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The effects of electrode spacing on interpretation of epicardial electrograms
Journal of Electrocardiology
Vol. 25 Supplement
The Effects of Electrode Spacing on Interpretation of Epicardial Electrograms
Stephanie M. Smith,* David B. Geselowitz, PhD,* and Edward J. Berbari, PhDt
In the 4-day postinfarction dogs, the electrograms obtained from the left ventricle often showed multiple deflections. The authors have postulated that successive downstrokes in an electrogram represent separate electrical activation wavefronts passing the electrode. The authors have shown that isochrones derived from the maximum negative derivative of each set of deflections reveal a coherent propagation. Using this technique, activation times from the first set of deflections were synchronous indicating a locally nonpropagating event arising from a distant source. Isochrones derived from the maximum negative slope of the second deflection progressed from apex to left anterior descending artery; a direction retrograde to normal propagation through the area and tended to block. The second deflection also occurred up to 100 ms after the first deflection. The 1 mm spacing indicated that the latest activation in the region occurred from 20 to 90 ms later than that revealed by the 4 mm spacing. The regions of block were found to be more spatially complex. In both electrode arrays adjacent electrograms showed that the second “late” deflection changed amplitude and/ or shape. Neither the 4 mm spacing nor the 1 mm spacing consistently showed smooth progression of waveform shape and amplitude, possibly indicating a nonuniform substrate even at the 1 mm level. Nonetheless, activation isochrones showed a smooth progression through the region.
Two silver wire electrode arrays were used in conjunction with a computer-based data acquisition system to record electrograms through healthy and infarcted canine myocardium. The first array contained 124 wires arranged in a 6 cm circular pattern with a central spacing of 4 mm. The silver wire tips were beaded to 1 mm in diameter in a gas flame and held in place by a flexible silicone matrix. The second electrode array was an 11 x 11 square of electrodes spaced at 1 mm intervals and embedded in a rigid epoxy resin matrix. Both arrays were placed over the anterior left ventricle between the left anterior descending artery and the apex in the region of infarction after left anterior descending artery occlusion. The orientation and location of the large 6-cm electrode was constant from experiment to experiment. The small 1.1 cm electrode’s location was varied within the region covered by the large electrode array. In normal canine myocardium, electrograms primarily exhibit a single intrinsic deflection. The maximum negative derivative of the electrogram was taken to indicate the time of local activation. Activity progressed from the left anterior descending artery to the apex as shown in previous studies.’ Similar results were obtained with both the 4 mm and 1 mm spaced arrays. The propagation velocity obtained from both electrode arrays was constant at 0.5 to 0.6 mm/ms through the region. Thus in normal myocardium it is concluded that 4 mm spacing is adequate to capture the details of activation progression through the anterior left ventricle.
Reference
*From the Bioengineering Program, Pennsylvania State University, University Park, Pennsylvania. fFrom The Oklahoma University Health Sciences Center, Oklahoma City, Oklahoma.
1. Arisi G, Macchi E, Baruff
S et al: Potential fields on the ventricular surface of the exposed dog heart during normal excitation. Circ Res 52:706, 1983
Reprint requests: Stephanie Smith, Pennsylvania State University, 205 Hallowell Building, University Park, PA 16802.
162
Vol. 25 Supplement
The Effects of Electrode Spacing on Interpretation of Epicardial Electrograms
Stephanie M. Smith,* David B. Geselowitz, PhD,* and Edward J. Berbari, PhDt
In the 4-day postinfarction dogs, the electrograms obtained from the left ventricle often showed multiple deflections. The authors have postulated that successive downstrokes in an electrogram represent separate electrical activation wavefronts passing the electrode. The authors have shown that isochrones derived from the maximum negative derivative of each set of deflections reveal a coherent propagation. Using this technique, activation times from the first set of deflections were synchronous indicating a locally nonpropagating event arising from a distant source. Isochrones derived from the maximum negative slope of the second deflection progressed from apex to left anterior descending artery; a direction retrograde to normal propagation through the area and tended to block. The second deflection also occurred up to 100 ms after the first deflection. The 1 mm spacing indicated that the latest activation in the region occurred from 20 to 90 ms later than that revealed by the 4 mm spacing. The regions of block were found to be more spatially complex. In both electrode arrays adjacent electrograms showed that the second “late” deflection changed amplitude and/ or shape. Neither the 4 mm spacing nor the 1 mm spacing consistently showed smooth progression of waveform shape and amplitude, possibly indicating a nonuniform substrate even at the 1 mm level. Nonetheless, activation isochrones showed a smooth progression through the region.
Two silver wire electrode arrays were used in conjunction with a computer-based data acquisition system to record electrograms through healthy and infarcted canine myocardium. The first array contained 124 wires arranged in a 6 cm circular pattern with a central spacing of 4 mm. The silver wire tips were beaded to 1 mm in diameter in a gas flame and held in place by a flexible silicone matrix. The second electrode array was an 11 x 11 square of electrodes spaced at 1 mm intervals and embedded in a rigid epoxy resin matrix. Both arrays were placed over the anterior left ventricle between the left anterior descending artery and the apex in the region of infarction after left anterior descending artery occlusion. The orientation and location of the large 6-cm electrode was constant from experiment to experiment. The small 1.1 cm electrode’s location was varied within the region covered by the large electrode array. In normal canine myocardium, electrograms primarily exhibit a single intrinsic deflection. The maximum negative derivative of the electrogram was taken to indicate the time of local activation. Activity progressed from the left anterior descending artery to the apex as shown in previous studies.’ Similar results were obtained with both the 4 mm and 1 mm spaced arrays. The propagation velocity obtained from both electrode arrays was constant at 0.5 to 0.6 mm/ms through the region. Thus in normal myocardium it is concluded that 4 mm spacing is adequate to capture the details of activation progression through the anterior left ventricle.
Reference
*From the Bioengineering Program, Pennsylvania State University, University Park, Pennsylvania. fFrom The Oklahoma University Health Sciences Center, Oklahoma City, Oklahoma.
1. Arisi G, Macchi E, Baruff
S et al: Potential fields on the ventricular surface of the exposed dog heart during normal excitation. Circ Res 52:706, 1983
Reprint requests: Stephanie Smith, Pennsylvania State University, 205 Hallowell Building, University Park, PA 16802.
162