Effects of post-treatment electroacupuncture on ventricular monophasic action potential and cardiac function in a rat model of ischemia/reperfusion injury

BACKGROUND

To determine the effects of post-treatment electroacupuncture (EA) on the electrophysiological properties of ventricular muscle in rats with ischemia/reperfusion (IR) injury.

METHODS

Male Sprague-Dawley (SD) rats were randomly assigned into sham-operated (SH), IR and IR + EA groups (n = 8 each). The IR model was generated by ligation of the left anterior descending (LAD) coronary artery for 30 min. After establishing the IR model, EA was administered at PC6 for 30 min while opening the coronary artery and allowing reperfusion for 30 min. Heart rate (HR), mean arterial pressure and monophasic action potential (MAP) of cardiac muscle in the outer membrane of the antetheca of the left ventricle before coronary artery ligation (T₀), after coronary artery ligation for 30 min (T₁) and after reperfusion for 30 min (T₂) were recorded. At the same time, ventricular electrophysiological parameters including ventricular effective refractory period (ERP), conduction velocity (CV) and ventricular fibrillation threshold (VFT) were measured. Then, the cardiac function and the levels of creatine kinase-muscle/brain (CK-MB) and cardiac troponin I (cTnI) were monitored. Based on these data, monophasic action potential amplitude (MAPA), the maximum depolarization velocity (V_max) and the MAP durations at 50% and 90% repolarization (MAPD₅₀ and MAPD₉₀) were calculated to determine the incidence of arrhythmia during reperfusion.

RESULTS

Compared with the SH group, the IR group showed an obviously decreased HR as well as reduced mean arterial pressure, V_max, CV, ERP and MAPA. All indices of cardiac function except left ventricular end-diastolic pressure (LVEDP) decreased (i.e. ventricular systolic pressure (LVSP), left ventricular ejection fraction (LVEF), fractional shortening (FS) and rate of the ventricular pressure rise/drop (±dp/dt)). Furthermore, the MAPD₅₀ and MAPD₉₀ were prolonged, and the levels of CK-MB and cTnI increased (p < 0.05). In comparison to the IR group, HR and the mean arterial pressure were increased. All indices of cardiac function except LVEDP increased (LVSP, LVEF, FS and ±dp/dt). V_max, CV, ERP and MAPA were also increased in the IR + EA group. However, MAPD₅₀ and MAPD₉₀ were distinctly shortened, and the levels of CK-MB and cTnI decreased (p < 0.05). There were no statistically significant differences in VFT between the three groups (p > 0.05).

CONCLUSION

EA post-treatment can relieve prolongation of repolarization and slowed depolarization of ventricular muscle during IR, thus decreasing the rate of incidence of reperfusion arrhythmia.

Prolonged duration of repolarization and decreased conduction velocity in the atrial myocardium after hypothermic ischemia-reperfusion may be related to expressions of inward rectifier potassium channel 2.1 protein and connexin 40

OBJECTIVES

The study aimed to determine the role of inward rectifier potassium channel 2.1 protein and connexin 40 expressions in regulating the duration of repolarization and conduction velocity of right atrial myocardium in rats following hypothermic ischemia-reperfusion.

METHODS

The Langendorff isolated rat cardiac perfusion models were divided into control (C) and hypothermic ischemia-reperfusion groups, with 8 models in group C and 16 models in group ischemia-reperfusion. Depending on the incidence of atrial arrhythmia after reperfusion, the models in group ischemia-reperfusion were further divided into reperfusion non-atrial arrhythmia or reperfusion atrial arrhythmia subgroup. Right atrial monophasic action potential duration at 50% and 90% of repolarization after 30 minutes of continuous perfusion in group C and group ischemia-reperfusion (T0), 105 minutes of continuous perfusion in group C or after 15 minutes of reperfusion in group ischemia-reperfusion (T1) and 120 minutes of continuous perfusion in group C or 30 minutes of reperfusion in group ischemia-reperfusion (T2) were recorded. Right atrial conduction velocity and effective refractory period were recorded at T2. Then, the expressions of inward rectifier potassium channel 2.1 protein and connexin 40 in the right atrial myocardium were detected.

