Impact of Heart Rate and Rhythm on Corrected QT Interval During Paroxysmal Atrial Fibrillation

Hydroethanolic extract of Cirsium setidens ameliorates doxorubicin-induced cardiotoxicity by AMPK-PGC-1α-SOD-mediated mitochondrial protection

BACKGROUND

Doxorubicin (DOX) is an effective anticancer agent. However, the clinical outcomes of DOX-based therapies are severely hampered by their significant cardiotoxicity.

PURPOSE

We investigated the beneficial effects of an ethanol extract of Cirsium setidens (CSE) on DOX-induced cardiomyotoxicity (DICT).

METHODS

UPLC-TQ/MS analysis was used to identify CSE metabolite profiles. H9c2 rat cardiomyocytes and MDA-MB-231 human breast cancer cells were used to evaluate the effects of CSE on DICT-induced cell death. To elucidate the mechanism underlying it, AMP-activated protein kinase (AMPK), peroxisome proliferator-activated receptor gamma co-activator l-alpha (PGC1-α), nuclear respiratory factor 1 (NRF1), NRF2, superoxide dismutase (SOD1), and SOD2 expression was detected using western blot analysis. The oxygen consumption rate (OCR), cellular ROS, and mitochondrial membrane potential were measured. Finally, we confirmed the cardioprotective effect of CSE against DICT in both C57BL/6 mice and human induced pluripotent stem cell-derived cardiomyocytes (hiPSCCMs) by observing various parameters, such as electrophysiological changes, cardiac fibrosis, and cardiac cell death.

RESULTS

Chlorogenic acid and nicotiflorin were the major compounds in CSE. Our data demonstrated that CSE blocked DOX-induced cell death of H9c2 cells without hindrance of its apoptotic effects on MDA-MB-231 cells. DOX-induced defects of OCR and mitochondrial membrane potential were recovered in a CSE through upregulation of the AMPK-PGC1-α-NRF1 signaling pathway. CSE accelerated NRF1 translocation to the nucleus, increased SOD activity, and consequently blocked apoptosis in H9c2 cells. In mice treated with 400 mg/kg CSE for 4 weeks, electrocardiogram data, creatine kinase and lactate dehydrogenase levels in the serum, and cardiac fibrosis, were improved. Moreover, various electrophysiological features indicative of cardiac function were significantly enhanced following the CSE treatment of hiPSCCMs.

CONCLUSION

Our findings demonstrate CSE that ameliorates DICT by protecting mitochondrial dysfunction via the AMP- PGC1α-NRF1 axis, underscoring the therapeutic potential of CSE and its underlying molecular pathways, setting the stage for future investigations into its clinical applications.

Case report: A 56-year-old woman presenting with torsades de pointes and cardiac arrest associated with levosimendan administration and underlying congenital long QT syndrome type 1

Torsades de Pointes (TdP) is a malignant polymorphic ventricular tachycardia with heart rate corrected QT interval (QTc) prolongation, which may be attributed to congenital and acquired factors. Although various acquired factors for TdP have been summarized, levosimendan administration in complex postoperative settings is relatively uncommon. Timely identification of potential causes and appropriate management may improve the outcome. Herein, we describe the postoperative case of a 56-year-old female with initial normal QTc who accepted the administration of levosimendan for heart failure, suffered TdP, cardiac arrest, and possible Takotsubo cardiomyopathy, further genetically confirmed as long QT syndrome type 1 (LQT1). The patient was successfully treated with magnesium sulfate, atenolol, and implantable cardioverter defibrillator implantation. There should be a careful evaluation of the at-risk populations and close monitoring of the electrocardiograms, particularly the QT interval, to reduce the risk of near-fatal arrhythmias during the use of levosimendan.

QTc intervals at rest and during exercise assessed by group correction formulas in survivors of childhood acute lymphoblastic leukemia

INTRODUCTION

Early signs of subclinical cardiac damage must be identified before they turn into clinical manifestations. Tailoring a formula is relevant for precise QTc evaluation in childhood acute lymphoblastic leukemia (ALL) survivors considering they are at risk of long-term cardiac problems. Therefore, we aim to develop group heart rate correction formulas for QT intervals in childhood ALL survivors at rest and during exercise, and to assess the applicability of these methods across a variety of risk groups exposed to diverse chemotherapy dosages.

