Behavior of Repolarization Variables during Exercise Test in the Athlete's Heart

Background: T peak–T end, QT peak/QT ratio and T peak–T end/QT ratio are markers able to test myocardial repolarization homogeneity, their increase has been related to a higher risk of ventricular tachyarrhythmias. These parameters have not yet been studied in left ventricular hypertrophy due to training. Aim of the research was to test the behavior of these variables in the athlete's heart during exercise. Methods: We examined 70 athletes, all males, divided into two groups according to the absence or the presence of a left ventricular mass index over 49 g/m^2.7 and a control group composed of 35 healthy, untrained males. All study participants underwent electrocardiogram at rest, transthoracic echocardiogram, and ergometric test. Repolarization markers (QT, corrected QT, QT dispersion, T peak–T end, QT peak/QT, T peak–T end/QT) were calculated at rest, at peak exercise and during recovery. Results: There was no statistically significant difference among the groups regarding all the parameters studied, except for corrected QT at rest between athletes with left ventricular hypertrophy and control group. The behavior of repolarization markers during exercise was not dissimilar in the three groups. Conclusions: Athlete's heart is not associated to any alteration in ventricular repolarization homogeneity, neither at rest nor during physical activity nor during recovery. Training‐induced left ventricular hypertrophy does not affect relationship QT parameters/RR interval.     

The effect of antihistamine cetirizine on ventricular repolarization in congenital long QT syndrome

Introduction: Many drugs are known to block cardiac potassium channels, thus prolonging QT interval and predisposing to malignant arrhythmias. Patients with congenital long QT syndrome are particularly vulnerable, but usually electrophysiological effects of drugs have not been assessed in these patients at risk.
Methods: Fifteen asymptomatic patients with type 1 (LQT1), 15 patients with type 2 (LQT2) long QT syndrome, and 15 healthy volunteers took a placebo and cetirizine 10 mg. In addition, healthy volunteers took cetirizine 50 mg. The study was single-blinded and randomized. Exercise tests were performed during stable plasma concentrations. The electrocardiogram was recorded with a body surface potential mapping system (BSPM). Data were analyzed with an automated analyze program. QT intervals to the T wave apex and T wave end and their difference (Tp-e) were determined at rest and at specified heart rates during and after exercise.
Results: Cetirizine did not lengthen the QT intervals at rest or during exercise and recovery in any group. It shortened Tp-e at rest in LQT1 and LQT2 patients and during exercise test in LQT1 patients, thus slightly decreasing electrocardiographic transmural dispersion of repolarization.
Conclusions: Cetirizine does not adversely modify ventricular repolarization in types 1 and 2 long QT syndrome, suggesting that it might be used safely in these long QT syndrome patients.     

Epinephrine Bolus Test in Detecting Long QT Syndrome Mutation Carriers with Indeterminable Electrocardiographic Phenotype

Background: In long QT syndrome (LQTS), prolonged and heterogeneous ventricular repolarization predisposes to serious arrhythmias. We examined how QT intervals are modified by epinephrine bolus in mutation carriers of three major LQTS subtypes with indefinite QT interval. Methods: Genotyped, asymptomatic subjects with LQTS type 1 (LQT1; n = 10; four different KCNQ1 mutations), type 2 (LQT2; n = 10; three different HERG mutations), and type 3 (LQT3; n = 10; four different SCN5A mutations), and healthy volunteers (n = 15) were examined. Electrocardiogram was recorded with body surface potential mapping system. After an epinephrine 0.04 μg/kg bolus QT end, QT apex, and T‐wave peak‐to‐end (Tpe) intervals were determined automatically as average of 12 precordial leads. Standard deviation (SD) of the 12 channels was calculated. Results: Heart rate increased 26 ± 10 bpm with epinephrine bolus, and similarly in all groups. QT end interval lengthened, and QT apex interval shortened in LQTS and normals, leading to lengthening of Tpe interval. However, the lengthening in Tpe was larger in LQTS than in normals (mean 32 vs 18 ms; P < 0.05) and SD of QT apex increased more in LQTS than in normals (mean 23 vs 7 ms; P < 0.01). The increase in Tpe was most pronounced in LQT2, and in SD of QT apex in LQT1 and LQT2. Conclusions: Abrupt adrenergic stimulation with a moderate dose of exogenous epinephrine affects ventricular repolarization in genotype‐specific fashion facilitating distinction from normals. This delicate modification may help in diagnosing electrocardiographically silent mutation carriers when screening LQTS family members. Ann Noninvasive Electrocardiol 2011;16(2):172–179     

