Transient alterations of the QRS complex and ST segment during percutaneous transluminal balloon angioplasty of the left anterior descending coronary artery

Evaluation of the phase-plane ECG as a technique for detecting acute coronary occlusion

OBJECTIVE

To evaluate the phase plane (PP) ECG as a method for detecting acute coronary occlusion (ACO).

BACKGROUND

Balloon inflation in a coronary artery during PTCA produces acute myocardial ischemia. The sensitivity of the standard ECG for detecting ACO is approximately 50%, depending on the number of leads recorded.

METHODS

The standard ECG signals of 18 patients (91 leads), undergoing PTCA were sampled and converted to digital data, prior to, and during acute coronary occlusion. PPs were constructed by projecting the ECG signals and their first derivatives onto a two-dimensional plane. Standard ECG signals and PPs, prior to ACO, were compared to their respective recordings and PPs during ACO.

RESULTS

Using the standard ECG analysis, the acute occlusion was detected in 39 of 91 leads (43%), and in 15 of 18 patients (83%), whereas using the PP analysis it was detected in 82 of 91 leads (90%), and in all 18 patients (100%) (P<0.001, for leads). The median number of leads per patient demonstrating standard ECG changes was 2.0, whereas for the PP analysis it was 5.5 (P<0.001). The specificity of the PP method was 83.5%.

CONCLUSIONS

The sensitivity of the PP method for detecting ACO during PTCA was superior to that of the standard ECG analysis. A smaller lead system is required to detect changes of ACO, during PTCA, when the PP method is used. The PP method is simple, low-priced, and may serve to detect acute myocardial ischemia in a number of clinical settings.

Giant R-waves in a patient with an acute inferior myocardial infarction

We describe a case of a male patient with "giant" R-waves (GRWs) in association with an acute inferior myocardial infarction (MI). Such electrocardiogram (ECG) pattern has been associated heretofore with the hyperacute phase of an anterior MI, and unstable, and variant angina, although it is found in illustrations of many previous publications in conjunction with inferior MI. The GRWs, along with ST-segment elevations, were noted transiently in the inferior ECG leads, early in the clinical course of our patient. Subsequent evolution of the ECG revealed classic appearances for an inferior MI. Cardiac enzymes, and thallium-201 myocardial perfusion scintigraphy revealed evidence for inferiorly-located myocardial necrosis. Coronary arteriography showed stenosis of the right coronary artery, for which the patient underwent an uneventful angioplasty and "stenting" of the culprit vessel. The pathophysiology of the syndrome of GRWs is briefly discussed.

Relationship between terminal QRS distortion on the admission electrocardiogram and the time course of left ventricular wall motion in anterior wall acute myocardial infarction

In order to clarify the time course of left ventricular (LV) wall motion in patients with anterior acute myocardial infarction (AMI) showing terminal QRS distortion on the admission electrocardiogram (ECG), the present study examined 106 patients with their first anterior AMI (< or =6 h) who underwent emergency coronary arteriography and cardiac cathetherization at 1 and 6 months after the infarction. The patients were classified into 2 groups according to the presence (group A, n=23) or absence (group B, n=83) of terminal QRS distortion (emergence of the J point at > or =50% of the R-wave amplitude in leads with QR configuration and/or absence of S waves in leads with RS configuration) on the admission ECG. Group A had a lower LV ejection fraction and more reduced regional wall motion (RWM) in the infarct region at both 1 and 6 months after AMI than group B. The degree of improvement in RWM between 1 and 6 months after AMI was less in group A than in group B (-0.1+/-0.5 vs 0.4+/-0.6 SD/chord, p<0.01). This study indicates that patients with anterior AMI showing terminal QRS distortion on the admission ECG have more severely depressed LV wall motion and less improvement in RWM in the infarct region in the healing stage, suggesting that this sign is an indicator of severe myocardial damage.

Changes in high-frequency QRS components are more sensitive than ST-segment deviation for detecting acute coronary artery occlusion

OBJECTIVES

This study describes changes in high-frequency QRS components (HF-QRS) during percutaneous transluminal coronary angioplasty (PTCA) and compares the ability of these changes in HF-QRS and ST-segment deviation in the standard 12-lead electrocardiogram (ECG) to detect acute coronary artery occlusion.

BACKGROUND

Previous studies have shown decreased HF-QRS in the frequency range of 150-250 Hz during acute myocardial ischemia. It would be important to know whether the high-frequency analysis could add information to that available from the ST segments in the standard ECG.

METHODS

The study population consisted of 52 patients undergoing prolonged balloon occlusion during PTCA. Signal-averaged electrocardiograms (SAECG) were recorded prior to and during the balloon inflation. The HF-QRS were determined within a bandwidth of 150-250 Hz in the preinflation and inflation SAECGs. The ST-segment deviation during inflation was determined in the standard frequency range.

RESULTS

The sensitivity for detecting acute coronary artery occlusion was 88% using the high-frequency method. In 71% of the patients there was ST elevation during inflation. If both ST elevation and depression were considered, the sensitivity was 79%. The sensitivity was significantly higher using the high-frequency method, p<0.002, compared with the assessment of ST elevation.

CONCLUSIONS

Acute coronary artery occlusion is detected with higher sensitivity using high-frequency QRS analysis compared with conventional assessment of ST segments. This result suggests that analysis of HF-QRS could provide an adjunctive tool with high sensitivity for detecting acute myocardial ischemia.

