ST Vector Magnitude Research Articles

Clinical Usefulness of a Functional Test of Neutralising Streptokinase Antibodies for the Prediction of the Thrombolytic Effect of Streptokinase in Acute Myocardial Infarction

We investigated whether the occurrence of neutralising streptokinase (SK) antibodies, as assessed by a new bedside test, was related to the effect of SK in acute myocardial infarction (AMI), assessed with continuous vectorcardiography (VCG). Twenty-eight patients with ST elevation, admitted ≤ 6 h after the onset of symptoms, treated with 1.5 MIU SK were included. The level of SK antibodies was assessed by the TAS Streptokinase Test Panel, measuring the lysis time of clotted fibrin in the sample. Clot lysis time was negatively correlated to ST vector magnitude (ST-VM) recovery at 90 min (r_S = –0.40, p = 0.03), and clot lysis time was positively correlated to time to reperfusion, (r_S = 0.42, p = 0.03). The predictive values of the test, however, were low. In conclusion, as the prediction of reperfusion in AMI after SK by the new test was poor, we cannot recommend it for clinical decision-making prior to the choice of the thrombolytic agent.

Dynamic QRS-complex and ST-segment monitoring by continuous vectorcardiography during carotid endarterectomy

Many authors report a high incidence of cardiac events during carotid endarterectomy. The aim of the present study was to evaluate the usefulness of dynamic continuous on-line vectorcardiography for monitoring the occurrence of myocardial ischaemia during carotid endarterectomy. We studied 21 patients undergoing carotid endarterectomy. Patients underwent general anaesthesia with isoflurane or sevoflurane. The vectorcardiogram was monitored continuously during carotid endarterectomy. Electrodes were placed according to the previously described lead system and connected to a computerized system for on-line vectorcardiography. Two trend variables were recorded: the QRS vector difference, which reflects changes in the shape of the QRS complex; and the ST vector magnitude, which represents deflection of the ST segment from the isoelectric level. The ST segment deflection was measured 60 ms after termination of the QRS complex. Vectorcardiography was successfully recorded in all 21 patients. Three patients showed intraoperative vectorcardiogram abnormalities. In one of these three patients, both ST vector magnitude and QRS vector difference increased after induction of anaesthesia and ST vector magnitude returned to baseline after administration of nitroglycerin. In the other two patients, both ST vector magnitude and QRS vector difference gradually increased after cross-clamping of the internal carotid artery and ST vector magnitude returned to baseline after unclamping. QRS vector difference remained elevated for several hours in all three patients. Monitoring ST vector magnitude and QRS vector difference by vectorcardiography may be useful for identifying myocardial ischaemia during carotid endarterectomy.

Use of baseline ST-vector magnitude to identify electrocardiographic injury in patients with suspected acute myocardial infarction

No information is currently available regarding optimal cut-off values of the ST-vector magnitude (ST-VM) for predicting acute myocardial infarction (AMI) in emergency department (ED) chest pain patients undergoing vectorcardiographic (VCG) monitoring. A prospective observational study was performed in 1,722 chest pain patients with suspected acute coronary syndrome and absence of bundle branch block (BBB) and left ventricular hypertrophy (LVH) on initial ECG who underwent continuous VCG ST-segment monitoring during the initial ED evaluation. Three cut-off values for baseline ST-VM are reported and represent the smallest values in which the positive likelihood ratio (+LR) for AMI is greater than 5, 10, and 20, respectively. AMI occurred in 158 of 1,722 patients (9.2%) without BBB or LVH on initial ECG. Optimal cut-off values at the predetermined +LR values of 5, 10, and 20, were 121 μV (sensitivity, 41.8%; specificity, 92.0%), 151 μV (sensitivity, 29.1%; specificity, 97.1%), and 175 μV (sensitivity, 25.9%; specificity, 98.7%), respectively. Combining the earlier-mentioned cut-off values with physician judgment of initial pretest probability (high, intermediate, or low, respectively) resulted in a relative increase in identification of injury of 37.5% as compared with the ED physician's interpretation of initial ECG (41.8% v 30.4%; P <.0001), and 65.2% as compared with the official ECG interpretation (41.8% v 25.3%; P <.0001). Increasing ST-VM results in increasing likelihood of AMI. Clinical studies need to be performed to determine if ST-VM cut-off values of 121, 151, and 175 μV in conjunction with physician pretest probability of AMI can be used as criterion for emergent reperfusion therapy in patients without LVH or BBB on the initial ECG. (Am J Emerg Med 2002;20:535-540. Copyright 2002, Elsevier Science (USA). All rights reserved.)

