Figure 1.
Illustration of electrocardiographic recording method, signal processing, and measurement of electrograms.
E1–E4 = endocardial – epicardial plunge needle electrodes. +/− = electrode terminals. Diff = differential of +/− terminals. Triangle = Analogue Amplifier. GND = Ground Terminal attached to rib-retractors. ADC = Analogue to Digital Converter (1 kHz sampling). Step Functions (f): Band-Pass filtering in analogue domain (0.2–300 Hz) and High-Pass filtering in the digital domain (not performed or 30 Hz). V-P = Maximum negative deflection amplitude of QRS complex. VP-P = Maximum peak positive to peak negative deflection amplitude of QRS complex.
Figure 2.
Left: Three dimensional electroanatomic map of the left ventricle (anterior projection) displaying activation time derived from non-contact electrograms during pacing from a needle (D) located at the left ventricular apex.
The figure shows earliest activation (dark blue) at the apex with gradual spreading towards the base (red). Numbers on electroanatomic map (fineprint) represent randomised locations of multipole needles (shown rightmost), which were deployed via the epicardium. Right: Panels A, B and C demonstrating transmural unipolar and bipolar contact electrograms recorded from multipole needles corresponding to sites A, B and C on the electroanatomic map. Y-axis is represented in mV. Electrodes; E1–E4 = endocardial-epicardial unipolar recording depth; E12–E34 = endocardial-epicardial bipolar recording depth.
Table 1.
Within subject analysis examining the effect of propagation distance (covariate), transmural recording depth (treatment), and pacing depth (treatment) on minimally filtered unipolar electrogram parameters measured.
Table 2.
Within subject analysis of the effect of propagation distance (covariate), transmural recording depth (treatment), and pacing depth (treatment) on unfiltered and 30 Hz high-pass filtered bipolar electrogram parameters measured.
Figure 3.
Plots showing effect of recording distance from stimulation source and recording depth on contact electrograms measured during multisite pacing of left ventricular myocardium.
There was a significant inverse relationship between recording distance from stimulus location and unipolar electrogram amplitude that was not significant for bipolar electrograms. Values represent between-sheep mean ± S.E, where; p↔ is the probability of effects relative to propagation distance; and p↕ is probability of transmural effects. A. Unipolar V-P; B. Unipolar VP-P; C. Bipolar VP-P; and D. Filtered bipolar VP-P. See figure 1 for electrode locations.
Figure 4.
Spatial representation of sub-endocardial electrogram parameters during sub-endocardial pacing from the apex (left panels) and base of the left ventricle (right panels).
Two dimensional space is based on spherical coordinates derived from needle locations, representing elevation (−1 = apex to +1 = base), and azimuth (−2 = mid lateral to +2 = anterior). Numbered contours represent parameters derived from unipolar contact electrograms represented in milliseconds (ms) for activation time (AT) and millivolts (mV) for V-P and VP-P corresponding to panels from top to bottom respectively. Solid arrows represent preferential path of activation. Dotted arrows represent the approximate electrophysiological gradient of V-P and VP-P away from the stimulus site.
Figure 5.
Transmural comparison of activation time between the epicardial and endocardial layer (shown as difference ΔAT) at various distances from the stimulus site during endocardial and epicardial pacing.
Comparisons shown are: A. Unipolar and B. Bipolar minimally filtered electrograms.
Figure 6.
Two representative stained histological sections using haematoxylin-eosin of normal myocardium from different sites in the Ovine left ventricle.
Left: unprocessed image. Right: convolved images identifying transmural anisotropy vectors in two dimensions from multiple sites indicated (circles) within each section. Circles arranged from epicardium (top) to endocardium (bottom). Anisotropy vectors orientated vertically at epicardial layer with distinct transitioning to horizontal orientation at the mid myocardial layer followed by diagonal orientation at the endocardial layer.