Methods
Studies conformed to the guiding principles of the Declaration of
Helsinki. In 15 dogs (14-25 kg) anesthesia was induced and maintained by
Nembutal 30 mg/kg. Positive pressure ventilation was maintained through
an endocardial tube to maintain normal blood gases. The chest was opened
through a medial sternotomy. The left anterior descending coronary
artery was dissected free along a 5 mm segment proximal to the first
diagonal branch. The left anterior descending coronary artery was
abruptly occluded with a hemoclip for a period of 15 minutes. 768
unipolar electrodes on 112 transmural multipolar needle electrodes were
inserted into the heart in a standardized array illustrated in Figure 1.
Care was taken to avoid epicardial vessels. Each needle was fabricated
from 23 gauge steel with either 4 or 8 tungsten wire electrodes set in
epoxy at 1, 2 or 4 mm intervals (8). This array provided a total of 768
unipolar electrograms with a reference electrode placed adjacent to the
left first costosternal junction. A 20 to 30 minute control period was
allowed after insertion of the last needle for injury currents to
subside. At the conclusion of each experiment the heart was excised with
the electrodes in place and the relative relationship of the needles
confirmed. Each of the 768 channels was sampled with a frequency of 960
samples/sec and filtered to provide a bandwidth of 0.07-170 HZ (7).
Local activation time was defined as dominant negative deflection in the
unipolar electrogram, an automated algorithm that determines slope of
-5V/sec was used to annotate detection in similar electrograms in
previous work (7,8) We focused our analysis on the spontaneous PVCs that
triggered ventricular arrhythmias.