长QT综合征患者心电图T波峰-末间期及其与QT比值的特征

目的探讨长QT综合征(LQTS)患者T波峰-末(Tp-e)间期及Tp-e/QT与室性心律失常发作的相关性。方法回顾性分析确诊为LQTS的14个家系,对家系成员的临床情况进行综合分析。记录先证者(包括发作期和稳定期)、无症状者及家族中正常者共149例成员的同步12导联心电图,测量计算心电图校正QT(QTc)间期、Tp-e间期以及Tp-e/QT,并进行比较。结果先症者发病年龄19.2岁。在20岁以前发病者占57.1%。患者以女性居多,均以晕厥为主要发病表现。运动及情绪激动诱发12例,休息或睡眠时发生2例。先证者和无症状患者的QTc间期、Tp-e间期及Tp-e/QT显著大于家系其他正常成员(P≤0.05)。先证者发作期的Tp-e间期及Tp-e/QT大于稳定期(P≤0.05)。结论伴有晕厥的长QT综合征患者Tp-e间期延长,Tp-e/QT增大提示增加跨壁复极离散度与恶性室性心律失常发生相关,动态观察LQTS患者心电图改变可能成为预测LQTS恶性心律失常发生危险的临床指标。     

Sinus node function and ventricular repolarization during exercise stress test in long QT syndrome patients with KvLQT1 and HERG potassium channel defects.

OBJECTIVES: This study was performed to evaluate the QT interval and heart rate responses to exercise and recovery in gene and mutation type-specific subgroups of long QT syndrome (LQTS) patients. BACKGROUND: Reduced heart rate and repolarization abnormalities are encountered among long QT syndrome (LQTS) patients. The most common types of LQTS are LQT1 and LQT2. METHODS: An exercise stress test was performed in 23 patients with a pore region mutation and in 22 patients with a C-terminal end mutation of the cardiac potassium channel gene causing LQT1 type of long QT syndrome (KVLQT1 gene), as well as in 20 patients with mutations of the cardiac potassium channel gene causing LQT2 type of long QT syndrome (HERG gene) and in 33 healthy relatives. The QT intervals were measured on electrocardiograms at rest and during and after exercise. QT intervals were compared at similar heart rates, and rate adaptation of QT was studied as QT/heart rate slopes. RESULTS: In contrast to the LQT2 patients, achieved maximum heart rate was decreased in both LQT1 patient groups, being only 76 +/- 5% of predicted in patients with pore region mutation of KvLQT1. The QT/heart rate slopes were significantly steeper in LQT2 patients than in controls during exercise. During recovery, the QT/heart rate slopes were steeper in all LQTS groups than in controls, signifying that QT intervals lengthened excessively when heart rate decreased. At heart rates of 110 or 100 beats/min during recovery, all LQT1 patients and 89% of LQT2 patients had QT intervals longer than any of the controls. CONCLUSIONS: LQT1 is associated with diminished chronotropic response and exaggerated prolongation of QT interval after exercise. LQT2 patients differ from LQT1 patients by having marked QT interval shortening and normal heart rate response to exercise. Observing QT duration during recovery enhances the clinical diagnosis of these LQTS types.     

