Repolarization abnormalities detected by magnetocardiography in patients with dilated cardiomyopathy and ventricular arrhythmias

Repolarization Abnormalities by Magnetocardiography. Introduction: Abnormal repolarization is one of the acknowledged mechanisms leading to malignant ventricular arrhythmias. We used a novel magnetocardiographic technique to investigate the role of inhomogeneous repolarization in patients with nonischemic dilated cardiomyopathy prone to sustained ventricular arrhythmias.
Methods and Results: Forty-nine dilated cardiomyopathy patients were studied, 18 with a history of sustained ventricular tachycardia (  n = 6  ) or ventricular fibrillation (  n = 12  ) and 31 with no ventricular arrhythmias. The magnetocardiogram was registered and QT apex and QT end intervals were determined by a computer algorithm. Inhomogeneity of repolarization was characterized with indices describing QT apex and QT end dispersion, and T wave end duration. In addition, time-domain late fields of the QRS complex in magnetocardiography and QT dispersion in 12-lead ECG were determined. T wave end was longer in the arrhythmia group in patients with sinus rhythm (  87 ± 15 msec vs 73 ± 12 msec; P = 0.005  ) and in those not having bundle branch block. Magnetocardiographic late fields of the QRS complex were not different between groups. QT apex and end dispersion on magnetocardiography or 12-lead ECG showed no difference.
Conclusion: Prolongation of the end part of the T wave revealed by magnetocardiography is related to malignant ventricular arrhythmias in dilated cardiomyopathy. The results suggest that abnormal repolarization rather than delayed conduction underlies the arrhythmias in this disease.     

Premature ventricular beats in healthy adult subjects 20 to 79 years of age

111 healthy subjects, 57 males and 54 females, 20–79 yearsof age, randomly selected among the participants of the CopenhagenCity Heart Study were tested for ventricular ectopic activityusing ambulatory 24-h ECG recording.One or more premature ventricularbeats (PVBs) appeared in 68 subjects (61%), 35 males and 33females (61% of each group). The prevalence of PVBs increasedsignificantly with age: 31, 68 and 84% in the respective agegroups: 20–39, 40–59 and 60–79 (P<0.05). The number of PVBs per 24 h was <24 in 88 (79%), <300in 105 (95%), and <500 in 107 (96%). More than 1000 PVBsper 24 h appeared in 3 (2.7%), one of whom had 11 669. The numberof PV Bs per 24 h increased with age, but the increase was notstatistically significant. The number of PV Bs per 100 000 recordedQRS-complexes did not differ significantly from the number ofPV Bs per 24 h. The number of PV Bs h^-1 was highest in daytime, and apparentlyhigher in males than in females. However, the difference betweenthe two sexes was not statistically significant. Multiform PV Bs appeared in 4 subjects, interpolated PV Bs in2, a run of 5 PV Bs in 1, dropped beats in 3, two pauses of1900 ms duration in 1, and several post-acceleration pausesof 1300 ms duration in 1.     

Comparison of magnetocardiography and electrocardiography: a study of automatic measurement of dispersion of ventricular repolarization.

AIMS: There is some dispute over the clinical significance of dispersion of ventricular repolarization measurements from the electrocardiogram. Recent studies have indicated that multichannel magnetocardiograms (MCGs), which non-invasively measure cardiac magnetic field strength from many sites above the body surface, may provide independent information from ECGs about ventricular repolarization dispersion. For this study, magnetocardiography and electrocardiography were compared from automatic measurements of dispersion of ventricular repolarization. METHODS AND RESULTS: Dispersion of ventricular repolarization time was determined in MCGs and standard ECGs recorded simultaneously from 27 healthy volunteers and 22 cardiac patients. Two automatic techniques were used to determine the interval of ventricular repolarization. There were significant differences in ventricular dispersion between ECG and MCG measurements, with multichannel MCG greater than ECG by 52 (47) ms [mean (SD)] (P<0.00001) and 12-channel MCG greater by 17 (40) ms (P<0.004) across techniques and all subjects. Magnetocardiograms had the greater discriminating power between normal and cardiac patients with differences of 46 (18) ms (P<0.017) for multichannel MCG and 44 (16) ms (P<0.005) for 12-channel MCG, compared with 16 (7) ms (P<0.04) for ECG. CONCLUSION: Magnetocardiography has the power to discriminate regional cardiac conduction differences.     

