QT离散度对室性心律失常发生的预测价值的再探讨

研究体表心电图QT离散度(QTd)对室性心律失常的发生是否有预测价值。将204例入选心脏病例的QTd按级差5ms分段,计算各时段病例中频发室性早搏(VPB≥30次/小时)以及室性心动过速(VT)+心室颤动(VF)的发生率。以各时段QTd的上限值为变量,对各时段室性心律失常的发生率与QTd上限值进行相关性研究。将上述室性心律失常者分设为VPB组(n=52)和VT+VF组(n=46)。在其余入选病例中选择未发现明显室性心律失常者(VPB<5次/小时)50例设为疾病对照组。另设正常对照组(n=50)。对各组QTd进行组间比较。结果:各时段VPB及VT+VF的发生率与QTd上限值无明显相关性(r1=0.2091,r2=0.1684,P>0.05)。VPB组及VT+VF组的QTd虽明显大于正常对照组(P<0.01),但与疾病对照组比较无显著差异(P>0.05)。结论:QTd对室性心律失常的发生似乎无预测价值。     

Effect of diurnal variability of heart rate on development of arrhythmia in patients with chronic obstructive pulmonary disease

We examined the possible effect of diurnal variability of heart rate on the development of arrhythmias in patients with chronic obstructive pulmonary disease (COPD). Forty-one COPD patients (M/F: 39/2, mean age: 59+/-8.5 years) and 32 (M/F: 27/5, mean age: 57+/-11 years) healthy controls were included. Twenty-four hour ECG recordings were analyzed for atrial fibrillation (AF) or ventricular premature beats (VPB), and circadian changes in heart rate variability (HRV) were assessed by dividing the 24-h period into day-time (08:00-24:00 h) and night-time (24:00-08:00 h) periods. Night-time total (TP), low frequency (LF) and high frequency (HF) powers were similarly lower from day-time parameters in AF(-) COPD patients (HF 3.91+/-1 vs. 4.43+/-1.04 ms(2), P=0.001) and controls (HF 3.95+/-0.72 vs. 4.82+/-0.66 ms(2), P<0.001). The LF/HF ratios were also significantly reduced in the same patient groups (AF(-) COPD 1.35+/-0.21 vs. 1.27+/-0.19, P=0.04, controls 1.43+/-0.14 vs. 1.24+/-0.09, P<0.001). Night-time TP and LF were increased, HF unchanged and LF/HF significantly increased (1.11+/-0.25 vs. 1.19+/-0.27, P<0.05) in AF(+) COPD patients. Frequency of VPB was correlated with corrected QT dispersion (QTc(d)) (r=0.52, P=0.001) and the day-time/night-time HF ratio (r=0.43, P=0.02). Patients with QTc(d)>or=60 ms did not have the expected increase in night-time HF and had a statistically insignificant increase in LF/HF ratio. In COPD patients with QTc(d)<60 ms, circadian changes in HRV parameters were parallel with the controls. We concluded that COPD patients with arrhythmia had circadian HRV disturbances such as unchanged night-time parasympathetic tone and disturbed sympatho-vagal balance in favor of the sympathetic system all day long, which may explain the increased frequency of arrhythmia.     

Flecainide-related alterations in the signal-averaged electrocardiogram: similarity between patients with or without ventricular tachycardia.

The signal-averaged electrocardiogram (SAECG) identifies patients at risk of sustained ventricular tachycardia (VT), but the influence of anti-arrhythmic agents on the SAECG is not yet established. We have evaluated the effects of flecainide on the SAECG (XYZ leads, high-pass filters 25 Hz and 40 Hz, noise level 0.2 microV-0.4 microV, Model 1200 EPX, ART) in 25 patients: 15 (VT group) had documented sustained VT (nine post-MI, two dilated cardiomyopathy, four normal hearts) and 10 (control group) had supraventricular arrhythmias and structurally normal hearts. The SAECG was recorded in all patients prior to, and 5 min following a flecainide infusion (2 mg.kg-1 over 10 min). Before flecainide administration an abnormal SAECG was recorded in six patients from the VT group and in no control patient. Following flecainide, 13 patients from the VT group and eight control subjects demonstrated abnormal SAECG. Flecainide produced similar significant percentage changes in all SAECG indices in both the VT and control groups: total QRS duration was prolonged by 26.0 +/- 10.4% vs 26.7 +/- 15.7%, late potential duration under 40 microV was prolonged by 55.5 +/- 62.0% vs 106.1 +/- 61.4%, and the root mean square voltage of the last 40 ms of the QRS was reduced by 42.1 +/- 34.9% vs 55.3 +/- 24.4%, respectively. We conclude that flecainide significantly changes the SAECG parameters in patients with and without a history of VT, irrespective of the underlying disease.     