QRS prolongation: a sensitive marker of ischemia during percutaneous transluminal coronary angioplasty

The purpose of this study is to measure QRS duration changes in the human model of ischemia during percutaneous transluminal coronary angioplasty (PTCA) and compare these results to the commonly used ischemia markers, chest pain, and classical ST-T changes. Using a computerized method, QRS duration was measured in 51 patients undergoing elective PTCA. Three milliseconds (msec) or more prolongation of the QRS at peak inflation was considered to be an ischemic response. The results were compared to chest pain and ST-T changes and were analyzed for inflation site within individual coronary arteries. Forty-two patients had a pathological prolongation of the QRS during PTCA. Thirty-two patients developed chest pain, while 19 had ischemic ST-T changes. QRS duration was more prolonged in PTCA to proximal or middle segments of major arteries or their large branches, while it was less prolonged in distal segments or smaller branches. Using our method, QRS prolongation was an ischemia marker in most patients during PTCA and was more sensitive than chest pain or ST-T changes. QRS duration was more prolonged with occlusion of proximal and middle segments of major arteries. Cathet. Cardiovasc. Intervent. 50:177-183, 2000.

Wavelet analysis and time-frequency distributions of the body surface ECG before and after angioplasty

In a pilot study, electrocardiographic (ECG) recordings of patients with left and right coronary stenosis taken before and after angioplasty were analyzed using the continuous wavelet transform. Time-frequency distributions were obtained for different leads in order to examine the dynamics of the QRS-spectrum and establish features specific of ischemia in the time-frequency domain. We found relevant changes in the mid-frequency range, reflecting the ECG's response to percutaneous transluminal coronary angioplasty (PTCA). The changes appeared in ECG leads close to ischemic zones of the myocardium. Time-frequency distributions of the ECG during the QRS may thus become another electrocardiographic indicator of ischemia, alternative to ST-level in standard ECG or body surface mapping. The paper demonstrates the ability of the continuous wavelet transform to detect short lasting events of low amplitude superimposed on large signal deflections.

Temporal evolution of traditional versus transformed ECG-based indexes in patients with induced myocardial ischemia

The time course of changes in the electrocardiogram as a result of myocardial ischemia induced during prolonged coronary angioplasty has been studied. We have analyzed the electrocardiogram evolution during the occlusion in terms of the Ischemic Changes Sensor, which is a parameter that describes the capacity of different indexes to detect induced changes. Traditional indexes at specific time locations (ST level, T wave amplitude and position, and durations of QT interval and QRS complex) and global indexes (based on the Karhunen-Loève transform as applied to the QRS complex, ST-T complex, ST segment and T wave) have been considered. The global indexes better detected ischemic changes than the traditional indexes. The most sensitive were the index for the ST-T complex (89%) in the Karhunen-Loève transform-derived group and for the ST level (61%) in the traditional group. Changes in the ventricular repolarization period usually appeared earlier (77% of patients) than changes in the depolarization period (23% of patients). A similar percentage of patients exhibited the earliest ischemic changes in the T wave (41%) and in the ST segment (36%). The evolution of the Ischemic Changes Sensor parameters showed that the majority (60%) of the total changes occurred during the first minute of occlusion. The results suggest that the use of global electrocardiogram indexes better reflect ischemic changes than do traditional indexes, such as the ST segment deviation.

Identification of the occluded artery in patients with myocardial ischemia induced by prolonged percutaneous transluminal coronary angioplasty using traditional vs transformed ECG-based indexes

We have studied the spatial properties of ischemic changes as induced by prolonged angioplasty and how the changes are related to different ECG indexes. Indexes based on measurements at specific points in time (ST level at J + 60 ms point, maximal T wave amplitude and position, QT interval, and QRS duration) and global indexes (based on the Karhunen-Loève transform and applied to the QRS complex, ST-T complex, ST segment, and T wave), considering both repolarization and depolarization information, were analyzed. The changes during the occlusion period of the different indexes were used as variables in a multivariate discriminant analysis to determine which indexes showed the best discrimination of the three major occlusion sites (corresponding to LAD, RCA, and LCX coronary arteries). Occlusions in LCX artery were the most difficult to classify. With three local indexes (ST60 level measured in lead V3, T wave amplitude in I, and ST60 in III) it was possible to correctly classify 76% of patients by the occlusion site, and with three KLT-derived indexes (first-order KLT index for ST-T complex in I and for QRS in leads V3 and I) 83% of correct classification was obtained. Using six indexes for local and KLT-derived indexes the correct classification was increased to 85 and 90% of patients, respectively. The use of different ECG indexes (from different intervals) on quasiorthogonal leads permitted the identification of the occluded artery in patients undergoing PTCA and may be extended to more general use.

Comparative study of local and Karhunen-Loève-based ST-T indexes in recordings from human subjects with induced myocardial ischemia

In this work we studied ST-T complex changes in the ECG as result of induced ischemia. The principal aim was to determine whether global changes in the ST-T complex were more sensitive markers of ischemic alterations than those based on measurements of changes at specific locations on ST segment or T wave. High-resolution ECGs from patients undergoing percutaneous transluminal coronary angioplasty in one of the major coronary arteries were analyzed to give a description of the period from the end of active depolarization (QRS complex) to the end of active repolarization (T wave). During artery occlusion traditional local measurements of the ST-T complex were compared to global measurements based on the Karhunen-Loève transform. An ischemic change sensor parameter was estimated for each of the studied indexes showing that global measurements detected changes better in the repolarization period in a larger number of leads and with higher sensitivity (more than 85%) than was done using local measurements (sensitivity of 64% with ST level, 33% with T-wave maximum position, and 37% with T-wave maximum amplitude). Using these global indexes it was found that most cases of ST-segment changes were accompanied by T-wave changes (72% of patients). With the use of traditional indexes 23% of patients showed no changes in the repolarization period, whereas with global indexes this percentage decreased to 8%. Thus a global representation of the entire ST-T complex appears to be more suitable than local measurements when studying the initial stages of myocardial ischemia.

