Gang Yi

Short- and long-term reproducibility of QT, QTc, and QT dispersion measurement in healthy subjects.

The study investigated interobserver and intrasubject reproducibility of QT interval duration and dispersion measured in standard 12‐lead ECGs recorded at 25 mm/sec. Twenty‐eight healthy volunteers were studied. Each undenvent four ECG recordings, which were performed 1, 7, and 30 days apart. Two independent observers analyzed each ECG record. In each lead with a distinguishable T wave pattern, the RR interval, Q‐peak of T interval, and Q‐end of T interval were measured using a digitizing board with a 0.1‐mm resolution. From each recording the following measures were derived: the maximum, minimum, and mean QT interval; maximum, minimum, and mean heart rate corrected QT interval (QTc); QT and QTc dispersion (the difference between the maximum and minimum QT interval among the 12 leads); and adjusted QT and QTc dispersion (dispersion divided by the square root of the number of leads measured). The interobserver and short‐term (1 day) and long‐term (1 week and 1 month) reproducibility of individual indices was assessed by computing the relative errors and comparing them by a standard sign test. In addition, the distributions of maximum and minimum QTc values among electrocardiographicleads, and the differences between QT‐end and QT‐peak based measurements were investigated. The results showed that: (1) the measurement of the QT interval from standard ECG recordings is feasible and not operator dependent (interobserver relative error <4%); (2) the duration of the QT interval in healthy volunteers is stable and its short‐ and long‐term reproducibility is high (intrasubject relative error < 6%); (3) parameters that characterize dispersion of the QT interval in the 12‐lead ECG are highly nonreproducible, both between subsequent recording (relative error of 25%–35%) and between observers (relative errar 28%–33%), the reproducibility of QT dispersion is significantly lower than that of QT duration (P < 0.01); and (4) the duration of the entire QT interval correlates only weakly with the duration of the Q‐peak of T interval.

Spatial, temporal and wavefront direction characteristics of 12-lead T-wave morphology

Three new approaches for the analysis of ventricular repolarisation in 12-lead electrocardiograms (ECGs) are presented: the spatial and temporal variations in T-wave morphology and the wavefront direction difference between the ventricular depolarisation and repolarisation waves. The spatial variation characterises the morphology differences between standard leads. The temporal variation measures the change in interlead relationships. A minimum dimensional space, constructed by ECG singular value decomposition, is used. All descriptors are measured using the ECG vector in the constructed space and the singular vectors that define this space. None of the descriptors requires time domain measurements (e.g. the precise detection of the T-wave offset), and so the inaccuracies associated with conventional QT interval related parameters are avoided. The new descriptors are compared with the conventional measurements provided by a commercial system for an automatic evaluation of QT interval and QT dispersion in digitally recorded 12-lead ECGs. The basic comparison uses a set of 1100 normal ECGs. The short-term intrasubject reproducibility of the new descriptors is compared with that of the conventional measurements in a set of 760 ECGs recorded in 76 normal subjects and a set of 630 ECGs recorded in 63 patients with hypertrophic cardiomyopathy (ten serial recordings in each subject of both these sets). The discriminative power of the new and conventional parameters to distinguish normal and abnormal repolarisation patterns is compared using the same set. The results show that the new parameters do not correlate with the conventional QT interval-related descriptors (i.e. they assess different ECG qualities), are generally more reproducible than the conventional parameters, and lead to a more significant separation between normal and abnormal ECGs, both univariately and in multivariate regression models.

Agreement and Reproducibility of Automatic Versus Manual Measurement of QT Interval and QT Dispersion

To determine whether the automatic measurement of the QT interval is consistent with the manual measurement, this study evaluated the reproducibility and agreement of both methods in 70 normal subjects and 54 patients with hypertrophic cardiomyopathy. The mean, minimum, and maximum QT interval and QT dispersion were computed in a set of 6 consecutive electrocardiograms (3 in the supine and 3 in the standing position) obtained from each subject. The automatic method determined the T-wave end as the intersect of the least-squares-fit line around the tangent to the T-wave downslope with the isoelectric baseline. Manual measurements were obtained using a high-resolution digitizing board. QT dispersion was defined as the difference between the maximum and minimum QT interval and as standard deviations of the QT interval duration in all and precordial leads. In patients with hypertrophic cardiomyopathy, the absolute values of the QT interval and QT dispersion were significantly higher than those in normal subjects (p < 0.0001). In both groups, the intrasubject variability of the QT interval was significantly lower with automatic than with manual measurement (p < 0.05). The agreement between automatic and manual QT interval measurements was surprisingly poor, but it was better in patients with hypertrophic cardiomyopathy (r2 = 0.46 to 0.67) than in normal subjects (r2 = 0.10 to 0.25). In both groups, the reproducibility and agreement of both methods for QT dispersion were significantly poorer than for QT interval. Hence, the automatic QT interval measurements are more stable and reproducible than manual measurement, but the lack of agreement between manual and automatic measurement suggests that clinical experience gained with manual assessment cannot be applied blindly to data obtained from the automatic systems.