Repolarization dynamics in patients with long QT syndrome

INTRODUCTION: Dynamics of ventricular repolarization may contribute to cardiac arrhythmias in subjects with the long QT syndrome (LQTS). The aim of the present study was to assess the dynamics of repolarization duration and the dynamics of repolarization complexity in LQTS patients and their unaffected family members. METHODS AND RESULTS: Twelve-lead 24-hour ambulatory ECG recordings were obtained from LQTS patients (n = 38) and unaffected family members (n = 20). The 24-hour dynamics of the QT interval, T wave complexity (TWC) index measured by principal component analysis, and the RR interval were analyzed using standard deviation (SD) and square root of the mean squared differences of successive values of the parameters (RMSSD). QT variability, mean TWC, and TWC variability were increased in the LQTS patients compared with unaffected family members (QT-SD: 38 +/- 20 msec vs 19 +/- 7 msec, P = 0.0001; QT-RMSSD: 36 +/- 20 msec vs 14 +/- 8 msec, P = 0.0001; TWC: 27.7% +/- 11.1% vs 20.4% +/- 6.7%, P = 0.003; TWC-SD: 6.7% +/- 2.8% vs 4.6% +/- 1.8%, P = 0.003; TWC-RMSSD: 5.3% +/- 2.8% vs 3.7% +/- 1.2%, P = 0.004, respectively). At the same time, the measures of heart rate variability were similar between the affected and unaffected LQTS subjects (SD of normal-to-normal RR intervals [SDNN]: 94 +/- 25 msec vs 89 +/- 37 ms, P = 0.56; RMSSD: 49 +/- 26 msec vs 49 +/- 34 ms, P = 0.97, respectively). CONCLUSION: Despite similar heart rate variability, QT variability and the variability of TWC are significantly increased in LQTS patients compared with unaffected family members, suggesting that disturbances in temporal dynamics of repolarization and repolarization complexity in LQTS patients possibly increase vulnerability to arrhythmias.     

QT interval measurement: Q to TApex or Q to TEnd?

OBJECTIVE: To study QT interval. QT interval is frequently measured, though there is variation in the literature as to whether it is more appropriate to measure from the Q wave to the apex of the T wave, which is methodologically easy, or to measure to the end of the T wave. HYPOTHESIS: For Q-TApex interval to be used as a measure of repolarization, the variability of the Q-T interval should lie in this early phase. This should be true in health and in disease, at rest and with physiological interventions such as exercise. If there is variability in the TApex - TEnd interval, this should be reflected by the variability in the Q-TApex interval. METHODS: Fifty-six subjects were recruited: 24 with heart failure, 16 with left ventricular hypertrophy and 16 controls. Q-TApex, Q-TEnd and TApex-TEnd intervals were measured at rest and on exercise. RESULTS: Q-TApex intervals at rest were not different amongst the three groups studied, being 339 +/- 7 ms for controls, 341 +/- 6 ms in left ventricular hypertrophy and 351 +/- 6 ms in heart failure. The Q-TEnd interval at rest was 421 +/- 6 ms in controls, 420 +/- 6 ms in hypertrophy and 461 +/- 9 ms in failure (P < 0.05 for failure versus hypertrophy or control). Thus the TApex-TEnd interval was prolonged in heart failure at rest. However, at peak exercise there was no difference between the TApex-TEnd intervals in the different groups. Variability in the TApex-TEnd interval induced by disease or by exercise was not related to variability in the Q-TApex interval. CONCLUSION: Q-TEnd rather than Q-TApex should be used when Q-T interval measurement is required.     

Interlead Difference in QT Interval Rate Adaptation During Exercise in Coronary Artery Disease Patients Susceptible to Ventricular Fibrillation

Background: Nonhomogeneity in ventricular repolarization predisposes to ventricular tachyarrhythmias. Rate adaptation of the QT interval parallels rate adaptation of the action potential, both of which reflect the repolarization phase in ventricular myocardium. The aim of this study was to examine in patients with coronary artery disease (CAD) the relation of interlead differences in QT interval rate‐adaptation to arrhythmia vulnerability. Methods: We studied 29 CAD patients with a history of ventricular fibrillation (VF) not associated with acute myocardial infarction (VF group), and their 29 individually matched CAD controls without arrhythmic events (controls). Rate adaptation of the QT intervals in the 12 leads of the electrocardiogram were determined from QT intervals measured at rest and at the end of each 3 minute load step during exercise test. The relation between heart rate (HR) and QT interval (QT/HR slope) was calculated separately in each lead by the linear regression equation. The slopes of these equations were used to characterize spatial QT interval rate adaptation. Results: The steepest QT_apex/ HR slopes in any lead were (mean ±mD SD) ?2.45 ± 0.63 in the VF group and ‐1.97 ± 0.45 in controls (P = 0.008), whereas the smallest slopes showed no difference (P = NS). The standard deviations of QT_apex/ HR slopes were 0.48 ± 0.23 in the VF group and 0.33 ± 0.12 in controls (P = 0.012). Conclusions: Rate adaptation of the QT_apex interval is locally exaggerated, resulting in nonhomogenous exercise response of the QT_apex intervals in CAD patients susceptible to life‐threatening ventricular arrhythmias. A.N.E. 2000;5(4):346–353     