Electrocardiographic changes during prolonged coronary artery occlusion in man: comparison of standard and high-frequency recordings

Detection of acute myocardial ischaemia using electrocardiographic methods is generally based on assessment of the ST segments in the standard 12-lead electrocardiogram (ECG). Several studies have also shown changes in high-frequency QRS components during acute ischaemia. The purpose of the present study was to determine the changes in high-frequency QRS components during prolonged percutaneous transluminal coronary angioplasty (PTCA) and to compare these changes with ST-segment deviations in the standard 12-lead ECG. The study population consisted of 19 patients receiving prolonged PTCA. Standard and high-resolution signal-averaged ECGs were recorded before and during balloon inflation. The high-resolution recordings were performed using bipolar X, Y and Z leads. The QRS complexes in the high-resolution signal-averaged ECGs were analysed within a bandwidth of 150-250 Hz. During inflation, significant reductions in high-frequency QRS components were observed (12-72%). Changes in the high-frequency QRS components were seen in four of the patients without ST-segments deviation in the standard ECG. The correlation between the ST-segment deviation and the reduction in high-frequency QRS components was weak (r = 0.27). Acute coronary artery occlusion produces changes in high-frequency QRS components, even in the absence of ST-segment deviation in the standard ECG. Further studies need to be carried out to evaluate whether analysis of high-frequency QRS components could provide a method for detecting myocardial ischaemia and give additional information to that available in the ST segment in the standard ECG.

Admission clinical and electrocardiographic characteristics predicting an increased risk for early reinfarction after thrombolytic therapy

BACKGROUND

This study assessed the ability of clinical and electrocardiographic variables routinely obtained on admission to identify patients with acute myocardial infarction treated with thrombolytic therapy at risk of early reinfarction.

METHODS AND RESULTS

The study included 2602 patients who received thrombolytic therapy for acute myocardial infarction. Baseline demographic variables and admission clinical and electrocardiographic variables were compared between patients with and without reinfarction. Multivariable logistic regression technique was used and included recurrent infarction as the dependent variable, and baseline demographic, clinical, and electrocardiographic variables as independent variables. History of hypertension (odds ratio [OR] 1.52, 95% confidence interval [CI] 1.00 to 2.31) and diabetes mellitus (OR 1.59, 95% CI 1.00 to 2.53) were associated with a higher risk, and current smoking was associated with a lower risk (OR [no versus yes] 1.64, 95% CI 1.05 to 2.58) of early hospital reinfarction. Distortion of the terminal portion of the QRS complex (OR 1.86, 95% CI 1.20 to 2.87) and absence of abnormal Q waves on admission (OR 1.54, 95% CI 0.98 to 2.43) were associated with increased risk of early reinfarction.

CONCLUSIONS

A simple electrocardiographic sign is a reliable predictor of early reinfarction among patients who receive thrombolytic therapy for acute myocardial infarction.

Body position effects on the ECG: implication for ischemia monitoring

Rotation of the heart in relation to surface electrocardiographic (ECG) electrodes when a patient turns to one side has been reported to cause ST-segment shifts, triggering false alarms with continuous ST-segment monitoring. We prospectively analyzed ST-segment and QRS complex changes in both standard and derived ECGs in 40 subjects (18 with heart disease and 22 healthy) in supine, right- and left-lying positions. Of the 40 subjects, 6 (4 cardiac, 2 healthy) developed positional ST deviations of 1 mm or more on the standard ECG. In the derived method, five of the same six subjects showed ST-segment deviation of which most occurred in the left-lying position. Positional ST changes were most frequent for males and for cardiac patients (33%). Changes in QRS complex morphology were common on the standard (28 of 40, 70%) and less frequent on the derived ECGs (17 of 40, 43%), occurring in both healthy and cardiac subjects. QRS axis changes occurred only on the standard ECG. It was concluded that (1) right and left side-lying positions frequently induce clinically significant ECG changes; (2) positional ST-segment deviation is less frequent than previously reported and is most likely to occur in males with cardiac disease; and (3) the derived method is less prone to positional QRS changes than the standard ECG.

Electrocardiographic differentiation of the ST-segment depression of acute myocardial injury due to the left circumflex artery occlusion from that of myocardial ischemia of nonocclusive etiologies

Lead distributions of peak ST-segment depression were compared between patients undergoing left circumflex artery percutaneous transluminal coronary angioplasty and exercise tolerance test. Localization of peak ST-segment depression to leads V2 or V3 was 96% specific and 70% sensitive for differentiating ischemia due to occlusion of left circumflex artery occlusion from nonocclusive ischemia.

QRS changes during percutaneous transluminal coronary angioplasty and their possible mechanisms

OBJECTIVES

The purpose of the study was to describe the configuration, and investigate the mechanisms, of QRS changes occurring during percutaneous transluminal coronary angioplasty (PTCA).

BACKGROUND

QRS changes during PTCA have been attributed to both a passive ST segment shift and conduction disturbances (peri-ischemic block). The direct relation between ST segment shift and QRS changes, however, has not been established, and the definition of conduction disturbances remains to be clarified.

METHODS

Twelve-lead electrocardiograms (ECGs) were recorded before PTCA, at the end of 2 min of PTCA and after return to baseline values in 29 patients (left anterior descending coronary artery [LAD] in 13 patients, right coronary artery [RCA] in 14 and left circumflex coronary artery in 2). Electrocardiographic complexes before and during PTCA were superimposed to determine the amplitudes of initial, terminal and total QRS deflection; the relations of QRS changes to baseline (TP segment) and ST segment shift; and the duration of QRS and corrected QT intervals. RESULTS. 1) The direction of the initial QRS deflection was unchanged, but changes of its amplitude occurred. 2) Terminal QRS deflection changed in all patients with a ST segment shift > 17% of the R amplitude, and the correlation between the decrease in the S amplitude and ST segment shift was significant (r = 0.9, p < 0.01) in patients with LAD PTCA. Correlation between changes in total QRS amplitude and ST segment shift in patients with RCA PTCA was weaker (r = 0.54, p = 0.056). 3) Transient conduction disturbance manifested by QRS widening in selected leads occurred in 2 of 29 patients. CONCLUSIONS. 1) Changes in terminal QRS deflection during PTCA are proportional to the magnitude of the ST segment shift. 2) Conduction disturbances manifested by increased QRS duration occurred infrequently. We suggest that the term peri-ischemic block be applied only to changes in QRS configuration associated with QRS widening.

