Interobserver Reproducibility of QT Interval Measurement and QT Dispersion in Patients After Acute Myocardial Infarction

Background: The study evaluated interobserver differences in the classification of the T-U wave repolarization pattern, and their influence on the numerical values of manual measurements of QT interval duration and dispersion in standard predischarge 12-lead ECGs recorded in survivors after acute myocardial infarction. Methods: Thirty ECGs recorded at 25 mm/s were measured by six independent observers. The observers used an adopted scheme to classify the repolarization pattern into 1 of 7 categories, based on the appearance of the T wave, and/or the presence of the U wave, and the various extent of fusion between these. In each lead with measurable QRST(U) pattern, the RR, QJ, QT-end, QT-nadir (i.e., interval between Q onset and the nadir or transition between T and U wave) and QU interval were measured, when applicable. Based on these measurements, the mean RR interval, the maximum, minimum, and mean QJ interval, QT-end and/or QT-nadir interval, and QU interval, the difference between the maximum and minimum QT interval (QT dispersion [QTD]), and the coefficient of variation of QT intervals was derived for each recording. The agreement of an individual observer with other observers in the selection of a given repolarization pattern were investigated by an agreement index, and the general reproducibility of repolarization pattern classification was evaluated by the reproducibility index. The interobserver agreement of numerical measurements was assessed by relative errors. To assess the general interobserver reproducibility of a given numerical measurement, the coefficient of variance of the values provided by all observers was computed for each ECG. Statistical comparison of these coefficients was performed using a standard sign test. Results: The results demonstrated the existence of remarkable differences in the selection of classification patterns of repolarization among the observers. More importantly, these differences were mainly related to the presence of more complex patterns of repolarization and contributed to poor interobserver reproducibility of QTD parameters in all 12 leads and in the precordial leads (relative error of 31%–35% and 34%–43%, respectively) as compared with the interobserver reproducibility of both QT and QU interval duration measurements (relative error of 3%–6%, P < 0.01). This observation was not explained by differences in the numerical order between QT interval duration and QTD, as the reproducibility of the QJ interval (i.e., interval of the same numerical order as QTD was significantly better (relative error of 7.5%–13%, P < 0.01) than that of QTD. Conclusions: Poor interobserver reproducibility of QT dispersion related to the presence of complex repolarization patterns may explain, to some extent, a spectrum of QT dispersion values reported in different clinical studies and may limit the clinical utility in this parameter.     

Comparison of QT/RR Relationship Using Two Algorithms of QT Interval Analysis for Identification of High Risk Patients for Life-Threatening Ventricular Arrhythmias

Objective: The purpose of this study was to evaluate the dynamic relationship between QT and RR intervals considering either the QTe interval (i.e., time between the onset of QRS and the end of the T wave) or the QTa interval (i.e., time between the onset of QRS and the apex of the T wave) from 30-second modules. Method: The Holter recordings in three groups of adult subjects (30 patients with malignant ventricular tachyarrhythmias [VT/VF patients], 40 patients with coronary artery disease [CAD], and 44 normal subjects) were analyzed using the ELATEC System. Results: In normal subjects the correlation coefficient between QTa and RR (QTa/RR) was significantly higher (0.87 ± 0.12) than those between QTe and RR (QTe/RR) (0.79 ± 0.17). In the other groups there was no significant difference between QTa/RR and QTe/RR: QTa/RR (CAD: 0.71 ± 0.3; VT/VF: 0.73 ± 0.19); and QTe/RR (CAD: 0.63 ± 0.33; VT/VF: 0.69 ± 0.21). The slope of QTe/ RR over 24 hours was significantly larger in VT/VF patients (0.23 ± 0.11) than in the other groups (control: 0.18 ± 0.08; CAD: 0.17 ± 0.1). Measuring the QTa/RR relation there was no difference between the three groups (VT/VF: 0.19 ± 0.09; CAD: 0.15 ± 0.09; normal: 0.19 ± 0.06). Conclusion: QTe/RR as well as QTa/RR analyses are methods of detecting a deranged rate dependence of QT intervals in high risk patients. An increased QTe/RR slope indicates a higher risk of life-threatening ventricular arrhythmias. Because there was no difference in QTa/RR we conclude that the end of the T wave gives important information about disorders in repolarization.     