QT dispersion and late potentials during doxorubicin therapy for non-Hodgkin's lymphoma

OBJECTIVES: To investigate effects of doxorubicin therapy on cardiac electrophysiology, with special emphasis on QT dispersion and late potentials, in lymphoma patients. DESIGN: Prospective study. SETTING: University hospital. SUBJECTS: Twenty-eight adult non-Hodgkin's lymphoma patients who received doxorubicin to a cumulative dose of 400-500 mg m-2. MAIN OUTCOME MEASURES: Standard 12-lead electrocardiogram (ECG) and signal-averaged ECG (SAECG) recordings were performed at baseline and after cumulative doxorubicin doses of 200, 400 and 500 mg m-2. RESULTS: Heart rate-corrected QT interval (QTc) increased from 402 +/- 4 to 416 +/- 5 ms (P = 0.002) during the study period. QT dispersion (variability in QT interval duration amongst the different leads of the standard 12-lead ECG) increased from 24.1 +/- 2.5 to 35.0 +/- 2.8 ms (P = 0.041) and QTc dispersion increased from 26.5 +/- 2.5 to 39.0 +/- 3.5 ms (P = 0.039). Five patients (18%) developed QT dispersion exceeding 50 ms. In addition, two patients (7%) developed late potentials during doxorubicin therapy. The changes in QTc duration, QT dispersion and late potentials occurred independently of the impairment of left ventricular function. CONCLUSIONS: Prolongation of QTc, increased QT dispersion and development of late potentials are indicative of doxorubicin-induced abnormal ventricular depolarization and repolarization. QT dispersion and late potentials are both known to be associated with increased risk of serious ventricular dysrhythmias and sudden death in various cardiac diseases. Thus, follow-up of these parameters might also be useful in assessing the risk of late cardiovascular events in cancer patients treated with anthracyclines.     

Is ventricular repolarization heterogeneity a cause of serious ventricular tachyarrhythmias in aortic valve stenosis?

BACKGROUND: It is well known that there is a close relation between sudden cardiac death and serious ventricular tachyarrhythmias in patients with aortic valve stenosis (AS). QT dispersion (QTd) reflects the ventricular repolarization heterogeneity and has been proposed as an indicator for ventricular arrhythmias. HYPOTHESIS: This study investigated the QTd and its relevance to the clinical and echocardiographic variables. METHODS: In all, 51 patients (33 men, 18 women, mean age 56 +/- 12) with isolated AS and 51 age- and gender-matched healthy controls comprised the study group. Left ventricular mass index (LVMI) was calculated by the Devereux formula, and we used continuous-wave Doppler (n = 15) and cardiac catheterization (n = 36) for the determination of the maximum aortic valve pressure gradient (PG). RESULTS: Corrected QTd (QTcd) (89 +/- 39 vs. 49 +/- 15 ms, p < 0.001) and LVMI (176 +/- 69 g/m2 vs. 101 +/- 28 g/m2, p < 0.001) in patients with AS were significantly different from those in the control group. The group of 21 patients had a significantly greater number of 24-h mean ventricular premature beats (VPB) and mean number of couplet VT episodes than did the control group (p < 0.05). QTcd also correlated significantly well with LVMI (r = 0.58, p < 0.001), PG (r = 0.41, p = 0.003), and number of 24-h VPB (r = 0.56, p = 0.008). With respect to symptoms (e.g., angina, syncope, and dyspnea) patients without symptoms (n = 19) displayed less QTcd (71 +/- 31 vs. 100 +/- 39 ms, p = 0.007) and less LVMI (144 +/- 80 g/m2 vs. 195 +/- 57 g/m2, p = 0.01) than patients with symptoms. Statistical analysis was similar for all variables with uncorrected QTd values. CONCLUSION: We found that ventricular repolarization heterogeneity was greater in patients with AS than in controls. Our findings also showed that QTd in the patient group correlates well with LVMI, severity of AS, and PG. The present results suggest that serious ventricular arrhythmias in patients with AS may be due to spatial ventricular repolarization abnormality.     