Changes in R wave amplitude: ECG differentiation between episodes of reocclusion and reperfusion associated with ST-segment elevation

This study assesses the electrocardiographic (ECG) differences between episodes of increased ST-segment amplitude induced by coronary artery occlusion and by reperfusion in the open-chest rabbit model. Nine anesthetized open-chest male New Zealand White rabbits were subjected to four episodes of 5 minutes of coronary artery occlusion followed by 5 minutes of reperfusion. The ST-segment and R wave amplitudes were measured from an ECG lead attached to the pericardium overlying the ischemic myocardium. In 10 out of 35 (29%) of the episodes, reperfusion resulted in a transient increase in ST-segment amplitude. While episodes of coronary artery occlusion were associated with increase in R wave amplitude (69% and 97% of the episodes after 1 and 5 minutes, respectively), all reperfusion episodes were associated with prompt decrease in R wave amplitude. There was no difference between the repeated episodes in the occurrence of ST-segment elevation during reperfusion. However, ST-segment elevation during reperfusion could be distinguished from the ischemic episodes by the prompt decline in the R wave amplitude in the former compared with no change or increase in the latter.

Distortion of the terminal portion of the QRS on the admission electrocardiogram in acute myocardial infarction and correlation with infarct size and long-term prognosis (Thrombolysis in Myocardial Infarction 4 Trial)

Previous studies have shown an association between distortion of the terminal portion of the QRS (QRS[+] pattern: emergence of the J point > or = 50%. of the R wave in leads with qR configuration or disappearance of the S wave in leads with an Rs configuration) on admission and in-hospital mortality in acute myocardial infarction (AMI). However, the mechanism for this association is not known. We assessed the relation between QRS(+) pattern and coronary angiographic findings, infarct size, and long-term prognosis in the Thrombolysis In Myocardial Infarction 4 trial. Patients were allocated into 2 groups based on the presence (QRS[+], n = 85) or absence (QRS[-], n = 293) of QRS distortion. The QRS(+) patients were older (mean +/- SD: 61.1 +/- 10.6 vs 57.5 +/- 10.6 years, p = 0.004), had more anterior AMI (49% vs 37%, p = 0.04), and less previous angina (42% vs 54%, p = 0.05). QRS(+) patients had larger infarct size as assessed by creatine kinase release over 24 hours (209 +/- 147 vs 155 +/- 129, p = 0.003), and predischarge sestamibi (MIBI) defect (17.9 +/- 15.9% vs 11.2 +/- 13.4%, p <0.001). When adjusting for difference in baseline characteristics, p values for the differences in 24-hour creatine kinase release were 0.03 and 0.64 for anterior and nonanterior AMI, respectively, and for MIBI defect size 0.03 and 0.02, respectively. One-year mortality (18% vs 6%, p = 0.03) was higher and the weighted end point of death, reinfarction, heart failure, or left ventricular ejection fraction <40% (0.33 +/- 0.37 vs 0.24 +/- 0.32, p = 0. 13), tended to be higher in the anterior AMI patients with QRS(+). No difference in clinical outcome was found in patients with non-anterior AMI. These findings suggest that this simple electrocardiographic definition of presence of QRS(+) pattern on admission may provide an early estimation of infarct size and long-term prognosis, especially in anterior AMI.

Prognostic significance of the admission electrocardiogram in acute myocardial infarction

OBJECTIONS

We sought to access the ST segment and the terminal portion of the QRS complex in the initial electrocardiogram (ECG) as tools to predict outcome in patients with acute myocardial infarction given thrombolytic therapy.

BACKGROUND

Previous studies assessing early risk stratification of patients with acute myocardial infarction by ECG criteria have focused on the number of leads with ST segment elevation or the absolute magnitude of ST deviation. A new classification independent of the absolute values of ST deviation was pursued.

METHODS

Patients with ST elevation and positive T waves in at least two adjacent leads who received thrombolytic therapy were classified into two groups based on the absence (1,232 patients) or presence (1,371 patients) of distortion of the terminal portion of the QRS complex on the admission ECG.

RESULTS

There were no differences between groups in the prevalence of previous angina, hypertension, current smoking, anterior infarction, time from onset of symptoms to therapy of type of thrombolytic regimen. Patients with QRS distortion were less likely to have had a previous infarction (12.0% vs. 18.4%, p = 0.02) or diabetes mellitus (16.9% vs. 21.4%, p = 0.003). They had higher peak creatine kinase levels (1,617 +/- 1,670 vs. 1,080 +/- 1,343 IU, p = 0.00001). Hospital mortality for those with and without QRS distortion was 6.8% and 3.8%, respectively (p = 0.0008). Multivariable logistic regression analysis confirmed that hospital mortality was independently associated with distortion of terminal portion of the QRS complex (odds ratio 1.78, 95% confidence interval 1.19 to 2.68, p = 0.004).

CONCLUSIONS

Distortion of the terminal portion of the QRS complex on the admission ECG is independently associated with a higher hospital mortality rate in patients with acute myocardial infarction given thrombolytic therapy.

