Long QT interval syndrome. A new look at an old electrocardiographic measurement--the power of the computer

Electrocardiographic changes in 1000 highly trained junior elite athletes

OBJECTIVES

To evaluate the spectrum of electrocardiographic (ECG) changes in 1000 junior (18 or under) elite athletes.

METHODS

A total of 1000 (73% male) junior elite athletes (mean (SD) age 15.7 (1.4) years (range 14-18); mean (SD) body surface area 1.73 (0.17) m2 (range 1.09-2.25)) and 300 non-athletic controls matched for gender, age, and body surface area had a 12 lead ECG examination.

RESULTS

Athletes had a significantly higher prevalence of sinus bradycardia (80% v 19%; p<0.0001) and sinus arrhythmia (52% v 9%; p<0.0001) than non-athletes. The PR interval, QRS, and QT duration were more prolonged in athletes than non-athletes (153 (20) v 140 (18) milliseconds (p<0.0001), 92 (12) v 89 (7) milliseconds (p<0.0001), and 391 (27) v 379 (29) milliseconds (p = 0.002) respectively). The Sokolow voltage criterion for left ventricular hypertrophy (LVH) and the Romhilt-Estes points score for LVH was more common in athletes (45% v 23% (p<0.0001) and 10% v 0% (p<0.0001) respectively), as were criteria for left and right atrial enlargement (14% v 1.2% and 16% v 2% respectively). None of the athletes with voltage criteria for LVH had left axis deviation, ST segment depression, deep T wave inversion, or pathological Q waves. ST segment elevation was more common in athletes than non-athletes (43% v 24%; p<0.0001). Minor T wave inversion (less than -0.2 mV) in V2 and V3 was present in 4% of athletes and non-athletes. Minor T wave inversion elsewhere was absent in non-athletes and present in 0.4% of athletes.

CONCLUSIONS

ECG changes in junior elite athletes are not dissimilar to those in senior athletes. Isolated Sokolow voltage criterion for LVH is common; however, associated abnormalities that indicate pathological hypertrophy are absent. Minor T wave inversions in leads other than V2 and V3 may be present in athletes and non-athletes less than 16 but should be an indication for further investigation in older athletes.

Electrocardiographic repolarization during stress from awakening on alarm call

OBJECTIVES

The present study aimed to characterize the electrocardiographic features of cardiac repolarization during an arousal reaction in healthy subjects.

BACKGROUND

Electrocardiographic ST segments and T waves may indicate the activity of cardiac autonomic nervous control. Abnormal dynamics of repolarization are considered to reveal susceptibility to cardiac arrhythmias. Responses in normal subjects may help to understand the effects on patients' arrhythmias.

METHODS

Ambulatory electrocardiography was performed in 30 healthy physicians during emergency calls while they were on duty in the hospital. Samples were taken before and during the 1st 30 s after the calls. Polarity of the T wave and ST segment depression were determined. The QT interval and the cardiac cycle length (CL) were measured, and their relation (QT/CL slope) was calculated. For comparison, the QT interval was also measured in stable conditions at specified heart rates of 60 to 110 beats/min.

RESULTS

During arousal, the T wave was inverted in 19 subjects (63%) and the ST segment depressed > or = 0.1 mV in 10 (33%). The proportional duration of the terminal T wave also varied. The time course of these alterations followed the change in heart rate. During the strongest arousal reaction, the heart rate increased from 55 +/- 7 to 112 +/- 18 beats/min (mean +/-SD) and reached maximum at 17s on average. The QT interval shortened only slightly and was on average 59 to 67 ms longer (p < 0.001) than that at similar heart rates during stable conditions. The QT/CL slope was almost horizontal, 0.085 +/- 0.061, during arousal and much steeper, 0.168 +/- 0.055 (p < 0.001), during stable conditions.

CONCLUSIONS

Derangements in the T wave and ST segment as signs of sympathetic overactivity are common during arousal and are associated with marked inertia in QT interval adaptation. These modifications of ventricular repolarization may mediate the generation of stress-provoked arrhythmias in electrically unstable hearts.