Predictive value of ventricular premature beats for subsequent ischaemic heart disease in apparently healthy subjects.

From 1978 to 1980, 260 healthy subjects, 40-79 years of age, underwent 24 h ambulatory electrocardiography in order to determine the prevalence and complexity of ventricular premature beats (VPBs) in adults without apparent heart disease. The number of types of VPBs seem in 5% or less were considered 'abnormal' and the present follow-up study undertaken in order to assess the significance of such 'abnormal' VPBs as predictors of subsequent ischaemic heart disease (IHD). Information concerning cardiac events within the follow-up period was available in 237 subjects. Nine were lost to follow-up and 24 refused clinical examination. IHD was documented in 13 (eight myocardial infarction, five angina pectoris). 'Abnormal' VPBs occurred in six out of 13 (46%) who later developed IHD compared to only 24 out of 213 (11%) without IHD (P less than 0.001). The presence of either more than 900 VPBs 24 h-1 or ventricular tachycardia of more than three beats, identified five out of 13 patients with IHD (sensitivity 38%), whereas 210 out of 213 with no evidence of IHD at follow-up were identified (specificity 98%). Four out of seven who initially had more than 900 VPBs 24 h-1 had IHD on follow-up. Our results have demonstrated a strong positive association between 'abnormal' VPBs observed in a random 24-h electrocardiographic recording of apparently healthy subjects 40-79 years of age and subsequent IHD. They also suggest that a 24-h ECG may be useful for the assessment of coronary risk even in asymptomatic subjects.     

Heart rate turbulence after ventricular and atrial premature beats in subjects without structural heart disease

INTRODUCTION: Studies assessing heart rate (HR) behavior after premature beats have focused on HR responses to ventricular premature beats (VBPs), but there is less information of HR behavior after atrial premature beats (APBs). METHODS AND RESULTS: HR turbulence after VPBs and APBs was first measured in response to ambient APBs and VPBs occurring during 24-hour ambulatory ECG recordings in 29 subjects without structural heart disease, and in response to programmed atrial (AE) and ventricular extrastimuli (VE) in 6 subjects undergoing electrophysiologic (EP) examination. Turbulence onset (TO) was more negative (-2.3 +/- 3.2% vs -0.9 +/- 2.8%, P < 0.01) and turbulence slope (TS) was steeper (11 +/- 11 vs 5.1 +/- 4.1 msec/R-R interval, P < 0.05) after VPBs than APBs. Compared to VPBs, the acceleration of HR after APBs was delayed by one beat, and APBs were associated with a short R-R interval preceding the APB, resulting in a blunted TO. Studies of patients undergoing an EP test confirmed the one-beat delay of HR acceleration and the blunted TO after programmed AE compared to VE (P < 0.05). TO and TS after VPBs were related to baroreflex sensitivity. TO also was related to 24-hour standard deviation of N-N intervals (SDNN). However, the TO or TS following APBs was not related to either SDNN or baroreflex sensitivity. CONCLUSION: HR behavior is different in response to APBs and VBPs among subjects without structural heart disease. Different definitions and calculation formulas should be used in the analysis of HR turbulence after APBs and VPBs.     

