Electrophysiological and Anatomical Substrates for Late Potential Recorded by Signal Averaging in Seven‐Day‐Old Myocardial Infarction in Dogs

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Abstract
A filtered QRS (fQRS) was recorded by signal averaging in 7‐day‐oJd myocardial infarction (MI) in dogs to detect late potential (LP). The criteria for the LP included a duration of fQRS (D) ≥ 60 msec and a voltage in the last 15 msec (VI5) ≤ 10 μV. These parameters were determined from the control data from 15 dogs without infarction (D: 45 to 60 msec and V15: 12.0 to 83.6 μV). On the seventh day of infarction, the D had increased from 53.5 ± 4.7 to 62.2 ± 9.6 msec (P < 0.05) and the V15 decreased from 38.6 ± 19.5 to 18.4 ± 16.0 μV (P < 0.01). Of 23 dogs, 14 met the LP criteria (group A) and 9 did not (group B). Sustained ventricular tachycardia (SVT) was induced in 12 group A dogs and in none of the group B dogs. The delayed epicardial activation (DEA) was recorded after the end of QRS at 5.1 ± 4.7 sites in group A dogs and 1.3 ± 1.8 sites in group B dogs (P < 0.05). The maximum value of epicardial activation time was more prolonged in group A than in group B (70.0 ± 28.3 vs 44.4 ± 9.8 msec, P < 0.01). The area of MI was more extensive in dogs with DEA than those without (24.9 ± 5.8% vs 10.3 ± 9.0% of the total left ventricular weight, P < 0.01). In 72 of 90 sites with DEA, the thickness of the surviving epicardial muscle was ≤1 mm. The sensitivity and specificity of the criteria for LP in detecting DEA were 71.4% and 55.6%, and 100% and 81.8% for predicting inducibility of SVT. It was thus concluded that LP, reflected the DEA, was identified from infarct areas of slow conduction within a reentry circuit of SVT.