QT dispersion in exercise-induced myocardial hypertrophy

Left Ventricular Geometric Pattern Impacts QT Dispersion in Males Athletes and Sedentary Men

AIM

To (1) compare QT dispersion (QTd) and echocardiographic features between athletes with concentric left ventricular (LV) hypertrophy, athletes with eccentric LV hypertrophy, and sedentary controls with a normal LV geometric pattern and (2) quantify associations between QTd and echocardiographic features within these groups.

METHODS

Male athletes competing in different sports and sedentary men were stratified into groups according to their LV geometric pattern. These groups included eccentric LV hypertrophy (LV index > 115 g/m2, relative wall thickness [RWT] < 0.42) consisting of 38 athletes, concentric LV hypertrophy (LV index > 115 g/m2, RWT > 0.42) consisting of 40 athletes, and normal LV geometric pattern (LV index < 115 g/m2, RWT < 0.42) consisting of 40 sedentary controls. Following a cross-sectional design, participants underwent electrocardiographic (ECG) and echocardiographic screening. Data were compared between groups using one-way analyses of variance with Bonferroni post hoc tests. Associations between corrected QTd and echocardiographic variables were quantified using Pearson correlations.

RESULTS

Alongside structural disparities between groups, corrected QTd was significantly (p < 0.001) lower in athletes with eccentric LV hypertrophy compared to athletes with concentric LV hypertrophy and sedentary controls. Significant, moderate-to-very-large correlations were found between corrected QTd and interventricular septal wall thickness in athletes with concentric (r = 0.416, p = 0.008) or eccentric LV hypertrophy (r = 0.734, p < 0.001), and sedentary controls (r = 0.464, p = 0.003).

CONCLUSION

The provided comparative and relationship data may inform the development of more precise approaches for ECG and echocardiographic screening in athletes, particularly in those with concentric LV hypertrophy who may be at greater risk for developing prolonged QTd.

Sport-related differences in QT dispersion and echocardiographic parameters in male athletes

The aim of this study was to compare QT dispersion (QTd) and echocardiographic parameters in male athletes competing across different sports (long-distance running, volleyball, football, powerlifting, and bodybuilding) and a control population. Significant moderate-strong differences (p < 0.001, [Formula: see text] = 0.52-0.71) were found in corrected QTd, intraventricular septal wall thickness (ISWT), posterior wall thickness (PWT), relative wall thickness (RWT) and LV (left ventricular) index between groups. Corrected QTd, ISWT, PWT, and RWT were significantly (p < 0.001) higher in powerlifters and bodybuilders compared to other athlete groups and controls. While all athlete groups displayed a significantly higher LV index (p < 0.05) compared to controls, corrected QTd was significantly lower (p < 0.001) only in long-distance runners, volleyball athletes, and football athletes compared to controls. Normal or eccentric LV hypertrophy (LVH) was observed in most long-distance runners (58% and 33%), volleyball athletes (50% and 50%), and football athletes (56% and 41%). In contrast, concentric LVH was observed in most powerlifters (58%) and bodybuilders (54%). Advanced LVH, predominantly concentric in nature, appears to be accompanied with increased QTd in powerlifters and bodybuilders. On the other hand, runners, volleyball athletes, and football athletes experienced LVH toward the upper threshold of the normal reference range alongside reduced QTd compared to other groups.

A 24-hour ambulatory ecg monitoring in assessment of qt interval duration and dispersion in rowers with physiological myocardial hypertrophy

Myocardial hypertrophy (MH) due to cardiac pathology is characterized by an increase in QT interval duration and dispersion, while the findings for exercise-induced myocardial hypertrophy are contradictory. The majority of published research findings have not explored this relationship, but there have only been a few conducted studies using 24-hour ECG monitoring. The aim of the study was to determine the QT interval duration and dispersion in short-term and 24-hour ECG in endurance athletes with myocardial hypertrophy and without it.

METHODS

A total of 26 well-trained rowers underwent a resting 12-lead ECG, 24-hour ECG monitoring and echocardiography.

RESULTS

Athletes with MH (n = 7) at rest did not show any increase in QTc interval duration and dispersion, or mean and maximal QTc duration in Holter monitoring compared to athletes without MH (n = 19). Left ventricular mass was not significantly correlated with any QTc characteristics. Furthermore, athletes with MH had significantly longer mean QT (P = 0.01) and maximal QT (P = 0.018) intervals in Holter monitoring and higher 24-hour heart rate variability indexes due to stronger vagal effects.