Rate-independent QT shortening during exercise in healthy subjects: terminal repolarization does not shorten with exercise

Introduction: QT interval for a given heart rate differs between exercise and recovery (QT hysteresis) due to slow QT adaptation to changes in heart rate. We hypothesized that QT hysteresis is evident within stages of exercise and investigated which component of the QT contributes to hysteresis. Methods and Results: Nineteen healthy volunteers performed a staged exercise test (four stages, 3 min each). Continuous telemetry was analyzed with software to compare QT intervals in a rate‐independent fashion. QRST complexes during each minute were sorted by RR interval, and complexes in bins of 20 ms width were signal‐averaged. QT and QTp (onset of QRS to peak T wave) were measured, and terminal QT calculated (peak to end of T wave, Tpe = QT – QTp). QT, QTp, and Tpe at the same heart rate were compared between the first and last minute of each stage. QT shortened from the first to last minute of exercise in each stage (Stage I: 358 ± 30 to 346 ± 25 ms, P < 0.001; Stage II: 342 ± 27 to 331 ± 24 ms, P = 0.003; Stage III: 329 ± 21 to 322 ± 18 ms, P = 0.03; Stage IV: 313 ± 22 to 303 ± 23 ms, P = 0.005). QTp also shortened in each stage, while Tpe was unchanged. Conclusion: QT hysteresis occurs during exercise in normals, and the major determinant is shortening of the first component of the T wave. Terminal repolarization (peak to end of T wave), a surrogate for transmural dispersion of repolarization, does not shorten significantly with exercise.     

QRST isointegral departure mapping after exercise in patients with congenital long QT syndrome

Congenital long QT syndrome (LQTS) is known to be a critical syndrome associated with a bizarre T wave, prolonged QT interval, and ventricular arrhythmias and is followed by syncope and/or sudden death. Body surface mapping, especially QRST isointegral departure mapping, was used after exercise to assess exercise-induced repolarization changes in patients with this syndrome. This study included 12 patients with the Romano-Ward syndrome (LQTS group, 9 women, 30 +/- 19 years) and 19 healthy adults (control group, 5 women, 24 +/- 5 years). In the LQTS group, there was a significant increase in the number of local extrema and abnormal points after exercise in the departure maps. In the LQTS group, QRST isointegral departure mapping presented more marked abnormalities of repolarization after an exercise stress test. In mild cases that revealed abnormalities only after the exercise stress, such testing may be helpful for LQTS diagnosis.     

Genetic susceptibility to acquired long QT syndrome: pharmacologic challenge in first-degree relatives.

OBJECTIVES: The purpose of this study was to test for a genetic component to risk for acquired long QT syndrome (LQTS). BACKGROUND: Many drugs prolong the QT interval, and some patients develop excessive QT prolongation and occasionally torsades de pointes-the acquired LQTS. Similarities between the acquired and congenital forms of the long QT syndrome suggest genetic factors modulate susceptibility. METHODS: Intravenous quinidine was administered to 14 relatives of patients who safely tolerated chronic therapy with a QT-prolonging drug (control relatives) and 12 relatives of patients who developed acquired LQTS, and ECG intervals between groups were compared. RESULTS: Baseline QT and heart-rate corrected QT (QTc) were similar (QT/QTc: 394 +/- 28/410 +/- 20 ms vs 395 +/- 24/418 +/- 20 ms; control vs acquired LQTS) and prolonged equally in the two groups. The interval from the peak to the end of the T wave, an index of transmural dispersion of repolarization, prolonged significantly with quinidine in acquired LQTS relatives (63 +/- 17 to 83 +/- 18 ms, P = .017) but not in control relatives (66 +/- 19 to 71 +/- 18 ms, P = 0.648). In addition, the baseline peak to end of the T wave as a fraction of the QT interval was similar in both groups but was longer in acquired LQTS relatives after quinidine (16.3 +/- 3.5% and 19.5 +/- 3.9% in control and acquired LQTS relatives, respectively, P = .042). CONCLUSIONS: First-degree relatives of patients with acquired long QT syndrome have greater drug-induced prolongation of terminal repolarization compared to control relatives, supporting a genetic predisposition to acquired long QT syndrome.     