QT Interval and the Risk of Myocardial Infarction and All-Cause Death: A Cohort Study

QT Interval and the Risk of Myocardial Infarction and All‐Cause Death . Introduction: The relationship between QT interval and cardiovascular disease is controversial. Methods: All male residents aged 20–61 years and female residents aged 20–56 years were invited to the Tromsø Study in 1986–1987. A total of 15,558 participants free of heart disease were prospectively followed over 20 years for myocardial infarction and death. QT interval at baseline was measured on lead I of the electrocardiogram. Hazard ratios (HRs) with 95% confidence intervals (CIs) per standard deviation change in QT interval were calculated using a Cox regression model. Results: We identified 756 cases of myocardial infarction and 1,183 all‐cause deaths. Prolonged QT interval was present in 792 (5%) participants. QT interval was not associated with increased risk of myocardial infarction (HR: 0.95, 95% CI: 0.84–1.07, after adjustment for potential confounders). Heart‐rate‐corrected QT interval was a significant predictor for all‐cause death in men (HR: 1.15, 95% CI: 1.03–1.29), but not in women (HR: 1.04, 95% CI: 0.91–1.18), after adjustment for potential confounders. Conclusions: The findings suggest that the previously observed relationship between QT interval and increased risk of cardiovascular death is not mediated by increased risk of myocardial infarction. The clinical utility of the QT interval to identify individuals at high risk for coronary events is limited in a general population without prior heart disease. (J Cardiovasc Electrophysiol, Vol. 23, pp. 846‐852, August 2012)     

Diagnostic performance of QT interval variables from 24-h electrocardiography in the long QT syndrome

Aims The long QT syndrome is mainly defined by QT interval prolongation(QTc >0·44s). However, data obtained in genotyped patientsshowed that resting QTc measurement alone may be inaccuratefor ascertaining the phenotype. The aim of this study was toevaluate the diagnostic performance of QT interval rate-dependencein untreated chromosome 11-linked patients. Methods The study population consisted of 25 untreated longQT patients linked to chromosome 11 and 25 age- and gender-matchedcontrols. QTc intervals were measured on 12-lead resting ECGrecordings. From 24-h Holter recordings, the slope of the relationshipbetween ventricular repolarization and heart rate was studiedseparately day and night to assess neural modulation. Mean heartrates and rate-dependences of QT and Q-maximum of T (QTm) intervalswere compared between long QT patients and controls for bothtime periods. Results In both groups, the rate-dependences were modulatedby day–night influences. When compared to controls, longQT patients showed a significant increase at night in QT/RRslopes (0·158±0·05 vs 0·117±0·03,P=0·002)and QTm/RR slopes (0·163±0·05 vs 0·116±0·04,P=0·0006).Multivariate analysis, adjusting QTc interval on age and gender,discriminated between long QT patients and controls with a 76%sensitivity and a 84% specificity. A 96% sensitivity and a 96%specificity were reached by taking into account the QTm/RR slopeat night, the QTc interval and the mean heart rate during theday. Conclusion QT interval variables obtained from 24-h ECG recordingsimprove long QT syndrome diagnosis by showing an increased nocturnalventricular repolarization rate-dependence in genotyped chromosome11-linked patients.     

A Study of the Association between the Prolongation of the QT Interval in the Resting ECG and Myocardial Infarction

ABSTRACT The relationship between the incidence of myocardial infarction in the 10 year follow-up period and the length of the QT interval and its two components (the time elapsing between the Q wave and the beginning of the T wave, and the duration of the T wave) was investigated in a study of the records of a group of men drawn from a random sample of all 55-year-old men living in Göteborg, Sweden. A significant association was found between the incidence of myocardial infarction and the first component but not with the second component or the QT interval itself. The two components were found to be independent and thus to have the potential to act as confounding factors if the QT interval is examined alone. Further, our results suggest that correcting the QT interval for heart rate needs careful reassessment.     