Comparative Reproducibility of QT, QT Peak, and T Peak-T End Intervals and Dispersion in Normal Subjects, Patients with Myocardial Infarction, and Patients with Hypertrophic Cardiomyopathy

Abnormal repolarizaiion is associated with arrhythmogenesis. Because of controversies in existing methodology, new computerized methods may provide more reliable tools for the noninvasive assessment of myocardial repolarization from the surface electrocardiogram (ECC). Measurement of the interval between the peak and the end of the T wave (TpTe interval) has been suggested for the detection of repolarization abnormalities, but its clinical value has not been fully studied. The intrasubject reproducibility and reliability of automatic measurements of QT, QT peak, and TpTe interval and dispersion were assessed in 70 normal subjects, 49 patients with acute myocardial infarction (5th day; MI), and 37 patients with hypertrophic cardiomyopathy (HC). Measurements were performed automatically in a set of 10 ECCs obtained from each subject using a commercial software package (Marquette Medical Systems, Milwaukee, WI, U.S.A.). Compared to normal subjects, all intervals were significantly longer in HC patients (P < 0.001 for QT and QTp; p < 0.05 for TpTe); in MI patients, this difference was only significant for the maximum QT and QTp intervals (P < 0.05). In both patient groups, the QT and QTp dispersion was significantly greater compared to normal subjects (P < 0.05) but no consistent difference was observed in the TpTe dispersion among all three groups. In all subjects, the reproducibility of automatic measurement of QT and QTp intervals was high (coefficient of variation, CV, 1%‐2%) and slightly lower for that of TpTe interval (2%–5%; p < 0.05). The reproducibility of QT, QTp, and TpTe dispersion was lower (12%–24%, 18%–28%, 16%–23% in normal subjects, MI and HC patients, respectively). The reliability of automatic measurement of QT, QTp, and TpTe intervals is high but the reproducibility of the repeated measurements of QT, QTp and TpTe dispersion is comparatively low.

Usefulness of signal-averaged electrocardiogram in idiopathic dilated cardiomyopathy for identifying patients with ventricular arrhythmias

In idiopathic dilated cardiomyopathy (IDC), the relation between the signal-averaged electrocardiogram and ventricular tachycardia (VT) remains unclear. In this study, conventional time domain and frequency domain analyses (2-dimensional, spectral temporal mapping and spectral turbulence analysis) of the signal-averaged electrocardiogram were performed in 64 patients with IDC. Eight patients had a history of symptomatic sustained VT and an additional 24 had nonsustained VT recorded during ambulatory electrocardiography. Conventional time domain analysis, using the 25 and 40 Hz filter, and spectral temporal mapping, detected late potentials within the terminal QRS in 8 (13%), 14 (22%) and 18 (28%) patients, respectively. Late potentials were seen more often in patients with than without VT, and in patients with sustained versus nonsustained VT, but these differences were not significant. The predictive accuracy of these techniques in detecting either form of VT were: sensitivity, 22, 25 and 31%; specificity, 97, 81 and 75%; and overall predictive value, 59, 53 and 50%, respectively. Two-dimensional frequency domain analysis of the signal-averaged electrocardiogram revealed a higher energy and area ratio in patients with than without VT (entire QRS), and in patients with sustained versus nonsustained VT (entire QRS and terminal QRS). Spectral turbulence analysis was abnormal in 24 patients (39%), but no differences were observed between patients with and without VT. During follow-up (mean duration 18 +/- 14 months), 5 patients had arrhythmic events (3 died suddenly, 1 had aborted sudden death and 1 developed sustained VT).(ABSTRACT TRUNCATED AT 250 WORDS)

QT dispersion and risk factors for sudden cardiac death in patients with hypertrophic cardiomyopathy

