Proarrhythmic changes in human cardiomyocytes during hypothermia by milrinone and isoprenaline, but not levosimendan: an experimental in vitro study

BACKGROUND

Accidental hypothermia, recognized by core temperature below 35 °C, is a lethal condition with a mortality rate up to 25%. Hypothermia-induced cardiac dysfunction causing increased total peripheral resistance and reduced cardiac output contributes to the high mortality rate in this patient group. Recent studies, in vivo and in vitro, have suggested levosimendan, milrinone and isoprenaline as inotropic treatment strategies in this patient group. However, these drugs may pose increased risk of ventricular arrhythmias during hypothermia. Our aim was therefore to describe the effects of levosimendan, milrinone and isoprenaline on the action potential in human cardiomyocytes during hypothermia.

METHODS

Using an experimental in vitro-design, levosimendan, milrinone and isoprenaline were incubated with iCell2 hiPSC-derived cardiomyocytes and cellular action potential waveforms and contraction were recorded from monolayers of cultured cells. Experiments were conducted at temperatures from 37 °C down to 26 °C. One-way repeated measures ANOVA was performed to evaluate differences from baseline recordings and one-way ANOVA was performed to evaluate differences between drugs, untreated control and between drug concentrations at the specific temperatures.

RESULTS

Milrinone and isoprenaline both significantly increases action potential triangulation during hypothermia, and thereby the risk of ventricular arrhythmias. Levosimendan, however, does not increase triangulation and the contractile properties also remain preserved during hypothermia down to 26 °C.

CONCLUSIONS

Levosimendan remains a promising candidate drug for inotropic treatment of hypothermic patients as it possesses ability to treat hypothermia-induced cardiac dysfunction and no increased risk of ventricular arrhythmias is detected. Milrinone and isoprenaline, on the other hand, appears more dangerous in the hypothermic setting.

Effect of Hypothermia on Myocardial Depolarization and Repolarization in Neonates with Hypoxic-Ischemic Encephalopathy Due to Asphyxia

Therapeutic hypothermia (TH) is effective for neonatal hypoxic-ischemic encephalopathy (HIE). The combination of abnormal myocardial repolarization and fatal arrhythmia in patients with accidental hypothermia has prompted clinical validation of the proarrhythmic potential of TH. However, to our knowledge, there have been few clinical studies on myocardial depolarization and repolarization abnormalities caused by TH in neonates. Therefore, we investigated the effects of TH on neonatal myocardial depolarization and repolarization by capturing the waveform changes in electrocardiograms (ECGs) associated with body temperature (BT) before and after TH. We included three neonates with HIE diagnosed at birth who were treated with TH in our hospital. The heart rate, RR interval, P wave duration, PR interval, QRS duration, QT interval, corrected QT (QTc) interval by Fridericia's formula, J point-T end (JT) interval, corrected JT (JTc) interval by Fridericia's formula, T peak-T end (Tpe) interval, Tpe/QT, and QRS/QTc were calculated retrospectively using an ECG. The correlations of ECG parameters recorded concurrently with 33 samples in which BT measurements were confirmed were performed. BT and heart rate were positively correlated (R: 0.589, p = 0.0003). BT was negatively correlated with Tpe/QT (R: - 0.470, p = 0.0058), the QTc interval (R: - 0.680, p < 0.0001), and the corrected JT interval (R: - 0.697, p < 0.0001). TH does not affect atrial or ventricular depolarization but prolongs the ventricular repolarization process in a temperature-dependent manner.

Repolarization and ventricular arrhythmia during targeted temperature management post cardiac arrest

BACKGROUND

Targeted temperature management (TTM) following out-of-hospital cardiac arrest (OHCA) prolongs the QT-interval but our knowledge of different temperatures and risk of arrhythmia is incomplete.

OBJECTIVE

To assess whether the QTc, QT-peak (QTp) and T-peak to T-end interval (TpTe) may be useful markers of ventricular arrhythmia in contemporary post cardiac arrest treatment.

METHODS

An ECG-substudy of the TTM-trial (TTM at 33 °C vs. 36 °C) with serial ECGs from 680 (94%) patients. Bazett's (B) and Fridericia's (F) formula were used for heart rate correction of the QT, QTp and TpTe. Ventricular arrhythmia (VT/VF) were registered during the first three days of post cardiac arrest care.