QT Dispersion as a Noninvasive Arrhythmiogenic Marker in Acute Myocardial Infarction

Backround: Prolongation of QT dispersion (QTD), defined as the difference between maximum and minimum QT intervals on surface ECG, has been proposed as a noninvasive arrythmogenic marker. The aim of this study was to estimate the value of QTD in identifing patients susceptible to ventricular fibrillation or ventricular tachycardia (VF/VT) after an acute myocardial infarction (AMI) and to evaluate the behavior of QTD in relation to the thrombolytic therapy. Methods: We studied 108 consecutive patients with AMI. All patients had a 12-lead surface ECG recorded upon admission and a second ECG 24 hours later. QT interval was measured from the onset of Q to the end of T in each of 12 standard ECG leads. QTD was the difference between the longest and shortest values of QT. All QTD measurements were corrected for heart rate (QTcD) using QTc values according to Bazzet formula. Results: Fifteen patients (13.8%) developed VF/VT in the first week after AMI (group 1A) and 93 patients (86.2%) did not have VF/NT (group 1B). QTD and QTcD values were significantly greater in group 1A in comparison to group 1B on admission and 24 hours later. Sixty-five patients (60%) received intravenous thrombolysis in the acute phase of AMI (group 2A) and 43 patients (40%) did not (group 2B). No significant difference in QTD and QTcD was observed in the first ECG on admission between the two groups. Conversely, QTD and QTcD were lower in group 2A patients in the second ECG 24 hours after admission. Conclusions: These results provide evidence that increased values of QTD are correlated well with occurrence of malignant ventricular arrhythmias after acute myocardial infarction while lower values associated with the thrombolytic therapy. A.N.E. 1999;4(1):35–38     

QT Interval in Patients with Unstable Angina and Non‐Q Wave Myocardial Infarction

Background: Non‐Q wave mvocardial infarction (NQMI) and unstable angina (UAP) have similar clinical presentations and similar ST‐T changes on the electrocardiogram. The purpose of this study was to assess whether changes in QT interval might help differentiating between these entities. Methods: The QT intervals of 52 patients hospitalized with NQMI were compared to those of 52 patients hospitalized for UAP. All patients had repeated ECG for at least 4 days. Results: Maximal QTc in patients with NQMI was significantly longer than in patients with UAP (475 vs 439 ms, P < 0.0001). QTc on the admission ECG was 450 ms in patients with NQMI compared to 417 ms in UAP P < 0.005). QTc > 460 ms was present in 48% patients with NQMI and in 19% of UAP patients. Maximal QT prolongation was observed within 36 hours of admission with return to normal within 96 hours. QT dispersion was within normal range, being longer in patients with NQMI than patients with UAP (55 vs 43 ms, P < 0.003). QT prolongation was not associated with increased frequency of arrhythmia. The cause of QT prolongation in NQMI may be related to the damage of subendocardial layer exposing the M cells layer which markedly prolong action potential duration. Conclusion: Transient QT prolongation is observed in about half of patients with NQMI. These ECG changes may help differentiating between patients with NQMI and UAP already on admission. A.N.E. 2002;7(4):343–348     

Impact of Left Ventricular Remodeling on Ventricular Repolarization and Heart Rate Variability in Patients after Myocardial Infarction Treated with Primary PCI: Prospective 6 Months Follow‐up

Background: The relation between postinfarction left ventricle remodeling (LVR), autonomic nervous system and repolarization process is unclear. Purpose of the study was to assess the influence of LVR on the early (QTpeak) and late (TpeakTend) repolarization periods in patients after myocardial infarction (MI) treated with primary PCI. The day‐to‐night differences of repolarization parameters and the relation between QT and heart rate variability (HRV) indices, as well left ventricle function were also assessed. Methods: The study cohort of 104 pts was examined 6 months after acute MI. HRV and QT indices (corrected to the heart rate) were obtained from the entire 24‐hour Holter recording, daytime and nighttime periods. Results: LVR was found in 33 patients (31.7%). The study groups (LVR+ vs LVR?) did not differ in age, the extent of coronary artery lesions and treatment. Left ventricle ejection fraction (LVEF) was lower (38%± 11% vs 55%± 11%, P < 0.001), both QTc (443 ± 26 ms vs 420 ± 20 ms, P < 0.001) and TpeakTendc (98 ± 11 ms vs 84 ± 12 ms, P < 0.005) were longer in LVR + patients, with no differences for QTpeakc. Trends toward lower values of time‐domain (SDRR, rMSSD) HRV parameters were found in LVR+ pts. Day‐to‐night difference was observed only for SDRR, more marked in LVR‐group. Remarkable relations between delta LVEF (6 months minus baseline), delta LVEDV and TpeakTendc were found, with no such relationships for QTpeakc. Conclusions: The patients with LVR have longer repolarization time, especially the late phase‐ TpeakTend, which represents transmural dispersion of repolarization. Its prolongation seems to be related to local attributes of myocardium and global function of the left ventricle but unrelated to the autonomic nervous influences. Remodeling with moderate LV systolic dysfunction is associated with insignificant decrease in HRV indices and preserved circadian variability.     