Isolated ultrafiltration affects dynamic vectorcardiographic ischemia monitoring parameters

The present study was undertaken to assess the role of isolated ultrafiltration (UF phase) and hemodialysis with minimal ultrafiltration (HD phase) in changes in parameters reflecting myocardial ischemia: QRS vector difference (QRS-VD), ST change vector magnitude (STC-VM) and ST vector magnitude (ST-VM6) registered by MIDA (myocardial infarction dynamic analysis). Twelve patients on maintenance hemodialysis were first ultrafiltrated for 2.5 h without dialysis (UF) followed by a 2.5-hour session of hemodialysis with minimal ultrafiltration (HD). Computerized vectorcardiography (VCG) was used for on-line dynamic analysis of ST segment and QRS complex changes. Blood volume (BV) changes were monitored non-invasively and continuously with the CRIT-LINE instrument. Whole-body bioelectric impedance analysis (BIA) was used for extracellular water (ECW) estimation. During the UF phase QRS-VD and STC-VM showed a statistically significant increasing linear trend (time effect for both QRS-VD and STC-VM p < 0.0001, while no changes were noted in ST-VM6; time effect p = 0.986). During the HD phase none of these parameters changed (time effect for QRS-VD p = 0.855, for STC-VM p = 0.275 and for ST-VM6 p = 0.976). During the UF, phase changes in QRS-VD were in close relation to those in ECW. Isolated ultrafiltration leads to an increase in the VCG ischemia monitoring parameters QRS-VD and STC-VM. The increase of QRS-VD is related to changes in ECW. Hemodialysis with minimal ultrafiltration has no effect on VCG ischemia monitoring parameters.

Assessment of Myocardium at Risk with Computerized Vectorcardiography and Technetium-99m-Sestamibi-Single Photon Emission Computed Tomography during Coronary Angioplasty

Objective - To compare the myocardium at risk (MAR) as estimated by computerized vectorcardiography (cVCG) with MAR determined by Tc-99m-sestamibi-SPECT using coronary angioplasty as the model for transient transmural ischemia in humans. Methods and results - In 37 patients with stable angina pectoris, cVCG was recorded continuously during coronary angioplasty. The scintigraphic defect was quantified using an automated software program (CEqual). The ST vector magnitude (ST-VM) and the ST change vector magnitude (STC-VM) correlated well with MAR estimated by scintigraphy, ST-VM ( r = 0.71, p < 0.001) and STC-VM ( r = 0.84, p < 0.001). All patients with STC-VM <50 w V during occlusion had defects of less than 10% of the left ventricle. Conclusion - 1) ST-VM and STC-VM give a reasonable useful estimate of MAR size during transient coronary occlusion. 2) STC-VM <50 w V is a reliable limit to identify patients with MAR size less than 10%. 3) ST-VM does not add information to STC-VM with respect to detection of ischemia. 4) The existence of collateral vessels has great impact on both ST-vector changes and scintigraphic imaging of myocardial ischemia.

