Dispersion of ventricular repolarization in hypertrophic cardiomyopathy

The electromechanical window for arrhythmia-risk assessment

The electromechanical window (EMW) is calculated by subtracting the repolarization duration from a mechanical reference representing contraction duration in the same heartbeat (eg, aortic valve closure during echocardiography with simultaneous electrocardiography). Here, we review the current knowledge on the role of the EMW as an independent parameter for ventricular arrhythmia-risk stratification. We (1) provide a standardized approach to echocardiographic EMW assessment, (2) define relevant cutoff values for both abnormal EMW negativity and positivity, (3) discuss pathophysiological underpinnings of EMW negativity, and (4) outline the potential future role of cardiac electromechanical relations in patients with proarrhythmic conditions.

Comparison of QT dispersion before and after PDA device closure in pediatrics

Background

Numerous studies have shown that QT dispersion (QTd) can be a suitable criterion for risk assessment of arrhythmia in patients with congenital heart disease. Pulmonary arterial hypertension (PAH) increases the risk of cardiac arrhythmia by changing ventricular repolarization homogeneity. In this study, we assessed QTd changes after PDA device closure and the effect of PAH on these changes.

Methods

Between October 2018 and March 2021, 97 patients (48 males; 49 females; mean age 31.36 ± 4.26 months; range 3 months to 14 years) who satisfied the primary inclusion criteria and did not meet the exclusion criteria and underwent PDA device closure intervention were included in the study. Echocardiography was performed before the procedure. QT corrected (QTc), and QTd and PR intervals were measured according to the patients’ standard 12‐lead ECGs in two periods, preoperative (1 day) and after (3 months).

Results

In the general group, QTc and QTd decreased significantly after PDA closure. Based on our classification of the patients in two groups of high PAP and normal PAP, the three parameters QTc, QTd, and PR interval were assessed separately in the two groups. All three parameters decreased significantly in the normal PAP and high PAP groups.

Conclusions

However, a left‐to‐right shunt through the patent ductus arteriosus can affect ventricular repolarization; this effect seems to be particularly more significant when there is pulmonary hypertension.

QT spatial dispersion and sudden cardiac death in hypertrophic cardiomyopathy: Time for reappraisal

BACKGROUND

The 12-lead surface electrocardiographic (ECG) analysis is able to provide independent predictors of prognosis in several cardiovascular settings, including hypertrophic cardiomyopathy (HCM). The present single-center study investigated the possible ability of several ECG-derived variables in stratifying sudden cardiac death (SCD) risk and, possibly, in improving the accuracy of the 2014 European Society of Cardiology guidelines.

METHODS

A total of 221 consecutive HCM outpatients were recruited and prospectively followed. All of them underwent a full clinical and instrumental examination, including a 12-lead surface ECG to calculate the dispersion for the following intervals: QRS, Q-Tend (QT), Q-Tpeak (QTp), Tpeak-Tend (TpTe), J-Tpeak (JTp), and J-Tend (JT). The study composite end-point was SCD, aborted SCD, and appropriate implantable cardioverter defibrillator (ICD) interventions.

RESULTS

During a median follow-up of 4.4 years (25th-75th interquartile range: 2.4-9.4 years), 23 patients reached the end-point at 5-years (3 SCD, 3 aborted SCD, 17 appropriate ICD interventions). At multivariate analysis, the spatial QT dispersion corrected according to Bazett's formula (QTcd) remains independently associated to the study endpoint over the HCM Risk-SCD score (C-index 0.737). A QTcd cut-off value of 93ms showed the best accuracy in predicting the SCD endpoint within the entire HCM study cohort (sensitivity 56%, specificity 75%, positive predictive value 22%, negative predictive value 97%).

CONCLUSION

Our data suggest that the QTcd might be helpful in SCD risk stratification, particularly in those HCM categories classified at low-intermediate SCD risk according to the contemporary guidelines.