Normal values and reproducibility of left ventricular filling parameters by radionuclide angiography

Background. In physiologic situations age, heart rate (HR) and left ventricular ejection fraction (EF) may influence left ventricular filling rate. In this study, we determined normal values for radionuclide angiography (RNA) derived diastolic filling parameters, the correlations with age, HR and EF and their reproducibility. Methods. The study was performed in 20 patients, 40–76 years old (mean 57), with normal findings at coronary angiography and left ventriculography. The first RNA was performed at rest (RNA1). Then, five minutes bicycle ergometry was performed and the patients were allowed five minutes rest before RNA was repeated (RNA2). From the left ventricular time activity curve we determined peak filling rate (PFR), time to peak filling rate (TPFR) and atrial contribution (AC) to ventricular filling. Results. Values for PFR1 were 2.2 ± 0.6 EDV/sec (PFR2 2.4 ± 0.7 EDV/sec, r = 0.82), for TPFR1 198 ± 22 msec (TPFR2 203 ± 24 msec, r = 0.45) and for AC1 31 ± 11% (AC2 31 ± 10%, r = 0.72). The correlations of PFR and TPFR with age were statistically significant (respectively r = - 0.68 and r = 0.48, P < 0.05). PFR was also influenced by HR and EF (resp. r = 0.51 and r = 0.50, P < 0.05). TPFR however was not influenced by HR and EF, whereas AC was positively correlated with HR (r = 0.79, P < 0.01). Conclusions. Radionuclide angiography is a reliable and reproducible method to assess parameters of diastolic left ventricular filling in individual patients. It may therefore be used to serially follow diastolic function. When used for interindividual comparison the dependency of RNA derived left ventricular filling parameters on age, HR and EF should however be considered.     

关于心室复极顺序的错误表述--浅谈心室除复极过程与 QRS-T 同向机制

传统观点认为 QRS-T 同向是由于“先除极的地方后复极”,这是除、复极概念上的混淆,是把3相当成了复极的全部,把2相当成了除极的延续,把复极进程的差异归于外因,而忽略了心室肌本身在细胞电生理特点上的巨大差异。实际上,先除极的地方必然先复极,但后除极的地方复极更快、结束更早,使整个心室的膜电位梯度指向外膜,故 QRS 向量与 T 向量大致同向。     

Effects of cardiac resynchronization therapy on ventricular repolarization in patients with congestive heart failure

INTRODUCTION: Biventricular pacing has been shown to improve the clinical status of patients with congestive heart failure, but little is known about its influence on ventricular repolarization. The aim of our study was to evaluate the effect of biventricular pacing on ECG markers of ventricular repolarization in patients with congestive heart failure. METHODS AND RESULTS: Twenty-five patients with congestive heart failure, sinus rhythm (SR), and complete LBBB (6 females; age 61 +/- 8 years; NYHA class II-III; echocardiographic ejection fraction 21 +/- 5%; QRS > or = 130 ms) underwent permanent biventricular DDDR pacemaker implantation. A high-resolution 65-lead body-surface ECG recording was performed at baseline and during right-, left-, and biventricular pacing, and the total 65-lead root mean square curve of the QRST complex and the interlead QT dispersion were assessed. The QRS duration was increased during right (RV)- and left ventricular (LV) pacing (127 +/- 26% and 117 +/- 40%; P < 0.05), as compared to SR (100%) and biventricular pacing (93 +/- 16%; ns). The QTc interval was increased during RV and LV pacing (112 +/- 12% and 114 +/- 14%; P < 0.05) as compared to SR (100%) or biventricular pacing (99 +/- 12%). There was no effect on JT interval during all pacing modes. The T(peak-end) interval was increased during right (120 +/- 34%; P < 0.01) and LV pacing (113 +/- 29%; P < 0.05) but decreased during biventricular pacing (81 +/- 19%; P < 0.01). A similar effect was found for the T(peak-end) integral and the T(peak) amplitude. QT dispersion was increased during right ventricular (129 +/- 16 ms; P < 0.05) and decreased during biventricular pacing (90 +/- 12 ms; P < 0.01), as compared to SR (114 +/- 22 ms). CONCLUSIONS: Using a high-resolution surface ECG, biventricular pacing resulted in a significant reduction of ECG markers of ventricular dispersion of repolarization.     