QT dispersion and left ventricular geometry in hypertensive patients

It has been shown that increased QT dispersion (QTd) reflects electrical inhomogeneity of the myocardium and is associated with high incidence of ventricular arrhythmias. In some cases increased QTd has also been found in some hypertensive patients with left ventricular hypertrophy. The aim of the study was to investigate the relation between QTd and left ventricular (LV) geometry in hypertensive patients (pts). Studied group consisted of 80 pts aged 52.5 +/- 12.6 yrs with mild, moderate and severe hypertension. Nineteen healthy subjects aged 50.5 +/- 9.6 yrs served as control group. QTd was calculated as a difference between the longest QT and shortest QT from the 12-leads of the standard electrocardiogram. Each subject underwent echocardiographic study to determine the pattern of LV geometry divided into: normal (NG), concentric remodeling (CR), excentric hypertrophy (EH) and concentric hypertrophy (CH). Significantly higher QTd was found out in pts with CH and EH as compared to CG (respectively 61 +/- 10 ms, 69 +/- 15 ms vs 46 +/- 14 ms, p < 0.01). Moreover, pts with CH had higher QTd than NG (69 +/- 15 ms vs 55 +/- 15 ms, p < 0.01). CONCLUSION: QTd is related to the pattern of LV geometry. As compared to healthy subjects it is increased in hypertensive pts with concentric and eccentric hypertrophy. In pts with CH QTd is significantly greater than in hypertensive pts with normal geometry.     

Angioplasty decreases prolonged QT dispersion in patients with angina pectoris but not in patients with prior myocardial infarction

BACKGROUND AND HYPOTHESIS: Prolonged QT dispersion (QTd) is shortened by successful percutaneous transluminal coronary angioplasty (PTCA) in patients with ischemic heart disease. Particularly, QTd plays an important role in the prognostication in patients with prior myocardial infarction (MI). However, whether the effect of PTCA on QTd differs in patients with and without prior MI is not clear, and this study sought to clarify this question. METHODS: In 41 consecutive patients with ischemic heart disease, we measured QTd from a routine 12-lead electrocardiogram taken at 72 h before and after successful PTCA. Patients were divided into two groups based on the presence or absence of prior MI: Group 1 consisted of 24 patients with angina (61 +/- 11 years old) without prior MI and Group 2 was comprised of 17 patients (69 +/- 10 years old) with prior MI. QTd was calculated as the difference between the maximum and minimum QT and QT corrected for heart rate (QTc), using Bazett's formula for calculating QTcd. All measurements were obtained manually and blindly. RESULTS: In Group 1, 15 of 24 patients (63%) demonstrated multivessel disease and 16 of 24 (67%) patients had high QTd > 60 ms. Percutaneous transluminal coronary angioplasty decreased QTd and QTcd in Group 1 (QTd, from 83 +/- 35 to 57 +/- 19 ms, p < 0.05 ; QTcd, from 89 +/- 37 to 63 +/- 33 ms, p < 0.05), whereas no changes were observed in Group 2 (QTd, from 73 +/- 25 to 69 +/- 22 ms, NS; QTcd, from 80 +/- 30 to 79 +/- 28 ms, NS). QTd is more sensitive to decrease by successful PTCA in patients with angina than in patients with prior MI. CONCLUSIONS: The effect of successful PTCA on inhomogeneity of ventricular repolarization reflected by QTd in patients with prior MI is different from that in patients without prior MI.     

Heart rate variability, late potentials and QT dispersion as markers of myocardial involvement in patients with Behçet's disease

