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Detection of myocardial ischemia: clinical and experimental studies with focus on vectorcardiography, heart rate and perioperative conditions.
Umeå University, Faculty of Medicine, Surgical and Perioperative Sciences, Anesthesiology and Intensive Care.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Introduction. Multiple clinical methods for detecting myocardial ischemia are utilised in the hospital setting each day, but there is uncertainty about their diagnostic accuracy. In the operating room, multiple methods may be employed, while in the CCU advanced electrophysiological (ECG) techniques for myocardial ischemia detection, and in particular, ST segment analysis, are common. Vectorcardiography (VCG) is one form of ECG.

Several conditions other than ischemia may cause marked ST changes, which can impair the process of diagnosis of clinical ischemia. Elevated HR is one of these factors, which is studied here. The hypotheses were about concordance of different methods to detect ischemia, and relation of ECG ST levels to HR with and without myocardial ischemia.

Methods. Study I. Anesthetised vascular surgical patients with coronary artery disease were studied during the start of anesthesia and surgery: ECG, hemodynamic, mechanical, and metabolic parameters were measured and categorised as positive or negative with reference to a specific definition of myocardial ischemia. Study II. Awake patients with no ischemic heart disease were paced in graded steps, and VCG ST analyses were performed.

Study III. Anesthetised pigs were studied for local metabolic and VCG ST changes related to controlled HR levels and transient coronary occlusion. Study IV. Thirty five anesthetised coronary artery disease (CAD) patients and ten non-CAD patients were paced at controlled levels, and great coronary artery vein (GCV) lactate measurement was used to determine presence or absence of myocardial ischemia. The CAD patients were paced up to HR levels where myocardial ischemia could be confirmed. The relation of HR-related VCG ST levels to presence or absence of ischemia was analysed. In Studies II,, III, and IV the ST vector magnitude (ST-VM), the change from baseline in ST-VM (STC-VM), and the vector angle change from baseline (STC-VA) were analysed for each step.

Results. Study I. Poor concordance was demonstrated for positive events (presumed myocardial ischemia) between the hemodynamic, ECG, mechanical, and metabolic detection methods. Study II. STC-VM but not ST-VM levels demonstrated HR-related increases in the presumed absence of myocardial ischemia in 18 awake subjects. J point time to ST measurement did not affect the response of VCG ST to HR. Study III. STC-VM levels showed HR-related increases in the absence of ischemia (tested by local metabolic observations). VCG ST parameters responded positively to transient regional ischemia. Study IV. CAD patients, which demonstrated a clear pattern of onset and progress of ischemia during pacing, were further analysed for the relation of VCG ST level to ischemia. Sensitivity and specificity of STC-VM levels were described by ROC analysis for a range of STC-VM levels.

Conclusions. Concordance of different measures for detection of onset of myocardial ischemia is difficult to assess in the absence of a very reliable reference method. The contribution of HR and ischemia to VCG ST levels were estimated in study subjects. HR-related increases in STC-VM occur in the absence of ischemia. HR levels need to be considered when interpreting STC-VM as a diagnostic test for ischemia. Further study is needed to establish criteria that take into account multiple clinical factors in order to improve the predictive value of our tests for myocardial ischemia.

Place, publisher, year, edition, pages
Umeå: Kirurgisk och perioperativ vetenskap , 2005. , 69 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 982
Keyword [en]
Anaesthesiology and intensive care, myocardial ischemia, pacing, vectorcardiography, electrocardiography, heart rate, myocardial lactate
Keyword [sv]
Anestesiologi och intensivvård
National Category
Anesthesiology and Intensive Care
Research subject
Cardiology
Identifiers
URN: urn:nbn:se:umu:diva-598ISBN: 91-7305-942-0 (print)OAI: oai:DiVA.org:umu-598DiVA: diva2:143919
Public defence
2005-10-15, Hörsal BETULA, 6M, NUS, Norrlands Universitetssjukhus, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2005-09-23 Created: 2005-09-23 Last updated: 2009-11-16Bibliographically approved
List of papers
1. Comparison of hemodynamic, electrocardigraphic, mechanical, and metabolic indicators of intraoperative myocardial ischemia in vascular surgical patients with coronary artery disease.
Open this publication in new window or tab >>Comparison of hemodynamic, electrocardigraphic, mechanical, and metabolic indicators of intraoperative myocardial ischemia in vascular surgical patients with coronary artery disease.
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1989 (English)In: Anesthesiology, ISSN 0003-3022, E-ISSN 1528-1175, Vol. 70, no 1, 19-25 p.Article in journal (Refereed) Published
Abstract [en]

