study endpoint, all subcutaneous leads (36/36) were within 1.4 cm of initial placement with an average migration distance of 0.52±0.10 cm. There was no lead fracture or permanent signal loss for all leads (36/36). Conclusion: In this study, the subcutaneous leads provided equivalent performance to epicardial leads in bovine during normal daily activity and treadmill exercise. The leads were easily implantable using standard surgical instruments, provided high reliability of QRS detection, and showed no significant migration from the initial placement site. These findings demonstrate the feasibility of using subcutaneous leads for synchronized timing of mechanical circulatory support while offering the advantage of less invasive surgery and associated risk factors.

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