BACKGROUND: Myocardial involvement in Beh?et's disease has been reported to be relatively rare. OBJECTIVE: To evaluate myocardial involvement noninvasively in patients with Beh?et's disease by measuring signal-averaged electrocardiography (SAECG), QT dispersion and heart rate variability (HRV). PATIENTS AND METHODS: The study group comprised 28 eligible patients (16 male, mean age 37+/-13 years) of 33 patients with Beh?et's disease, and 25 age- and sex-matched control subjects. RESULTS: The echocardiographic left ventricular measurements were within normal limits and similar in both groups except the E/A ratio, which was significantly lower in patients with the disease than in control patients. Minimal pericardial effusion was detected in four patients. Considering the SAECG recordings, values of root mean square voltage in the last 40 ms were 30+/-18 microV and 38+/-18 microV in patients with Beh?et's disease and in the control group, respectively. The number of cases with a value less than 20 microV was seven (25%) and one (4%) in the same groups, respectively. Both QT dispersion and the corrected QT interval dispersion were significantly increased in patients with Beh?et's disease compared with the control patients (50.2+/-16.6 versus 20.4+/-18.8, P<0.01). Although all HRV measures appeared to be decreased in the Beh?et's group, only the standard deviation of all filtered RR intervals in the entire 24 h ECG recordings and the percentage of differences between adjacent filtered RR intervals that are greater than 50 ms for the whole analysis values differed significantly between the groups (P<0.05). No significant difference was observed in frequency domain parameters. In the Holter ECG recording, grade 2 or greater premature ventricular complexes were observed in seven patients from the Beh?et's group (25%) but in only one subject from the control group (4%) (P<0.05). CONCLUSIONS: Patients with Beh?et's disease appeared to have significantly increased QT dispersion, a left ventricular diastolic dysfunction pattern in echocardiography, a high incidence of positive late potentials and more complex ventricular arrhythmias, suggesting myocardial involvement and the existence of an arrhythmogenic substrate, whereas the HRV measures do not suggest a clear autonomic abnormality in Beh?et's disease.     

Electrocardiographic signal-averaging during atrial pacing and effect of cycle length on the terminal QRS in patients with and without inducible ventricular tachycardia

Electrocardiographic signal-averaging during sinus rhythm (61 to 99 beats/min) and atrial pacing (100 to 171 beats/min) were performed to determine the effect of heart rate on late potentials in 15 patients without (group 1) and 7 patients with (group 2) inducible sustained ventricular tachycardia (VT). In sinus rhythm (79 +/- 12 vs 77 +/- 12 beats/min, difference not significant), the duration of the low-amplitude signal less than 40 microV was longer in group 2 than group 1 (43 +/- 21 vs 26 +/- 8 ms, p = 0.034) and more patients had late potentials (57 vs 7%, p = 0.021), but QRS duration (121 +/- 32 vs 98 +/- 19 ms) and terminal voltage (33 +/- 33 vs 50 +/- 26 ms) were not significantly different. With atrial pacing in group 1 (128 +/- 16 beats/min), 3 patients developed a simultaneous decrease in terminal voltage and an increase in terminal QRS duration consistent with a late potential, but mean total and terminal durations were unchanged. Terminal voltage increased (50 +/- 26 to 59 +/- 40) but not significantly. With atrial pacing in group 2 (119 +/- 12 beats/min) all patients either had a late potential or developed a simultaneous decrease in terminal voltage and an increase in terminal QRS duration (p = 0.001 vs group 1). Root mean square (p = 0.001 vs group 1). Root mean square voltage decreased (33 +/- 23 to 22 +/- 23) and became significantly different from group 1 (p = 0.017). Mean QRS duration, root mean square terminal voltage and low-amplitude terminal QRS duration, however, were unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)     

Diagnostic value of ventricular late potentials,heart rate variability and QT dispersion in patients with acute myocardial infarction

Late ventricular potentials (LVP), heart rate variability (HRV) and dispersion of QT interval (QTd) were studied in 91 patients with myocardial infarction with various ventricular arrhythmias. Patients with episodes of sustained ventricular tachycardia (group 4) had the following characteristics: prevalence of LVP 73.7%, QTd 82.5 ms, standard deviation of RR intervals (SD) 26.5 ms; spectral analysis of HRV revealed preponderance of sympathetic influences and lowered vagal activity. Frequency of LVP detection, QTd and SD in patients with ventricular extrasystoles (Lown classes 3-5) (group 3) were 33.3%, 72.8 ms, and 42.8 ms, respectively. Patients of group 3 also had augmented sympathetic and lowered parasympathetic influences. These data significantly differed from those obtained in patients with Lown class 1-2 ventricular extrasystoles (group 2) and patients without extrasystoles (group 1). Groups 3 and 4 had significantly different prevalences of LVP and values of some HRV parameters but similar QTd. There was close correlation between presence of severe ventricular arrhythmias and some parameters of HRV and signal averaged ECG. Stepwise regression analysis showed that the following group of parameters was related to the presence of malignant ventricular rhythm disturbances: heart rate, SD and total QRS duration (p<0.05). Thus patients with life threatening ventricular arrhythmias were characterized by the presence of LVP and changes of some parameters of HRV and QTd. Registration of these parameters can apparently be used for prediction of potentially fatal ventricular arrhythmias in patients with myocardial infarction.     