Factors of importance to Doppler indices of left ventricular filling in 50-year-old healthy subjects

Age is an important determinant of Doppler indices of left ventriculardiastolic filling in normal subjects. To define reference valuesand factors of importance to Doppler indices of left ventricularfilling in subjects of similar age, 58 men and 76 women aged50 years underwent Doppler echocardiography. All those takingpart in the study were healthy. When gender was analysed ina multivariate model it showed a significant independent correlationwith the peak velocity of early diastolic filling (E wave) (P<0·00l)and the early to atrial peak velocity (E/A) ratio (P<0·0l).The peak E wave velocity was 0·75±0·11m . s^–1 vs 0·66±0·10 m . s^–1(P<0·0O1) and the E/A ratio was 1·24±0·25vs 1·14±0·20 (P<0·05) in womenand men, respectively. In multivariate analyses, heart rate,diastolic blood pressure and body mass index correlated independentlywith the E/A ratio in women (P<0·00l for all), whereasin men, heart rate, diastolic blood pressure, body mass indexand left ventricular diameter correlated independently withthe E/A ratio (P<0·00l for all). Doppler measurementsof left ventricular filling in 50-year-old healthy subjectsshowed a wide variation and were significantly associated withheart rate, diastolic blood pressure, body mass index and gender.     

Premature beats in healthy subjects 40-79 years of age

In order to determine the prevalence and complexity of prematurebeats (PBs) in an adult population without apparent heart disease,260 healthy subjects 40–79 years of age had a 24 h ambulatoryECG recording performed. A total of 221 subjects (87%) had one or more atrial prematurebeats (APBs) in the 24 h period, which was statistically significantlymore than the number of subjects (179 or 69%) with ventricularpremature beats (VPBs). Only 19 subjects (7%) had no PBs. Morethan 200 VPBs/24 h were seen in only 5% of the subjects, anda similar percentage had more than 200 APBs/24 h. There wasa statistically significant increase in the number of VPBs aswell as APBs with an increase in age. Multiform VPBs, VPB pairs,multiform APBs and atrial tachycardia (AT) were ‘normal’findings(seen in more than 5% of the subjects), whereas > 2 differentVPB configurations, > 2 episodes of VPB pairs, ventricularbigeminy, R-on-T VPBs, ventricular tachycardia, > 2 episodesof AT and AT with more than 10 beats per episode were ‘abnormal’findings (seen in less than 5% of the subjects). The number of VPBs was almost identical in two 24 h ECG recordingsobtained at a mean interval of 22 months in 17 out of 22 subjectsstudied. Only two out of 22 had a significant change in thenumber of VPBs/24 h over the 22 month period. As a ‘normal’ range for the number of APBs as wellas VPBs per 24 h a figure of 200 is proposed, and it is concludedthat most complex types of PBs may occur as incidental findingsin healthy adult subjects, but usually in small numbers.     

Electrocardiographic measures of repolarization dispersion and their relationships with echocardiographic indices of ventricular remodeling and premature ventricular beats in hypertension

Objective To examine the relationship between Tpeak- Tend interval (Tpe) and Tpe/QT ratio with occurrence of ventricular premature beats (VPBs) and left ventricular remodeling in hypertension. Methods A total of 52 patients with mild to moderate essential hypertension were included, undergoing echocardiography and 24-hours Holter monitoring. Ventricular remodeling was assessed by left ventricular mass index (LVMI) using the Devereux formula and diastolic function by transmittal E and A wave velocities and E/A ratio. Tpe was measured in the precordial leads. The end of the T wave was set by the method of the tangent to the steepest descending slope of the T wave. Results Tpe and Tpe/QT in leads V2 (r = 0.33, P = 0.01; r = 0.27, P = 0.04 respectively) and V3 (r = 0.40, P = 0.002; r = 0.40, P = 0.003, respectively) correlated significantly with LVMI. A significant inverse relationship was observed between E/A ratio and QT (r = -0.33, P = 0.01), Tpe in V3 (r = -0.39, P = 0.003) and Tpe/QT in V3 (r = -0.31, P = 0.02). Tpe in V3, V5, mean Tpe and maximum Tpe with cut-off values of 60 ms, 59 ms, 62 ms and 71 ms, respectively, associated with the occurrence of ventricular premature beats. Conclusions The repolarization parameters Tpe interval and Tpe/QT ratio correlate with LVMI and indices of left ventricular diastolic function and show better predictive values than traditional parameters such as QT interval and QT dispersion. Lead V3 is the best lead for measuring Tpe and Tpe/QT. These ECG indices can therefore be used in clinical practice to monitor LV remodeling and predict occurrence of VPBs.     