Asymptomatic coronary artery disease detection: update 1996. A screening protocol using 16-lead high-resolution ECG, ultrafast CT, exercise testing, and radionuclear imaging

The authors have proposed a new four-step screening algorithm to detect asymptomatic coronary artery disease (CAD) in flight school candidates, cadets, and rated flyers of the Unites States Air Force (USAF). In step 1, the USAF Armstrong Laboratory (USAF/AL) risk profile and improved 16-lead high-resolution electrocardiogram/vectorcardiogram will be recorded at baseline. On routine follow-up evaluations, quantitative serial comparisons will be performed by the method of Kornreich. In step 2, beginning with flight school candidates and cadets, all three groups will be studied by the ultrafast computed tomograph (CT) protocol. Those candidates positive for coronary calcium will be studied by coronary angiography and ventriculography, and their eligibility for continued rated flight status will be determined by present criteria. In step 3, those candidates negative for coronary calcium by ultrafast CT will then be screened by the newly defined and improved high-sensitivity treadmill exercise test criteria. In step 4, candidates with a positive treadmill exercise test result, or who are also found in the upper quintile of the USAF/AL risk profile, wild also have exercise nuclear wall motion studies and perfusion scans. If these are abnormal and suggestive of myocardial ischemia, this subset will also be studied by heart catheterization and coronary angiography, and their eligibility for continued rated flight status will be determined by present criteria. The incidence of coronary calcium/no calcium for each degree of stenosis in the 6,000 flyers in each quintile was used to develop the following projections: (1) that more than 3 of 4 rated flyers with unsuspected CAD, and (2) more than 9 of 10 with severe flow-limiting CAD can be identified by these upgraded screening procedures. Evidence is herein presented that these enhancements will result in a major (5-8-fold) increase in case finding of this disease. Based on the estimate of four lost high-performance aircrafts per year from sudden incapacitation of the pilot due to CAD, when this four-step screen is fully operational, it can be expected to reduce the $80 million annual losses to the United States government from CAD by 85%, a savings of $68 million per year.

Dynamic on-line vectorcardiography improves and simplifies in-hospital ischemia monitoring of patients with unstable angina

OBJECTIVES

This study sought to validate computerized vectorcardiography against the established technique of Holter electrocardiographic (ECG) monitoring and to compare the feasibility of the two methods for monitoring patients with unstable angina pectoris.

BACKGROUND

Detection of myocardial ischemic episodes is an important objective in patients admitted to the hospital for unstable angina pectoris. Standard ECG monitoring may be sufficient for detection of symptomatic episodes but will often overlook silent ischemia. Holter ECG monitoring has a higher likelihood of discovering such episodes, but analysis is time-consuming, and the results are not available on-line.

METHODS

We simultaneously monitored 53 consecutive patients with unstable angina, 46 of whom had technically adequate 24-h Holter ECGs and computerized vectorcardiograms.

RESULTS

The Holter tapes had a mean (+/- SD) of 15.3 +/- 10.3 h of recording with both channels technically adequate for analysis compared with 23.7 +/- 1.77 h of vectorcardiographic recording that could be analyzed (p < 0.01). Of the 15 symptomatic episodes detected by Holter ECG monitoring, 13 were also detected with dynamic vectorcardiography. In contrast, eight patients had 18 episodes of chest pain, with simultaneous ST segment changes detected by dynamic vectorcardiography; only 9 of these episodes were also detected by Holter ECG monitoring.

CONCLUSIONS

Monitoring of myocardial ischemia with dynamic vectorcardiography seems to be more efficient than Holter monitoring and may have a higher sensitivity. Computerized, continuous vectorcardiography has a complete real-time capacity, allowing monitoring over prolonged periods of time, and the results are immediately available without time-consuming analysis.

Metoprolol treatment for two years after coronary bypass grafting: effects on exercise capacity and signs of myocardial ischaemia

OBJECTIVE

To evaluate whether prophylactic treatment with metoprolol for two years after coronary artery bypass grafting improves working capacity and reduces the occurrence of myocardial ischaemia in patients with coronary artery disease.

METHODS

After coronary artery bypass grafting, patients were randomised to treatment with metoprolol or placebo for two years. Two years after randomisation, a computerised 12-lead electrocardiogram was obtained during a standardised bicycle exercise test in 618 patients (64% of all those randomised).

RESULTS

The median exercise capacity was 140 W in the metoprolol group (n = 307) and 130 W in the placebo group (n = 311) (P > 0.20). An ST depression of > or = 1 mm at maximum exercise was present in 34% of the patients in the metoprolol group and 38% in the placebo group (P > 0.20) and an ST depression of > or = 2 mm at maximum exercise was present in 11% in the metoprolol group and 16% in the placebo group (P = 0.09). The median values for maximum systolic blood pressure were 200 mm Hg in the metoprolol group and 210 mm Hg in the placebo group (P < 0.0001), while the median values for maximum heart rate were 126 beats/min in the metoprolol group and 143 beats/min in the placebo group (P < 0.0001). The occurrence of cardiac and neurological clinical events two years postoperatively among exercised patients was comparable in the treatment groups.

CONCLUSIONS

Treatment with metoprolol for two years after coronary artery bypass grafting did not significantly change exercise capacity or electrocardiographic signs of myocardial ischaemia.

Comparison using dynamic vectorcardiography and MIBI SPECT of ST-segment changes and myocardial MIBI uptake during percutaneous transluminal coronary angioplasty of the left anterior descending coronary artery

