Epicardial Mapping: How to Measure Local Activation? THOMAS PAUL, JEFFREY P. MOAK,* CODY MORRIS,* and ARTHUR GARSON, JR.** From the Department of Petdiatric Cardiology, Children's Hospital, Medizinische Hochschule Hannover, Hannover, Federal Republic of Germany, and the *Ullie Frank Abercrombie Section of Cardiology, Department of Pediatrics, Baylor College of Medicine, and the **Texas Children's Hospital, Houston, Texas
PAUL, T., ET AL.: Epicardial Mapping: How to Measure Local Activation? Epicardial ventricular mapping was performed in 5 dogs during sinus rhythm with a sock array containing 41 eiectrodes. Maps were generated with a computer-assisted mapping system using four different definitions of local epicardial activation: {1} maximal negative slope [intrinsic deflection} ofthe unipolar electrogram, (2) maximal slope of the bipolar electrogram, (3) maxima/ amplitude of the bipolar electrogram, and (4) first onset by 45° from the baseline of the bipolar electrogram. The site of earliest and latest epicardial activation was identical with maximal negative slope in the unipolar eJectrogram and maximal slope and maximal amplitude ofthe bipolar electrogram in all five animals. Times of earliest and latest epicardial activation calculated with maximal amplitude of the bipolar electrogram were most similar to those evaluated with maximal negative slope of the unipolar electrogram. Using onset of the bipolar electrogram, activation times were measured 10 to 12 msec earlier than with each ofthe other three definitions of local activation, and in two of the five animals, jirst epicardial breakthrough was mapped Io a different site than with the three other methods. Conclusions: (I) Maximal amplitude ofthe bipolar electrogram coincided with maximal negative slope of the unipolar electrogram; {2} Using onset of the bipolar electrogram, timing and location of earliest epicardial activation may he misinterpreted. (PACE, Vol. 13, March 3990) epicardial mapping, unipolar electrogram, bipolar eiectrogram
Introduction In order to determine local activation times during epicardial mapping, the time ofthe most rapid deflection in the unipolar electrogram [intrinsic deflection^'^] has been demonstrated to correlate with depolarization of the tissue immeDr, Paul was supported by Deutsche Forschungsgemeinschaft grant Pa 3S2/1-1 Bonn-Bad Godesberg, FRG. A part of this work has been presenled a.s an abstract at the 61st Scientific Sessions of the American Heart Association, Washington. D.C, November 14-17, 1988. Address for reprints: Arlhur Garson, )r,. M.D., Texas Ghildren's Hospital, Division of Pediatric Cardiology, 6621 Fannin, Houston. TX 77030, Received September 25, 1989; Revision December 5. 1989; Accepted December 7, 1989.
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diately adjacent to the unipolar electrode.^ In clinical practice, the low frequency response tends to make the unipolar electrogram unstable.'' Therefore, bipolar electrograms often have been used that provide a sharp deflection.^^ However, it is not known which measure of the bipolar electrogram correlates best in the operating room witb tbe intrinsic deflection of the unipolar electrogram. Since it is difficult to determine visually the maximum slope of an electrogram, if tbe amplitude or onset of the electrogram provided the same data, this measurement would be preferable for rapid inspection of tbe data, Tbe purpose of the present study was to assess in an animal model wbat measure of the bipolar electrogram reflects local epicardial activation.
Marcb 1990
285
PAUL, ET AL.
Materials and Methods Animals Five beagle dogs weighing 10 to 12 kg were anesthetized w^ith 40% nitrous oxide/60% oxygen plus 2.5% isoflurane. Under continual artificial ventilation, the chest was opened by a median sternotomy and the heart was suspended in a pericardial cradle. Epicardial Mapping
While the animals were in sinus rhythm, mapping of the epicardial activation was performed using the Bard 48 Cardiac Mapping System (C.R. Bard. Inc.. Billerica, MA, USA). Sock Recording Procednre
An expandable Xspan sock^ (Alba Health Care, Valdese, NC, USA) electrode array, fitting
the epicardial contour, was placed over the animal's heart. The socks were sized to allow good epicardial electrode contact while avoiding hemodynamic compromise of the animals (length: 8.5 cm; width at the base: 7 cm). The socks contained 41 button electrodes each 8 mm in diameter; each button contained two stainless steel electrodes (each 1,0 mm diameter), 2 mm apart, which were suitable for unipolar (one member of the pair) and bipolar recordings (betvireen members of the pair). The electrodes were arranged in five concentric rows from base to apex and covered the entire surface of botb ventricles (Fig. 1). Interelectrode distance averaged 1 cm. For alignment, socks were marked with a blue line extending from the base to the apex. The socks were positioned in an identical fashion on each of the hearts with the blue line over the left
anterior
LAD
posterior Figure 1. Arrangemenf of 41 epicardiaJ electrodes/maps of epicardial activation (apical view). The letters denote the ring and numbers along each radius.