QT dispersion and left ventricular hypertrophy in athletes: relationship with angiotensin-converting enzyme I/D polymorphism

BACKGROUND: QT dispersion (QTd) is a measure of inhomogeneous repolarization of myocardium and is used as an indicator of arrhythmogenicity. QTd is increased in myocardial hypertrophy secondary to systemic hypertension. The relation between left ventricular (LV) enlargement in endurance trained subjects and QTd is unknown. The cloning of the angiotensin-converting enzyme (ACE) gene has made it possible to identify a deletion (D)-insertion (I) polymorphism that appears to affect the level of serum ACE activity. The aim of this study was to assess whether physiologic left ventricular hypertrophy as a result of physical training is associated with an increased QT length or dispersion depending on ACE I/D polymorphism. METHODS: 56 endurance athletes and 46 sedentary subjects were included in this study, and they underwent both complete echocardiographic and electrocardiographic examination, the QT interval was measured manually as an average based on a 12-lead ECG. We also analysed ACE I and D allele frequencies in all patients. RESULTS: Athletes had a significantly increased LV mass (235.1 +/- 68.5 g vs. 144.9 +/- 44.5 g, p < 0.001) and corrected QTd (QTcd) (55.5 +/- 18.1 ms vs. 42.9 +/- 17.2 ms, p < 0.001) in comparison to control subjects. There was a positive correlation between left ventricular mass index and QTcd in athletes (r = 0.3, p = 0.024). Left ventricular mass and mass index in ACE DD, DI and II genotypes were significantly different (p < 0.001). QTcd was significantly different between ACE DD (63.2 +/- 12.8 ms) and ACE II (44.9 +/- 17.6 ms) genotypes in athletes (p < 0.05). CONCLUSION: These data show that myocardial hypertrophy induced by exercise training might be associated with increased QTd as observed in systemic hypertension and might be affected by ACE I/D polymorphism.     

Effects of ischemia on QT dispersion during spontaneous anginal episodes.

Myocardial ischemia induced by pacing, angioplasty, or stress results in a significant increase in QT dispersion (QTd = QT maximum - QT minimum). This study investigated the effects of ischemia on QTd and the rate-corrected QTd (QT(c)d) during spontaneous anginal episodes in patients with coronary artery disease (CAD). Ninety-five patients with CAD and typical angina pectoris and 15 control subjects complaining of anginalike symptoms were studied. QTd and QT(c)d were calculated from 12-lead surface electrocardiograms recorded during and after the relief of pain. QTd and QT(c)d were significantly higher during the anginal episode (84+/-31 ms and 98+/-51 ms) compared to the painless conditions (69+/-24 ms and 71+/-24 ms) (P = .003 and P = .001 for QTd and QT(c)d, respectively) only in the 57 CAD patients who had a history of an old previous myocardial infarction. QTd and QT(c)d are significantly increased during spontaneous angina in patients with documented CAD and history of previous myocardial infarction.     

Patients Operated for Tetralogy of Fallot and with Non-Sustained Ventricular Tachycardia Have Reduced Heart Rate Variability

