The significance of late-phased dart T wave in the electrocardiogram of children

Dome-and-dart T Waves and Hyperthyroidism - A Case Report

We briefly describe a case of a 31-year-old man with persistent hyperthyroidism, despite medical treatment with high dose methimazole. Twelve-lead 24-hour Holter monitoring showed bifid (or dome-and-dart) T waves and echocardiography revealed mild left ventricle dilatation. Hyperthyroidism was eventually treated with total thyroidectomy, and thereafter, T waves became normal and the left ventricle returned to normal dimensions. Hyperthyroidism should be considered among the differential diagnoses when T wave abnormalities are observed on electrocardiogram and when mild left ventricle dilatation is observed on an echocardiogram. The correction of hyperthyroidism can reverse these abnormalities.

Bifid T waves in leads V2 and V3 in children: a normal variant

Introduction

The T wave is rarely bifid, apart from patients with long QT syndrome or subjects treated with antiarrhythmic drugs. At times, a U wave partially superimposed upon the T wave is responsible for an apparently bifid T wave. Bifid T waves, in contrast, have been described in normal children in the past, but the phenomenon has not received any attention in recent years, to the extent that it is not mentioned in current textbooks of paediatric cardiology. Aim of the present study was to determine the incidence and clinical counterpart of bifid T waves in a paediatric population.

Methods

We selected 604 consecutive children free from clinically detectable heart disease; subjects whose electrocardiogram showed a bifid T wave underwent a complete clinical and echocardiographic examination. In addition, the electrocardiograms of 110 consecutive adults have also been analyzed. A T wave was considered as bifid whenever it was notched, being the 2 peaks separated from each other by a notch with duration ≥ 0.02 sec and voltage ≥ 0.05 mV. Moreover, in 7 children with bifid T wave in lead V2 further precordial recordings were obtained: a small electrode was gradually moved from V1 to V3, and 4 additional leads were recorded: 2 between V1 an V2, and 2 between V2 and V3.

Results

A bifid T wave was observed in 110 children (18,3%), with a relatively age-related incidence; the highest rate of bifid T waves (53%) occurred in the group of 5-year-old children. The bifid T wave was detected only in lead V2 in 51 cases (46,4%), only in lead V3 in 5 cases (4,6%), in both leads V2 and V3 in 50 cases (45,4%), and in leads other than V2 and V3 in 4 cases (3,6%). In the adult group, none of the examined electrocardiograms showed bifid T waves in any lead.

In the bifid T wave paediatric population, the echocardiogram did not reveal any abnormality, apart from 3 subjects which had an asymptomatic mitral valve prolapse; a trivial mitral and/or tricuspid regurgitation detected by color Doppler, as well as a patent foramen ovale in infants, were not considered as abnormal findings. The QTc interval was normal in all of the subjects; the average QTc interval was not different in the bifid T wave population (402 ± 46 msec) with respect to the control group (407 ± 39 msec).

Conclusion

The incidence of bifid T waves in leads V2 and V3 in normal children is high, and awareness of this phenomenon avoids possible misinterpretations leading to a diagnosis of ECG abnormalities.

Resolution of Abnormal Body Surface Maps in Children with Atrial Septal Defect after Intracardiac Repair

INTRODUCTION

The genesis of repolarization abnormalities of ECG waveforms in atrial septal defect (ASD), which typically is characterized by right ventricular (RV) volume overload, has not been explored, particularly in association with postoperative hemodynamic improvement. The aim of this study was to evaluate the effects of reduced RV overload after ASD closure on depolarization and repolarization abnormalities on body surface maps (BSMs).

METHODS AND RESULTS

BSMs of 14 children with ASD were recorded preoperatively and at early postoperative (1-6 months) and late postoperative (>9 months) stages. BSMs of 31 age-matched healthy children were studied as normal controls. Before intracardiac repair, QRS isopotential maps of children with ASD showed delayed RV breakthrough and subsequent rightward enlargement of the positive area with a maximum shifting to the right. Delayed conduction of the RV, particularly at the outflow tract area, was noted. The preoperative QRST isointegral maps exhibited the two-maximum pattern reflecting repolarization abnormality. The delayed appearance of breakthrough and delayed RV conduction on the QRS isopotential maps persisted from the preoperative to the late postoperative stage, whereas the two-maximum pattern on the QRST isointegral maps normalized to the one-dipole pattern at an early stage after repair.