To compare mechanical, electrocardiographic, and metabolic indices of myocardial ischemia, the cardiokymogram (CKG), the V5 ECG, left anterior descending coronary artery territory lactate extraction, and pulmonary capillary wedge pressure (PCWP) were measured in 53 vascular surgical patients with coronary artery disease. Measurements were performed preoperatively and at four specific intraanesthetic intervals: after tracheal intubation, before surgery, and 10 and 30 min after incision. Measurements and sampling sequence took 5-7 min, and therapy for the probable cause of ischemia was instituted following completion of this sequence. Myocardial ischemia was defined as type II or III CKG, 0.1 mV or greater horizontal or downsloping depression of V5 ECG ST segment, 0.2 mV or greater elevation of V5 ECG ST segment, or myocardial lactate production. Thirty-nine patients (74%) had a total of 89 episodes of myocardial ischemia. Seventy-four episodes (83%) were detected by the CKG, 31 (44%) were evident on the ECG, and 13 (15%) by evidence of lactate production. The concordance among the indices of myocardial ischemia was poor. Patients with an abnormal preoperative ECG experienced a greater number of ischemic episodes (P less than 0.001). Elevation of PCWP or the presence of A-C or V-waves greater than 5 mmHg above the mean did not individually reflect ischemia reliably. Intraoperative myocardial ischemia is common in vascular surgical patients and is most sensitively detected by ventricular wall motion abnormality.

Identifiers
urn:nbn:se:umu:diva-4702 (URN)2912311 (PubMedID)
Available from: 2005-09-23 Created: 2005-09-23 Last updated: 2017-12-14Bibliographically approved
2. ST-segment deviations during pacing-induced increased heart rate in patients without coronary artery disease.
Open this publication in new window or tab >>ST-segment deviations during pacing-induced increased heart rate in patients without coronary artery disease.
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2005 (English)In: Clinical Physiology and Functional Imaging, ISSN 1475-0961, E-ISSN 1475-097X, Vol. 25, no 4, 246-522 p.Article in journal (Refereed) Published
Abstract [en]

INTRODUCTION: In order to interpret ST-segment changes as an indicator of ischemia in patients with higher heart rates (HRs), the relation between ST-segment levels and HR needs to be well defined in subjects without coronary artery disease. METHODS: Eighteen patients with normal ECGs in the catheterization laboratory, after radiofrequency ablation of AV nodal re-entry tachycardia or an accessory pathway were included. Computerized online vectorcardiography (VCG) was performed during step-wise atrial pacing-induced increases in HR up to 150 beats min(-1) (bpm). The ST-vector magnitude (ST-VM) and the relative ST change vector magnitude (STC-VM) were analysed at the J point, J + 20 and J + 60 ms. RESULTS: There was no divergence in the course of ST-VM or STC-VM based on J point + 0, 20, or 60 ms during increasing HR. The STC-VM mean values increased progressively during increases in HR above 100 bpm, with an average increase in STC-VM of 15-20 microV per 10 bpm increases in HR. The ST-VM response during HR increases showed a heterogeneous and unpredictable pattern. CONCLUSION: The STC-VM increases linearly with rising HRs above 100 bpm. The STC-VM can exceed widely recognized ischemic thresholds during higher HRs in the absence of ischemia. The choice of J point time to ST-VM measurements as tested here is not important for the STC-VM relation to HR at these HR levels. Further clinical testing is needed to improve the diagnostic specificity of STC-VM measurements during increased HRs.