BACKGROUND: To study heart rate variability (HRV) in patients operated for tetralogy of Fallot (ToF) and to identify any correlation between HRV and ventricular tachycardia (VT). PATIENTS AND METHODS: We studied HRV in 23 consecutive patients operated for ToF (mean age 14 +/- 6.6 years; mean follow-up 10.6 +/- 5.2 years). Seven patients had non-sustained VT on Holter monitoring. Two control groups were included: 18 healthy subjects and 15 patients operated for other congenital heart disease. There were no differences in age, age at surgery (in the operated groups), follow-up, and mean heart rate between the three groups. Four time and four frequency domain indices were calculated: mean duration of RR intervals, standard deviation of all RR intervals (SD), square root of the mean squared differences of successive RR intervals (r-MSSD), percent of differences between adjacent RR intervals (pNN50), total power (TP), low frequency (LF), high frequency (HF), and LF/HF ratio. RESULTS: HRV indices were identical in the two control groups but were significantly reduced in patients with ToF. Within the patients who had been operated on for ToF, HRV indices were significantly lower in the seven with non-sustained VT than in those without arrhythmias: SD (95 +/- 15 vs. 135 +/- 54 ms; p = 0.01), r-MSSD (26 +/- 9 vs. 45 +/- 20 ms; p = 0.03), pNN50 (4.4 +/- 3.4 vs. 16.5 +/- 12.5%; p = 0.001) and HF (111 +/- 97 vs. 352 +/- 291 ms(2); p = 0.009). Using stepwise multivariate regression analysis, pNN50, age at surgery, degree of pulmonary regurgitation and higher right/left ventricular ratio were independent predictive variables for VT (p < 0.0001; r(2) = 0.85). CONCLUSIONS: ToF patients, particularly those with ventricular arrhythmias, have significant impairment of sympatho-vagal balance, characterized by a reduction of vagal drive.     

Absence of change of signal-averaged electrocardiogram identifies patients with ventricular arrhythmias who are non-responders to amiodarone

OBJECTIVES: The aim of this study was to assess the ability of a non-invasive study, the signal-averaged ECG (SAECG), to predict the effect of amiodarone at ventricular level. BACKGROUND: Amiodarone is the main drug drug used in the treatment of ventricular arrhythmias. Standard ECG does not detect any change in QRS complex resulting from amiodarone therapy. SAECG is more sensitive than ECG for detecting changes in QRS complex. METHODS: The study examined the effects of amiodarone on SAECG in relation to the results of programmed ventricular stimulation in 68 patients with old myocardial infarction, spontaneous and inducible sustained ventricular tachycardia (VT). RESULTS: Amiodarone prolonged the total QRS duration (dur) (129+/-28 vs. 140+/-30 ms, P<0.05) and low amplitude signal (LAS) dur (45+/-20 vs. 51+/-20 ms, P<0.1), whereas the root-mean-square voltage of the last 40 ms of QRS complex (RMS 40) was significantly reduced (20+/-16 vs. 14+/-9 microV, P<0.05). Changes in SAECG parameters did not differ significantly in patients in whom amiodarone prevented the inducibility of VT (n=15) and those in whom VT remained inducible with amiodarone (n=53), but in baseline QRS duration was significantly shorter in patients in whom amiodarone prevented the VT induction (118+/-26 vs. 133+/-28 ms, P<0.05). In patients in whom amiodarone did not prolong the cycle length of VT (n=15), SAECG did not change significantly (QRS dur 131+/-29 vs. 132+/-27 ms, LAS 42+/-20 vs. 42+/-19 ms, RMS 40 22+/-14 vs. 19+/-11 microV). Comparison of the SAECG data in patients with no inducible VT and those with slowed VT differed significantly (P<0.05) between the control state and the recording with amiodarone. CONCLUSIONS: The effects of amiodarone on VT inducibility are predicted by a shorter baseline QRS duration and the degree of drug-induced prolongation of filtered QRS duration. Amiodarone prolonged the QRS duration, LAS duration and decreased RMS 40; this effect was more important in patients with no inducible VT and in those with only slowed VT, than in patients with unchanged or accelerated VT. The absence of changes of QRS duration predicted the induction of a more rapid or not slowed VT with amiodarone with a sensitivity of 87% and a specificity of 83%. Therefore, SAECG appears as an useful and simple means to predict the effects of amiodarone in patients with myocardial infarction and VT.     

Long-term follow-up of the signal-averaged ECG in arrhythmogenic right ventricular cardiomyopathy: correlation with arrhythmic events and echocardiographic findings.