Early assessment of long-term risk with continuous ST-segment monitoring among patients with unstable coronary syndromes. Results from 1-year follow-up in the TRIM study

A total of 323 patients who took part in the TRIM trial underwent an initial 24 h continuous electrocardiogram ST-segment monitoring. A ST vector magnitude (ST-VM) maximum ≥ 144 μV predicted death or myocardial infarction within 1 year with a 78% specificity and a 52% sensitivity, an area under the ST-VM trend curve ≥ 162 μ with a 86% specificity and a 42% sensitivity and presence of ST-VM episodes with a 70% specificity and a 68% sensitivity. Patients who had neither ST-VM episodes nor a ST-maximum ≥ 144 μV had only a 4.5% incidence of death or myocardial infarction within one year as compared to 18% among those patients who met any of these criteria. ST-segment monitoring with continuous vectorcardiography is feasible for risk stratification at least up to 1 year after an episode of unstable coronary artery disease and several vectorcardiographic parameters may be used.

Deterioration in peak systolic velocity is closely related to ischaemia during angioplasty: a vectorcardiographic and tissue Doppler imaging study.

We tested the hypothesis that the extent of signs of ischaemia detected by vectorcardiography (VCG) during elective coronary angioplasty (percutaneous transluminal coronary angioplasty; PTCA) is related to systolic and diastolic myocardial velocities, as determined by tissue Doppler echocardiography. A total of 15 patients undergoing PTCA (12 men/three women; age 61+/-9 years), without prior myocardial infarction and with an ejection fraction of >50%, were included. The balloon inflation was repeated three times, with minimum intervals of 2 min between inflations. Tissue Doppler echocardiography was performed, in an apical two- or four-chamber view, before and at the end of each inflation. Peak systolic velocity, time-to-peak systolic velocity (TTP), peak early (E(m)) and late (A(m)) diastolic velocities, the E(m)/A(m) ratio and isovolumic relaxation time were measured in the basal segments of the left ventricle. VCG recordings were carried out during the whole procedure. ST vector magnitude (ST-VM) and ST change vector magnitude (STC-VM) were monitored. The total duration and area of each VCG change during inflation were calculated for each patient. Isovolumic relaxation time, peak E(m) and A(m) values and the E(m)/A(m) ratio did not change significantly during inflation. Peak systolic velocity decreased (6.7+/-2.0 to 5.3+/-1.9 cm/s; P<0.001) and TTP increased (157+/-60 to 192+/-60 ms; P<0.01) during inflation. Both STC-VM time (r=-0.68, P<0.01) and STC-VM area (r=-0.68, P<0.01) were related to peak systolic velocity during inflation. STC-VM time was also related (r=0.55, P<0.05) to the difference in peak systolic velocity during compared with before inflation. ST-VM was less closely related to peak systolic velocity. Thus the duration and degree of ischaemia, as measured by VCG, are related to peak systolic velocity in the basal segments of the left ventricle.

Prognostic Value of Ischemia Monitoring with On-Line Vectorcardiography in Patients with Unstable Coronary Artery Disease

Aim: The aim of this study was to determine whether on-line vectorcardiography (VCG) gives independent prognostic information, regarding death, myocardial infarction (MI), and revascularization in patients with unstable coronary artery disease, i.e. unstable angina or non-Q-wave MI. Methods and Results: One hundred and fifty patients (mean age 69 ± 10), participating in a randomized study of low-molecular-weight heparin in unstable coronary artery disease, were studied with on-line VCG recordings for 24 h. During a 5–6-month follow-up, 11 patients died, 14 suffered a nonfatal MI and 31 were revascularized. Univariate predictors of death were diabetes mellitus (p < 0.01), maximum ST vector magnitude (ST-VM; p < 0.001), maximum ST change vector magnitude (STC-VM; p < 0.001), number of ST-VM (p < 0.01) and STC-VM episodes (p < 0.001). In multivariate analysis, the number of STC-VM episodes (p < 0.01) and diabetes mellitus (p < 0.02) each gave independent prognostic information regarding death. When all cardiovascular events were combined, the inhability to perform an exercise test (p < 0.05), maximum value of ST-VM (p < 0.01) and STC-VM (p < 0.001), the number of episodes of STC-VM (p < 0.001) and ST-VM (p < 0.001) all gave prognostic information. In multivariate analysis, the inability to perform an exercise test and the number of STC-VM episodes were independent predictors. Conclusion: VCG monitoring during the first 24 h of hospitalization for unstable coronary artery disease gives independent prognostic information.