Keyword
Adult, Arrhythmias; Cardiac/*diagnosis/*physiopathology/therapy, Cardiac Pacing; Artificial/*methods, Coronary Disease/diagnosis/physiopathology/therapy, Female, Heart Rate, Humans, Male, Middle Aged, Statistics as Topic, Vectorcardiography/*methods
Identifiers
urn:nbn:se:umu:diva-6814 (URN)10.1111/j.1475-097X.2005.00613.x (DOI)15972028 (PubMedID)
Available from: 2007-12-18 Created: 2007-12-18 Last updated: 2017-12-14Bibliographically approved
3. Vectorcardiographic ST deviations related to increased heart rate in the absence of ischemia in an experimental pig model.
Open this publication in new window or tab >>Vectorcardiographic ST deviations related to increased heart rate in the absence of ischemia in an experimental pig model.
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2006 (English)In: Journal of Electrocardiology, ISSN 0022-0736, E-ISSN 1532-8430, Vol. 39, no 2, 169-176 p.Article in journal (Refereed) Published
Abstract [en]

The electrocardiographic ST segment may change when heart rate (HR) increases. We aimed to analyze vectorcardiographic ST relation and myocardial conditions during controlled HR increases in anesthetized pigs. The relative parameters ST change vector magnitude and ST change vector angle were calculated at paced HRs ranging from 85 to 175 beats per minute. ST change vector magnitude increased from baseline 6.3 +/- 1.3 to 26.0 +/- 3.1 microV (P < .01; range, 4-50 microV) at HR 175 beats per minute with similar changes in ST change vector angle, whereas the absolute parameter ST vector magnitude demonstrated a heterogeneous pattern without any systematic relation to HR changes. Microdialysis results from left ventricular wall, with analysis of glucose, lactate, and pyruvate, showed no sign of ischemia during pacing. Potassium concentrations did not change during pacing. We conclude that significant HR-related ST vector changes can occur in the absence of myocardial ischemia.

Keyword
Animals, Cardiac Pacing; Artificial, Female, Heart Rate/physiology, Myocardial Ischemia/*physiopathology, Swine, Tachycardia/physiopathology, Vectorcardiography
Identifiers
urn:nbn:se:umu:diva-15346 (URN)10.1016/j.jelectrocard.2005.08.014 (DOI)16580414 (PubMedID)
Available from: 2007-12-18 Created: 2007-12-18 Last updated: 2017-12-14Bibliographically approved
4. Contributions of myocardial ischemia and heart rate to ST segment changes in patients with or without coronary artery disease.
Open this publication in new window or tab >>Contributions of myocardial ischemia and heart rate to ST segment changes in patients with or without coronary artery disease.
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2008 (English)In: Acta Anaesthesiologica Scandinavica, ISSN 0001-5172, E-ISSN 1399-6576, Vol. 52, no 2, 219-228 p.Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: ST changes related to ischemia at different heart rates (HRs) have not been well described. We aimed to analyze ST dynamic changes by vectorcardiography (VCG) during pacing-induced HR changes for subjects with proven coronary artery disease (CAD) and without (non-CAD). METHODS: Symptomatic CAD patients scheduled for elective surgery were enrolled along with a non-CAD group. During anesthesia, both groups were placed at multiple ascending levels. VCG ST data, and in particular in ST change vector magnitude (STC-VM) from baseline, along with arterial and great coronary artery vein (GCV) blood samples were collected to determine regional myocardial lactate production. RESULTS: A total of 35 CAD and 10 non-CAD patients were studied over six incremental 10 beat/min HR increases. STC-VM mean levels increased in the CAD group from 9+/-5 to 131+/-37 microV (standard deviation) compared with non-CAD subjects with 8+/-3-76+/-34 microV. Myocardial ischemia (lactate production) was noted at higher HRs and the positive predictive value for STC-VM to detect ischemia was 58% with the negative predictive value being 88%. STC-VM at 54 microV showed a sensitivity of 88% and a specificity of 75% for identification of ischemia. CONCLUSIONS: Both HR and ischemia at higher HRs contribute to VCG ST elevation. Established ST ischemia detection concerning HR levels is suboptimal, and further attention to the effects of HR on ST segments is needed to improve electrocardiographic ischemia criteria.

Identifiers
urn:nbn:se:umu:diva-8755 (URN)10.1111/j.1399-6576.2007.01507.x (DOI)17999710 (PubMedID)
Available from: 2008-02-08 Created: 2008-02-08 Last updated: 2017-12-14Bibliographically approved

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