Intramyocardial pacing and sensing for the enhancement of cardiac stimulation and sensing specificity.
BACKGROUND
Intracardiac electrodes create an "antenna" capable of unintentionally recording and stimulating tissue beyond the chamber in which they are positioned, resulting in far-field R wave oversensing in pacemakers and inappropriate detection in defibrillators. This feasibility study sought to determine whether a specially constructed lead with two distal totally intramyocardial electrodes could overcome these limitations.


METHODS
Two mongrel dogs were anesthetized and a median sternotomy performed. Epicardial intramyocardial pacing and sensing function was assessed and compared to standard active fixation pacing and sensing placed at the same atrial and ventricular sites. Right ventricular pacing was also assessed.


RESULTS
For the novel intramyocardial lead, the average R wave amplitude was 7.2 mV, compared to an average R wave of 8.4 mV for the standard active fixation lead placed at identical ventricular sites; P-waves were also similar. Cross-chamber sensing was present in the ventricle and atrium with the standard lead, and absent with the intramyocardial lead. The average pacing threshold was 0.7 mA at 0.2 ms for the novel lead compared to 1.1 mA for the standard lead. With the standard lead, phrenic stimulation was seen at threshold (cathode distal) and at 3 mA (cathode proximal electrode). No phrenic stimulation was seen with the novel intramyocardial lead despite outputs up to 20 mA at sites located 3-5 mm from the phrenic nerve.


CONCLUSIONS
Totally intramyocardial pacing is feasible, and results in site-specific pacing and sensing function. This may eliminate far-field signal oversensing and phrenic stimulation in future devices.
Asirvatham
Samuel J
SJ
Mayo Clinic, Rochester, Minnesota 55905, USA.
Bruce
Charles J
CJ
Danielsen
Andrew
A
Johnson
Susan B
SB
Okumura
Yasuo
Y
Kathmann
Eva
E
Packer
Douglas L
DL
Friedman
Paul A
PA
D000818:Animals; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D004285:Dogs; D004867:Equipment Design; D009206:Myocardium; D010138:Pacemaker, Artificial