Prognostic Role of On-Line Vectorcardiography as Regards Repeat Revascularization after Successful Coronary Angioplasty

This study evaluated the prognostic significance of continuous on-line vectorcardiography (VCG) during elective coronary angioplasty (percutaneous transluminal coronary angioplasty, PTCA). Patients (n = 192, mean age 58 ± 10), treated with elective and initially successful PTCA, were included. VCG monitoring was started before start of the PTCA procedure and was carried out during the entire procedure. ST vector magnitude (ST-VM) was monitored. A 6-month follow-up was obtained. Main outcome measures were the frequency of cardiac events and revascularization during follow-up. During follow-up, 1 patient died, 6 suffered a nonfatal myocardial infarction and 50 were revascularized. Angiography revealed restenosis in 88% of the patients who had a revascularization. In the total patient group, the VCG predictor of revascularization was the total ischemic time of all ST-VM episodes (p = 0.05). Clinical predictors of revascularization were diabetes mellitus (p < 0.01), a more severe type of lesion (type B; p < 0.01), percent post-PTCA stenosis (p < 0.05), nominal balloon size (p < 0.01), maximum balloon pressure (p < 0.05) and no stent implanted (p < 0.001). In a multivariate analysis all the above significant univariate variables of revascularization were entered. Total ischemic time of ST-VM (p < 0.01) was the best variable giving independent prognostic information. In the nonstent group, total ischemic time of ST-VM (p < 0.01) was the only independent predictor of a further revascularization. In conclusion, VCG monitoring during elective PTCA gives on-line information that identifies patients at an increased risk of a revascularization during 6 months after the initial procedure.

Prognostic value of maximum ST-vector magnitude during the first 24 h of vectorcardiographic monitoring in patients with unstable angina pectoris.

To assess the prognostic importance of alternate ways of quantifying myocardial ischaemia by continuous ST analysis, the maximum ST vector magnitude and the area under the ST vector magnitude trend curve during the first 24 h of continuous ST monitoring. During a 22-month period from 1991 to 1993, 195 patients admitted to our CCU with suspected unstable angina pectoris, were included in the study. During the first 24 h the patients were monitored for ischaemic episodes with computerized vectorcardiography, using a MIDA 1000 system. Twenty seven (14%) of the 195 patients died or had a non-fatal myocardial infarction within 1 year and the maximum ST vector magnitude among those patients was, on average, 201 microV compared with 118 microV in patients who survived 1 year free of myocardial infarction (P<0.01). The area under the ST vector magnitude trend curve was, on average, 1598 microVmin compared with 164 microVmin (P<0.01). By multivariate analysis, the maximum ST vector magnitude emerged as a superior predictor of death or myocardial infarction, compared with the area under the ST vector magnitude trend curve and the number of ST vector magnitude and ST change vector magnitude episodes. The maximum ST vector magnitude and age were independent predictors of death or non-fatal myocardial infarction within 1 year. Maximum ST vector magnitude during the first 24 h of vectorcardiographic monitoring seems to be a strong predictor of subsequent death or non-fatal myocardial infarction.