CONCLUSIONS

The present study demonstrated that athlete's heart syndrome with myocardial hypertrophy as a benign phenomenon does not lead to an increase in QT interval duration, or increases in maximal and mean duration in a 24-hour ECG. An increase in QT interval duration in athletes may have an autonomic nature.

Behavior of repolarization variables during exercise test in the athlete's heart

BACKGROUND

T peak-T end, QT peak/QT ratio and T peak-T end/QT ratio are markers able to test myocardial repolarization homogeneity, their increase has been related to a higher risk of ventricular tachyarrhythmias. These parameters have not yet been studied in left ventricular hypertrophy due to training. Aim of the research was to test the behavior of these variables in the athlete's heart during exercise.

METHODS

We examined 70 athletes, all males, divided into two groups according to the absence or the presence of a left ventricular mass index over 49 g/m(2.7) and a control group composed of 35 healthy, untrained males. All study participants underwent electrocardiogram at rest, transthoracic echocardiogram, and ergometric test. Repolarization markers (QT, corrected QT, QT dispersion, T peak-T end, QT peak/QT, T peak-T end/QT) were calculated at rest, at peak exercise and during recovery.

RESULTS

There was no statistically significant difference among the groups regarding all the parameters studied, except for corrected QT at rest between athletes with left ventricular hypertrophy and control group. The behavior of repolarization markers during exercise was not dissimilar in the three groups.

CONCLUSIONS

Athlete's heart is not associated to any alteration in ventricular repolarization homogeneity, neither at rest nor during physical activity nor during recovery. Training-induced left ventricular hypertrophy does not affect relationship QT parameters/RR interval.

Is the 'athlete's heart' arrhythmogenic? Implications for sudden cardiac death

Whether the ventricular hypertrophic response to athletic training can predispose to fatal ventricular dysrhythmias via mechanisms similar to that of pathological hypertrophy is controversial. This review examines current information regarding the metabolic and electrophysiological differences between the myocardial hypertrophy of heart disease and that associated with athletic training. In animal studies, the biochemical and metabolic profile of physiological hypertrophy from exercise training can largely be differentiated from that of pathological hypertrophy, but it is not clear if the former might represent an early stage in the spectrum of the latter. Information as to whether the electrical remodelling of the athlete's heart mimics that of patients with heart disease, and therefore serves as a substrate for ventricular dysrhythmias, is conflicting. If ventricular remodelling associated with athletic training can trigger fatal dysrhythmias, such cases are extraordinarily rare and thereby impossible to investigate by any standard experimental approach. Greater insight into this issue may come from a better understanding of the electrical responses to both acute bouts of exercise and chronic training in young athletes.

Possible mechanisms of sudden cardiac death in top athletes: a basic cardiac electrophysiological point of view

Sudden death among athletes is very rare (1:50,000-1:100,000 annually) but it is still 2-4 times more frequent than in the age-matched control population and attracts significant media attention. We propose a mechanism underlying sudden cardiac death in athletes that does not relate to myocardial ischemia but is based on repolarization abnormalities due to potassium channel downregulation and can also be best explained by the concurrent presence of several factors such as cardiac hypertrophy (athlete's heart), and/or hypertrophic cardiomyopathy, increased sympathetic tone, genetic defects, drugs, doping agents, food, or dietary ingredients. These factors together can increase the repolarization inhomogeneity of the heart ("substrate") and an otherwise harmless extrasystole ("trigger") occurring with a very unfortunate timing may sometimes induce life-threatening arrhythmias. The effective and possible prevention of sudden cardiac death requires the development of novel cost effective cardiac electrophysiological screening methods. Athletes identified by these tests as individuals at higher proarrhythmic risk should then be subjected to more costly genetic tests in order to uncover possible underlying genetic causes for alterations in ionic channel structure and/or function.

An evaluation of the impact of gender and age on QT dispersion in healthy subjects

OBJECTIVES

To determine if gender, age, and gender per age category, have an impact on QT and QTc dispersion in healthy volunteers.

METHODS

This study was undertaken in 150 patients (50 per age group, 75 males, 75 females). The age groups included young (20-40 years), middle-aged (41-69 years) and elderly (> 70 years) subjects. The QT intervals on a 12 lead ECG were determined and Bazett's formula was used to derive the QTc intervals. The QT and QTc dispersion were determined by subtracting the shortest QTc interval from the longest on each 12-lead recording.

RESULTS

Males had higher QT dispersion than females (50 +/- 22 vs 42 +/- 18 ms, P = 0.017) but QTc dispersion was not significantly changed. No significant differences were seen among the different age categories for QT or QTc dispersion. In elderly subjects, males had higher QT and QTc dispersion than females (54 +/- 23 vs 42 +/-15 ms, P = 0.039 and 63 +/- 23.7 vs 48 +/- 21 ms, P = 0.032, respectively).

