James Nasmith

New Body Surface Isopotential Map Evaluation Method to Detect Minor Potential Losses in Non–Q-Wave Myocardial Infarction

BACKGROUNDnPotential losses caused by stable non-Q-wave myocardial infarction (MI) are too small to diagnose with the use of standard ECG. The aim of the present study was to obtain accurate diagnostic criteria for this prognostically important disease with the help of body surface mapping.nnnMETHODS AND RESULTSnBody surface potentials were recorded with the use of 63 unipolar leads in 45 patients with a non-Q-wave MI (41 to 75 years old); 24 healthy adults, 42 patients with unstable angina, and 70 patients with Q-wave MI served as reference groups. Qualitative pathological features of the isopotential maps, such as onset time and site and magnitude of the first right-anterior/anterior minimum, as well as pathological negativities at that time, were defined in non-Q-wave MI cases. These features, which account for the activation sequence and the body surface projections of specific cardiac regions (Selvester classification), showed a 91% sensitivity and an 88% specificity for the detection of non-Q-wave MI. In comparison, the different departure maps (first third QRS, QRS, and QRST isoarea) resulted in less favorable specificities (50% to 58%). Concordance between the isopotential maps and the acute-phase ECG (90%), hypokinesis (64%), fixed perfusion defects (59%), and significant stenosis of the infarct-related coronary artery (87%) supported the concept that these isopotential map changes correspond to the supposed sites of MI. There were pathological features in 69% of patients with unstable angina, with similar concordances as in non-Q-wave MI.nnnCONCLUSIONSnIsopotential maps revealed characteristic features that were suitable for the detection and localization of non-Q-wave MI in the clinical setting of unstable coronary artery disease.

Body surface potential mapping of ST-segment shift in patients undergoing percutaneous transluminal coronary angioplasty: Correlations with the ECG and vectorcardiogram☆

The purpose of this study was to investigate the thoracic patterns of ST-segment shift induced by the occlusion of different coronary arteries during percutaneous transluminal coronary angioplasty. Body surface potential maps were recorded with 63 leads during sinus rhythm before, during, and after balloon inflation in 20 patients. Two patients underwent dilatation of both the right and circumflex coronary arteries. A 12-lead scalar electrocardiogram and a Frank vectorcardiogram with orthogonal leads X, Y, and Z were obtained with the body surface potential maps. The body surface potential maps at 40 ms during the ST-segment showed patterns that were specific to the dilated vessel. The left anterior descending coronary artery (n = 10) was associated with the largest ST-segment shifts with a precordial maximum and negative potentials over the back; for the right coronary artery (n = 7), negative potentials covered the upper left torso with a left mid-axillary minimum and positive potentials over the rest of the torso; for the left circumflex coronary artery (n = 5), negative potentials covered the anterior torso with a precordial minimum and positive potentials over the back. These changes dissipated rapidly after balloon deflation. ST levels measured on orthogonal leads showed values greater than standard electrocardiographic leads for circumflex and right coronary arteries. In conclusion, body surface potential mapping provides a comprehensive approach for the evaluation of electrocardiographic changes and the development of optimal leads for the detection of acute occlusion of a coronary artery.

A Computer Heart Model Incorporating Anisotropic Propagation IV. Simulation of Regional Myocardial Ischemia

The main goal of this study was to simulate clinical body surface potential maps, recorded during percutaneous transluminal coronary angioplasty protocols, using a realistic geometry computer heart model. Other objectives were to address the question of reciprocal ST-segment changes observed in the 12-lead electrocardiogram during ischemia and to verify the hypothesis that the shortening of the QRS duration observed in left anterior descending (LAD) coronary artery occlusion may be explained by conduction delay in the septal His-Purkinje system. Simulation was achieved by first introducing into the heart model three transmural zones of mild, moderate, and severe ischemia for assumed occlusions in the LAD, left circumflex, and right coronary arteries. The heart model was then excited, in turn, with these three zones present for assumed occlusions in the LAD, left circumflex, and right coronary arteries. Myocardial conduction velocities in the regions of moderate and severe ischemia were assumed to be reduced to 75 and 50% of normal, respectively. Model action potentials in the mild, moderate, and severely ischemic zones were also altered to reflect known ischemic changes in these action potentials. Body surface potential maps and electrocardiograms were computed by placing the heart inside a numerical torso model. Simulated map patterns during both ST-segment and QRS were qualitatively similar to clinical maps. Reciprocal ST-segment depression was observed for all three occlusions in remote leads that did not overlie the ischemic zones. QRS shortening due to septal His-Purkinje conduction delay was verified. The simulation results attest to the models ability to reproduce body surface potential distributions recorded following percutaneous transluminal coronary angioplasty protocols. The simulations also showed that reciprocal ST-segment changes occur as a natural consequence of the primary ischemic region and that there is no need to invoke a second region of ischemia. Finally, the model demonstrated that QRS shortening can occur in LAD occlusion despite a slowing of conduction down the septal His-Purkinje system.