Relationship between rate-corrected QT interval and wall motion abnormalities in the setting of acute myocardial infarction

We studied 108 patients (73 men and 35 women, mean age of 63.1 +/- 11.2 years) with Q-wave acute myocardial infarction (anterior -52, inferior -41, and combined anteroinferior -15) 4 days after infarct onset to determine whether any correlation exists between rate-corrected QT interval (QTc) and functional infarct size, expressed as wall motion index. QTc was calculated by Hodges' linear algorithm [QT + (1.75 x heart rate - 60)]. Wall motion index was determined using a 16-segments model, as recommended by the American Society of Echocardiography. Wall motion index was significantly higher in anterior and in combined infarctions. QTc was shortest in inferior infarction. There was a statistically significant overall correlation between wall motion index and QTc (r = 0.83, p < 0.001). The relationship was weakest in inferior infarction. In conclusion, prolonged QTc may be implicated as an additional marker of left ventricular dysfunction in patients with acute anterior and combined anteroinferior myocardial infarction.

Dose-response relation between terfenadine (Seldane) and the QTc interval on the scalar electrocardiogram: distinguishing a drug effect from spontaneous variability

The primary goal of this investigation was to describe the effect of terfenadine on the QT interval corrected for heart rate (QTc) of the scalar electrocardiogram (ECG). The design was double-blind, four-period crossover, dose escalation, which involved 28 normal healthy volunteers and 28 patients with stable cardiovascular disease. At baseline, the normal subjects had a mean QTc interval of 407 msec, whereas the patients with cardiovascular disease had a mean QTc interval of 417 msec (p<0.01). The largest increase in mean QTc on terfenadine was 24 msec in a normal subject and 28 msec in a patient with cardiovascular disease. The longest average QTc observed was 449 msec and 501 msec in any normal subject and patient with cardiovascular disease, respectively. Compared to baseline, terfenadine 60 mg twice daily is associated with a QTc increase of 6 msec in normal subjects and a 12 msec increase in patients with cardiovascular disease (p<0.01 vs baseline; p>0.05 when the two populations were compared). Although the QTc increase from baseline are statistically significant, the magnitude of the spontaneous variability in QTc in the same patients is much greater. Because 40 ECGs were obtained while taking placebo in each participant, the spontaneous variability in QTc interval with placebo was also described. Only one of the 28 normal subjects had a mean baseline QTc=440 msec, yet 14 of the 28 normal subjects had at lease one of the 40 placebo ECGs with a QTc=440 msec. The 28 patients with cardiovascular disease had a mean QTc at baseline of 417 msec; yet 20 of 28 had at lease one ECG on placebo with a QTc interval = 440 msec. On the average, the QTc fluctuated 56 msec in each patient during placebo administration. From the observed placebo variability, we calculated that an increase in QTc of=35 msec while receiving drug therapy is likely to represent a drug effect at the 95% confidence interval.

Variability of the QTc interval: impact on defining drug effect and low-frequency cardiac event

Prolongation of the QT interval corrected for heart rate (QTc) can lead to the development of torsades de pointes, a life-threatening form of polymorphic ventricular tachycardia. However, the QTc interval duration exhibits a high degree of spontaneous variability and is not necessarily a direct predictor of the risk of torsades. This observation holds implications for the assessment of the potential proarrhythmic effects of noncardiac pharmacologic agents. To date, the antihistamine terfenadine is the only noncardiac drug that has undergone a comprehensive and systematic evaluation related to the consequences of its causing QTc prolongation. The results suggest that QTc prolongation resulting solely from terfenadine at clinical doses does not have an important impact on clinically relevant endpoints. The risk of serious ventricular arrhythmias with terfenadine using epidemiologic data is the same or less than that associated with traditional first-generation antihistamines. The risk of a clinical cardiac event (QTc prolongation, ventricular arrhythmias, syncope, or sudden death) with terfenadine is similar to that of other antihistamines. Factors associated with increased risk in patients taking terfenadine include significant liver disease, hypokalemia, overdose, and concomitant administration of ketoconazole-like agents or erythromycin; use of terfenadine is relatively contraindicated in these settings. No increased risk of serious arrhythmias has been confirmed in conjunction with the use of terfenadine in patients with cardiac disease.