CONCLUSIONS

When evaluating the effect of gender in different age categories, elderly males have significantly greater QT and QTc dispersion than elderly female subjects. No other gender differences were noted for QT or QTc dispersion in the other two age categories. When evaluating a population of healthy volunteers, regardless of age, gender has an impact on QT dispersion but no significant interaction with QTc dispersion. Evaluating age without dividing the data by gender yields no significant differences in QT or QTc dispersion.

QT dispersion in patients with different etiologies of left ventricular hypertrophy: the significance of QT dispersion in endurance athletes

Left ventricular hypertrophy (LVH) increases the risk of ventricular arrhythmias and sudden death and has a significant effect on total cardiovascular mortality. QT dispersion (QTd) is a measure of inhomogeneous repolarization and is used as an indicator of arrhythmogenicity. In this study we detected QTd in patients with different etiologies of left ventricular hypertrophy and the effect of LVH in QTd on endurance athletes. The study group consisted of 147 white male subjects with 3 different etiologies of LVH and 30 healthy male individuals. The underlying etiologies of LVH were essential hypertension, valvular aortic stenosis and long-term training (athletic heart). QTd was measured by surface electrocardiogram and Bazett's formula was used to correct QTd for heart rate (QTcd). Left ventricular mass was determined by transthoracic echocardiography and left ventricular mass index was calculated in relation to body surface area. The QTcd was significantly higher in patients with pathological LVH (due to hypertension and aortic stenosis) than in the athletes' group (physiological LVH) and healthy subjects (P<0.05). The magnitude of QTcd was similar between athletes and the control group (P=0.6). The difference of QTcd between the groups with pathological LVH was not statistically significant (P=0.1). In conclusion; the increasing of QT dispersion is associated with only pathological conditions of LVH. The left ventricular hypertrophy has not a negative effect in QT dispersion on endurance athletes. The measurement of QT dispersion may be a non-invasive useful method for screening additional pathological conditions in endurance athletes.

Relation of QT interval and QT dispersion to echocardiographic left ventricular hypertrophy and geometric pattern in hypertensive patients. The LIFE study. The Losartan Intervention For Endpoint Reduction

OBJECTIVE

In hypertensive patients, left ventricular hypertrophy (LVH) predicts increased mortality, in part due to an increased incidence of sudden death. Repolarization-related arrhythmogenesis may be an important mechanism of sudden death in hypertensive patients with LVH. Increased QT interval and QT dispersion are electrocardiographic (ECG) measures of ventricular repolarization, and also risk markers for ventricular tachyarrhythmias. We assessed the relation of QT intervals and QT dispersion to echocardiographically determined left ventricular (LV) mass and geometry in a large population of hypertensive patients with ECG evidence of LVH.

METHODS

QT intervals and QT dispersion were determined from baseline 12-lead ECGs in 577 (57% male; mean age 65 +/- 7 years) participants in the LIFE study. LV mass index (LVMI) and geometric pattern were determined by echocardiography and QT interval duration and QT dispersion were assessed in relation to gender-specific LVMI quartiles.

RESULTS

In both genders, increasing LVMI was associated with longer rate-adjusted QT intervals. QT dispersion measures showed a weaker association with LVMI quartiles. Both concentric and eccentric LVH were associated with increased QT interval duration and QT dispersion. These relations remained significant after controlling for relevant clinical variables.

CONCLUSIONS

In hypertensive patients with ECG evidence of LVH, increased LVMI and LVH are associated with a prolonged QT interval and increased QT dispersion. These findings suggest that an increased vulnerability to repolarization-related ventricular arrhythmias might in part explain the increased risk of sudden death in hypertensive patients with increased LV mass.

Left ventricular hypertrophy increases transepicardial dispersion of repolarisation in hypertensive patients: a differential effect on QTpeak and QTend dispersion

BACKGROUND

Ventricular arrhythmias in left ventricular hypertrophy (LVH) are related to regional electrical heterogeneity. The significance of noninvasive electrocardiographic indices of electrical heterogeneity in LVH has not been established. The aim of the study was to investigate changes in the Tpeak-Tend interval (an index of transmural dispersion of repolarisation) in addition to other traditional electrocardiographic indices of electrical dispersion in patients with hypertensive LVH.