The normal electrocardiograms in the conscious newborn lambs in neonatal period and its progression

BACKGROUND

Veterinary cardiology, especially electrocardiography, has shown major advancements for all animal species. Consequently, the number of ovine species used as experimental animals has increased to date. Few studies have been published on ovine systematic electrocardiography, particularly with respect to lamb physiology and neonatology. This study aimed to standardize the values of normal waves, complexes, and intervals of the electrocardiogram (ECG) in clinically Bergamasca healthy neonatal lambs, used as experimental animals. Serial computerized electrocardiography was performed in 10 male and 12 female neonates on the 1st, 7th, 14th, 21st, 28th, and 35th days of age. The following parameters were analyzed: heart rate and rhythm, duration and amplitude of waves, duration of intervals, and heart electrical axis.

RESULTS

During the first 35 days of life, (1) the sinusal heart rhythm was predominant, (2) there was a progressive decrease in the heart rate and R and T wave amplitude, and (3) a progressive increase in the PR, QT, and RR intervals. Finally, we confirmed that various components of neonatal evolution were more discernible in the augmented unipolar leads (aVF), which we recommend should be preferentially used in future studies. No significant statistical alterations were observed between males and females in relation to the analyzed parameters.

CONCLUSIONS

The information assimilated in this study is anticipated to enhance the diagnosis of multiple congenital heart defects in Bergamasca lambs and could be implemented in studies that use ovine species as experimental models.

Spatial QT Dispersion Predicts Nonsustained Ventricular Tachycardia and Correlates with Confined Systodiastolic Dysfunction in Hypertrophic Cardiomyopathy

Objectives: An increased dispersion of myocardial repolarization represents one of the mechanisms underlying the arrhythmic risk in hypertrophic cardiomyopathy (HCM). We investigated spatial myocardial repolarization dispersion indices in HCM patients with nonsustained ventricular tachycardia (NSVT) and, contextually, their main clinical determinants. Methods: Fifty-two well-matched HCM outpatients were categorized into two groups according to the presence or the absence of NSVT at 24-hour Holter electrocardiogram (ECG) monitoring. Each patient underwent a clinical examination, including Doppler echocardiogram integrated with tissue Doppler imaging, cardiac magnetic resonance, and 12-lead surface ECG to calculate the dispersion for the following intervals: QRS, Q-Tend (QTe), Q-Tpeak, Tpeak-Tend (TpTe), J-Tpeak, and J-Tend. Results: The NSVT group showed only QTe dispersion and TpTe dispersion values to be significantly higher than their counterparts. NSVT occurrence was independently predicted by late gadolinium enhancement presence (p = 0.021) and QTe Bazett dispersion (p = 0.030), the latter strongly associated with the myocardial performance index (MPI) obtained at the basal segment of the interventricular septum (p = 0.0004). Conclusion: Our data support QTe dispersion as an easy and noninvasive tool for identifying HCM patients with NSVT propensity. The strong relationship between QTe dispersion and MPI allows us to hypothesize an intriguing link between electrical instability and confined myocardial areas of systodiastolic dysfunction.

Prolonged QT dispersion in the infants of diabetic mothers

Myocardial hypertrophy and cardiac dysfunction frequently occur in newborns of diabetic mothers. The authors hypothesized that wall hypertrophy or disproportionate left ventricular wall thickness in newborns of diabetic mothers may affect both QT and QTc dispersion. This study aimed to assess whether left ventricular hypertrophy affects the QT variables of infants born to diabetic mothers. This prospective cross-sectional study was conducted with 47 consecutively selected neonates of gestational diabetic mothers and 30 healthy neonates born to healthy mothers. All the subjects were evaluated during the neonatal period. Electrocardiography with echocardiography was performed for the patients and the control subjects. The newborns of the diabetic mothers were classified according to septal thickness as group 1 (16 newborns with septal hypertrophy) or group 2 (31 newborns without septal hypertrophy). The study group consisted of three cohorts: groups 1, 2, and 3 (control group). Both QT and QTc dispersion were computed from a randomly selected beat as well as from an average beat derived from 12 beats included in a 10-s electrocardiography. A total of 16 infants (34%) had a septal thickness of 6 mm or greater. The left ventricular end-systolic diameter in group 1 was smaller (p = 0.0029) than in groups 2 and 3 (p = 0.003). The interventricular septal thickness at end diastole (IVSTd) and the left ventricular posterior wall thickness at end diastole in group 1 were higher than in of groups 2 and 3. The QT and QTc dispersion intervals were longer in group 1 than in groups 2 and 3 (p < 0.001), and a highly significant positive correlation was detected between IVSTd and QT dispersion (r = 0.514, p = 0.042). Elevated QT and QTc dispersions may be risk factors for the development of arrhythmias in newborns of diabetic mothers. These patients may critically need systematic cardiac screening.