This study examines the relation of QT dispersion (QTd) on a surface electrocardiogram (ECG) to clinical features and established risk factors of sudden cardiac death (SCD) in patients with hypertrophic cardiomyopathy (HC). One hundred fifty-six consecutive patients with HC (91 men, mean age 41+/-15 years, range 7 to 79) and 72 normal subjects (41 men, mean age 39+/-9 years, range 20 to 60) were studied. Standard 12-lead ECGs were recorded from each subject using a MAC VU electrocardiograph. Patients with nonsinus rhythm, atrioventricular conduction block, QRS duration > 120 ms, age < 15 years, and low amplitude T waves were excluded from the analysis (n=51). Another 22 patients who were receiving amiodarone and/or sotalol therapy were also excluded. QT interval and QTd were measured using automated analysis in the remaining 83 patients (46 men, age 40+/-14 years, range 16 to 76). QT interval (406+/-38 ms), QTc interval (432+/-27 ms), and QTd (43+/-25 ms) were significantly greater in patients with HC than in normal controls (386+/-31 ms, 404+/-16 ms, 26+/-16 ms, respectively) (p <0.0001). QTd was significantly greater in patients with HC with chest pain compared with asymptomatic or mildly symptomatic patients (50+/-28 ms vs 37+/-20 ms, p=0.02). Increased QTd was found in patients with dyspnea New York Heart Association functional classes II/III than in those with dyspnea New York Heart Association functional class I (50+/-27 ms vs 38+/-22 ms, p=0.04). QTd was weakly correlated with maximum left ventricular wall thickness (r=0.228, p=0.038). No significant association was found between QTd and any risk factors for SCD. Thus, patients with HC have increased QTd. The QTd correlates with symptomatic status. Assessment of QTd might provide complementary clinical characterization of patients with HC but its relation to SCD remains uncertain.

Circadian Variation of the QT Interval in Patients With Sudden Cardiac Death After Myocardial Infarction

To evaluate the potential prognostic value of the circadian variation of QT intervals in predicting sudden cardiac death (SCD) in patients after myocardial infarction (MI), 15 pairs of post-MI patients (15 died suddenly within 1 year after MI [SCD victims] and 15 remained event-free [MI survivors]) were studied (mean age 60 +/- 8 years; 24 men and 6 women). The pairs were matched for age, gender, infarct site, presence of Q wave, left ventricular ejection fraction, thrombolytic and beta-blocker therapy. Fourteen normal subjects served as controls (mean age 55 +/- 9 years; 12 men). A 24-hour Holter electrocardiographic (ECG) recording was obtained from each subject. All recordings were analyzed using a Holter ECG analyser. QT, RR, and heart rate-corrected QT intervals (QTc) were automatically calculated by the analyzer, and hourly and 24-hour mean values of each measurement were derived from each recording. There was a pronounced circadian variation in the QT interval in parallel with the trend in the RR interval in normal subjects and in MI survivors. Circadian variation in both indexes was blunted in SCD victims. The QT interval was significantly longer at night than during the day in normal subjects (388 +/- 28 vs 355 +/- 21 ms, p = 0.001) and in MI survivors (358 +/- 25 vs 346 +/- 15 ms, p = 0.008), but not in SCD victims (357 +/- 32 vs 350 +/- 31 ms, p = 0.6). The 24-hour mean value of the QT interval in SCD victims did not differ significantly from that in normal subjects or MI survivors. The QT interval at night was significantly shorter in SCD victims than in normal subjects (357 +/- 32 vs 388 +/- 28 ms, p = 0.02), but daytime values were similar. The QT interval in SCD victims did not differ significantly from that of MI survivors at any time. The QTc interval exhibited a small circadian variation in normal subjects. This variation was abolished in SCD victims and MI survivors. The 24-hour mean value of QTc was significantly longer in SCD victims than in normal subjects (424 +/- 25 vs 402 +/- 21 ms, p = 0.02), and in MI survivors (424 +/- 25 vs 404 +/- 32 ms, p < 0.05). The QTc interval of SCD victims differed from that of normal subjects during both the day (421 +/- 25 vs 400 +/- 17 ms, p = 0.02) and night (424 +/- 26 vs 403 +/- 23 ms, p = 0.03). Thus, blunted circadian variation in QT intervals, abolished circadian variation in QTc intervals, and prolonged QTc intervals may suggest an increased risk of SCD in patients after MI.

Exercise-induced changes in the QT interval duration and dispersion in patients with sudden cardiac death after myocardial infarction

