Electrical inhomogeneity in left ventricular hypertrophy

The anti-aging factor Klotho protects against acquired long QT syndrome induced by uremia and promoted by fibroblast growth factor 23

BACKGROUND

Chronic kidney disease (CKD) is associated with increased propensity for arrhythmias. In this context, ventricular repolarization alterations have been shown to predispose to fatal arrhythmias and sudden cardiac death. Between mineral bone disturbances in CKD patients, increased fibroblast growth factor (FGF) 23 and decreased Klotho are emerging as important effectors of cardiovascular disease. However, the relationship between imbalanced FGF23-Klotho axis and the development of cardiac arrhythmias in CKD remains unknown.

METHODS

We carried out a translational approach to study the relationship between the FGF23-Klotho signaling axis and acquired long QT syndrome in CKD-associated uremia. FGF23 levels and cardiac repolarization dynamics were analyzed in patients with dialysis-dependent CKD and in uremic mouse models of 5/6 nephrectomy (Nfx) and Klotho deficiency (hypomorphism), which show very high systemic FGF23 levels.

RESULTS

Patients in the top quartile of FGF23 levels had a higher occurrence of very long QT intervals (> 490 ms) than peers in the lowest quartile. Experimentally, FGF23 induced QT prolongation in healthy mice. Similarly, alterations in cardiac repolarization and QT prolongation were observed in Nfx mice and in Klotho hypomorphic mice. QT prolongation in Nfx mice was explained by a significant decrease in the fast transient outward potassium (K⁺) current (I_tof), caused by the downregulation of K⁺ channel 4.2 subunit (Kv4.2) expression. Kv4.2 expression was also significantly reduced in ventricular cardiomyocytes exposed to FGF23. Enhancing Klotho availability prevented both long QT prolongation and reduced I_tof current. Likewise, administration of recombinant Klotho blocked the downregulation of Kv4.2 expression in Nfx mice and in FGF23-exposed cardiomyocytes.

CONCLUSION

The FGF23-Klotho axis emerges as a new therapeutic target to prevent acquired long QT syndrome in uremia by minimizing the predisposition to potentially fatal ventricular arrhythmias and sudden cardiac death in patients with CKD.

Widened QRS-T Angle May Be a Measure of Poor Ventricular Stretch During Exercise Among On-duty Firefighters

BACKGROUND

The spatial QRS-T angle is a measure of repolarization heterogeneity and may be a predictor of poor ventricular health. It is unknown whether a relationship exists between QRS-T angle and blood pressure (BP) during exercise.

OBJECTIVE

The purpose of this study was to evaluate the potential relationship between QRS-T angle and BP during exercise, which may be indicative of ventricular stretch.

METHODS

Ambulatory 12-lead 24-hour Holter electrocardiographic monitoring for QRS-T angle measurement was followed by exercise testing with BP (mm Hg) recordings taken preexercise, maximum achieved BP during exercise, and 2 minutes postexercise. Blood pressure recovery was calculated by subtracting the maximal and 2-minute postexercise BPs. Means (± standard deviation) and percentages are presented. Pearson correlations (r) among all QRS-T angles and all BP measures were performed. One-way analysis of variance was conducted on classification of QRS-T angle and all BP measures.

RESULTS

One hundred eleven firefighters (95.5% male; mean age, 44 years) were included in this analysis. Twenty-seven percent of the firefighters had either a borderline (100°-139°) or widened (≥140°) QRS-T angle. Although the analysis of variance was not statistically significant, a near-statistically significant negative correlation existed between QRS-T angle and maximum diastolic BP (r = -0.190, P = .05), and a statistically significant relationship existed between QRS-T angle and postexercise diastolic BP (r = -0.261, P = .008).

CONCLUSIONS

A negative correlation existed between QRS-T angle and maximal diastolic BP and postexercise diastolic BP. Lower maximum diastolic BP during and after exercise may be a sign of poor ventricular stretch. A widened spatial QRS-T angle may represent poor ventricular stretch.

Reproducibility and Reliability Of QTc and QTcd Measurements and Their Relationships with Left Ventricular Hypertrophy in Hemodialysis Patients

Background

Left ventricular hypertrophy (LVH) is very common in hemodialysis patients and an independent risk factor for mortality in this population. The myocardial remodeling underlying the LVH can affect ventricular repolarization causing abnormalities in QT interval.

Objective

to evaluate the reproducibility and reliability of measurements of corrected QT interval (QTc) and its dispersion (QTcd) and correlate these parameters with LVH in hemodialysis patients.

Methods

Case-control study involving hemodialysis patients and a control group. Clinical examination, blood sampling, transthoracic echocardiogram, and electrocardiogram were performed. Intra- and interobserver correlation and concordance tests were performed by Pearson´s correlation, Cohen’s Kappa coefficient and Bland Altman diagram. Linear regression was used to analyze association of QTc or QTcd with HVE.

Results

Forty-one HD patients and 37 controls concluded the study. Hemodialysis patients tended to have higher values of QTc, QTcd and left ventricular mass index (LVMi) than controls but statistical significance was not found. Correlation and concordance tests depicted better results for QTc than for QTcd. In HD patients, a poor but significant correlation was found between QTc and LVMi (R² = 0.12; p = 0.03). No correlation was found between values of QTcd and LVMi (R²= 0.00; p=0.940). For the control group, the correspondent values were R²= 0.00; p = 0.67 and R²= 0.00; p = 0.94, respectively.

Conclusion

We found that QTc interval, in contrast to QTcd, is a reproducible and reliable measure and had a weak but positive correlation with LVMi in HD patients.