QRS Amplitude and Volume Changes during Hemodialysis

Background: According to several studies the QRS amplitude of the ECG increases during hemodialysis. The detailed background to this phenomenon has not been defined. Two main mechanisms have been suggested: myocardial ischemia and volume changes. New noninvasive technologies make possible a comparison of QRS complex changes synchronously with myocardial ischemia and extracellular water (ECW)/blood volume (BV) changes during hemodialysis. Methods: In this study hemodialysis-related changes in body weight, biochemical blood variables, BV, ECW, ST segment and QRS complex were analyzed in 15 patients (age 36–76, time on dialysis 0–6 years) undergoing chronic hemodialysis treatment. QRS complex and ST segment changes were measured using a dynamic vectorcardiographic monitoring system. The ECG parameters measured were QRS vector difference (QRS-VD) and ST vector magnitude (ST-VM6). Bioimpedance analysis was used to detect changes in the ECW. Continuous measurement of BV changes was implemented using an on-line optical reflection method based on the reflection of infrared light by erythrocyte membranes. Blood hemoglobin (B-Hb), hematocrit (B-Hcr), plasma sodium (P-Na), chloride (P-Cl), magnesium (P-Mg), potassium (P-K), ionized calcium (P-iCa), phosphate (P-Pi), creatinine (P-Crea) and urea (S-Urea) were monitored. Results: The mean QRS-VD increase during the dialysis session was almost fourfold (372 ± 300%) from 4.16 ± 2.40 to 15.60 ± 7.0 μVs (p < 0.001). This change was due to a change in amplitude, since the duration of the QRS complex did not alter significantly. The correlation between the changes in QRS-VD and body weight from the start to the end of the dialysis session was moderate and statistically significant (r = –0.55, p < 0.05). The correlation between the changes in QRS-VD and ECW varied from r = –0.67 to –0.97, being statistically significant in all patients (p < 0.001). The correlation between BV and QRS-VD was assessed at one minute intervals during the dialysis and varied from r = –0.22 to –0.98, being significant in 14 of the 15 patients (p < 0.001). Significant ST segments alterations (ST-VM6 elevation > 100 μV) did not occur during dialysis. Laboratory parameters reflecting volume and osmotic changes during hemodialysis correlated with QRS-VD change: B-Hcr (r = 0.56, p < 0.05), B-Hb (r = 0.63, p < 0.05), P-Na (r = 0.62, p < 0.05) and S-Urea (r = –0.62, p < 0.05). Conclusions: The increase in QRS complex amplitude during hemodialysis is correlated to reduced ECW. The mechanism involved is most probably augmentation of electrical resistance of the tissues around the heart caused by loss of interstitial fluid.

Streptokinase antibodies inhibit reperfusion during thrombolytic therapy with streptokinase in acute myocardial infarction.

To evaluate the influence of pretreatment IgG against streptokinase on the outcome of streptokinase treatment in acute myocardial infarction. Coronary care unit. From 88 patients admitted to the coronary care unit due to chest pain, blood samples were taken for determination of the pre-existing titre of antibodies against streptokinase. The patients were treated and monitored according to standard protocols. Fifty of the patients received thrombolytic therapy with streptokinase due to acute myocardial infarction and were monitored with continuous dynamic vectorcardiography, making possible the continuous analysis of ST- and QRS-vector changes and determination of the event of reperfusion. None of these 50 patients had been given streptokinase therapy previously. According to the vectorcardiographic criteria 21(42%) patients had signs of early (within 2 h) reperfusion after streptokinase therapy. These patients had lower pre-existing antibody titres than patients without signs of reperfusion (mean values 0.20 and 0.45 arbitrary units, P = 0.01). None of the patients with a titre higher than 0.50 arbitrary units (nine patients) had signs of early reperfusion. Of the 41 patients with a titre lower than 0.50 arbitrary units 52.5% had signs of early reperfusion. The present investigation indicates that pre-existing streptokinase antibodies play an important role in reperfusion failure during thrombolytic therapy with streptokinase in acute myocardial infarction. Therefore, the determination of streptokinase antibodies may differentiate between those patients who may benefit from streptokinase treatment and those who should be treated with some other regime.

Temporal and positional variability of the ST segment during continuous vectorcardiography monitoring in healthy subjects

Continuous vectorcardiography ST-segment monitoring (cVST) is a well-established method in the diagnosis and risk evaluation of patients with acute myocardial ischemia. Previous investigations have demonstrated that electrocardiographic ST-segment changes are to be expected, during both repeated measurements and changes in body position. We prospectively analyzed the influence of spontaneous temporal variation (technical and biological noise) and changes in body position on the ST segment (ST-vector magnitude [ST-VM]) during cVST of 21 healthy human subjects. The 95% expectancy range of the spontaneous intraindividual ST-VM variation was found to be ±8 μV for the error of measurement, and ±14 and ±24 μV during 24-hour and day-to-day cVST measurements, respectively. Positional ST-segment changes in the orthogonal leads were frequent, especially in leads X and Z, and in the left lateral position. Positional orthogonal ST-segment changes resulted in significant ST-VM changes in two of seven subjects. It is concluded that the low spontaneous temporal ST-VM variation must be considered as good reproducibility. Moreover, the present findings support currently used ST-VM ischemia criteria. However, the impact of positional changes on ST-VM seems to be of importance (with the possibility of false-positive results) and should be taken into account during cVST.