QRS alterations in body surface potential distributions during percutaneous transluminal coronary angioplasty in single-vessel disease*

Body surface QRS potentials were recorded with 63 chest leads in 20 patients with proximal single-vessel disease located on either the left anterior descending coronary artery (n = 10), the right coronary artery (n = 6), or the left circumflex coronary artery (n = 4) before, during, and after percutaneous transluminal coronary angioplasty. In each case, three consecutive inflations of relatively short duration (37 +/- 14 seconds) were carried out. Electrical activity was displayed as unipolar electrograms and body surface potential maps. The total QRS complex duration decreased in 14 of the 20 patients. Focal conduction disturbances were observed in six cases; all six had left anterior descending coronary artery occlusion and two were also accompanied by a clear shortening of the right epicardial breakthrough time. In these two cases, an initial activation loss seemed to be characteristic, whereas in the other four cases, a rather diffuse slowing of intraventricular conduction, especially during the terminal portion of the QRS, could be observed. Individual and group mean isointegral difference body surface potential maps (during-minus-before dilation) were considered valuable for the interpretation of localized changes in intraventricular conduction during percutaneous transluminal coronary angioplasty, and their individual variations could, at least partly, be explained by the presence or absence of collateral circulation. Two different hypotheses are suggested to account for the QRS complex shortening observed during short-term myocardial ischemic injury: (1) coronary artery occlusion delayed activation of the portion of the septal region that is normally activated early during the QRS, and/or (2) coronary artery occlusion increased the speed of propagation within the ventricles. Both of these hypotheses are discussed in light of earlier clinical and experimental results.

Continuous ST-segment monitoring during coronary angioplasty using orthogonal ECG leads

In order to characterize ST-segment shifts during transient coronary artery occlusion, 24 patients with single-vessel disease were continuously monitored during percutaneous transluminal coronary angioplasty by use of a computerized orthogonal lead system. Changes of ST-segment (J + 60 ms) in leads X, Y, and Z and of the ST vector magnitude were analyzed by using 20 microV as a threshold for significant ST-segment shift. The sensitivity and magnitude of this shift were compared among the left anterior descending, right coronary, and circumflex artery groups (11, 8, and 5 patients, respectively) during balloon inflation. Significant ST-segment shifts were seen in 22 patients (92%) in ST-VM, Y, and Z leads and all patients in lead X (100%). There was no significant difference in sensitivity of either the ST vector magnitude or the most sensitive lead for occlusion detection among the three groups. There was a significantly greater magnitude of ST shift during left anterior descending artery occlusion than during right coronary artery and circumflex artery occlusions in ST-VM. Analysis of the direction of ST shifts in the X, Y, and Z leads showed a characteristic pattern, which could distinguish among the three coronary groups in 21 patients (88%). The presence of collaterals was significantly associated with ST-segment depression in leads oriented toward ischemia (3 of 6 patients) as compared with ST-segment elevation in the absence of collaterals (all of 15 patients), P > .01. It is concluded that ST-segment shift in the orthogonal leads is a reliable marker for myocardial ischemia. It is equally sensitive to occlusion of each of the three major coronary arteries and can thus identify the occluded coronary. An ST-segment depression instead of an elevation was related to the presence of collaterals, which may reflect a lesser degree of ischemia.

Transfer of Patients With ST-Elevation Myocardial Infarction for Primary Percutaneous Coronary InterventionCLINICAL PERSPECTIVE

Background— Interhospital transfer of patients with ST-elevation myocardial infarction (STEMI) for primary percutaneous coronary intervention (PPCI) is associated with longer delays to reperfusion, related in part to turnaround (“door in” to “door out,” or DIDO) time at the initial hospital. As part of a systematic, province-wide evaluation of STEMI care, we examined DIDO times and associations with patient, hospital, and process-of-care factors.nnMethods and Results— We performed medical chart review for STEMI patients transferred for PPCI during a 6-month period (October 1, 2008, through March 31, 2009) and linked these data to ambulance service databases. Two core laboratory cardiologists reviewed presenting ECGs to identify left bundle-branch block and, in the absence of left bundle-branch block, definite STEMI (according to both cardiologists) or an ambiguous reading. Median DIDO time was 51 minutes (25th to 75th percentile: 35–82 minutes); 14.1% of the 988 patients had a timely DIDO interval (≤30 minutes as recommended by guidelines). The data-to-decision delay was the major contributor to DIDO time. Female sex, more comorbidities, longer symptom duration, arrival by means other than ambulance, arrival at a hospital not exclusively transferring for PPCI, arrival at a center with a low STEMI volume, and an ambiguous ECG were independently associated with longer DIDO time. When turnaround was timely, 70% of patients received timely PPCI (door-to-device time ≤90 minutes) versus 14% if turnaround was not timely ( P <0.0001).nnConclusions— Benchmark DIDO times for STEMI patients transferred for PPCI were rarely achieved. Interventions aimed at facilitating the transfer decision, particularly in cases of ECGs that are difficult to interpret, are likely to have the best impact on reducing delay to reperfusion.nn# CLINICAL PERSPECTIVE {#article-title-17}Background— Interhospital transfer of patients with ST-elevation myocardial infarction (STEMI) for primary percutaneous coronary intervention (PPCI) is associated with longer delays to reperfusion, related in part to turnaround (“door in” to “door out,” or DIDO) time at the initial hospital. As part of a systematic, province-wide evaluation of STEMI care, we examined DIDO times and associations with patient, hospital, and process-of-care factors. Methods and Results— We performed medical chart review for STEMI patients transferred for PPCI during a 6-month period (October 1, 2008, through March 31, 2009) and linked these data to ambulance service databases. Two core laboratory cardiologists reviewed presenting ECGs to identify left bundle-branch block and, in the absence of left bundle-branch block, definite STEMI (according to both cardiologists) or an ambiguous reading. Median DIDO time was 51 minutes (25th to 75th percentile: 35–82 minutes); 14.1% of the 988 patients had a timely DIDO interval (⩽30 minutes as recommended by guidelines). The data-to-decision delay was the major contributor to DIDO time. Female sex, more comorbidities, longer symptom duration, arrival by means other than ambulance, arrival at a hospital not exclusively transferring for PPCI, arrival at a center with a low STEMI volume, and an ambiguous ECG were independently associated with longer DIDO time. When turnaround was timely, 70% of patients received timely PPCI (door-to-device time ⩽90 minutes) versus 14% if turnaround was not timely (P<0.0001). Conclusions— Benchmark DIDO times for STEMI patients transferred for PPCI were rarely achieved. Interventions aimed at facilitating the transfer decision, particularly in cases of ECGs that are difficult to interpret, are likely to have the best impact on reducing delay to reperfusion.