286
March 1990
PACE, Vol. 13
HOW TO MEASURE LOCAL ACTIVATION? anterior descending coronary artery. The individual arrangement of the 41 electrodes was stored on a schematic computer drawing of the epicardial surface which was later used to display maps of activation. Data Acquisition, Analysis, and Mapping Electrograms from the 41 epicardial electrodes were simultaneously recorded together with the six limb leads and a precordial lead (Vi). Unipolar or bipolar inputs from each electrode were filtered as follows: 0.05 to 300 Hz (unipolar data) or 30 to 300 Hz (bipolar data). For each ofthe mapping sessions, 8-second windows of the recorded potentials were digitized (12-bit accuracy; 1000 samples per second) with a 48-channel computer-assisted data acquisition system and stored on a computer disk. To allow the quality of the signals to he inspected, recorded potentials were displayed in 2-second segments on a computer terminal. With the onset ofthe surface QRS-complex in lead II as a stable reference/ times of local epicardial activation at each recording site were
unipolar max. neg. slope
bipolar max. slope
calculated consecutively with four different modes of definition of local activation: (1) maximal negative slope in the unipolar electrogram, (2) maximal slope in the bipolar electrogram, (3) maximal amplitude in the bipolar electrogram, and (4) onset (first deflection greater than 45° from the baseline) of the bipolar electrogram (Fig. 2). The points of maximal negative slope in tbe unipolar mode and of maximal slope and maximal amplitude in the bipolar mode in each of the 41 epicardial electrograms were selected by the computer and displayed on the screen for visual verification (Fig. 2). The point of onset in the bipolar mode in each of the recordings was assigned by the operator, as a change from baseline of 45° or more at a paper speed of 100 mm/sec. Finally, maps of epicardial activation were generated by the computer for each mode of definition of local activation with the activation times assigned to each ofthe 41 electrode positions. To assess the measurement of local epicardial activation with the three modes of definition of local activation in the bipolar electrogram, earliest and
bipolar max. amplitude
bipolar onset
Figure 2. Di_fferent modes o/definition o/epicardial activation (see text). The vertical part of each cross hair shoivs the timing.
PACE, VoL 13
March 1990
287
PAUL, ET AL. latest epicardial activation calculated with these modes, were compared with maps generated with maximal negative slope of the unipolar electrogram. Evaluation of activation times was performed in duplicate on two consecutive cardiac beats in each of the mapping procedures. Unipolar and bipolar recordings were done sequentially rather than simultaneously. Activation times in each of the animals were calculated as the mean of the 2 beats. Statistical Analysis Analysis of variance [ANOVA) was performed for comparisons of activation times evaluated with the four different modes of definition of local activation. If the ANOVA was statistically significant, Bonferroni's modification of the t-test was subsequently used for pairwise comparisons.^ Statistical significance was inferred, if the probability of a difference occurring by chance was
PAUL, T., ET AL.: Epicardial Mapping: How to Measure Local Activation? Epicardial ventricular mapping was performed in 5 dogs during sinus rhythm with a sock array containing 41 eiectrodes. Maps were generated with a computer-assisted mapping system using four different definitions of local epicardial activation: {1} maximal negative slope [intrinsic deflection} ofthe unipolar electrogram, (2) maximal slope of the bipolar electrogram, (3) maxima/ amplitude of the bipolar electrogram, and (4) first onset by 45° from the baseline of the bipolar electrogram. The site of earliest and latest epicardial activation was identical with maximal negative slope in the unipolar eJectrogram and maximal slope and maximal amplitude ofthe bipolar electrogram in all five animals. Times of earliest and latest epicardial activation calculated with maximal amplitude of the bipolar electrogram were most similar to those evaluated with maximal negative slope of the unipolar electrogram. Using onset of the bipolar electrogram, activation times were measured 10 to 12 msec earlier than with each ofthe other three definitions of local activation, and in two of the five animals, jirst epicardial breakthrough was mapped Io a different site than with the three other methods. Conclusions: (I) Maximal amplitude ofthe bipolar electrogram coincided with maximal negative slope of the unipolar electrogram; {2} Using onset of the bipolar electrogram, timing and location of earliest epicardial activation may he misinterpreted. (PACE, Vol. 13, March 3990) epicardial mapping, unipolar electrogram, bipolar eiectrogram
Introduction In order to determine local activation times during epicardial mapping, the time ofthe most rapid deflection in the unipolar electrogram [intrinsic deflection^'^] has been demonstrated to correlate with depolarization of the tissue immeDr, Paul was supported by Deutsche Forschungsgemeinschaft grant Pa 3S2/1-1 Bonn-Bad Godesberg, FRG. A part of this work has been presenled a.s an abstract at the 61st Scientific Sessions of the American Heart Association, Washington. D.C, November 14-17, 1988. Address for reprints: Arlhur Garson, )r,. M.D., Texas Ghildren's Hospital, Division of Pediatric Cardiology, 6621 Fannin, Houston. TX 77030, Received September 25, 1989; Revision December 5. 1989; Accepted December 7, 1989.