AIMS: The aims of our study were to evaluate late potential changes during long-term follow-up in patients with arrhythmogenic right ventricular cardiomyopathy (ARVC) and to correlate these results with echocardiographic findings and sustained ventricular tachycardia (VT) occurrence. METHODS AND RESULTS: We studied 31 patients (22 males and 9 females; mean age 29+/-16) during 8 years of follow-up by signal-averaged ECG (SAECG) and echocardiography. Ten subjects experienced episodes of sustained VT. During follow-up, all the SAECG parameters showed a progressive significant increase in late potentials. In contrast, echocardiographic indices did not show evidence of relevant modifications. Patients with sustained VT were characterized by significantly lower left and right ventricular ejection fractions, longer values of filtered QRS at 25/40/80-250 Hz filters, and longer high-frequency low-amplitude (HFLA) signals at 25-250 Hz at baseline. The analysis of SAECG modification during follow-up indicated that only HFLA signals at 25-250 Hz increased significantly in the sustained VT group. CONCLUSION: We detected a progressive increase in delayed ventricular conduction by SAECG not associated with significant echocardiographic changes. Therefore, the conduction disturbance seems to increase independently from anatomical alterations. The baseline SAECG and echocardiographic parameters, more than their modifications during follow-up, appear to be useful in identifying patients with sustained VT.     

Late fields of the magnetocardiographic QRS complex as indicators of propensity to sustained ventricular tachycardia after myocardial infarction

INTRODUCTION: Magnetocardiographic (MCG) mapping is a new method to record cardiac signals. This study examined the association of MCG late fields with the propensity to sustained ventricular tachycardia (VT) after myocardial infarction (MI). METHODS AND RESULTS: One hundred patients with remote MI were studied, 38 with and 62 without history of VT. High-resolution MCG and signal-averaged ECG (SAECG) as a comparative method were recorded. Time-domain parameters describing the abnormal low-amplitude end QRS activity, MCG late fields, and SAECG late potentials were analyzed. Late field parameters differed significantly between the patient groups: filtered QRS duration was 137 +/- 26 msec in the VT group and 110 +/- 18 msec in the control group (P < 0.001), and root mean square amplitude of the last 40 msec was 260 +/- 170 and 510 +/- 360 fT (P < 0.001), respectively. The optimal MCG parameter combination yielded a sensitivity of 92% and a specificity of 61% in classification to the VT group, whereas those for SAECG were 63% and 66%. In a subgroup of 63 patients with marked left ventricular dysfunction and comparable stage of coronary heart disease, only MCG (sensitivity 73%, specificity 67%) but not SAECG could assign a patient to the VT group. CONCLUSION: Late fields of the MCG QRS complex indicate propensity to life-threatening arrhythmias in post-MI patients. This discriminative ability persists in the presence of severe left ventricular dysfunction where ECG late potentials lose their informative value. MCG late field analysis is a potential new method for noninvasive risk assessment in post-MI patients.     

陈旧性心肌梗死室性早搏与QT离散度及心率变异性的关系

目的:探讨陈旧性心肌梗死(OMI)患者室性早搏Lown's分级与QT离散度及心率变异性(HRV)的关系。方法:82例OMI患者,按室性早搏Lown's级别分组:A组:Lown's 1-3级,60例;B组:Lown's 4-5级,22例;检测各组HRV时域指标和QTd,并与正常对照组比较。结果:(1)A组的QTd与正常对照组比较无显著差异(P>0.05);而B组的QTd显著增加,明显大于A组和正常对照组(P<0.01);(2)与正常对照组和A组比较,B组的HRV各项时域参数指标显著降低(P<0.001)。结论:室性早搏Lown's 4-5级OMI患者的QTd明显增大、HRV显著降低;预示其发生恶性室性心律失常的危险性增高。     

Detection of atrial late potentials with P wave signal averaged electrocardiogram among patients with paroxysmal atrial fibrillation