The quantitative relation between ST-segment changes and the severity and extent of myocardial ischemia during coronary occlusion remains unclear. This study assesses whether ST-segment changes during percutaneous transluminal coronary angioplasty (PTCA) correlate with the amount of myocardium at risk, measured with technetium-99m hexakis 2-methoxyisobutyl isonitrile (MIBI; also called sestamibi) single-photon emission computed tomography (SPECT). Quantitative continuous dynamic vectorcardiography was performed during PTCA of the left anterior descending coronary artery in 11 patients (mean age 64.3 years) without previous myocardial infarction. Change in the magnitude of the ST vector (STc-VM) was continuously recorded. A standardized protocol of balloon inflations was used and technetium-99m MIBI was injected intravenously at the onset of the third inflation. SPECT imaging was performed 60 minutes later and compared to a rest acquisition. SPECT was quantified by bull's-eye analysis using: (1) the change in the pathologic/normal area count ratio (delta P/N) as an index of the severity of ischemia; and (2) planimetered defect size during PTCA as an indicator of the size of the area at risk. The delta P/N from baseline to balloon occlusion (22 +/- 11%) was correlated, albeit loosely, to the maximum value of STc-VM (245 +/- 186 microV, r = 0.62, p < 0.05), but there was no correlation between the size of the scintigraphic defect and STc-VM. Likewise, the sum of ST-segment elevation was correlated to delta P/N (r = 0.72, p < 0.02), but not to the size of the scintigraphic defect.(ABSTRACT TRUNCATED AT 250 WORDS)

Appearance of abnormal Q waves early in the course of acute myocardial infarction: implications for efficacy of thrombolytic therapy

OBJECTIVES

The purpose of this study was to determine the time course of the appearance of abnormal Q waves on the electrocardiogram (ECG) over the first 6 h of symptoms of myocardial infarction and to determine what implications, if any, such Q waves have for the efficacy of thrombolytic therapy.

BACKGROUND

Severe myocardial ischemia can produce early QRS changes in the absence of infarction. Abnormal Q waves on the baseline ECG may not be an accurate marker of irreversibly injured myocardium.

METHODS

Data from 695 patients who had no past history of myocardial infarction and whose admission ECG allowed prediction of myocardial infarct size in the absence of thrombolytic therapy (Aldrich score) were pooled from four prospective trials of thrombolytic therapy. The presence and number of abnormal Q waves on each patient's initial ECG were recorded. Four hundred thirty-six patients had left ventricular infarct size measured using quantitative thallium-201 tomography a mean (+/- SD) of 52 +/- 43 days after admission.

RESULTS

Of patients admitted within 1 h of symptoms, 53% had abnormal Q waves on the initial ECG. Both predicted and final infarct size were larger in patients with abnormal Q waves on the initial ECG independent of the duration of symptoms before therapy (p < 0.001). Despite this finding, the presence of abnormal Q waves on the admission ECG did not eliminate the effect of thrombolytic therapy on reducing final infarct size (p < 0.0001).

CONCLUSIONS

Abnormal Q waves are a common finding early in the course of acute myocardial infarction. However, there is no evidence that abnormal Q waves are associated with less benefit in terms of reduction of infarct size after thrombolytic therapy.

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.

Maximal spatial ST-vector patterns in patients with acute anteroseptal myocardial infarction

Seventy patients with acute myocardial infarction were studied by serial vectorcardiography. Eleven out of 70 patients had acute myocardial infarction, which consistently met the vectorcardiographic QRS-loop criteria of anteroseptal myocardial infarction within the 21 days follow-up period. From the first vectorcardiographic tracings three types of the maximal spatial ST-vector were seen. Their directions belonged to one of the following octants: (1) right-anterior-superior, (2) left-anterior-superior, or (3) left-anterior-inferior. The directions were the same as the types of initial activity of the normal depolarization process of the interventricular septum revealed by the intracardiac mapping in dogs. The subsequent vectorcardiograms showed no change in direction of the maximal spatial ST-vector in all patients except one. This study suggested that there are three types of the maximal spatial ST-vector concealed in patients with first acute anteroseptal myocardial infarction. Each type of the maximal spatial ST-vectors is capable of causing S-T segment elevation from leads V1 to V3 in the acute electrocardiogram. Why the subgroup of the right-anterior-superior maximal spatial ST-vector in patients with acute anteroseptal myocardial infarction had poor outcomes during the acute stage needs further investigation.

QRST changes during and after percutaneous transluminal coronary angioplasty

This study reports preliminary results on 45 patients who underwent percutaneous transluminal coronary angioplasty (PTCA); 120-lead data (including the 12-lead standard electrocardiogram [ECG]) were recorded before, during, and after balloon inflation. Twenty-one patients underwent PTCA for left anterior descending coronary disease, 13 for right coronary artery disease, and 10 for left circumflex; 1 patient had combined left anterior descending and right coronary artery disease. In each patient, voltage data recorded during the various phases of the procedure were compared with the patient's own baseline data. In 18 patients, 120 leads were also recorded 24 hours after PTCA. In this study, the usefulness of the standard 12-lead ECG was investigated in locating the coronary artery being occluded, in elucidating the mechanisms of the QRS changes, and in identifying changes occurring 24 hours after completion of the procedure. Results indicate that the observation of ST elevation in the 12-lead ECG may lead to ambiguous interpretation. Also, limiting observation to ST-T patterns alone instead of including QRS changes further hampers correct identification of the involved vessel. QRS modifications during inflation are interpreted as conduction disturbances, although other mechanisms are evoked: study of surface maps may contribute to the understanding of these mechanisms. Changes present 24 hours later are visible in the standard leads, but again, in the absence of the thoracic potential distribution, these are difficult to interpret. These changes were different from those observed after cessation of inflation at the end of the procedure. It is hypothesized that next-day changes may reflect reperfusion injury and/or represent myocardial stunning. Presence of injury and reversibility of changes require further investigation. Also, biochemical markers such as creatine kinase-MB mass, creatine kinase-MB activity, myoglobin, and troponin-T may help elucidate the significance of these findings.