Relative contributions of a single-admission 12-lead electrocardiogram and early 24-hour continuous electrocardiographic monitoring for early risk stratification in patients with unstable coronary artery disease

Patients with unstable coronary syndromes are a heterogeneous group with varying degrees of ischemia and prognosis. The present study compares the prognostic value of a standard electrocardiogram (ECG) obtained at admission to the hospital with the information from 24-hour continuous electrocardiographic monitoring obtained immediately after admission. The admission ECGs and 24 hours of vectorcardiographic (VCG) monitoring from 308 patients admitted with unstable coronary artery disease were analyzed centrally regarding standard electrocardiographic ST-T changes, ST-vector magnitude (ST-VM), and ST change vector magnitude episodes. End points were death, acute myocardial infarction, and refractory angina pectoris within a 30-day follow-up period. ST-VM episodes (≥50 μV for ≥1 minute) during VCG monitoring was the only independent predictor of death or acute myocardial infarction by multivariate analysis. ST-VM episodes during vectorcardiography was associated with a relative risk of 12.7 for having a cardiac event, hypertension was associated with a relative risk of 1.7, and ST depression on the admission ECG was associated with a relative risk of 5.7. Patients with ST depression at admission had an event rate (death or acute myocardial infarction) of 17% at 30-day follow-up. Patients without ST depression could further be risk stratified by 24 hours of VCG monitoring into a subgroup with ST-VM episodes at similar (8%) risk and a subgroup without ST-VM episodes at low (1%) risk (p = 0.00005). Continuous VCG monitoring provides important information for evaluating patients with unstable coronary artery disease. It is recommended that patients not initially estimated at high risk based on the admission ECG are referred for 24 hours of VCG monitoring for further risk stratification.

Continuous vectorcardiographic monitoring of ischemia during coronary angioplasty in patients with bundle-branch block.

Patients with the combination of bundle-branch block and ischemic heart disease have a poor outcome. There is no established criterion for detection of transient ischemia when bundle-branch block is present. To elucidate vectorcardiographic changes during coronary angioplasty of patients with bundle-branch block. The QRS complex and ST-segment changes of 29 patients with bundle-branch block were studied during elective coronary angioplasty using continuous vectorcardiography. Data for the patients with bundle-branch block were compared with data for narrow-QRS-complex controls, matched for the vessel dilated, sex, and age. Patients with bundle-branch block were found to have more pronounced changes in the QRS-vector difference as a response to coronary occlusion than did controls. ST-vector magnitude responded in a similar way during coronary occlusion of patients with and without bundle-branch block but from different baselines. ST change-vector magnitude was found to be the most sensitive parameter for detection of ischemia in patients with bundle-branch block as well as for controls. Monitoring of transient ischemia during coronary angioplasty for patients with bundle-branch block is feasible using continuous vectorcardiography. A change in ST vector magnitude > 100 microV is suggested to indicate significant ischemia in the presence of bundle-branch block.

Ischaemia monitoring with on‐line vectorcardiography during dobutamine stress echocardiography in patients after an episode of unstable coronary artery disease