Impact of QT variables on clinical outcome of genotyped hypertrophic cardiomyopathy

BACKGROUND

Although QT variables such as its interval and/or dispersion can be clinical markers of ventricular tachyarrhythmia, few data exist regarding the role of QT variables in genotyped hypertrophic cardiomyopathy (HCM). Therefore, we analyzed QT variables in genotyped subjects with or without left ventricular hypertrophy (LVH).

METHODS

QT variables were analyzed in 111 mutation and 43 non-mutation carriers who were divided into three groups: A, those without ECG abnormalities and echocardiographically determined LVH (wall thickness > or =13 mm); B, those with ECG abnormalities but LVH; and C, those with ECG abnormalities and LVH. We also examined clinical outcome of enrolled patients.

RESULTS

Maximal LV wall thickness in group C (19.0 +/- 4.3 mm, mean +/-SD) was significantly greater than that in group A (9.2 +/- 1.8) and group B (10.4 +/- 1.8). Under these conditions, maximum QTc interval and QT dispersion were significantly longer in group C than those in group A (438 +/- 38 ms vs 406 +/- 30 and 64 +/- 31 vs 44 +/- 18, respectively; P < 0.05). QTc interval and QT dispersion in group B (436 +/- 50 and 64 +/- 22 ms) were also significantly greater than those in group A. During follow-up periods, four sudden cardiac deaths and one ventricular fibrillation were observed in group C, and two nonlethal ventricular tachyarrhythmias were observed in group B.

CONCLUSIONS

Patients with HCM-related gene mutation accompanying any ECG abnormalities frequently exhibited impaired QT variables even without LVH. We suggest that careful observation should be considered for those genotyped subjects.

Effects of Methadone on QT-Interval Dispersion

STUDY OBJECTIVE

To evaluate the effects of methadone on QT-interval dispersion.

DESIGN

Single-center, prospective, cohort study.

SETTING

Methadone maintenance treatment facility.

PATIENTS

One hundred eighteen patients who were newly admitted to the facility. Intervention. Twelve-lead electrocardiograms (ECGs) were performed in patients at both baseline and 6 months after the start of methadone therapy.

MEASUREMENTS AND MAIN RESULTS

The ECGs were manually interpreted, and investigators were blinded to time interval and methadone dose. At least eight discernible ECG leads were required for study inclusion. Mean differences between baseline and follow-up rate-corrected QT (QTc) interval and QT dispersion were compared. Multivariate associations between clinical characteristics and magnitude of change in QT dispersion were assessed using linear regression. Mean +/- SD baseline QT dispersion was 32.9 +/- 12 msec, which increased to 42.4 +/- 15 msec (+9.5 +/- 18.6 msec, p<0.0001) after 6 months of therapy. The QTc increased by a similar magnitude (+14.1 msec, p<0.0001). No QT dispersion value exceeded 100 msec. The only variable associated with a greater increase in QT dispersion was antidepressant therapy (20 vs 8.5 msec, p=0.04).

CONCLUSION

Methadone modestly increased both QTc interval and QT dispersion. Increased QT dispersion reflects heterogeneous cardiac repolarization and occurs with nonantiarrhythmic agents, such as synthetic opioids. However, the magnitude of this effect appears to be substantially less with methadone than with antiarrhythmic drugs.

Hypertrophic cardiomyopathy: electrical abnormalities detected by the extended-length ECG and their relation to syncope

BACKGROUND

Ventricular repolarization abnormalities can represent a trigger for lethal arrhythmias in hypertrophic cardiomyopathy (HCM). We sought to assess whether multiparametric computerized surface ECG analysis identifies repolarization abnormalities in HCM patients, and whether this approach allows identification of patients with syncope.