Correlation Between Beat‐to‐Beat QT Interval Variability and Impaired Left Ventricular Function in Patients with Previous Myocardial Infarction

Background: Beat‐to‐beat QT interval variability (QTV) is associated with sudden cardiac death and New York Heat Association functional class severity. We sought to evaluate the relationship between QTV and left ventricular (LV) function in patients with previous myocardial infarction (MI). Methods: Fifty‐nine patients with previous anterior MI were enrolled. LV ejection fraction (EF), LV end‐systolic volume index (LVESVI), and LV end‐diastolic volume index (LVEDVI) were measured by LV contrast angiography. QT interval was measured by automated analysis of 512‐beat records of 12‐lead electrocardiogram. The mean interval, standard deviation and variance in RR and QT intervals, and the QT variability index (QTVI) were calculated for each patient using two leads that corresponded with and without the infarction site. High‐frequency power, low‐frequency power, total‐frequency power, and the ratio of low‐frequency to high‐frequency power in RR and QT intervals were calculated. Results: While measured indices of RR intervals and indices of QT intervals, which did not correspond with the infarction site, did not correlate with differences in LV function, measured indices of QT intervals, which corresponded with the infarction site, did correlate with differences in LV function. However, there were no correlations between the ratio of low‐frequency to high‐frequency power in QT intervals and EF or LVEDVI. Correlations between QTVI and LV function were observed, particularly between QTVI and LVESVI (r = 0.712, P < 0.0001). Conclusion: In patients with previous anterior MI, there was variability in temporal dispersion of QT interval and a strong correlation between QTV corresponded with the infarcted site and LV function.     

Reproducibility of Computerized Measurements of QT Interval from Multiple Leads at Rest and During Exercise

Background: Accurate measurement of the QT interval is important for diagnosing long QT syndrome (LQTS), and in research on determinants of ventricular repolarization time. We tested automatic analysis of QT intervals from multiple ECG leads on chest. Methods: Eleven healthy volunteers and 10 genotyped LQTS patients were tested at rest and during exercise with a bicycle ergometer twice 1–31 months apart. Electrocardiograms were recorded with the body surface potential mapping system, and 12 precordial channels were selected for analysis. Averaged QT peak and QT end intervals were determined with an automated algorithm, and the difference QT end minus QT peak (Tp‐e) was calculated. Repeatability was assessed by coefficient of variation (CV) between measurements. Results: Within one test at rest the QT end intervals were highly repeatable with CV 0.6%. In repeated tests CV was 4.4% for QT end interval and 3.5% when the QT interval was corrected for heart rate. In exercise test at specified heart rates, mean CV was 3.0% for QT end and 2.9% for QT peak interval. The CV of Tp‐e interval was 10.2% at rest, and 9.3% in exercise test. Reproducibility was comparable between healthy subjects and LQTS patients. Conclusions: The BSPM system with automated analysis produced accurate and highly repeatable QT interval measurements. Reproducibility was adequate also over prolonged time periods both at rest and in exercise stress test. The method can be applied in studying duration of ventricular repolarization time in different physiologic and pharmacologic interventions.     

