Electrode charge-neutral sensing of evoked ECG

An apparatus for cardiac pacing and sensing, comprising:

• (a) a unipolar cardiac pacing lead adapted for positioning within a heart chamber, said lead having a distal end with a first electrode;
• (b) a second electrode and a reference electrode each electrically isolated from said first electrode and each other;
• (c) means for transmitting to both said first and second electrode an electrical stimulus pulse;
• and
• (d) circuit means connected to both said first and second electrodes and said reference electrode for obtaining an evoked electrical potential, said circuit means comprising first means for sensing a first electrical signal at said first electrode in a unipolar mode in reference to said reference electrode, second means for sensing a second electrical signal at said second electrode in a unipolar mode in reference to said reference electrode, and means for adding said first and second signals from said first and second sensing means to cancel out any residual opposite polarized potentials and to obtain the evoked electrical potential.

An apparatus for obtaining an evoked electrical potential, comprising:

• (a) a first electrode adapted to be positioned within a heart chamber;
• (b) a second electrode adapted to be located proximate the heart chamber and electrically isolated from said first electrode;
• (c) a reference electrode electrically isolated from both first and second electrodes;
• and
• (d) circuit means connected to both said first and second electrodes and said reference electrode for obtaining the evoked electrical potential, said circuit means comprising first means for sensing a first electrical signal at said first electrode in a unipolar mode in reference to said reference electrode, second means for sensing a second electrical signal at said second electrode in a unipolar mode in reference to said reference electrode, and means for adding said first and second signals from said first and second sensing means to cancel out any residual opposite polarized potentials on said first and second electrodes and to obtain the evoked electrical potential.

A method of pacing a heart and obtaining an evoked ECG signal, comprising the steps of:

• (a) applying an electrical stimulus pulse to said heart via an electrically isolated first and second electrode;
• (b) sensing a first electrical signal at said first electrode in a unipolar mode in reference to a reference electrode which is electrically isolated from said first and second electrodes;
• (c) sensing a second electrical signal at said second electrode in a unipolar mode in reference to said reference electrode;
• and
• (d) adding said first and second signal to cancel any oppositely polarized potentials on said first and second electrodes and to obtain a third signal including the evoked ECG signal from said heart.