PQ segment depression in patients with short QT syndrome: a novel marker for diagnosing short QT syndrome?

BACKGROUND: Patients with short QT syndrome (SQTS) have an increased risk for atrial tachyarrhythmias, ventricular tachyarrhythmias, and/or sudden cardiac death. PQ segment depression (PQD) is related to atrial fibrillation and carries a poor prognosis in the setting of acute inferior myocardial infarction and is a well-defined electrocardiographic (ECG) marker of acute pericarditis. OBJECTIVE: To evaluate the prevalence of PQD in SQTS and to analyze the association with atrial arrhythmias. METHODS: Digitalized 12-lead ECGs of SQTS patients were evaluated for PQD in all leads and for QT intervals in leads II and V5. PQD was defined as ≥0.05 mV (0.5 mm) depression from the isoelectric line. RESULTS: A total of 760 leads from 64 SQTS patients (mean age 36 ± 18 years; 48 [75%] men) were analyzed. PQD was seen in 265 (35%) leads from 52 (81%) patients and was more frequent in leads II, V3, aVF, V4, and I (n = 43 [67%], n = 30 [47%], n = 27 [42%], n = 25 [39%], and n = 25 [39%], respectively). Nine of 64 (14%) patients presented with atrial tachyarrhythmias, and all of them had PQD. CONCLUSION: Fifty-two of 64 (81%) patients with SQTS reveal PQD. As PQD is rarely observed in healthy individuals, this ECG stigma may constitute a novel marker for SQTS in addition to a short QT interval.

QRS-T angle as a predictor of sudden cardiac death in a middle-aged general population.

AIMS: Spatial QRS-T angle measured from a 12-lead electrocardiogram (ECG) has been shown to predict cardiac mortality. However, there is a paucity of studies on the prognostic significance of frontal QRS-T angle, which is more readily available from the standard 12-lead ECG. The purpose of the present study was to investigate the importance of wide frontal QRS-T angle, QRS-axis, and T-wave axis as cardiac risk predictors in general population. METHODS AND RESULTS: We evaluated the 12-lead ECGs of 10 957 Finnish middle-aged subjects from the general population recorded between 1966 and 1972, and followed them for 30 ± 11 years. QRS-T angle 0 to 90°, QRS-axis -30 to 90°, and T-wave axis 0 to 90° were considered normal. The primary endpoint was death from arrhythmia, and the secondary endpoints were all-cause mortality and non-arrhythmic cardiac mortality. QRS-T angle ≥ 100° was present in 2.0% of the subjects, and it was associated with an increased risk of sudden arrhythmic death [relative risk (RR) 2.26; 95% confidence interval (CI) 1.59-3.21; P< 0.001) and all-cause mortality (RR 1.57; CI 1.34-1.84; P< 0.001), but not with non-arrhythmic cardiac mortality (RR 1.34; CI 0.93-1.92; P= 0.13). The prognostic significance of wide QRS-T angle was mainly due to abnormal T-wave axis, which predicted death from arrhythmia (RR 2.13; CI 1.63-2.79; P< 0.001), all-cause mortality (RR 1.39; 1.24-1.55; P< 0.001), and non-arrhythmic cardiac death (RR 1.87; CI 1.50-2.34; P< 0.001). CONCLUSION: Frontal QRS-T angle ≥ 100° increases the risk of arrhythmic death, this being mainly the result of an altered T-wave axis.

Electrocardiographic transmural dispersion of repolarization in patients with inherited short QT syndrome.

BACKGROUND: Short QT syndrome (SQTS) carries an increased risk for sudden cardiac death. However, only a short QT interval does not express the risk of ventricular arrhythmias. Thus, additional evaluation of the repolarization abnormality in SQTS patients is essential. In experimental models of SQTS, increased transmural dispersion of repolarization (TDR) and its electrocardiographic counterpart T-wave peak to T-wave end interval (TPE) appeared critical for induction of polymorphic ventricular tachycardia (PMVT). In a clinical study with acquired long QT syndrome patients, TPE/QT ratio > 0.28 indicated arrhythmia risk. We hypothesized that the TPE/QT ratio would be greater in SQTS patients than in control subjects. METHODS AND RESULTS: We compared the behavior of the electrocardiographic TDR in three seriously symptomatic SQTS patients of unknown genotype presenting baseline QTc values < 320 ms and in nine healthy age-matched control subjects. We determined QT and TPE intervals as well as TPE/QT ratio from 24-hour ECG recordings using a computer-assisted program. Diurnal average of TPE/QT ratio was 0.28 +/- 0.03 in SQTS patients and 0.21 +/- 0.02 in control subjects (P = 0.01). SQTS patients had also lesser capacity to change TPE intervals from steady-state conditions to abrupt maximal values than control subjects. CONCLUSION: SQTS patients have increased and autonomically uncontrolled electrocardiographic TDR. According to experimental SQTS models, the present results may in part explain increased vulnerability of SQTS patients to ventricular arrhythmias.