Evaluation of QT Interval Dispersion in a Multiple Electrodes Recording System versus 12‐Lead Standard ECG in an In Vitro Model

Background: QT interval dispersion (QTID) as assessed on conventional surface electrocardiogram (ECG) has been used as a clinical tool to identify patients at high risk of ventricular arrhythmia. However, the results obtained have been controversial. The main purpose of this study was to compare QTID measured from an array of 5 × 6 electrodes homogeneously distributed against the values found when the 12‐lead standard ECG was used. Methods: QTID was calculated in a modified Langendorff‐perfused rabbit heart model immersed in a cylindrical chamber. Dispersion in ventricular repolarization was artificially increased by d‐sotalol (60 μ;m) perfusion. Results: All the duration variables measured from any of the lead systems used were significantly increased after d‐sotalol perfusion. The most commonly used variables in clinical studies, such as QTID (maximum ‐ minimum), do not reach a level of statistical significance, except when measured from the 30‐electrodes array or 15 electrodes covering the left or right side of the heart. The standard deviation of the QT interval (QTI) hardly reached a significant level (P = 0.0499) when calculated from the 12‐lead standard ECG. QTID measured at the peak of the T wave exhibited the highest level of significance when calculated from any of the lead systems used. Conclusion: Thirty electrodes homogeneously distributed on the body surface can better discriminate changes in heterogeneity of repolarization. These data further support the importance of multiple recording systems for the evaluation of QTID and may help to provide an understanding of the discrepancies found in clinical applications.     

QT Dynamics from Holter Recordings: A Comparison of Two Averaging Methods

Background: QT dynamics is the adaptation of repolarization duration on heart rate. There are several automatic computer algorithms for Holter analysis to describe this process. Our study was performed to compare results of two averaging algorithms inherent in an automatic Holter QT module. Methods: Two different methods of the automatic QT module of the ELATEC system were applied to digitized Holter ECGs of 50 healthy men. The first method, “QT/RR,” calculates the linear regression up to 2880 mean QT intervals (values over 30 s) and corresponding RR intervals containing the preceding 60 seconds of the QT value and the 30 seconds while QT averaging. The second method, “QT/RR class,” correlates the averaged QT duration over the corresponding 25-ms RR interval classes. Possible differences in rate adaptive behavior between two portions of QT duration were of further interest. Results: The main result of the study was that the linear regression obtained by the “QT/RR” method was slightly, but significantly, steeper than those obtained by the “QT/RR class” method. Conclusion: Rate adaptation of QTe and QTa is the same if measured by one particular method. Studying the same population using different averaging methods leads to different results. In contrast to the “QT/RR” method, “QT/RR class” method leads to an overestimation of extreme and rare RR values. Therefore, results of “QT/RR class” method cannot be used as a surrogate for “QT/RR” methods.     

Circadian Pattern of QT/RR Adaptation in Patients with and Without Sudden Cardiac Death after Myocardial Infarction

Background: Abnormalities in the adaptation of the QT interval to changes in the RR interval may facilitate the development of ventricular arrhythmias. Methods: This study sought to evaluate the dynamic relation between the QT and RR intervals in patients after acute myocardial infarction. The study population consisted of 14 patients after myocardial infarction (age 60 ± 7 years, 12 men) who died suddenly (SCD victims) within 1 year after the myocardial infarction and 14 pair-matched age, sex, left ventricular ejection fraction, infarct site, thrombolytic therapy) patients who remained event-free after myocardial infarction (Ml survivors) for at least 3 years. Fourteen normal subjects were studied as controls (age 55 ± 9 years, 11 men). QT and RR intervals were measured on a beat-to-beat basis automatically with a visual control from 24-hour ambulatory ECGs using Reynolds Pathfinder 700. Mean hourly values of the QT/RR slope (QT =α+βRR) and corrected QT interval at 1000 ms of RR interval (QT_1s) were derived for each subject using an inhouse program (QT_1s=α+1000β). The dynamics of the QT/RR slope and QT_1s were assessed on the basis of hourly mean values. The circadian rhythm of ventricular repolarization (QT_1s and QT/RR slope) was examined by harmonic regression analysis. Results: There was a trend towards a significant difference in 24-hour mean value of QT_1s between study groups (408 ± 26 ms vs 381 ± 43 ms and 386 ± 22 ms, P = 0.06), and a significant difference was found between SCD victims and normal subjects (408 ± 26 vs 386 ± 22 ms, P = 0.02). The QT_1s differed significantly between study groups (P = 0.038) only during the day time (09:00–19:00 hour), when QT_1s was significantly longer in SCD victims than in normal subjects (409 ± 33 vs 380 ± 27 ms, P = 0.02) and tended to be longer than in Ml survivors (409 ± 33 vs 379 ± 42 ms, P = 0.08). The 24-hour mean value of QT/RR slope was significantly different between study groups (P = 0.04), with a significantly steeper slope in SCD victims than in normal subjects (0.15 ± 0.07 vs 0.09 ± 0.02, P = 0.008). During day time, the QT/RR slope differed significantly between study groups (P = 0.04), while the difference was less marked at night (P = 0.08). The slope was significantly steeper in SCD victims than in normal subjects during both day and night (P < 0.05). A marked circadian variation of QT_1s was observed in normal subjects, which was blunted in Ml survivors and SCD victims. Conclusions: Abnormal repolarization behaviors, characterized by longer QT_1s and impaired adaptation of QT to variations in RR intervals, were found in SCD victims. Hence, lethal ventricular tachyarrhythmias might be provoked by the altered repolarization dynamics in patients after myocardial infarction. A.N.E. 1999;4(3):286–294     

