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The Clinical Significnce of QTc Interval Acute Myocardial Ischemia

Author: ZhangHaiBo
Tutor: ChuYingJie
School: Henan University
Course: Internal Medicine
Keywords: acute myocardial infarction non-ST-segment elevation acute coronary syndrome QTcinterval Clinical significance
CLC: R542.22
Type: Master's thesis
Year: 2012
Downloads: 47
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Abstract


Background and PurposeThe QT interval is the distance between the starting point of QRS wave and the end of the T wave inECG, representing the whole process of ventricular depolarization and repolarization. But its maincomponent is the ventricular repolarization, thus the QT interval is largely affected by the changes ofrepolarization and it is the indicator index of repolarization time. The occurrence of acute myocardialischemia affects myocardial depolarization and repolarization which can be showed in each wave orsegment in the electrocardiogram. In1927, Parkinson et al reported the phenomenon of the evolution ofacute myocardial infarction ECG. Until now, people only know the tall T waves, ST segment elevation andQ-wave formation of common ECG. The latest development is the diagnostic and therapeutic value of leftbundle branch block appeared in acute myocardial infarction. Recently, ischemic J wave has attracted greatattention. The clinical trials have showed that acute myocardial ischemia immediately leads to the prolongation of the QT interval. In2010, Yang Lei et al found that in early stage of myocardial ischemia,QTc interval changes. However, in recent years, the clinical applications of the QTc interval changes inacute myocardial ischemia is lagging behind and leading to the patients miss the best time of treatment.Besides, its diagnosis and emergency coronary reperfusion treatment measures are still inadequate, so thisarticle is to study it.Methods1. The Object of StudyExperimental group1includes170cases of acute ST-segment elevation myocardial infarction(STEMI) patients (124males and46females; the average age of54.6±10.6years) from June2008to June2011who had received treatment in hospital and underwent emergency PCI. And according to the length ofthe QTc interval after the onset of30min, experimental group1is divided into three sub-groups: theprolongation group (56cases), the shortening group (16cases) and the normal group (98cases).Experimental group2includes76cases of non-ST-segment elevation acute coronary syndrome patients (50males and26females; the average age of54.6±10.6years) from June2008to June2011who had receivedtreatment in hospital. And according to the length of the QTc interval after the onset of30min,experimental group2is also divided into three sub-groups: the prolongation group (19cases), theshortening group (4cases) and the normal group (53cases). The control group includes200cases ofhealthy persons (145males and55females; the average age of56.3±10.2years).2. Inclusion Criteria(1) The definition of QTc interval prolongation and shortening: QTc interval prolongation meansQTc>440ms; QTc interval shortening means QTc <320ms. (2) The inclusion criteria of experimental group1:①Acute STEMI diagnostic criteria follow the newdefinition of2007ESC/ACCF/AHA/WHF standards;②Acute STEMI patients have urgent PCIindications, and no relative and absolute contraindications;③Body electrocardiogram are sinus table;④Acute STEMI cases are handled according to the2007ACC/AHA acute myocardial infarction treatmentguidelines.(3) The inclusion criteria of experimental group2:①Unstable angina patients: presenting with typicalchest pain, within24hours of admission no troponin (cTnT) and myocardial enzymes (CK-MB) increasing,and with or without ischemic electrocardiographic changes;②Non-ST-segment elevation myocardialinfarction patients: presenting the occurrence of cTnT>0.4ng/L, or CK-MB>25mmol/L within24hoursof admission, but no occurrence of ST-segment elevation.3. Outcome Measures(1) Experimental group1:①the emerging time of QTc interval prolongation and shortening and theduration of reperfusion before and after treatment;②the peak concentration of serum creatine kinase(CK-MB);③myocardial infarction position and the culprit artery;④hospital cardiac functional class(Killip class);⑤the incidence of arrhythmia;⑥hospital mortality.(2) Experimental group2:①the incidence of QTc interval prolongation and shortening at the momentof chest pain;②patients’ cardiac functional class (NYHA functional class) within six months afterdischarging from hospital, the cardiogenic death, and the incidence of revascularization and acutemyocardial infarction. 4. Research MethodsAdopting Cardico1210ECG machine at paper speed of25mm/s synchronous traces12lead ECG,measuring the infarct-related QT interval and RR interval of each ECG by assigned person. QT interval isfrom the starting point of QRS wave to the end of T wave.Using formula (QTc=QT/RR1/2) proposed byBazett in1920calculates the corrected QT interval (QTc).5. Statistical MethodsUse SPSS17.0statistical software, indicating measurement data with X±s. Use t-test or rank sumT-test to test the comparison between the two groups. Use the X2test to test enumeration data, and p <0.05is considered statistically significant.Results(1) Experimental group1: Compared with the control group, QTc interval prolongation and QTcinterval shortening of patients in experimental group1has high incidence, and the difference is statisticallysignificant (p <0.05). After operation1h, QTc interval of the shortening group and the normal group isprolonged compared with preoperation, and the difference is statistically significant (p <0.05); comparingafter operation1h with postoperation24h of the normal group, the QTc interval is prolonged, and thedifference is statistically significance (p <0.05). Comparing the prolongation group with the normal group,the prolongation group often occurres anterior and (or) high lateral infarction, and the culprit vessel ismostly the left anterior descending artery, the difference is statistically significant (p <0.05); theprolongation group and the shortening group have a high rate of serious pump failure, the comparisionswith the normal group are statistically significant (p <0.05); comparing the shortening group with thenormal group, the incidence of arrhythmia in the shortening group has significantly increased, and thedifference is statistically significant (p <0.05). (2) Experimental group2: comparing with the normal group, QTc prolongation and QTc shorteningpatients with angina have high incidence of doing recurrent revascularization and reoccurring acutemyocardial infarction, and comparisons are statistically significant (p <0.05).Conclusion(1) QTc interval prolongation or shortening is a new predictor of adverse cardiovascular events ofacute ST-segment elevation myocardial infarction patients, and can help determine the myocardialinfarction position, the culprit artery and the occurence of arrhythmias and has certain guiding significancefor the assessment of patients’ prognosis.(2) QTc interval prolongation or shortening is a new predictor of short term adverse cardiovascularevents of the non-ST-segment elevation acute coronary syndrome patients and an important prognosticfactor for adult cardiovascular accidents.

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CLC: > Medicine, health > Internal Medicine > Heart, blood vessels ( circulatory ) disease > Heart disease > Myocardial diseases > Myocardial infarction
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