METHODS

Consecutive patients were screened for the presence of hypertensive echocardiographic LVH and compared with a control group. LVH was identified as left ventricular mass > 134 g m-2 in men and > 110 g m-2 in women. Twelve-lead ECGs were analysed in respect of various indices of electrical dispersion.

RESULTS

Left ventricular mass was greater in the LVH than in the control group (174 +/- 39 vs. 101 +/- 18 g m-2, P < 0.0001). The Tpeak-Tend interval was not affected by LVH. The main effect of LVH was an increase in QTpeak dispersion (40 +/- 13 vs. 53 +/- 21 ms, P < 0.05), which resulted from an increase in the maximum QTpeak interval (337 +/- 24 vs. 358 +/- 30 ms, P < 0.04), without any change in the minimum QTpeak interval. There was a significant correlation between the left ventricular mass index and QTpeak dispersion (r = 0.40; P < 0.01). In contrast, LVH did not exert any effect on QTend dispersion (65 +/- 21 vs. 65 +/- 16 ms, ns), because LVH increased both the maximum QTend interval (430 +/- 30 vs. 449 +/- 28 ms, P < 0.05) and the minimum QTend interval (365 +/- 29 vs. 384 +/- 27 ms, P < 0.04).

CONCLUSIONS

Hypertensive LVH exerts a differential effect on QTpeak and QTend interval dispersion. The most likely explanation is that these changes reflect a nonuniform prolongation of action potential duration across the epicardium, leading to an increase in transepicardial dispersion of repolarisation.

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.

Can the assessment of dynamic QT dispersion on exercise electrocardiogram predict sudden cardiac death in hypertrophic cardiomyopathy?

Premature sudden cardiac death (SD) is a critical event in the natural history of hypertrophic cardiomyopathy (HCM), and occurs during or just after physical exertion in approximately 60% of instances. Abnormalities in ventricular repolarization may not be present at rest in some patients but may become apparent under certain conditions. This study was performed to examine whether dynamic QT dispersion during exercise is associated with SD in HCM. Twenty-four HCM patients with catastrophic events (group I; 18 SD, 6 ventricular fibrillation) and 24 event-free survivors (group II) were studied. The two groups were pair-matched for age, gender, and maximum left ventricular wall thickness. QT intervals were manually measured from 12-lead exercise electrocardiogram (ECG) with a digitizing board. A custom-developed program was used to calculate QT and JT dispersion. The QT/RR relationship was evaluated by the slope of linear regression analysis. Before exercise, significant differences in heart rate and JT dispersion were found between group I and II. During exercise, heart rate increased and QT decreased significantly in both groups. QT and JT dispersion decreased in both groups, though the magnitude of reduction was greater in group I than in group II. No significant differences in QTc interval and QT or JT dispersion were found between the groups at any stages. At 3 minutes of recovery, heart rate had decreased but remained higher than before exercise, and all measurements of QT components remained shorter compared with those made before exercise in both groups. There was a strong correlation between QT and RR interval during exercise in all study patients (r = 0.95). No difference in the slope of QT against RR intervals was found between the groups (0.317 vs 0.319). In conclusion, exercise reduced QT dispersion in patients with HCM. The dynamic changes in QT dispersion examined by this method on exercise ECG did not make additional contributions in their risk stratification.

Measurement and interpretation of QT dispersion

QT dispersion was proposed as an index of the spatial inhomogeneity of ventricular recovery times. The results of studies that found significant correlation between dispersion of ventricular recovery times measured with monophasic action potentials and QT dispersion were interpreted as proof of the direct link between QT dispersion and the dispersion of ventricular recovery times. Later it was shown that QT dispersion is not a direct reflection of the spatial variation of the recovery times and cannot be used for quantification of this variation. The interlead variability of the QT intervals is a result of different projections of the spatial T-wave loop into the various electrocardiographic leads. The reliability of both manual and automatic measurement of QT dispersion is low and is often of the order of the differences of Qt dispersion between different patient groups. The measurement reliability is influenced by intrinsic factors (e.g., amplitude of the T wave) and extrinsic factors (e.g., noise, paper speed of recording, instruments for manual measurements, and type of algorithm and interalgorithmic settings for automatic measurement). There is very little to choose between the different indices of expression of QT dispersion, as well as between the different lead configurations used for its measurement. QT dispersion is not simply a result of measurement error, but a crude measure of abnormalities during the whole course of repolarization. Only grossly prolonged QT dispersion (e.g., > or =100 ms), must be interpreted simply as a sign of the abnormal course of the repolarization, and inferences about the actual dispersion of the ventricular recovery times should not be made. Newer concepts of assessment of the morphology of the T wave are already emerging and will probably be of higher clinical value.