QT/RR Relationship in Patients after Remote Anterior Myocardial Infarction with Left Ventricular Dysfunction and Different Types of Ventricular Arrhythmias

Background: QT/RR relationship was found to be both rate‐dependent and rate‐independent, what suggests the influence of autonomic drive and other not‐autonomic related factors on it. The steeper QT/RR slope in patients after acute myocardial infarction (MI) was described, but the relationship to ventricular arrhythmias is unknown. The purpose of this study was to calculate differences in QT/RR relationship in patients after remote anterior MI with left ventricular dysfunction and different types of ventricular arrhythmias. Methods: The cohort of 95 patients (age: 63 ± 11 years, LVEF: 35 ± 9%) with previous anterior MI (mean 1.1 years) was divided into two well‐matched groups—50 patients without episodes of ventricular tachycardia (VT) or ventricular fibrillation (VF) (NoVT/VF: 39 males, 64 ± 12 years, LVEF 37 ± 8%) and 45 patients with VT and/or VF (all with ICD implanted) (VT/VF: 35 males, 62 ± 10 years, LVEF 34 ± 10%). No true antiarrhythmics were used. QT/RR slope was calculated from 24‐hour Holter ECG for the entire recording (E), daytime (D) and nighttime (N) periods. Results: Groups did not differ in basic clinical data (age, LVEF, treatment). QT/RR slopes were steeper in VT/VF than in NoVT/VF group in all analyzed periods: E ‐ 0.195 ± 0.03 versus 0.15 ± 0.03 (P < 0.001), N – 0.190 ± 0.03 versus 0.138 ± 0.03 (P < 0.001) and D ‐ 0.200 ± 0.04 versus 0.152 ± 0.03 (P < 0.001). No significant day‐to‐night differences were found in both groups. Conclusions: Steeper QT/RR slope and complete lack of day‐to‐night differences in VT/VF patients show inappropriate QT adaptation to the heart rate changes. The prognostic significance of this parameter needs prospective studies.     

QT Dynamics and Variability

Repolarization dynamics and variability are of increasing interest as Holter‐derived parameters reflecting changes in myocardial vulnerability and contributing to increased risk of arrhythmic events and sudden death. Repolarization dynamics is usually defined as phenomenon describing and quantifying QT adaptation to changing heart rate. The analysis of QT–R‐R slopes in long ECG recordings is one of the ways to evaluate repolarization dynamics. Increased QT–R‐R slopes are frequently observed in patients at risk for cardiac death and arrhythmic events: postinfarction patients, long QT syndrome patients, patients with nonischemic cardiomyopathy as well as in patients taking drugs affecting repolarization. QT variability reflects beat‐to‐beat changes in repolarization duration and morphology and such changes can be quantified using a number of algorithms currently in various phases of development and validation. Increased QT variability is observed in several conditions with increased risk of arrhythmias. Recent data from MADIT II indicate that increased QT variability is a powerful predictor of arrhythmic events in postinfarction patients with left ventricular dysfunction. More studies are needed to determine further the potential clinical usefulness for diagnosing patients and for risk stratification purposes using both QT dynamics and QT variability methods, and compare these methods with exercise‐induced T wave alternans.     