METHODS

In 28 HCM patients and 102 healthy subjects (14 and 51 males, mean age 44 +/- 15 and 41 +/- 14 years, respectively), 8-lead ECG (I, II, V1-V6) was recorded for 5 min, acquired in digital format and analyzed. Heart-rate corrected QT (QTc) and T wave complexity index (TWCc), QT dispersion, activation-recovery interval (ARI) and its dispersion, signal duration in the terminal portion of the filtered QRS at 25 Hz (LAS(25 Hz)) were analyzed among other parameters.

RESULTS

Compared to healthy subjects, HCM patients exhibited longer QRS, filtered QRS, QTc and QTd, greater TWCc, minor ARId and LA(25 Hz). QRS duration and maximal septum thickness were linearly correlated (r=0.231 p<0.001). ARId shortening depended on ARI shortening in lead V1 (241 +/- 51 vs. 287 +/- 45, HCM vs. healthy subjects, p<0.0001) and lengthening in V6 (257 +/- 42 vs. 209 +/- 34, HCM vs. healthy subjects, p<0.0001). Significant factors for syncope at Wilks' stepwise discriminant analysis were TWCc, QRSd and LAS(25 Hz) (F=14.394, 10.098 and 9.226, respectively) with 92.3% positive predictive accuracy.

CONCLUSIONS

In HCM, longer QRS and QT intervals are consequences of increased left ventricular mass, while ARI seems to reflect myocardial activation rather than inhomogeneity of recovery. The simultaneous evaluation of TWC, QRSd and LAS(25 Hz), unable by itself to hold a predictive value, yielded high accuracy in predicting cardiogenic syncope.

The usefulness of surface electrocardiogram as a prognostic predictor in children with idiopathic dilated cardiomyopathy

We investigated the interrelations between surface electrocardiographic changes and clinical outcomes in children with idiopathic dilated cardiomyopathy (DCMP). 33 patients (19 boys, 14 girls) were classified into two groups; group I (15) who were in poor clinical status or dead; and group II (18) who showed good clinical status. Group I had larger LV dimensions compared to group II (Gr I vs. Gr II; LVEDD, 52 +/-11 vs. 42+/-7 (mm); LVESD, 43+/-12 vs. 30+/-5 (mm); p<0.05). QRS duration was prolonged in Gr I compared to Gr II and normal (Gr I, 84+/-28; Gr II, 66+/-12; normal control, 67+/-9). The QRS duration was correlated with the dimensions of left ventricle (LV). Corrected QT and JT interval and dispersions of QT in the DCMP group showed a significant difference compared to the normal control, however there was no significant difference between Gr I and II. In conclusion, QRS duration was correlated with ventricular dimension and clinical outcome in children with idiopathic dilated cardiomyopathy. Irrespective of increased ventricular inhomogeneity, QT dispersion could not be used to predict long-term prognosis.

Abnormal QT interval variability in patients with hypertrophic cardiomyopathy

We sought to determine QT variability pattern in patients with hypertrophic cardiomyopathy (HCM) and its relationship with the risk of syncope. QT interval variability was assessed from 24-hour Holter monitoring in 10 HCM patients with history of syncope, 10 HCM patients without history of syncope, and 10 healthy subjects. QT variability was higher in patients with HCM, in particular in those with history of syncope, than in healthy controls. Time domain QT variability did not vary between waking and sleeping hours in HCM patients, whereas it was significantly shorter while asleep in the control group. Increased QT SDANN identified HCM patients with history of syncope with an accuracy of 75%. Our data show that QT variability is abnormal in HCM patients and indirectly support the concept that arrhythmia-related syncope in these patients may be, at least in part, related to an altered control of repolarization.

QT dispersion and left ventricular morphology in patients with hypertrophic cardiomyopathy

OBJECTIVE

To evaluate the relation between QT variables and disproportion of left ventricular wall hypertrophy in patients with hypertrophic cardiomyopathy.

DESIGN

Retrospective analysis of the results of echocardiography and electrocardiography.

SETTING

University hospital (tertiary referral centre).