CONCLUSION

Abnormal repolarization parameters in ASD patients showed rapid improvement postoperatively, despite the persistence of depolarization abnormalities. Therefore, the two-maximum pattern on the QRST isointegral maps indicates a primary T wave change due to hemodynamic RV volume overload.

Analysis of T wave changes by activation recovery interval in patients with atrial septal defect

We examined the distributions of the activation recovery interval (ARI), which is correlated with the local action potential duration (APD), to clarify the origin of the repolarization changes in ASD. The ECGs, QRST isointegral maps and ARI isochronal maps of 21 children with ASD from 3 to 5 years old in age were studied in comparison with 21 age-matched normal children. A conventional and 87 unipolar body surface ECG were simultaneously recorded. The ARIs were determined from the first derivatives of the ECG waveforms. Abnormal ST-T patterns were observed in 11 of 21 ASD, but only in two normal children. The QRST maps of a split positive area pattern were seen in 15 of ASD but none of the normal. In the ARI maps, all the normal children exhibited a short-ARI area on the left and a long-ARI area on the right side of the chest. In 19 of ASD, the ARI distribution revealed a leftward extension of the long-ARI area on the anterior chest, a relative shortening on the right anterior chest, and a localized prolonged ARI on the left anterior chest. The results suggest that right ventricular (RV) volume overload in ASD produces a localized prolongation of the APD on the RV epicardium.

Prominent bifid T waves observed in the QT prolongation caused by complete atrioventricular blockade in a hypokalemic diabetic patient

A 63-year-old diabetic man was admitted with general fatigue. Electrocardiogram (ECG) on admission showed complete atrioventricular (AV) blockade associated with prominent bifid T waves. The second component of the bifid T waves was distinguished from U waves by the beat-to-beat varying bifidity and the nadir between the two components located at > or = 1 mm above the isoelectric line. Range of absolute QT interval was 535 to 650 ms. Hypokalemia (3.6 mEq/L) was noted at admission. Partial restoration of the potassium level (3.9 mEq/L) prior to temporary ventricular demand pacing obscured the bifid T waves and attenuated the QT prolongation and dispersion to some extent (absolute QT interval ranging 520 to 620 ms). It was concluded that marked bradycardia caused by complete AV blockade (ie, a junctional escaped rhythm at a rate of 42 beats/min), hypokalemia, and underlying diabetes mellitus contributed in concert to the QT prolongation and dispersion leading to the prominent bifid T waves.

Precordial leads QRST time integrals for evaluation of right ventricular overload in children with congenital heart diseases

It was previously shown that body surface QRST isointegral maps of the anterior chest were abnormal in patients with right ventricular overload and that the abnormalities varied with hemodynamic status. The QRST isointegral maps were first characterized by using a departure index map for normal controls. The study group consisted of 14 patients with pulmonary stenosis (PS), 20 with tetralogy of Fallot, (TOF) and 43 with atrial septal defect (ASD). The QRST isointegral maps of these three groups were compared with the data on 23 to 65 age-matched normal children. In mean departure index maps, the patients with right ventricular pressure overload (PS or TOF) showed an increase in departure index on the anterior midchest, while those of right ventricular volume overload (ASD) showed two maxima on the anterior and left lateral chest, with a trough-like negative area between them. Since the abnormal findings were seen on the anterior chest, we evaluated the diagnostic usefulness of QRST time integral values for precordial leads of the routine electrocardiogram (ECG) in a second part of this study. The precordial QRST time integral values from 9 patients with PS and 11 with TOF (0-2 years of age, mean 1.1 years) and 22 ASD patients (6-15 years, mean 10.1 years) were compared with those of the age-matched control children. The QRST time integral values of the precordial leads in right ventricular pressure overload were significantly increased in the right precordial leads (V1, V2). In right ventricular volume overload, the QRST time integral values of the V1, V2, V4, and V6 leads demonstrated a significant deviation from those of the control group. Therefore, a discrimination formula was constructed by using the values of these leads, and the criteria derived from this formula revealed good (98%) diagnostic accuracy. In detection of right ventricular overload, the QRST time integral values of the precordial lead ECG, if confirmed in a larger data set, may be useful as a simple screening method.