RESULTS

The QT, QTc and QTp intervals were prolonged more at 33 °C compared to 36 °C and restored to similar and lower levels after rewarming. The TpTe-interval remained between 92-100 ms throughout TTM in both groups. The QTc intervals were associated with ventricular arrhythmia, but not after adjustment for cardiac arrest characteristics. The QTp-interval was not associated with risk of ventricular arrhythmia. Heart rate corrected TpTe-intervals were associated with higher risk of arrhythmia (Odds ratio (OR): TpTe(B): 1.12 (1.02-1.23, p = 0.01 TpTe(F): 1.12 (1.02-1.23, p = 0.02) per 20 ms). Further a prolonged TpTe-interval ≥ 90 ms was consistently associated with higher risk (OR_adjusted: TpTe(B): 2.05 (1.25-3.37), p < 0.01, TpTe(F): 2.14 (1.32-3.49), p < 0.01).

CONCLUSIONS

TTM prolongs the QT-interval by prolongation of the QTp-interval without association to increased risk. The TpTe-interval is not significantly affected by core temperature, but heart rate corrected TpTe intervals are robustly associated with risk of ventricular arrhythmia.

TRIAL REGISTRATION

The TTM-trial is registered and accessible at ClinicalTrials.gov (Identifier: NCT01020916).

Experimental verification of the value of the Tpeak -Tend interval in ventricular arrhythmia inducibility in an early repolarization syndrome model

INTRODUCTION

In patients with early repolarization patterns on ECG, many researchers have studied to find predictors of fatal arrhythmia. However, there are no satisfying clinical predictors. We evaluated the value of the T_peak -T_end interval on pseudo-ECG in canine myocardial wedge preparation models of early repolarization syndrome.

METHODS AND RESULTS

Transmural pseudo-ECG and endocardial/epicardial action potentials were recorded from coronary-perfused canine left ventricular wedge preparations (n = 34). The I_to agonist NS5806 (8-10 µM), the calcium channel blocker verapamil (3 µM) and acetylcholine (2-3 µM) were used to mimic the disease model. A ventricular arrhythmia induction test was performed. QT_peak , QT_end , T_peak -T_end , and T_peak -T_end /QT_end were measured at 15 to 20 minutes after the provocative agent infusion. Polymorphic ventricular tachycardias (pVT) developed in 23 of the 34 preparations (67%). The maximal values of T_peak -T_end and T_peak -T_end /QT_end were recorded just before pVT induction. At baseline, without the provocative agents, T_peak -T_end and T_peak -T_end /QT_end were not different between pVT-induced and pVT-noninduced preparations. The T_peak -T_end of the pVT-induced preparations was longer than that of non-induced preparations (58 ± 26.8 msec vs 33 ± 6.8 msec, P < .001). The T_peak -T_end /QT_end of pVT- induced preparations was larger than that of noninduced preparations (0.220 ± 0.1017 vs 0.128 ± 0.0312, P < .001). The transmural and epicardial dispersion of repolarization of pVT-induced preparations were larger than those of pVT-noninduced preparations. The transmural dispersion of repolarization showed a positive correlation with T_peak -T_end .

CONCLUSION

T_peak -T_end predicted malignant ventricular arrhythmias in early repolarization syndrome models. T_peak -T_end reflects the repolarization heterogeneity of ventricular myocardium.

Electrocardiographic conduction and repolarization markers associated with sudden cardiac death: moving along the electrocardiography waveform

The QT interval along with its heart rate corrected form (QTc) are well-established ECG markers that have been found to be associated with malignant ventricular arrhythmogenesis. However, extensive preclinical and clinical investigations over the years have allowed for novel clinical ECG markers to be generated as predictors of arrhythmogenesis and sudden cardiac death. Repolarization markers include the older QTc, QT dispersion and newer Tpeak - Tend intervals, (Tpeak - Tend) / QT ratios, T-wave alternans (TWA), microvolt TWA and T-wave area dispersion. Meanwhile, conduction markers dissecting the QRS complex, such as QRS dispersion (QRSD) and fragmented QRS, were also found to correlate conduction velocity and unidirectional block with re-entrant substrates in various cardiac conditions. Both repolarization and conduction parameters can be combined into the excitation wavelength (λ). A surrogate marker for λ is the index of Cardiac Electrophysiological Balance (iCEB: QT / QRSd). Other markers based on conduction-repolarization are [QRSD x (Tpeak-Tend) / QRSd] and [QRSD x (Tpeak-Tend) / (QRSd x QT)]. Advancement in technology permitted sophisticated electrophysiological analyses such as principal component analysis and periodic repolarization dynamics to further improve risk stratification. This was closely followed by other novel indices including ventricular ectopic QRS interval, the f99 index and EntropyXQT, which integrates mathematical and physical calculations for determining the risk markers. Though proven to be effective in limited patient cohorts, more clinical studies across different cardiac pathologies are required to confirm their validity. As such, this review seeks to encapsulate the development of old and new ECG markers along with their associated utility and shortcomings in clinical practice.