PATIENTS

70 patients with hypertrophic cardiomyopathy were divided into four groups according to the distribution of left ventricular wall hypertrophy on cross sectional echocardiography: group A--hypertrophy confined to the interventricular septum; group B--hypertrophy confined to the interventricular septum and left ventricular anterior wall; group C--hypertrophy confined to the interventricular septum, left ventricular anterior wall, and lateral free wall; group D--hypertrophy involving all portions of the left ventricle.

MAIN OUTCOME MEASURES

QT intervals and QT dispersion in precordial six lead ECGs.

RESULTS

There were no significant differences in the maximum left ventricular wall thickness among the four groups, and maximum and minimum QTc intervals also did not differ. QTc dispersion was increased significantly in groups A and B compared with groups C and D. Dispersions of the interval from the J point to the end of the T wave (JTc dispersions) in groups A and B were also increased significantly compared with groups C and D. By linear regression analysis, QTc and JTc dispersions correlated with the ratio of the interventricular septal thickness to left ventricular posterior wall thickness (p = 0.0152 and p = 0.0075, respectively).

CONCLUSIONS

QT dispersion may be affected by not only electrical inhomogeneity but also by morphological inhomogeneity of the left ventricle in patients with hypertrophic cardiomyopathy.

Seasonal variability of QT dispersion in healthy young males

BACKGROUND

There are few data related to the seasonal influences on the QT dispersion.

METHODS

We analyzed the effects of seasons on QT dispersion in a large group of healthy young males. We studied the seasonal variability of QT dispersion in 523 healthy male subjects aged 22 +/- 4 years (ranging from 20 to 26). Four seasonal 12-lead resting electrocardiograms (ECGs) recorded at double amplitude were performed at 25 mm/s at intervals of 3 months. Subsequent ECGs were recorded within 1 hour of the reference winter recording. QT dispersion was defined as the difference between the longest and the shortest mean QT intervals.

RESULTS

There was a significant seasonal variation in QT dispersion (P = 0.001), with the largest QT dispersion in winter (71 +/- 18 ms) and the smallest one in spring (43 +/- 19).

CONCLUSION

There exists a significant seasonal variation in QT dispersion of healthy subjects and such variability should be taken into consideration in the evaluation process of QT dispersion.

Relation between QT duration and maximal wall thickness in familial hypertrophic cardiomyopathy

BACKGROUND

QT abnormalities have been reported in left ventricular hypertrophy and hypertrophic cardiomyopathy.

OBJECTIVE

To determine the relation between left ventricular hypertrophy and increased QT interval in familial hypertrophic cardiomyopathy.

METHODS

The QT interval was measured in 206 genotyped adult subjects with familial hypertrophic cardiomyopathy from 15 unrelated families carrying mutations in the beta myosin heavy chain (beta-MHC) gene (five families, n = 68) or the cardiac myosin binding protein C (MyBPC) gene (10 families, n = 138). Subjects were classified as genetically unaffected (controls, n = 112), affected with left ventricular hypertrophy (penetrants, n = 58), or affected without left ventricular hypertrophy (non-penetrants, n = 36).

RESULTS

There was a significant increase in QTmax and QTmin from controls to non-penetrants and penetrants for both the MyBPC group (p < or = 0.001 and p < or = 0.001, respectively) and the beta-MHC group (p < or = 0.001 and p < or = 0.001, respectively). In the MyBPC group, the increase in the QT interval could be explained by increased left ventricular hypertrophy. In the beta-MHC group, non-penetrants had a significantly longer QTmax than controls despite the absence of left ventricular hypertrophy, and a similar QT interval to penetrants despite a lesser degree of left ventricular hypertrophy.

CONCLUSIONS

In familial hypertrophic cardiomyopathy, genetically affected subjects without left ventricular hypertrophy may have a prolonged QT duration, which depends not only on the degree of left ventricular hypertrophy, when present, but also on the causative mutation.

Increased QT dispersion does not reflect the increased regional variation of cardiac sympathetic nervous activity in hypertrophic cardiomyopathy

BACKGROUND

QT dispersion (QTD) reflects regional variation of ventricular repolarization. However, the relationship between QTD and the regional variation of cardiac sympathetic nerve activity in hypertrophic cardiomyopathy (HCM) is not yet elucidated.