Long QT Interval and Ventricular Tachycardia of “Torsade de Pointe” Type in Hypothyroidism

ABSTRACT We have observed two patients with long QT interval, ventricular tachycardias of “torsade de pointe” type and repeated ventricular fibrillation episodes, who also turned out to have significant hypothyroidism. This was suspected from the clinical picture in one patient and after haematological test in the other. In addition to hypothyroidism, both patients had associated factors which may have contributed to the development of the arrhythmia. After having reached an euthyroid state, both patients normalized their QT intervals, were relieved from earlier symptoms of cardiac arrhythmias and exhibited no longer any documented arrhythmia. Before thyroid substitution, both patients had marked signs of delayed ventricular repolarization even by invasive electrophysiological methods. Our observations indicate that hypothyroidism should be considered a possible primary cause in cases with long QT syndrome (LQTS). Furthermore, the possibility of LQTS in patients with hypothyroidism should be considered.     

Effect of Phenylephrine Provocation on Dispersion of Repolarization in Congenital Long QT Syndrome

Introduction: Syncope and sudden death are associated with sympathetic stimulation in LQT1 while LQT2 patients are more susceptible to arrhythmias during nonexertional states. Abnormal spatial (QTd)‐ and transmural (TDR)‐dispersion of repolarization may indicate increased arrhythmogenicity. This study compares the effect of phenylephrine on QTd and TDR in genotyped LQTS to control (C). Methods and Results: Seventeen LQT1, 12 LQT2, and 18 age‐ and sex‐matched normal controls received 2 mcg/kg of phenylephrine intravenously. At baseline and peak phenylephrine effect, BP, QT, RR, Bazett's QTc, precordial QTd (QTmax?QTmin), and T‐peak to T‐end (Tp‐e) intervals were determined blinded to the patient's clinical and genotype status. Baseline QT intervals and QTc were significantly longer in LQT1 and LQT2 compared to C. Baseline QTd and Tp‐e were greater in LQT2 than either LQT1 or C: QTd = 79 ± 29 ms (LQT2), 53 ± 26 (LQT1) , and 45 ± 15 (C) and Tp‐e = 120 ± 30 ms (LQT2), 99 ± 20 (LQT1) , and 90 ± 11 (C) . Overall, phenylephrine exerted no significant effect on either QTd or Tp‐e except with subgroup analysis of symptomatic LQTS where LQT1 and LQT2 patients had a divergent response with TDR. Conclusions: Phenylephrine‐induced bradycardia decreased TDR in symptomatic LQT1 but increased TDR in symptomatic LQT2. The observed effects of phenylephrine are consistent with the protective effect of beta‐blocker in LQT1 and the increased arrhythmogenicity noted during nonexertional states in LQT2.     

Occult T Wave Alternans in Long QT Syndrome

T Wave Alternans in LQTS. T wave alternans that is visually apparent on the ECG is a known risk factor for sudden death in idiopathic long QT syndrome (LQTS). To determine if occult and visually undetectable forms of T wave alternans are also present in LQTS, we measured T wave alternans from a 16-year-old girl with LQTS during exercise using spectral analysis methods and a recording system designed to minimize exercise-related noise. While there was no alternans at rest, statistically significant, yet visually inapparent T wave alternans were measured both during exercise and recovery. Using identical recording techniques, no significant T wave alternans was detected from the subject's mother, who had a prolonged QT interval but was not experiencing arrhythmias, nor from five healthy volunteers with normal QT intervals. This report suggests that electrocardiographically occult, yet prognostically important forms of T wave alternans may be present in patients with LQTS.     