Abstract. Lundin P, Eriksson SV, Andrén B, Lindahl B, Tornvall P, Melcher A (Danderyd Hospital, Danderyd, University Hospital, Uppsala, Karolinska Hospital, Stockholm, Sweden). Ischaemia monitoring with on‐line vectorcardiography during dobutamine stress echocardiography in patients after an episode of unstable coronary artery disease. J Intern Med 1998; 244: 61–70.ObjectivesThis study investigated the ability of on‐line vectorcardiography (VCG) to detect myocardial ischaemia as assessed by dobutamine stress echocardiography after an episode of unstable coronary artery disease.DesignDobutamine stress test (incrementally infused doses of 5, 10, 20, 30 and 40 μg kg−1 per minute) was performed during simultaneous VCG monitoring. QRS vector difference (QRS‐VD), ST vector magnitude (ST‐VM), ST change vector magnitude (STC‐VM) and T change vector magnitude (TC‐VM) were monitored. A new wall motion abnormality or worsening of abnormal wall motion was regarded as indicating a positive dobutamine stress test.SubjectsFifty‐five patients with unstable angina pectoris and 16 patients with an acute non‐Q‐wave myocardial infarction were studied 5–8 days after admission.ResultsA positive dobutamine stress test was observed in 37 patients (52%). The sensitivity, specificity and total accuracy of identifying patients with a positive dobutamine stress test by VCG were: 38%, 91% and 63% for QRS‐VD; 59%, 88% and 73% for ST‐VM; 84%, 79% and 82% for STC‐VM; and 86%, 23% and 56% for TC‐VM. Patients with a positive dobutamine stress test showed higher maximum VCG values than patients with a negative dobutamine stress test (QRS‐VD, P &lt; 0.01; ST‐VM, P &lt; 0.001; STC‐VM, P &lt; 0.001). The maximum VCG values were related to the number of segments showing new or worsening wall motion abnormality (QRS‐VD: r= 0.41, P &lt; 0.001; ST‐VM: r= 0.44, P &lt; 0.001; STC‐VM: r= 0.57, P &lt; 0.001).ConclusionSTC‐VM and ST‐VM seem to be the best VCG variables for detection of myocardial ischaemia as assessed by dobutamine stress echocardiography.

Heparin Is More Effective Than Inogatran, a Low-Molecular Weight Thrombin Inhibitor in Suppressing Ischemia and Recurrent Angina in Unstable Coronary Disease

Thrombin has been suggested as one of the main pharmacologic targets in unstable coronary syndromes. Electrocardiographic signs of ischemia during continuous monitoring convey prognostic information in these patients. This study assessed the anti-ischemic and clinical effects of the novel low-molecular weight thrombin inhibitor inogatran in patients with unstable angina and non–Q-wave infarction without persistent ST-segment elevation on hospital admission. Within 24 hours of the last episode of chest pain, 324 patients were randomized to 72 hours of treatment with inogatran or heparin. Continuous ST-segment analysis with computerized vectorcardiography was used to monitor ischemia for 24 hours. The occurrence of cardiac events during the first 7 days were studied and compared with ischemic episodes during the initial 24 hours. The heparin-treated patients had less episodes of ischemia (ST vector magnitude [ST-VM]: 1 ± 2.6 vs 2 ± 4.5, p <0.001 and ST change vector magnitude [STC-VM]: 3 ± 4.7 vs 6 ± 7.6, p <0.001) than the patients receiving inogatran. This was paralleled by a lower incidence of the combined end point of death, nonfatal infarction, refractory or recurrent angina during the first 7 days for the heparin-treated patients (35%) compared with the inogatran-treated patients (50%) (p <0.05). Patients who had episodes of ischemia in spite of anti-ischemic therapy were at increased risk of all events studied. Heparin is more effective than inogatran in suppressing myocardial ischemia and clinical events at short-term follow-up. Continuous ST-segment monitoring with vectorcardiography identifies nonresponders who are at an increased level of risk.

Vectorcardiographic changes during laparoscopic cholecystectomy may mimic signs of myocardial ischaemia.