METHODS

Cardiac sympathetic nerve activity was evaluated in 25 patients with HCM by iodine 123 metaiodobenzylguanidine (MIBG) myocardial scintigraphy. With planar MIBG imaging, heart and mediastinum ratios (H/M) at early (20 minutes) and delayed (3 hours) acquisition and the washout rate (WR) were calculated. Polar maps of left ventricular myocardium were divided into 20 segments. The SD of early uptake (EU-SD), delayed uptake (DU-SD), and WR (WR-SD) in 20 segments as indices of regional variation were calculated. QT intervals were corrected by use of the Bazett formula.

RESULTS

Maximum QTc correlated positively with H/M early, WR, and left ventricular wall thickness (LVWT). Minimum QTc correlated positively with WR and LVWT. Corrected QTD (QTDc) correlated negatively with EU-SD, DU-SD, and WR-SD and positively with the interventricular septal thickness/posterior wall thickness ratio. Stepwise regression analysis revealed that the most powerful determinants for maximum QTc, minimum QTc, and QTDc were WR, LVWT, and EU-SD, respectively.

CONCLUSIONS

QTD correlated negatively rather than positively with the regional variability index of cardiac sympathetic nerve activity. These results suggest that increased QTD in patients with HCM may not reflect increased heterogeneity of cardiac sympathetic nerve activity.

Measurement, interpretation and clinical potential of QT dispersion

QT dispersion was originally proposed to measure spatial dispersion of ventricular recovery times. Later, it was shown that QT dispersion does not directly reflect the dispersion of recovery times and that it results mainly from variations in the T loop morphology and the error of QT measurement. The reliability of both automatic and manual measurement of QT dispersion is low and significantly lower than that of the QT interval. The measurement error is of the order of the differences between different patient groups. The agreement between automatic and manual measurement is poor. There is little to choose between various QT dispersion indices, as well as between different lead systems for their measurement. Reported values of QT dispersion vary widely, e.g., normal values from 10 to 71 ms. Although QT dispersion is increased in cardiac patients compared with healthy subjects and prognostic value of QT dispersion has been reported, values are largely overlapping, both between healthy subjects and cardiac patients and between patients with and without adverse outcome. In reality, QT dispersion is a crude and approximate measure of abnormality of the complete course of repolarization. Probably only grossly abnormal values (e.g. > or =100 ms), outside the range of measurement error may potentially have practical value by pointing to a grossly abnormal repolarization. Efforts should be directed toward established as well as new methods for assessment and quantification of repolarization abnormalities, such as principal component analysis of the T wave, T loop descriptors, and T wave morphology and wavefront direction descriptors.

Persistent ST segment elevation: a new ECG finding in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is a primary disease of myocardium resulting in myocardial hypertrophy without any inciting pressure or volume overload. The typical triad of symptoms includes exertional angina, syncope, and shortness of breath. Sudden cardiac death, the most dreadful complication of this disorder, can be the first manifestation of the disease and is more common in young patients. Elderly patients, on the other hand, may have a relatively benign course with normal or near-normal life span. The electrocardiogram (ECG) and echocardiography are the two most useful measures to diagnose hypertrophic cardiomyopathy. The electrocardiographic features of hypertrophic cardiomyopathy are numerous, including ST segment elevation that may simulate other ST segment elevation syndromes, including acute myocardial infarction, variant angina pectoria, acute pericarditis, bundle branch blocks, ventricular paced rhythm, dyskinetic ventricular segment, ventricular aneurysm, left ventricular hypertrophy, Wolff-Parkinson-White syndrome, and early repolarization syndrome. This report describes a case of an asymptomatic patient who presented with ST segment elevation of acute injury type and, therefore, was admitted to rule out silent myocardial infarction. Myocardial infarction was ruled out by cardiac enzyme levels, but ST segment elevation remained persistent in all of the subsequent ECGs. Echocardiography was performed, which clearly showed hypertrophic cardiomyopathy with left ventricular outflow tract obstruction and a high intracavity pressure gradient. Subsequently, retrieval of old ECGs showed a similar type of ST segment elevation in the patient's previous ECGs.

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.