PACE, Vol. 13
diately adjacent to the unipolar electrode.^ In clinical practice, the low frequency response tends to make the unipolar electrogram unstable.'' Therefore, bipolar electrograms often have been used that provide a sharp deflection.^^ However, it is not known which measure of the bipolar electrogram correlates best in the operating room witb tbe intrinsic deflection of the unipolar electrogram. Since it is difficult to determine visually the maximum slope of an electrogram, if tbe amplitude or onset of the electrogram provided the same data, this measurement would be preferable for rapid inspection of tbe data, Tbe purpose of the present study was to assess in an animal model wbat measure of the bipolar electrogram reflects local epicardial activation.
Marcb 1990
285
PAUL, ET AL.
Materials and Methods Animals Five beagle dogs weighing 10 to 12 kg were anesthetized w^ith 40% nitrous oxide/60% oxygen plus 2.5% isoflurane. Under continual artificial ventilation, the chest was opened by a median sternotomy and the heart was suspended in a pericardial cradle. Epicardial Mapping
While the animals were in sinus rhythm, mapping of the epicardial activation was performed using the Bard 48 Cardiac Mapping System (C.R. Bard. Inc.. Billerica, MA, USA). Sock Recording Procednre
An expandable Xspan sock^ (Alba Health Care, Valdese, NC, USA) electrode array, fitting
the epicardial contour, was placed over the animal's heart. The socks were sized to allow good epicardial electrode contact while avoiding hemodynamic compromise of the animals (length: 8.5 cm; width at the base: 7 cm). The socks contained 41 button electrodes each 8 mm in diameter; each button contained two stainless steel electrodes (each 1,0 mm diameter), 2 mm apart, which were suitable for unipolar (one member of the pair) and bipolar recordings (betvireen members of the pair). The electrodes were arranged in five concentric rows from base to apex and covered the entire surface of botb ventricles (Fig. 1). Interelectrode distance averaged 1 cm. For alignment, socks were marked with a blue line extending from the base to the apex. The socks were positioned in an identical fashion on each of the hearts with the blue line over the left
anterior
LAD
posterior Figure 1. Arrangemenf of 41 epicardiaJ electrodes/maps of epicardial activation (apical view). The letters denote the ring and numbers along each radius.
286
March 1990
PACE, Vol. 13
HOW TO MEASURE LOCAL ACTIVATION? anterior descending coronary artery. The individual arrangement of the 41 electrodes was stored on a schematic computer drawing of the epicardial surface which was later used to display maps of activation. Data Acquisition, Analysis, and Mapping Electrograms from the 41 epicardial electrodes were simultaneously recorded together with the six limb leads and a precordial lead (Vi). Unipolar or bipolar inputs from each electrode were filtered as follows: 0.05 to 300 Hz (unipolar data) or 30 to 300 Hz (bipolar data). For each ofthe mapping sessions, 8-second windows of the recorded potentials were digitized (12-bit accuracy; 1000 samples per second) with a 48-channel computer-assisted data acquisition system and stored on a computer disk. To allow the quality of the signals to he inspected, recorded potentials were displayed in 2-second segments on a computer terminal. With the onset ofthe surface QRS-complex in lead II as a stable reference/ times of local epicardial activation at each recording site were
unipolar max. neg. slope
bipolar max. slope
calculated consecutively with four different modes of definition of local activation: (1) maximal negative slope in the unipolar electrogram, (2) maximal slope in the bipolar electrogram, (3) maximal amplitude in the bipolar electrogram, and (4) onset (first deflection greater than 45° from the baseline) of the bipolar electrogram (Fig. 2). The points of maximal negative slope in tbe unipolar mode and of maximal slope and maximal amplitude in the bipolar mode in each of the 41 epicardial electrograms were selected by the computer and displayed on the screen for visual verification (Fig. 2). The point of onset in the bipolar mode in each of the recordings was assigned by the operator, as a change from baseline of 45° or more at a paper speed of 100 mm/sec. Finally, maps of epicardial activation were generated by the computer for each mode of definition of local activation with the activation times assigned to each ofthe 41 electrode positions. To assess the measurement of local epicardial activation with the three modes of definition of local activation in the bipolar electrogram, earliest and
bipolar max. amplitude
bipolar onset
Figure 2. Di_fferent modes o/definition o/epicardial activation (see text). The vertical part of each cross hair shoivs the timing.
PACE, VoL 13
March 1990
287
PAUL, ET AL. latest epicardial activation calculated with these modes, were compared with maps generated with maximal negative slope of the unipolar electrogram. Evaluation of activation times was performed in duplicate on two consecutive cardiac beats in each of the mapping procedures. Unipolar and bipolar recordings were done sequentially rather than simultaneously. Activation times in each of the animals were calculated as the mean of the 2 beats. Statistical Analysis Analysis of variance [ANOVA) was performed for comparisons of activation times evaluated with the four different modes of definition of local activation. If the ANOVA was statistically significant, Bonferroni's modification of the t-test was subsequently used for pairwise comparisons.^ Statistical significance was inferred, if the probability of a difference occurring by chance was