The analysis of the QRS-complex with signal averaged ECG (SAECG) has been evaluated for patients affected by ventricular tachycardia for a long time. A longer filtered QRS-complex was a marker of a slower ventricular conduction velocity and reentry tachycardia. This method was modified for an analysis of the P wave (P-SAECG). Different filter methods were evaluated for the analysis of atrial late potentials. METHOD: We measured the bidirectional P wave signal averaged ECG of 45 consecutive patients with (group A) and without (group B) paroxysmal atrial fibrillation (PAF) and 15 young volunteers without a cardiac disease (group C). RESULTS: As a result patients with PAF had a significantly lower root mean square voltage of the last 20 ms (RMS 20) (2.59 +/- 0.89) vs 4.08 +/- 1.45 microV, p < 0.0003) and a significantly longer filtered P wave duration (FPD) than patients of the control collective (139.2 +/- 17.5 vs 115.1 +/- 17.7 ms, p < 0.0001) and the young volunteers (3.44 +/- 0.95 microV, p < 0.0001/101.9 +/- 14.2 ms, p < 0.009). Furthermore we found an age-dependent relationship of FPD between group B and C (115.1 +/- 17.7 vs 101.9 +/- 14.2 ms, p < 0.05) but not an age-dependent relationship of the RMS 20 (4.08 +/- 1.45 vs 3.44 +/- 0.95 microV, p = n.s.). A specificity of 80% and a sensitivity of 78% was achieved for identifying patients with atrial fibrillation by using a definition of atrial late potentials as FPD > 120 ms and a RMS 20 < 3.5 microV. CONCLUSIONS: The analysis of the P-SAECG can be used as a non-invasive method for identifying atrial late potentials. Atrial late potentials might be a reason for PAF. The predictive power of atrial late potentials has to be examined by prospective investigations of a larger patient population.     

Impact of diabetes mellitus on the improvement in signal-averaged electrocardiography after coronary artery bypass grafting.

BACKGROUND: Although it has been reported that coronary artery bypass grafting (CABG) for multivessel disease markedly improves several parameters of signal-averaged electrocardiography (SAECG), its beneficial effect on SAECG is variable. The hypothesis of the present study was that the presence of diabetes mellitus (DM) affects the improvement in SAECG after CABG. METHODS AND RESULTS: Pre- and post-operative SAECGs were recorded in 100 consecutive patients who underwent complete surgical revascularization. Changes in the following parameters were compared between the diabetic (n=43) and non-diabetic (n=57) patients: filtered QRS duration (dQRS), root mean square voltage in the terminal 40 s of the QRS complex (RMS40), and duration of the terminal low-amplitude signal lower than 40 microV (LAS40). Although baseline characteristics and the occurrence of late potentials were similar in both groups, quantitative improvements in the SAECG parameters after CABG were significantly greater in non-diabetic than in diabetic patients (dQRS: 109 +/- 22 ms vs 102 +/- 19 ms in diabetics and 106 +/- 21 ms vs 88 +/- 11 ms in non-diabetics; p=0.028, RMS40: 55 +/- 46 microV vs 65 +/- 38 microV in diabetics and 50 +/- 37 microV vs 76 +/- 37 microV in non-diabetics; p=0.037, LAS40: 31 +/- 20 ms vs 26 +/- 17 ms in diabetics and 32 +/- 12 ms vs 17 +/- 8 ms in non-diabetics; p=0.007, respectively). CONCLUSIONS: The presence of DM limits the CABG-induced improvement in SAECG. In diabetic patients, therefore, perioperative changes of the SAECG must be interpreted with caution.     

Ventricular arrhythmia and late potentials in patients with hypertrophic cardiomyopathy]

Holter monitoring (48 h) and registration of signal-averaged late potentials (method of Simson, high pass filter 40 Hz) were performed in outpatiens with hypertrophic cardiomyopathy. A prevalence of spontaneous ventricular arrhythmias could be determined in 51 patients; the results of 45 patients not taking antiarrhythmic drugs are presented here. 96% of these showed ventricular premature beats, 76% had multiform extrasystoles, 27% showed pairs of ectopic beats and 20% had runs of ventricular tachycardia (more than 3 QRS complexes). Absolute counts of premature beats were low in most patients, but important interindividual differences could be observed: M = 34 extrasystoles/24 h (0-4943). Ventricular tachycardias were of short duration (maximum 11 QRS) with heart rate ranging from 120 to 200/min. All patients were asymptomatic during tachycardia. Signal-averaged late potentials could be registered in 30 patients, 28 of them without antiarrhythmic drug therapy. Mean QRS duration (QRSdur) was 108 +/- 12 ms, mean duration of low amplitude signals (less than 40 microV) in the terminal portion of the QRS (LAdur) was 27 +/- 13 ms, and mean amplitude of the last 40 ms of the filtered QRS (LAamp) was 65 +/- 43 microV. A patient was considered to show late potentials if two of the following criteria were present: QRSdur greater than 120 ms, LAdur greater than or equal to 40 ms, LAamp less than 20 microV. This was found in four patients.(ABSTRACT TRUNCATED AT 250 WORDS)