The "giant R waves" ECG pattern of hyperacute phase of myocardial infarction. A case report

The author describes a rarely appreciated electrocardiographic (ECG) pattern of the hyperacute phase of myocardial infarction, characterized by the transient development of very tall R waves merging with maximally elevated ST-segments, and the reduction of the depth, or complete disappearance of S waves. Similar ECG findings are frequently recorded in epicardial and precordial tracings in the animal laboratory, immediately following experimental occlusion of a coronary artery. In patients with acute myocardial infarction, the "giant R waves" ECG pattern is seen very early in the clinical course. Often the ECG appearances described above are missed either because patients suffering a myocardial infarction do not present to the hospital shortly after the inception of symptoms, or are attributed to conduction abnormalities of the classic variety or to ventricular tachycardia. The incidence of the giant R waves ECG pattern in the setting of clinical acute myocardial infarction is not known. Also its pathophysiologic, clinical, and prognostic correlates remain to be defined by appropriately designed research protocols.

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.

Electrocardiographic prediction of the success of coronary reperfusion by intravenous thrombolytic therapy: an experimental study

The accuracy of electrocardiograms (ECGs) in predicting the success of coronary reperfusion by intravenous (IV) thrombolytic therapy was studied in 49 canine acute myocardial infarctions (MI), induced by occlusive thrombus in the left anterior descending (LAD) coronary artery. Two hours after the onset of MI, urokinase (UK, 3 x 10(4) U/kg) was administered IV and the heart was observed for one further hour. LAD flow and epicardial ECGs were recorded continuously. LAD flow was restored by UK in 26 of 49 animals (Group I); restored LAD flow was stable in 17 of the 26 (Group IA) and unstable with repeated fluctuations in the other 9 (Group IB) during the follow-up period. No coronary reflow was obtained by thrombolysis in 23 of 49 animals (Group II). The best electrocardiographic criterion for predicting coronary reperfusion was reduction of ST elevation by more than 25%, which had a predictive accuracy of 86%. There was a significant correlation between the grade of improvement of coronary blood flow and reduction of ST elevation in Group IA (p less than 0.01), but not in Group IB, indicating that unstable coronary blood flow following thrombolysis due to residual thrombus appears to be one of the major factors preventing accurate prediction of coronary reperfusion with thrombolysis on the basis of changes in ST elevation.

Dynamic QRS complex and ST segment vectorcardiographic monitoring can identify vessel patency in patients with acute myocardial infarction treated with reperfusion therapy

Reperfusion therapy has lowered the mortality in patients suffering acute myocardial infarction. Failure to reperfuse is associated with significantly higher risk of short- and long-term mortality. Detection of reperfusion is thus important. In a prospective pilot study, we used continuous on-line computerized vectorcardiography to monitor 21 patients with acute myocardial infarction treated with reperfusion therapy to noninvasively detect coronary patency. By using trend analysis of QRS vector difference, we were able to correctly blindly identify 15 of 16 patients with a perfused infarct-related artery and four of six patients with a persistently occluded artery at an early angiogram. The present results are based on a limited number of patients, but suggest that QRS complex and ST segment monitoring with continuous on-line vectorcardiography has substantial potential for monitoring patients with acute myocardial infarction treated with reperfusion therapy.

Dynamic QRS-complex and ST-segment monitoring in acute myocardial infarction during recombinant tissue-type plasminogen activator therapy. The TEAHAT Study Group

Changes of the QRS complex are the electrocardiographic expression of irreversible injury of the myocardium. In humans, the process of infarction occurs over several hours. A more rapid development of QRS changes has been reported in patients treated with thrombolytic agents. Patients with strongly suspected acute myocardial infarction (AMI) included in a placebo-controlled trial of 100 mg of recombinant tissue-type plasminogen activator (rt-PA) were monitored for 24 hours with continuous, on-line vectorcardiography. The magnitude of the QRS vector changes correlated with infarct size estimated by the maximal value of lactate dehydrogenase-1 (r = 0.69, p less than 0.001) as well as with left ventricular ejection fraction 30 days after randomization (r = 0.49, p less than 0.001). Treatment with intravenous rt-PA limited total QRS vector change but the QRS vector changes observed occurred more rapidly and reached a plateau 131 minutes earlier in patients treated with rt-PA than in those receiving placebo (p less than 0.01). A certain pattern of highly variable ST vector magnitude was identified and was associated with higher maximal lactate dehydrogenase-1 values (23 +/- 13 vs 14 +/- 10 mu kat/liter, p less than 0.001) and a tendency to higher 1-year mortality (24 vs 9%, p = 0.08) than in patients without this pattern. In patients with this pattern, rt-PA did not affect maximal lactate dehydrogenase-1, time to maximal creatine kinase and final magnitude of QRS vector change.

Evaluation of formulas for estimating the final size of acute myocardial infarcts from quantitative ST-segment elevation on the initial standard 12-lead ECG

Previously developed formulas for predicting the final QRS estimated sizes of acute myocardial infarcts from the initial ST segment deviation are tested. The population contains patients with either anterior or inferior infarcts from two hospitals in Copenhagen, Denmark. The formula for anterior location that considers only the number of ECG leads with ST elevation achieved a high correlation (r = 0.70). However, the formula for inferior location that considers the quantity of ST elevation in inferior leads achieved a lower value (r = 0.52). Empiric modifications of this formula were constructed that considered either the quantity of ST elevation in (A) or the number of (B) involved non-inferior leads. Each modification achieved improvement in correlation with QRS estimated MI size in the original population (A: r = 0.63 and B: r = 0.65), and also in an independent test population (A: r = 0.57 and B: r = 0.62). These results suggest that the formula of Aldrich et al. for anterior location is valid for clinical application, but that further studies are required to determine if a comparably accurate method can be developed for inferior MI.

Continuous vectorcardiography in cardiac surgery: natural course of vector changes and relationship to myocardial oxygen uptake

Continuous vectorcardiography was registered before and during the first 18 hours after cardiac surgery in 53 patients. QRS vector changes (QRS-VD) occurred during the operation, but no further changes were observed postoperatively. The ST vector (ST-VM) increased during the operation, and a further slight increase occurred postoperatively. Perioperative myocardial infarction occurred in three patients. Their ST-VM was higher than the average in patients without myocardial infarction, while QRS-VD did not differ from the average pattern. Twelve other patients were studied in pacemaker-induced moderate tachycardia. QRS-VD increased in proportion to heart-rate changes (rs median = 0.93, p less than 0.01). QRS-VD also correlated with myocardial oxygen uptake (rs median = 0.62, p less than 0.05). The ST-VM responses were not uniform. The data suggest that vectorcardiogram variables can provide information related to myocardial energy metabolism.