Gender Specificities in Risk Stratification After Myocardial Infarction

Objective: Although gender specificities of various risk factors have been well documented, risk stratification after myocardial infarction has never been compared in women and men. Methods: The power of left ventricular ejection fraction, heart rate variability, and mean RR interval computed from 24-hour Holter recordings, was compared in women and men for the prediction of cardiac mortality after an acute myocardial infarction. The study population consisted of 456 patients (108 women, 348 men) aged 50–75 years. Results: During a follow-up of 3 years, there were 41 cardiac deaths (13 women vs 28 men, P = NS). The positive predictive accuracy of left ventricular ejection fraction, heart rate variability, and mean RR interval at all sensitivity levels was higher in women than in men. For a 40% sensitivity, positive predictive accuracy of left ventricular ejection fraction was 46% in women and 16% in men (P < 0.05), positive predictive accuracy of mean RR interval was 90% in women and 28% in men (P < 0.05), and positive predictive accuracy of heart rate variability was 61% in women and 43% in men (P = NS). Mean RR interval had the highest positive predictive accuracy for cardiac mortality in women, but its superiority over heart rate variability was not statistically significant. In men, heart rate variability was the strongest predictor of mortality that was significantly more powerful than mean RR interval and left ventricular ejection fraction (P < 0.05). Conclusion: Increased 24-hour mean heart rate is the strongest predictor of cardiac mortality in women in whom it performs significantly better than in men. While in men, heart rate variability is a significantly better predictor of postinfarction cardiac mortality than 24-hour mean heart rate, this is not the case in women.     

Value of the Corrected QT Interval Dispersion Obtained Exercise Electrocardiography in Determining Remote Vessel Disease in Patients with Healed Q‐Wave Myocardial Infarction

Background: QT and corrected QT dispersion (QTD, QTcD) obtained by using the standard 12‐lead ECG is a marker of nonhomogenous ventricular repolarization. QTD obtained from exercise ECG increases the diagnostic reliability of ST‐segment changes. The aim of this study was to investigate the diagnostic accuracy of the QTD and QTcD obtained by a 12‐lead ECG during the peak exercise in determining remote vessel disease in patients with healed Q‐wave MI. Methods: Eighty patients with healed Q‐wave Ml (mean age 54 ± 8 years; 71 men, 9 women; 29 anterior; 51 inferior Ml) who underwent exercise stress testing and coronary angiography were included in this study. Patients were divided into two groups, with (group I) and without (group II) remote vessel coronary artery disease. During peak exercise, sensitivity, specificity, negative and positive predictive value of the ST‐segment depression, and QTcD were compared between both groups. Moreover, the resting and peak exercise ECG parameters were compared between group I and group II. Results: In coronary angiography, remote vessel disease was detected in 48 patients (group I). In determining remote vessel disease, the sensitivity, specificity, and the negative and positive predictive values of the peak exercise QTcD ≧ 70 ms were significantly higher than those of the peak exercise ST‐segment depression (81%, 63%, 69%, and 76% vs 71%, 53%, 55%, and 69%, respectively; P < 0.01 for all comparisons). In group I, QTD and QTcD were significantly higher in patients with anterior wall Ml than those with inferior wall Ml both during the resting and peak exercise ECG. In group II, the resting QTD and QTcD were significantly higher in patients with anterior wall MI than those with inferior wall MI. In patients with anterior wall MI and inferior wall Ml, QTD and QTcD significantly increased with exercise in group I. Conclusion: In patients with healed Q‐wave Ml, the value of QTcD ≧ 70 ms increases the diagnostic: accuracy of the exercise stress testing in determining remote vessel disease. A.N.E. 2002;7(3):228–233     

急性心肌梗死Tp-e时间与恶性室性，心律失常关系的研究

目的 研究急性心肌梗死患者T波峰-末时间（Tp—e时间）与恶性心律失常的关系。方法将62例急性心肌梗死患者分为恶性室性心律失常组（观察组,n=17）和非恶性室性心律失常组（对照组,n=45）。比较两组各导联和12导联平均Tp—e时间、经心率校正的Tp—e（Tp-ec）时间。结果与对照组比较,观察组各导联和12导联平均Tp—e时间及Tp—ec显著延长,差异有显著或非常显著性意义（P〈0．05或0．01）。结论Tp—e时间可以作为预测急性心肌梗死恶性室性心律失常的指标。