Transfer of Patients With ST-Elevation Myocardial Infarction for Primary Percutaneous Coronary Intervention

Background— Interhospital transfer of patients with ST-elevation myocardial infarction (STEMI) for primary percutaneous coronary intervention (PPCI) is associated with longer delays to reperfusion, related in part to turnaround (“door in” to “door out,” or DIDO) time at the initial hospital. As part of a systematic, province-wide evaluation of STEMI care, we examined DIDO times and associations with patient, hospital, and process-of-care factors.nnMethods and Results— We performed medical chart review for STEMI patients transferred for PPCI during a 6-month period (October 1, 2008, through March 31, 2009) and linked these data to ambulance service databases. Two core laboratory cardiologists reviewed presenting ECGs to identify left bundle-branch block and, in the absence of left bundle-branch block, definite STEMI (according to both cardiologists) or an ambiguous reading. Median DIDO time was 51 minutes (25th to 75th percentile: 35–82 minutes); 14.1% of the 988 patients had a timely DIDO interval (≤30 minutes as recommended by guidelines). The data-to-decision delay was the major contributor to DIDO time. Female sex, more comorbidities, longer symptom duration, arrival by means other than ambulance, arrival at a hospital not exclusively transferring for PPCI, arrival at a center with a low STEMI volume, and an ambiguous ECG were independently associated with longer DIDO time. When turnaround was timely, 70% of patients received timely PPCI (door-to-device time ≤90 minutes) versus 14% if turnaround was not timely ( P <0.0001).nnConclusions— Benchmark DIDO times for STEMI patients transferred for PPCI were rarely achieved. Interventions aimed at facilitating the transfer decision, particularly in cases of ECGs that are difficult to interpret, are likely to have the best impact on reducing delay to reperfusion.nn# CLINICAL PERSPECTIVE {#article-title-17}Background— Interhospital transfer of patients with ST-elevation myocardial infarction (STEMI) for primary percutaneous coronary intervention (PPCI) is associated with longer delays to reperfusion, related in part to turnaround (“door in” to “door out,” or DIDO) time at the initial hospital. As part of a systematic, province-wide evaluation of STEMI care, we examined DIDO times and associations with patient, hospital, and process-of-care factors. Methods and Results— We performed medical chart review for STEMI patients transferred for PPCI during a 6-month period (October 1, 2008, through March 31, 2009) and linked these data to ambulance service databases. Two core laboratory cardiologists reviewed presenting ECGs to identify left bundle-branch block and, in the absence of left bundle-branch block, definite STEMI (according to both cardiologists) or an ambiguous reading. Median DIDO time was 51 minutes (25th to 75th percentile: 35–82 minutes); 14.1% of the 988 patients had a timely DIDO interval (⩽30 minutes as recommended by guidelines). The data-to-decision delay was the major contributor to DIDO time. Female sex, more comorbidities, longer symptom duration, arrival by means other than ambulance, arrival at a hospital not exclusively transferring for PPCI, arrival at a center with a low STEMI volume, and an ambiguous ECG were independently associated with longer DIDO time. When turnaround was timely, 70% of patients received timely PPCI (door-to-device time ⩽90 minutes) versus 14% if turnaround was not timely (P<0.0001). Conclusions— Benchmark DIDO times for STEMI patients transferred for PPCI were rarely achieved. Interventions aimed at facilitating the transfer decision, particularly in cases of ECGs that are difficult to interpret, are likely to have the best impact on reducing delay to reperfusion.