Body surface isopotential T map for assessment of right ventricular volume and pressure overloads in secundum atrial septal defect

The body surface isopotential T map was analyzed to detect right ventricular volume and pressure overloads in 25 patients with secundum atrial septal defect. Three patterns were distinguished: a T map resembling normal (type A, n = 9); that with an isolated negative area in a positive area (type B, n = 11); and that with rightward movement of maximum (type C, n = 5). Right ventricular end-diastolic volumes in types B (161 +/- 19% of normal; %N) and C (175 +/- 40% N) were significantly (p < 0.01) greater than those in controls (100 +/- 9% N) and type A (113 +/- 18% N). Right ventricular systolic pressure in type C (48 +/- 11 mmHg) was significantly (p < 0.01) higher than those in the controls (30 +/- 5 mmHg), type A (31 +/- 4 mmHg), or type B (34 +/- 5 mmHg). These results suggest that the patients with type B have right ventricular volume overload and those with type C have both volume and pressure overloads.

T wave "humps" as a potential electrocardiographic marker of the long QT syndrome

OBJECTIVES

This study attempted to determine the prevalence and electrocardiographic (ECG) lead distribution of T wave "humps" (T2, after an initial T wave peak, T1) among families with long QT syndrome and control subjects.

BACKGROUND

T wave abnormalities have been suggested as another facet of familial long QT syndrome, in addition to prolongation of the rate-corrected QT interval (QTc), that might aid in the diagnosis of affected subjects.

METHODS

The ECGs from 254 members of 13 families with long QT syndrome (each with two to four generations of affected members) and from 2,948 healthy control subjects (age > or = 16 years, QTc interval 0.39 to 0.46 s) were collected and analyzed. Tracings from families with long QT syndrome were read without knowledge of QTc interval or family member status (210 blood relatives and 44 spouses).

RESULTS

We found that T2 was present in 53%, 27% and 5% of blood relatives with a "prolonged" (> or = 0.47 s, "borderline" (0.42 to 0.46 s) and "normal" (< or = 0.41 s) QTc interval, respectively (p < 0.0001), but in only 5% and 0% of spouses with a borderline and normal QTc interval, respectively (p = 0.06 vs. blood relatives). Among blood relatives with T2, the mean [+/- SD] maximal T1T2 interval was 0.10 +/- 0.03 s and correlated with the QTc interval (p < 0.01); a completely distinct U wave was seen in 23%. T2 was confined to leads V2 and V3 in 10%, whereas V4, V5, V6 or a limb lead was involved in 90% of blood relatives with T2. Among blood relatives with a borderline QTc interval, 50% of those with versus 20% of those without major symptoms manifested T2 in at least one left precordial or limb lead (p = 0.05). A T2 amplitude > 1 mm (grade III) was observed, respectively, in 19%, 6% and 0% of blood relatives with a prolonged, borderline and normal QTc interval with T2 in at least one left precordial or limb lead. Among the 2,948 control subjects, 0.6% exhibited T2 confined to leads V2 and V3, and 0.9% had T2 involving one or more left precordial lead (but none of the limb leads). Among 37 asymptomatic adult blood relatives with QTc intervals 0.42 to 0.46 s, T2 was found in left precordial or limb leads in 9 (24%; 5 with limb lead involvement) versus only 1.9% of control subjects with a borderline QTc interval (p < 0.0001).

CONCLUSIONS

These findings are consistent with the hypothesis that in families with long QT syndrome, T wave humps involving left precordial or (especially) limb leads, even among asymptomatic blood relatives with a borderline QTc interval, suggest the presence of the long QT syndrome trait.

Correlation of electrocardiographic and echocardiographic changes in Kawasaki syndrome