Prevention of ventricular extrasystole by mexiletine in patients with normal QT intervals is associated with a reduction of transmural dispersion of repolarization

BACKGROUNDS: Antiarrhythmic potential of mexiletine in patients with congenital and acquired long-QT syndrome (LQTS) has been attributed to a reduction of transmural dispersion of repolarization (TDR). A similar mechanism could be involved in the antiarrhythmic activity of the drug in patients with normal QT intervals, but the issue remains to be investigated. METHODS AND RESULTS: We analyzed 24-h Holter ECG recordings from 17 patients in sinus rhythm showing premature ventricular complexes (PVCs) with normal QT intervals (age, 62+/-10 years, mean+/-S.D.). Treatment of the patients with oral mexiletine (300 mg/day for 21-40 days) resulted in a significant reduction of PVCs (from 13899+/-18887 to 6949+/-12822 beats/24 h, p<0.01). Rate-dependent behavior of ventricular repolarization was analyzed by plotting QT intervals (QT(peak), QT(end)), and the interval from T-wave peak to T-wave end (TPE) against preceding respective RR intervals of sinus beats. Both the QT(peak) and QT(end) tended to be shortened by mexiletine at RR intervals from 600 ms to 1000 ms, although the changes did not reach statistical significances. TPE, which reflects TDR, was shortened significantly at relatively long RR intervals (by 14+/-9% at RR of 900 ms, p<0.05). There was a linear relationship between the percentage shortening of TPE and the percentage reduction of PVCs (r=0.86, p<0.04). TPE> or =70 ms was significantly associated with PVC suppression >75% with an odds ratio of 0.60 (95% confidence interval 0.36-0.98, per 1 ms increment). CONCLUSION: Inhibitory effect of mexiletine against PVCs in patients with normal QT intervals is mediated at least in part by a reduction of TDR. Mexiletine may be effective in patients exhibiting longer baseline TPE.     

Enhanced Transmural Dispersion of Repolarization in Patients with J Wave Syndromes

J Wave Syndromes . Introduction: Recently, great attention has been paid to the risk stratification of asymptomatic patients with an electrocardiographic early repolarization (ER) pattern. We investigated several repolarization parameters including the Tpeak‐Tend interval and Tpeak‐Tend/QT ratio in healthy individuals and patients with J wave syndrome who were aborted from sudden cardiac death. Methods and Results: Ninety‐two subjects were enrolled: 12 patients with ventricular fibrillation associated with J waves, 40 healthy subjects with an uneventful ER pattern and 40 healthy control subjects (C) without any evident J waves. Using ambulatory electrocardiogram recordings, the average QT interval, corrected QT interval (QTc), Tpeak‐Tend (Tp‐e) interval, which is the interval from the peak to the end of the T wave, and Tp‐e/QT ratio were calculated. Using ANOVA and post hoc analysis, there was no significant difference in the average QT and QTc in all 3 groups (QT; 396 ± 27 vs 405 ± 27 vs 403 ± 27 m, QTc; 420 ± 26 vs 421 ± 21 vs 403 ± 19 milliseconds in the C, ER pattern and J groups, respectively). The Tp‐e interval and Tp‐e/QT ratio were significantly more increased in the J wave group than the ER Pattern group (Tp‐e: 86.7 ± 14 milliseconds vs 68 ± 13.2 milliseconds, P < 0.001, Tp‐e/QT; 0.209 ± 0.04 vs 0.171 ± 0.03, P < 0.001), but they did not significantly differ between the C and ER pattern groups (Tp‐e: 68.6 ± 7.5 vs 68 ± 13.2, P = 0.97, Tp‐e/QT 0.174 ± 0.02 vs 0.171 ± 0.03, P = 0.4). Conclusion: As novel markers of heterogeneity of ventricular repolarization, Tpeak‐Tend interval and Tp‐Te/QT ratio are significantly increased in patients with J wave syndromes compared to age and sex‐matched uneventful ER. (J Cardiovasc Electrophysiol, Vol. 23 pp. 1109‐1114, October 2012)     

New parameters in the interpretation of exercise testing in women: QTc dispersion and QT dispersion ratio difference

