Effects of pink grapefruit juice on QT variability in patients with dilated or hypertensive cardiomyopathy and in healthy subjects.

Recent evidence shows that pink grapefruit juice, which is a recommended dietary addition that contains high amounts of the antioxidant flavonoid naringenin, prolongs the corrected QT (QT(c)), a noninvasive electrophysiological marker of spatial myocardial repolarization, and does so by inhibiting the rapid component of the delayed rectifier K+ current (I(Kr)). Prompted by the observation that all class III antiarrhythmic drugs inhibit this current, thereby sometimes provoking torsades de pointes, we compared the effects of a liter of freshly squeezed pink grapefruit juice with those of 2 commonly used class III antiarrhythmics amiodarone and sotalol on the major noninvasive markers of temporal variability in myocardial repolarization used to stratify the risk of sudden death from malignant ventricular arrhythmias. In 32 subjects, 10 with postischemic dilated cardiomyopathy, 12 with hypertensive cardiomyopathy, and 10 healthy, we assessed QT(c) and QT variability index (QTVI) after administration of fresh pink grapefruit juice, placebo, amiodarone, or sotalol. After pink grapefruit juice and sotalol, all these indexes increased significantly from values observed after placebo (P<0.05) and from values after amiodarone (P<0.05). Conversely, after amiodarone, QT(c), but not QTVI, increased significantly from values after placebo (P<0.05). Presumably because of its high naringenin glycoside content, pink grapefruit juice prolongs cardiac repolarization and concurrently increases temporal cardiac repolarization dispersion. The potential proarrhythmic actions of pink grapefruit juice might be of concern in patients with major myocardial structural disorders.

Early impairment of myocardial function in young patients with beta-thalassemia major.

BACKGROUND AND OBJECTIVE: One of the chief causes of death in patients with beta-thalassemia major (TM) remains heart failure due to iron overload. We investigated possible differences in myocardial function between a population of young asymptomatic patients with TM and healthy controls all of whom underwent an echocardiographic study, including tissue Doppler (TDI) and strain imaging (SI) analysis and cardiac magnetic resonance imaging (MRI). METHODS: 30 young asymptomatic patients with TM (16 taking deferoxamine and 14 taking deferiprone) and 30 healthy subjects underwent a cardiac MRI with T2* technique and an echocardiographic evaluation including systolic myocardial velocities (Sm), early (Em) and late (Am) diastolic velocities and systolic strain (S) at the level of basal segments of the lateral left ventricle (LV), interventricular septum (Septal) and lateral right ventricle (RV) wall. The differences in T2* values and echocardiographic parameters were also compared in patients with TM subgrouped according to iron chelation therapy. RESULTS: The following TDI and SI measures were lower in patients than in controls: LV-Sm (P < 0.05), S-LV (P < 0.001), Septal-Sm (P < 0.05), Septal-Em (P < 0.001), S-Septal (P < 0.001), RV-Sm (P < 0.001), RV-Em (P < 0.001), RV-Em/Am (P < 0.05) and S-RV (P < 0.05). Myocardial function was better in the patients receiving deferiprone than those receiving deferoxamine. T2* values were higher in controls than in patients with TM and in those treated with deferiprone than those treated with deferoxamine. MRI data well correlated with SI parameters. CONCLUSIONS: Study underlines that, even in a population of young, asymptomatic and well-chelated patients with TM, there is an impairment of myocardial function and that this condition could be easily detected by more advanced ultrasound techniques such as TDI and SI. The better indices of myocardial function in patients treated with deferiprone clearly needs confirmation from larger prospective studies.

Increased QT variability in young asymptomatic patients with beta-thalassemia major.

BACKGROUND: Despite recent progress in iron chelation therapy, sudden cardiac death due to malignant ventricular arrhythmias remains a vexing, clinical problem in patients with beta-thalassemia major (TM). In this study we assessed whether the major indices of QT variability, emerging tools for risk stratification of sudden cardiac death, differ in young asymptomatic patients with TM and healthy persons. METHODS: Thirty patients with TM and 30 healthy control subjects underwent a 5-min electrocardiography recording to calculate the following variables: QT variance (QT(v)), QT(v) normalized for mean QT (QTVN) and QT variability index (QTVI). All subjects also underwent a two-dimensional and Doppler echocardiography study and magnetic resonance imaging (MRI) to determine cardiac and hepatic T2* values. RESULTS: No differences were observed in clinical and conventional echo-Doppler findings in healthy control subjects and patients with TM whereas QT(v), QTVN and QTVI values were significantly higher in patients than those in controls (QT(v), P < 0.001; QTVN, P < 0.05 and QTVI, P < 0.001) and cardiac T2* and hepatic MRI T2* values were significantly lower in patients with TM (P < 0.001). The indices of temporal QT variability correlated significantly with MRI data. CONCLUSIONS: Young asymptomatic patients with TM have increased cardiac repolarization variability as assessed by QT variability indices, probably due to cardiac iron deposition. These easily assessed, non-invasive markers could be used to identify increased myocardial repolarization lability early in asymptomatic patients with TM.

QT variability strongly predicts sudden cardiac death in asymptomatic subjects with mild or moderate left ventricular systolic dysfunction: a prospective study.

AIMS: The most widely accepted marker for stratifying the risk of sudden cardiac death (SCD) in post myocardial infarction patients is a depressed left ventricular function. Left ventricular ejection fractions (EF) of 35% or less increase the risk of sudden death but values between 35 and 40% raise concern. The underlying pathophysiological mechanism is sustained ventricular tachycardia or fibrillation, both associated with increased cardiac repolarization variability. We assessed whether the indices of QT variability from a short-term electrocardiographic (ECG) recording predict sudden death. METHODS AND RESULTS: A total of 396 subjects with chronic heart failure (CHF) due to post-ischaemic cardiomyopathy, with an EF between 35 and 40% and in NYHA class I, underwent a 5 min ECG recording to calculate the following variables: QT variance (QT(v)), QT normalized for the square of the mean QT (QTVN), and QT variability index (QTVI). Corrected QT (QT(c)) was calculated from a 12-lead ECG recording. All participants were followed for 5 years. A multivariable survival model indicated that a QTVI greater than or equal to the 80th percentile indicated a high risk of SCD [hazards ratio (HR) 4.6, 95% confidence interval (CI) 1.5-13.4, P = 0.006] and, though to a lesser extent, a high risk of total mortality (HR 2.4, 95% CI 1.2-4.9, P = 0.017). The model including QTVI as a continuous variable confirmed a similar high risk for SCD (HR 2.9, 95% CI 1.3-6.5, P = 0.01) and for total mortality (HR 2.6, 95% CI 1.3-5.2, P = 0.008). CONCLUSION: Although asymptomatic patients with CHF who have a slightly depressed EF are at low risk of sudden death, the category is extraordinarily numerous. The QTVI could be helpful in stratifying the risk of sudden death in this otherwise undertreated population.