Anatomic validation of electrocardiographic estimation of the size of acute or healed myocardial infarcts

Seventeen new criteria added to the simplified version of the Selvester QRS scoring system to comprise the complete version were evaluated to determine their value in estimating the size of single infarcts. These non-Q-wave criteria might be particularly useful regarding posterolateral infarcts in the distribution of the left circumflex artery. The study population was made up of 21 anterior, 30 inferior and 20 posterolateral single myocardial infarction (MI) patients with no evidences of bundle branch or fascicular blocks, ventricular hypertrophy or previous MI on their final stable electrocardiogram. The complete system's maximum 32 points is capable of indicating MI in 96% of the left ventricle and it estimated a mean electrocardiographic MI size that better approximated the anatomic size compared with the simplified version in all MI locations. The correlation between anatomic and electrocardiographic MI size using the complete system was better and statistically significant for the posterolateral MI group (simplified r = 0.55, p less than 0.01 vs complete r = 0.70, p less than 0.0006). Criteria such as Q and S amplitude less than or equal to 0.3 mV in V1 and less than or equal to 0.4 mV in V2 were particularly helpful. This study documents the improved ability provided by the 17 additional non-Q-wave criteria which have been added in the complete version of this scoring system regarding the sizing of infarcts in the region of the left ventricle supplied by the left circumflex artery.

R- and S-wave amplitude changes with acute anterior transmural myocardial ischemia. Correlations with left ventricular filling pressures

The value of R- and S-wave amplitude changes as electrocardiographic (ECG) markers of myocardial ischemia and dysfunction was evaluated using coronary angioplasty as a model of acute transmural ischemia and ST segment elevation. Hemodynamic data and 12-lead ECGs were recorded at baseline and during coronary occlusion in 34 patients with left anterior descending artery angioplasty. In the precordial leads V1 through V4, the sum of R-wave amplitude increased in 17 patients, was unchanged in ten, and decreased in seven; the sum of S-wave amplitude decreased in 33 patients (including two patients with complete loss of S wave) and increased in one. Mean R-wave change was 2.7 +/- 6.2 mm, mean S-wave change was -12.9 +/- 9.0 mm, and mean precordial ST elevation was 12.5 +/- 8.7 mm. Absolute R-wave change correlated directly with ST elevations (p = .013), while S-wave change correlated inversely (p less than .007). Only ST elevations correlated with changes in pulmonary capillary wedge pressure (PW) (p less than .007). In the precordial lead with maximum ST elevations, only R-wave changes correlated with ST elevations (p = .002), and both R-wave changes and ST elevations correlated with changes in PW (R:p = .027; ST:p = .007). The presence of large increases in R waves or decreases in S wave, or of high-magnitude ST elevations identified patients with the highest elevations in PW. In conclusion, decreases in S waves and, less commonly, increases in R waves are seen with diagnostic ST elevations and may have some limited clinical value. The correlation between magnitude of acute anterior ST elevations and changes in left ventricular filling pressures may have important clinical consequence.

ST deviation in right chest leads V3R to V7R during percutaneous transluminal coronary angioplasty

ST elevation in right chest leads during evolving inferior myocardial infarction indicates right ventricular involvement. Theoretically, such changes may be due to reversible or irreversible myocardial ischemia. Whether similar ST elevations can be recorded in patients with myocardial ischemia without infarction is unknown. To clarify this, right chest leads V3R to V7R were recorded during percutaneous transluminal coronary angioplasty in 43 patients who had a total of 45 arteries dilated. Balloon occlusion of the right coronary artery caused transient ST elevation, whereas closure of the left anterior descending coronary artery or the left circumflex artery was associated with transient ST depression. These findings were 100% discriminative in leads V5R and V6R. Furthermore, ST elevation greater than or equal to 1 mm in one or more of leads V4R to V7R was seen only when the right coronary artery was occluded. Thus transient myocardial ischemia without infarction may cause ST elevation in the right chest leads and ST elevation greater than or equal to 1 mm in one or more leads V4R to V7R is seen exclusively with occlusion of the right coronary artery.

Transient alterations of the QRS complex and ST segment during percutaneous transluminal balloon angioplasty of the right and left circumflex coronary arteries

The dynamic QRS amplitude changes that appear during 1-vessel percutaneous transluminal coronary angioplasty of the right and left circumflex coronary arteries were studied in 20 patients using continuous 3-lead electrocardiographic recordings representing leads aVF, V2 and V5. The balloon inflations that produced the greatest extent of ST-segment deviation were identified for each lead ("maximally ischemic periods"). QRS amplitude measurements were performed manually at both the PR and shifted J-ST baselines at 10-second intervals during these periods to determine that baseline from which the R and S waves most nearly maintained their control amplitudes. There was no significant baseline relation for either the R or the S waves in leads V2 and V5 during ischemia. However, the R-wave changes in lead aVF were significantly associated with the PR- versus the J-ST-segment baseline (p = 0.007); the S wave, when it occurred, had no tendency for either baseline. The electrocardiographic records were also examined visually for characteristics of left posterior (inferior) "periischemic block" likely to occur uniquely in patients with a dominant right or left circumflex occlusion. There were 2 patients with obstruction of the right circumflex artery who exhibited the characteristics of periischemic block during percutaneous transluminal coronary angioplasty, as evidenced by an increase in R-wave duration, amplitude or both in lead aVF.