Body surface potential mapping to monitor the effects of thrombolytic therapy following acute myocardial infarction

Noninvasive assessment of reperfusion after fibrinolytic therapy for acute myocardial infarction

Assessment of reperfusion by the 12-lead electrocardiogram (ECG) or biochemical markers is limited by suboptimal sensitivity and/or specificity. Body surface mapping (BSM) improves the spatial sampling of the 12-lead ECG. Serial 12-lead ECGs and 64-lead anterior BSMs were recorded from 67 patients with acute myocardial infarction undergoing coronary angiography 90 minutes after fibrinolytic therapy. ECG-1 and BSM-1 were recorded before/shortly after therapy (median 18 minutes). ECG-2 and BSM-2 were recorded after the 90-minute angiogram (median 30 minutes). The maximum ST elevation on ECG-1 was noted and > or = 30% ST resolution on ECG-2 was taken to represent partial/complete reperfusion. Patients were randomly divided into a training set and validation set. Isointegral and isopotential ST-T variables from BSMs of training-set patients were compared with Thrombolysis In Myocardial Infarction (TIMI) trial flow using discriminant analysis to identify which variables best classified reperfusion. Reperfusion (TIMI 2/3 flow) occurred in 32 of 34 training-set patients and in 29 of 33 validation-set patients. In the training set, > or = 30% ST resolution correctly classified reperfusion with 72% sensitivity (23 of 32) and 50% specificity (1 of 2). In the validation set, > or = 30% ST resolution classified reperfusion with 59% sensitivity (17 of 29) and 50% specificity (2 of 4). In comparison, a model containing 24 BSM variables correctly classified all training-set patients, and when prospectively tested in the validation-set, correctly classified 28 of 29 patients who achieved reperfusion (97% sensitivity) and all 4 patients who failed to reperfuse (p = 0.035). In conclusion, BSM is more useful than the 12-lead ECG for noninvasive assessment of reperfusion after fibrinolytic therapy for acute myocardial infarction.

Variability maps of body surface ECG in normal subjects

A method for quantifying the fluctuations of the QRS electrocardiogram over the flat (unrolled) thoracic surface in normal subjects is presented. Serial comparisons were performed on 32-lead ECG recordings and body surface maps from seven healthy men, using as similarity measures correlation and RMS-difference in both time-signal and 2D map domain. Recordings were made on one and the same day, and on different days. The time-signal correlation and RMS-differences were plotted as 2D distributions. Correlation was higher on the front of the torso and RMS-differences were largest in the precordial area. The average time-signal correlation calculated over the QRS in comparisons of signals taken on different days was 0.9717, whereas the corresponding RMS-difference was 57.8 microV. Additionally, 2D comparisons between reconstructed map frames at different time instants in the QRS were carried out, using the 2D versions of the correlation and RMS-difference. The averaged results of the 2D comparisons were close to the time-signal comparison values (respectively 0.9696 and 68.9 microV). Finally, 2D comparisons between isointegral maps (mapping the QRS signal integral) were performed. They yielded even higher correlations (0.98, 3.453 microV s). Although the number of subjects studied was not large, the investigation brought to light important variability ranges that may serve as a basis when detecting pathologies. In addition, the topology of normal ECG variability on the body surface was revealed. This study confirmed the pertinence of correlation and RMS-difference as measures of time-signal and map similarity.

Assessment of reperfusion in myocardial infarction by body surface electrocardiographic mapping

To determine the efficacy of body surface potential mapping to detect and quantify reperfusion in acute infarction, 66 patients were studied by repeated body surface potential mapping before and after administration of the thrombolytic agent. The QRS and ST-segment were analyzed and compared to the arterial patency as assessed by arteriography within 10 days. The infarct-related vessel was patent in 50 patients and occluded in the remaining 16. In 6 of the 15 patients in whom thrombolytic therapy was started within 2 hours of the onset of chest pain the ST-segment changed from that of an acute infarction pattern to that of a normal pattern, and the QRS pattern either remained normal or recovered prior to discharge. In two additional patients the QRS pattern returned to normal prior to discharge from the hospital. In the 51 patients with later thrombolytic therapy (> or = 2 hours) the degree of ST elevation and depression decreased more than either the control infarction group (36 inferior and 73 anterior patients) or the group in whom reperfusion attempts were unsuccessful, but the pattern of the map remained that of an infarction. The QRS maps showed that in the first 48 hours recovery of potential was insufficient to distinguish those with successful thrombolysis. Early reperfusion could be detected by body surface potential mapping and the eventual damage predicted from the degree of change in the QRS map. Later reperfusion could be surmised but not quantified.