METHODS

Two hundred and fifty childhood ALL survivors in the PETALE study were classified into 3 groups depending on their prognostic risk group. ECG measurements (QT and RR intervals) were made at rest and during a cardiopulmonary exercise test. QT correction for heart rate was applied using 5 different formulas, which included 2 previously published formulas and 3 group-specific formulas for each sex.

RESULTS

The QT/RR relation showed 2 different curves between rest and during exercise, which was worse for females. Group-specific QTc formulas allowed adequate heart rate-corrected QT interval, independently of the cumulative dose of doxorubicin received during treatment. Group-specific formulas showed significantly shorter QTc intervals than QTc from Bazett's formula. QTc (Bazett's formula) values surpassed the established clinical norm in 22 males (11%) and 22 females (11%), with a majority occurring during exercise, affecting 15 males (7.5%) and 10 females (5%).

CONCLUSION

This study shows the applicability of personalized group correction of QT/RR data in childhood ALL survivors. Our comprehensive assessments (spanning rest, exercise, and recovery) is an effective approach for risk stratification of cardiac complications in childhood ALL survivors.

Atrial fibrillation and QT corrected. What is the best formula to use?

BACKGROUND

QT interval varies with the heart rate (HR), so a correction in QT calculation is needed (QTc). Atrial fibrillation (AF) is associated with elevated HR and beat-to-beat variation.

AIM

To find best correlation between QTc in atrial fibrillation (AF) versus restored sinus rhytm (SR) after electrical cardioversion (ECV) (primary end point) and to determine which correction formula and method are the best to determine QTc in AF (secondary end point).

METHODS

During a 3-month period, we considered patients who underwent 12-lead ECG recording and received an AF diagnosis with indication for ECV. Exclusion criteria were as follows: QRS duration >120 ms, therapy with QT-prolonging drugs, a rate control strategy and a nonelectrical cardioversion. The QT interval was corrected using Bazzett's, Framingham, Fridericia and Hodges formulas during the last ECG during AF and the first one immediately after ECV. QTc mean was calculated as mQTc (average of 10 QTc calculated beat per beat) and as QTcM (QTc calculated from the average of 10 raw QT and RR for each beat).

RESULTS

Fifty consecutive patients were enrolled in the study. Bazett's formula showed a significant change in mean QTc value between the two rhythms (421.5 ± 33.9 vs. 446.1 ± 31.9; p < 0.001 for mQTc and 420.9 ± 34.1 vs. 441.8 ± 30.9; p = 0.003 for QTcM). On the contrary, in patients with SR, QTc assessed by the Framingham, Fridericia, and Hodges formulas was similar to that in AF. Furthermore, good correlations between mQTc and QTcM are present for each formula, even in AF or SR.

CONCLUSIONS

During AF, Bazzett's formula, seems to be the most imprecise in QTc estimation.

QTc interval measurement in patients with right bundle branch block: A practical method

BACKGROUND AND AIM

Prolonging the QT interval in the right bundle branch block (RBBB) can create challenges for electrophysiologists in estimating repolarization time and eliminating the effect of depolarization changes on QT interval. In this study, we aimed to develop a practice formula to eliminate the effect of depolarization changes on QT interval in patients with RBBB.

METHODS

This prospective study evaluated accidentally induced RBBB in patients undergoing electrophysiological study. Two expert electrophysiologists recorded the ECG parameters, including QRS duration, QT interval, and cycle length, in the patients. The formula was developed based on QT interval differences (with and without RBBB) and its proportion to QRS. Additionally, the Bazzet, Rautaharju, and Hodge formulas were used to evaluate QTc.

RESULTS

We evaluated 96 patients in this study. The mean QT interval without RBBB was 369.39 ± 37.38, reaching 404.22 ± 39.23 after inducing RBBB. ΔQT was calculated as 34.83 ± 17.61, and the ratio of ΔQT/QRS with RBBB was almost 23%. Our formula is: (QT_{with RBBB}  - 23% × QRS). Subtraction of 25% instead of 23% seems more straightforward and practical. Our formula could also predict the QTc interval in RBBB based on the Bazzet, Rautaharju, and Hodge formulas.

CONCLUSION

Previous formulas for QT correction were hard to apply in the clinical setting or were not specified for RBBB. Our new formula allows a rapid and practical method for QT correction in RBBB in clinical practice.