BACKGROUND Prolongation of the QT interval and increased QT dispersion have been proposed to be associated with arrhythmic risk after myocardial infarction. However, controversy remains regarding the prognostic value of ventricular repolarization abnormalities in the risk stratification of patients surviving acute myocardial infarction. HYPOTHESIS AND OBJECTIVE: The QT interval is sensitive to myocardial ischaemia, and exercise-induced ischaemia may change the QT interval regionally, resulting in increased QT dispersion. This study examined whether there are abnormalities of ventricular repolarization during exercise and whether assessment of the exercise-induced changes in QT interval duration and dispersion would be able to differentiate patients at high risk from those at low risk of sudden cardiac death after myocardial infarction. METHODS Twenty-six post-myocardial infarction patients (mean age 54.5+/-8.9 years, 22 men) were retrospectively studied. Thirteen patients who died suddenly (SCD patients) during a follow-up of 39+/-6 months were compared to 13 patients who remained event-free, i.e. no ventricular tachyarrhythmias, no reinfarction, no by-pass (MI survivors). The two groups were pair-matched for age, gender, site of infarction, left ventricular ejection fraction and use of beta blocker. A further 13 patients with chest pain, normal coronary arteriograms and negative exercise test results were studied as controls. They were age and gender matched with the post-infarction patients. A 12-lead exercise ECG was recorded from each patient before, during and after exercise. QT and RR interval were measured on the exercise ECGs at each stage and QT dispersion was defined as the difference between the maximum and minimum QT intervals across the 12-lead ECG. RESULTS There were no significant differences in RR, QT and QTc (Bazetts and Fridericias correction) intervals, or QT dispersion between any groups before exercise. A significant difference in QT and QT dispersion was found at peak exercise between post-infarction patients and controls (P=0.03 and P=0.0001, respectively), but no difference was observed between SCD patients and MI survivors. The maximum QTc at peak exercise was longer in SCD patients compared with MI survivors (P=0.02) and a maximum QTc>440 ms (Bazetts correction) was common in SCD patients but not in MI survivors or controls (62%, 15%, 15%, P=0.01). The differences in QT, QTc or QT dispersion observed at peak exercise were no longer significant after exercise. CONCLUSIONS Exercise-induced prolongation of the QTc interval differentiates patients at high risk of sudden cardiac death from those at low risk, whereas exercise-induced changes in QT dispersion failed to identify patients at high risk of sudden cardiac death after myocardial infarction.

Prognostic significance of spectral turbulence analysis of the signal-averaged electrocardiogram in patients with idiopathic dilated cardiomyopathy

The aim of this study was to assess whether spectral turbulence analysis (STA) of the signal-averaged electrocardiogram (SAECG) is of prognostic use in patients with idiopathic dilated cardiomyopathy. SAECGs were recorded at presentation in 84 patients with idiopathic dilated cardiomyopathy and STA was performed using 183 Del Mar software. STA was abnormal (> or = 3 of the 4 standard parameters beyond the normal range) in 31 patients (37%). Patients were followed for a mean duration of 24 +/- 18 months (range 1 to 59) during which time 24 (29%) developed progressive heart failure (14 underwent cardiac transplantation), 4 died suddenly or had aborted sudden death, and the others remained clinically stable. Progressive heart failure occurred more often in patients who had an abnormal versus a normal STA result (15 [48%] vs 9 [17%]; p < 0.002). Actuarial survival revealed a 1-year survival of 90% in patients with a normal STA result, and 63% in patients with an abnormal STA result (p < 0.01). The predictive ability of STA to identify patients with progressive heart failure was sensitivity 63%, specificity 77%, positive predictive value 54%, and negative predictive value 83%. Univariate analysis identified peak oxygen consumption as having the largest relative risk for the development of progressive heart failure (9.55, 95% confidence interval [CI] 2.1 to 43.9). Left ventricular end-diastolic dimension (relative risk 4.18, 95% CI 1.5 to 11.4) and STA (relative risk 3.81, 95% CI 1.7 to 8.8) were also significantly associated with the development of progressive heart failure.(ABSTRACT TRUNCATED AT 250 WORDS)

T Wave Complexity in Patients with Hypertrophic Cardiomyopathy

The complexity of the T wave assessed by principal component analysis (PCA) has been proposed to reflect obnormal repolarization, which may be arrhythmogenic. To determine whether PCA can differentiate patients with hypertrophic cardiomyopathy (HCM) from normal subfects and whether PCA is of prognostic importance in HCM, 112 patients with HCM (41 ±14 years, 64 males) and 72 healthy subjects (39 ± 9 years, 41 males) were studied. Patients with sinus node dysfunction, AV conduction block, flat T waves, QRS > 140 ms, and those < 15 years were excluded from this study. Standard 12‐lead ECGs were recorded digitally using the MAC‐VU system (Marquette Medical Systems). PCA parameters were computed using the QT Guard software package by Marquette. PCA ratio was significantly greater in HCM patients than in normal controls (23.9%± 12.4% vs 16.1%± 7.6%, P < 0.0001) and was correlated with QT‐end dispersion (r = 0.24. P = 0.01) and QT peak (Q point to T peak) dispersion (r = 0.35, P < 0.0001). HCM patients with syncope (n = 23) had increased PCA ratios compared with those without syncope (29.1%± 11.5% vs 22.5%± 12.3%, P = 0.01). PCA ratio was similar in patients with and without nonsustained ventricular tachycardia on Holter (25.9%± 11.4% vs 22.7%± 12.1%, P = 0.2), as well as in patients treated with amiodarone or sotalol versus those not on therapy. In conclusion, assessment of the complexity of the T wave by PCA differentiates HCM patients from normal subjects. PCA ratio correlated with QT dispersion and an increased PCA ratio was associated with a history of syncope in HCM.