BACKGROUND: It has been reported that the increase of QT dispersion (QTD) that occurs due to increased inhomogeneity of the ventricular repolarization because of transient ischemia obtained by standard 12-lead electrocardiogram (ECG), the changes during exercise, and the differences between exercise and rest increase the accuracy of exercise test in the diagnosis of coronary artery disease (CAD). HYPOTHESIS: This study was designed to investigate the value of QTD parameters, which are reported to increase the diagnostic accuracy of exercise test in women. METHODS: Ninety-seven women who had undergone coronary angiography and exercise test were evaluated for diagnosis of chest pain. QT dispersion was calculated using the measurements of the highest and lowest values of QT interval obtained by ECG during peak exercise. The QTc using Bazett's equation, and the QTD ratio (QTDR) using QT/RR were calculated, and QTcD and QTD ratios were obtained. The difference between QTcD and QTDR was determined by extracting the rest values from the exercise values. RESULTS: The groups with normal coronaries (n = 48), single-vessel CAD (n = 24), and multivessel CAD (n = 25) were compared. The obtained QTD parameters at peak exercise and their differences between exercise and rest were found to be significantly increased in patients with CAD (p <0.001). Furthermore, these parameters were found to be higher in the patients with multivessel CAD than in those with single-vessel disease (p < 0.05). With the parameters QTcD > 60 ms and QTDR > 10%, greater sensitivity and specificity were obtained compared with ST-segment depression. The highest diagnostic accuracy was obtained with the QTD parameters calculated from the differences between rest and exercise values. The diagnostic accuracy of the difference of QTcD > 15 ms and the difference of QTDR > 5% was relatively higher than the other parameters (sensitivity, specificity, and negative and positive predictor values are 84, 88, 84, 87% and 84, 96, 85, 95%, respectively). CONCLUSION: The use of QTD parameters as variables of ECG, which is easily obtainable in the evaluation of exercise ECG in women, increases the diagnostic accuracy of the exercise test. In addition, the evaluation of QTD variables may provide information about the incidence of CAD.     

Dynamics of the QT interval during and after exercise in healthy children

The dynamics and homogeneity of the QT interval have been usedas indicators of susceptibility to ventricular arrhythmias.We determined the relationship between QT intervals and heartrate during exercise testing and subsequent recovery in 18 healthychildren. The QT intervals were measured to the apex (earlyQT), to the end (total QT), and from the apex to the end ofthe Twave (late QT) (inhomogeneity of repolarization) at heartrates from 60 by steps of 10 to 180 beats. min^–1. Groupmean total QT and early QT exhibited better linear correlationswith heart rate (r 0.998 and 0.999) than with cardiac cyclelength (r 0.954 and 0.959). The slope relating total QT to heartrate was – 1.30 during exercise and – 1.42 duringrecovery (P<0.05). The corresponding slopes relating earlyQT to heart rate were – 1.11 and – 1.30 (P<0.05).Late QT, as a proportion of total QT, increased at high heartrates. Rate correction using Bazett's method gave abnormal totalQT values (>440 ms) in 12 children (67%) whereas linear correctiongave values below 440 ms only. In conclusion, the relationshipbetween QT and heart rate is linear and differs during exerciseand recovery. Inhomogeneity of repolarization increases at highheart rates. Linear correction of total QT and early QT intervalsimproves the evaluation of repolarization duration in exercisetesting in children.     

儿童先天性长QT综合征患者的QT滞后现象

目的观察儿童先天性长QT综合征(LQTS)患者进行运动试验时QT间期的变化。方法因QT间期延长而行运动平板试验的患儿共33例入选本研究,按照1993年Schwartz等的LQTS诊断标准的计分分值分为两组:LQTS组:总计分值为4分及以上的患者17例,男13例、女4例,年龄11.6±3.7岁;可疑组:评分为1.5~3.5分的患者16例,男9例、女7例,年龄13.8±4.2岁。另选行运动试验的18例正常儿童作为对照组,男11例、女7例,年龄12.4±3.1岁。记录整个运动试验中和恢复期的心电图,观察QT间期和心率的变化,记录并计算恢复期第1,2,4,6 m in QT间期与运动过程中同心率时QT间期的差值(ΔQT)。结果三组患者在运动中随着心率的增加,QT间期逐渐缩短。运动恢复期,随着心率的减慢,三组的QT间期也逐渐延长,但LQTS组恢复期QT间期却显著短于运动过程中处于同心率时的QT间期。LQTS组在恢复期1,2,4 m in的ΔQT值均显著大于其它两组(P均<0.05)。LQTS组在QT间期与心动周期的关系图上呈现明显的“QT滞后环”。结论儿童LQTS患者运动试验恢复期与运动过程中相比,QT间期的变化明显滞后于心率的变化。