Changes of the T-wave amplitude and angle: an early marker of altered ventricular repolarization in hypertension

BACKGROUND: The heterogeneity of ventricular repolarization is an important proarrhythmic factor. QT dispersion has been proposed to reflect the inhomogeneity of ventricular repolarization, but a poor reproducibility limits its clinical applicability. Reliable noninvasive methods to quantify abnormalities in ventricular repolarization are still lacking. The T-loop morphology analysis is a novel method aimed at quantifying ventricular repolarization. HYPOTHESIS: To test the ability of the T-loop morphology analysis to discriminate between hypertensive patients and healthy subjects, 105 hypertensive patients (mean age 63.6 +/- 12.3 years) and 110 healthy controls (mean age 49.7 +/- 14.3 years) were evaluated. METHODS: The maximum QT interval (QT maximum), the minimum QT interval (QT minimum), and their difference (QT dispersion) were calculated from a digitally recorded 12-lead electrocardiogram (ECG) in both study groups. X, Y, and Z leads were reconstructed from the 12-lead ECG, and the amplitude of the maximum T vector (T amplitude) and the angle between the maximum T vector and X axis (T angle) were calculated from the projection of the T loop in the frontal plane. RESULTS: T amplitude (p < 0.001), T angle (p = 0.05), and QT dispersion (p = 0.04) were significantly different between hypertensive patients and controls, while QT maximum (p = 0.14) and QT minimum (p = 0.35) did not differ between the groups. T amplitude was the only marker which differed between hypertensive patients without ECG criteria for left ventricular hypertrophy and controls (p = 0.002). CONCLUSIONS: T-loop features and particularly T amplitude are significantly different between hypertensive patients and healthy controls and may serve as early markers of repolarization abnormalities in a hypertensive population.     

Left ventricular mass by 12-lead electrocardiogram in healthy subjects: comparison to cardiac magnetic resonance imaging

The ability to estimate left ventricular mass (LVM) from the standard 12-lead electrocardiogram (ECG) has been shown to be limited because there is a considerable variability of the normal 12-lead ECG due to demographic and anthropometric variables. We sought to study LVM in healthy subjects and its relationship with QRS duration, and established electrocardiographic criteria for left ventricular hypertrophy. Cardiac magnetic resonance imaging was used to measure LVM. Seventy-one healthy volunteers (36 men; age range, 21-82 years) were studied. All ECG criteria tested showed a statistically significant relationship with LVM. The highest R value was found between LVM and QRS duration, as well as the 12-lead voltage-duration product (R = 0.59, P < .001 for both). The lowest R value was found for the Sokolow-Lyon voltage criterion (R = 0.25, P = .033). Left ventricular mass differed significantly between sexes, as did all ECG criteria except the Sokolow-Lyon criterion. Thus, in healthy subjects, QRS duration alone is equally or more strongly correlated to LVM than are established electrocardiographic left ventricular hypertrophy criteria.     

健康人与冠心病人心室复极时间的昼夜节律对比研究

目的探讨冠心病和冠心病高危因素对心室复极时间及其昼夜节律的影响。方法观察冠心病、冠心病高危因素病人、健康人的心室复极时间昼夜分布曲线，并进行对比分析。结果各组均显示J-T间期呈夜长昼短。午后稍回升的节律，经心率校正后，这种节律变小，冠心病人则消失。结论经心率校正后，心室复极时间本身存在夜长昼短节律。冠心病人的心室复极时间昼夜变化消失。与心肌缺血、自主神经病变、心脏结构重构等相关，可能是其易发生室性心律失常的原因。