Body surface mapping improves early diagnosis of acute myocardial infarction in patients with chest pain and left bundle branch block

Abstract

Objective: To test prospectively depolarisation and repolarisation body surface maps (BSMs) for mirror image reversal, which is less susceptible to artefact, in patients with acute ischaemic-type chest pain, and to compare these BSM criteria with previously published 12 lead ECG criteria.

Methods: An 80 lead portable BSM system was used to map patients presenting with acute ischaemic-type chest pain and a 12 lead ECG with left bundle branch block (LBBB). Acute myocardial infarction (AMI) was defined by serial cardiac enzymes. Each 12 lead ECG was assessed by the criteria of Sgarbossa et al and Hands et al for diagnosis of AMI. Depolarisation and repolarisation BSMs were assessed for loss of mirror image reversal of QRS with ST-T isointegral map patterns and a change in vector angle from QRS to ST-T outside 180+/-15 degrees -findings typically seen in LBBB with AMI.

Results: Of 56 patients with chest pain and LBBB, 18 had enzymatically confirmed AMI. Patients with loss of BSM image reversal were significantly more likely to have AMI (odds ratio 4.9, 95% confidence interval 1.5 to 16.4, p = 0.007). Loss of BSM image reversal was significantly more sensitive (67%) for AMI than either 12 lead ECG method (17%, 33%) albeit with some loss in specificity (BSM 71%, 12 lead ECG 87%, 97%). Patients with AMI compared with those without AMI had a greater mean change in vector angle outside the normal range (180+/-15 degrees ), particularly between QRS isointegral and ST60 isopotential (the potential 60 ms after the J point at each electrode site) BSMs (19 degrees v 9 degrees, p = 0.038). Loss of image reversal and QRS-ST60 vector change outside 180+/-15 degrees had 61% sensitivity and 82% specificity for AMI (odds ratio 7.0, 95% confidence interval 2.0 to 24.4, p = 0.001).

Conclusions: BSM compared with the 12 lead ECG improved the early diagnosis of AMI in the presence of LBBB.

Figure 1

(A) QRS and ST-T isointegral maps from a patient with left bundle branch block without acute myocardial infarction. The change in vector angle (θ) between QRS and ST-T is within normal limits at 194°. There is also normal image reversal—that is, QRSmin and ST-Tmax lie within one electrode space of each other, as do QRSmax and ST-Tmin. (B) QRS and ST-T isointegral maps from a patient with left bundle branch block with acute myocardial infarction. The change in vector angle (θ) between QRS and ST-T is outside normal limits at 145°. There is loss of image reversal—that is, although QRSmin and ST-Tmax are located at the same electrode site, QRSmax and ST-Tmin are located apart by >1 electrode space both horizontally (x) and vertically (y). Max, maximum; min, minimum; R, right; L, left. Minimum and maximum loci are shown by white circles.