Laparoscopic surgery involves the use of intra-abdominal carbon dioxide insufflation (pneumoperitoneum). The increased intra-abdominal pressure causes marked haemodynamic changes, which may influence electrocardiographic monitoring. The aim of the present study was to elucidate the influence of pneumoperitoneum on vectorcardiographic recordings. Vectorcardiographic changes (QRS vector difference = QRS-VD, QRS loop area, QRS magnitude, ST vector magnitude, spatial ST vector change) were recorded continuously applying computerized vectorcardiography in 12 anaesthetised cardiovascularly healthy patients, scheduled for laparoscopic cholecystectomy. Measurements were made before and during pneumoperitoneum in three different body positions (supine, Trendelenburg and reversed Trendelenburg), also employing transesophageal echocardiography and invasive blood pressure monitoring. Pneumoperitoneum significantly increased QRS-VD, in parallel with an enlargement in loop area and magnitude. The magnitude was significantly increased in the transversal and frontal planes and there was a tendency to increase the magnitude in the sagittal plane. The increase in QRS-VD reached levels previously associated with the development of myocardial ischaemia in patients with coronary artery disease. The ST-variables were not changed by the pneumoperitoneum. The positional changes also influenced QRS-VD significantly. When computerized vectorcardiography is used for ischaemia monitoring during pneumoperitoneum, the ST-variables seem reliable. However, vectorcardiographic QRS-changes should be interpreted with caution, as the QRS alterations found during pneumoperitoneum mimic the changes seen during myocardial ischaemia.

Vectorcardiographic monitoring of patients with acute myocardial infarction and chronic bundle branch block.

This study was set up to describe vectorcardiographic patterns in patients with bundle-branch block and acute myocardial infarction. Sixty-five patients admitted to the coronary care unit with bundle-branch block and suspected acute myocardial infarction were monitored by dynamic vectorcardiography with trend analysis. In 28 patients, a clinical diagnosis of acute myocardial infarction was made. In patients with left bundle-branch block and acute myocardial infarction, the pattern of QRS vector-difference evolution was similar to that in patients with the narrow QRS complex, while ST vector-magnitude changes increased over time. Using a cut-off value for QRS vector-difference at 12 h of more than 20 microVs and a specific trend curve pattern, acute myocardial infarction in the presence of left bundle-branch block could be diagnosed with an accuracy of 71%. For patients with right bundle branch block, using a maximum ST vector-magnitude of > 200 microV during the first 4 h, acute myocardial infarction could be diagnosed with a 78% accuracy. Our results indicate that dynamic vectorcardiography is a valuable tool in diagnosing and monitoring acute myocardial infarction in patients with bundle branch block.

Reproducibility of on-line vectorcardiography measurements in patients with and without acute ischaemic heart disease.

The aim of the present study was to determine inter and intraobserver variations of measurements with on-line vectorcardiography (VCG). The VCG registrations were evaluated by two independent observers. One observer also evaluated the VCG registrations on two separate occasions. Monitored VCG variables were: ST vector magnitude (ST-VM), ST vector lead X (ST-X), ST change vector magnitude (STC-VM) and QRS vector difference (QRS-VD). On-line VCG was performed for 24 hours in 60 patients (10 with low probability of ischaemic heart disease, 25 with unstable angina pectoris and 25 with acute myocardial infarction). A close correlation between the two observers and small coefficients of variation were found regarding the ST-VM initial value (r = 0.99, 4.7), the ST-X maximum depression (r = 0.99, 3.2) and the QRS-VD end value (r = 0.98, 5.6). A less close correlation and higher coefficients of variation were found regarding the number of QRS-VD episodes (r = 0.94, 41.5), ST-VM episodes (r = 0.89, 37.8) and STC-VM episodes (r = 0.87, 35.1). Correlation coefficients and coefficients of variations for VCG measurements performed on two separate occasions by one observer ranged from 0.97 to 0.99 and from 18.1 to 1.8 respectively. Three (12%) of 25 patients with acute myocardial infarction did not meet the VCG infarction criterion (QRS-VD > or = 15 microVs) by both observers. In addition, five (20%) of the 25 patients with unstable angina pectoris met the VCG infarction criterion by both observers. The inter and intraobserver variation for VCG interpretations was low, but the number of QRS-VD, ST-VM and STC-VM episodes varied between the two observers. This finding suggests that additional training may improve the results. Caution is also recommended in using VCG to rule out or establish the diagnosis of acute myocardial infarction.