To determine whether changes in ECGs correlated with abnormalities in echocardiograms in children with acute and convalescent Kawasaki syndrome, we undertook a retrospective analysis of 44 patients examined during the first 2 weeks of illness and followed for at least 6 months, 31 for longer than 1 year. We analyzed 360 ECGs, 282 echocardiograms, and clinical status. Results of echocardiography showed 18 children with myocardial dysfunction, pericardial effusion, and/or coronary arterial abnormalities (41%); 26 children had no abnormalities. All 18 of the former and all but 10 of the latter had abnormalities on serial ECGs that normalized on recovery. Thirty-four of 44 patients (77%) had ECG abnormalities. These abnormalities were most prevalent in the first month: 68% appeared in the first week, about 50% in the second to fourth weeks, 16% at 2 months, and 10% at 3 months. The type of ECG change did not predict the type of echocardiographic abnormality, except that low voltage of QRS was found only with pericardial effusion. The most frequent early changes were in T waves, which were flattened in 28 (64%). Later 12 patients had high, peaked, abnormal T waves. Prolonged PR interval occurred in 13 patients, seven of whom had echocardiographic abnormalities. Of six with prolonged QT interval, four had abnormal echocardiograms. The possibility of having an abnormal echocardiogram increased with the number of ECG changes: from 0 risk with no change to 37% for one, 47% for two, 80% for three, and 100% for four changes in serial ECGs. Both ECGs and echocardiograms are important in early and subsequent evaluation of these patients. Inasmuch as the ECGs showed abnormalities in 77% whereas echocardiograms showed changes in 41%, we believe that serial ECGs in comparison with prior tracings offer the more sensitive noninvasive indicator of pancarditis in young children during acute and convalescent Kawasaki syndrome.

Clinical electrocardiographic studies of bifid T waves

In 129 electrocardiograms from 129 patients showing bifid T waves as well as U waves the intervals from the beginning of the QRS complex to the two T wave apices (QaT1, QaT2), to the end of the T wave (QeT), and to the apex of the U wave (QaU) were measured. Eighty additional electrocardiograms from matched control subjects showing single peaked T waves were also studied. The precordial distribution of bifid T waves was assessed by calculating lead prevalence indices. This index progressively increased from 2.15 in the age range 20-29 years to 3.72 in the age range 60-69 years, and was significantly higher in patients with left ventricular hypertrophy and ischaemia (4.04) than in those with otherwise normal electrocardiograms (2.35). Thus older age and left ventricular pathology were accompanied by a more leftward location of bifid T waves. Exercise accentuated the bifid nature of the T wave in 12 of 18 patients with otherwise normal electrocardiograms, and diminished it in 11 of 19 cases with left ventricular hypertrophy and ischaemia. When 41 otherwise normal tracings showing bifid T waves were compared with those of 42 matched controls showing single peaked T waves, the QTc was longer and the eTaU interval shorter in the group with bifid T waves. Similarly, 40 patients with left ventricular hypertrophy and ischaemia showing bifid T waves had longer QTc and shorter eTaU intervals than 38 patients with the same diagnosis with single peaked T waves. These findings suggest that right precordial bifid T waves in younger patients with otherwise normal electrocardiograms probably result from delayed right ventricular repolarisation, whereas left precordial bifid T waves in older patients with left ventricular hypertrophy and ischaemia may indicate repolarisation delay in the ischaemic left ventricle.

The genesis of bifid T waves: experimental demonstration in isolated perfused rabbit hearts

In an attempt to elucidate the genesis of bifid T waves, we recorded transmembrane potentials of subepicardial ventricular muscle fibers simultaneously with a bipolar ventricular electrogram in isolated, perfused rabbit hearts, and the timing of the two apices of the T wave (aT1, aT2) was correlated with ventricular repolarization. The following results were obtained. (1) In seven of the nine hearts in which the repolarization process was mapped on the anterior and posterior surfaces of both ventricles, the 80% repolarization times of the left and the right ventricles were scattered around aT1 and aT2, respectively, and their average values closely corresponded to Q-aT1 and Q-aT2 intervals. This suggested that aT1 and aT2 depended on repolarization of the left and the right ventricles, respectively. (2) In one heart, aT1 appeared to reflect repolarization of the posterior ventricular wall, and aT2 that of the anterior wall. (3) In the remaining heart, aT2 coincided with repolarization of the anterobasal portion of the right ventricle, and aT1 that of the remaining portions of the ventricles. Even when ventricular repolarization was modified by low K+, low Ca2+ or procainamide perfusion, or by premature atrial stimulation, the close temporal correlation of the left and right ventricular repolarization with the two apices of the T wave was maintained. Selective cooling of the perfusate in either the left or the right coronary artery resulted in the production of bifid T waves in which aT2 coincided with the delayed repolarization of the cooled ventricle. We conclude that either physiologically or pathologically delayed repolarization in certain portions of the ventricles is most likely the cause of bifid T waves.