RESULTS

Monophasic action potential duration at 50% and 90% were higher at T1 and T2 than those at T0 in subgroup reperfusion atrial arrhythmia (p < 0.05); monophasic action potential duration at 50% in subgroup reperfusion atrial arrhythmia were larger than group C and subgroup reperfusion non-atrial arrhythmia at T1 and T2 (p < 0.05); monophasic action potential duration at 90% in subgroup reperfusion atrial arrhythmia were larger than group C and subgroup reperfusion non-atrial arrhythmia at T1 and T2 (p < 0.05); effective refractory period in subgroup reperfusion atrial arrhythmia was greater than that in group C and subgroup reperfusion non-atrial arrhythmia, and the conduction velocity and the expressions of inward rectifier potassium channel 2.1 protein and connexin 40 were significantly lower than group C and subgroup reperfusion non-atrial arrhythmia (p < 0.05).

CONCLUSIONS

The prolonged duration of repolarization and a decrease in conduction velocity of the atrial myocardium occur in rats after hypothermic ischemia-reperfusion. These observed effects may be related to the downregulated expressions of connexin 40 and inward rectifier potassium channel 2.1.

Progression of infarct-mediated arrhythmogenesis in a rodent model of heart failure

Heart failure (HF) post-myocardial infarction (MI) presents with increased vulnerability to monomorphic ventricular tachycardia (mmVT). To appropriately evaluate new therapies for infarct-mediated reentrant arrhythmia in the preclinical setting, chronologic characterization of the preclinical animal model pathophysiology is critical. This study aimed to evaluate the rigor and reproducibility of mmVT incidence in a rodent model of HF. We hypothesize a progressive increase in the incidence of mmVT as the duration of HF increases. Adult male Sprague-Dawley rats underwent permanent left coronary artery ligation or SHAM surgery and were maintained for either 6 or 10 wk. At end point, SHAM and HF rats underwent echocardiographic and invasive hemodynamic evaluation. Finally, rats underwent electrophysiologic (EP) assessment to assess susceptibility to mmVT and define ventricular effective refractory period (ERP). In 6-wk HF rats (n = 20), left ventricular (LV) ejection fraction (EF) decreased (P < 0.05) and LV end-diastolic pressure (EDP) increased (P < 0.05) compared with SHAM (n = 10). Ten-week HF (n = 12) revealed maintenance of LVEF and LVEDP (P > 0.05), (P > 0.05). Electrophysiology studies revealed an increase in incidence of mmVT between SHAM and 6-wk HF (P = 0.0016) and ERP prolongation (P = 0.0186). The incidence of mmVT and ventricular ERP did not differ between 6- and 10-wk HF (P = 1.0000), (P = 0.9831). Findings from this rodent model of HF suggest that once the ischemia-mediated infarct stabilizes, proarrhythmic deterioration ceases. Within the 6- and 10-wk period post-MI, no echocardiographic, invasive hemodynamic, or electrophysiologic changes were observed, suggesting stable HF. This is the necessary context for the evaluation of experimental therapies in rodent HF.NEW & NOTEWORTHY Rodent model of ischemic cardiomyopathy exhibits a plateau of inducible monomorphic ventricular tachycardia incidence between 6 and 10 wk postinfarction.

[Effects of hypothermia on the repolarization duration of ventricular myocytes in rats and its mechanism]

Objective: To observe the effects of hypothermia on the repolarization duration and the expression of Kir2.1 protein of ventricular myocytes in isolated rat heart and explore the role of Kir2.1 protein.Methods: Eighteen healthy adult male Sprague-Dawley rats were randomly divided into three groups (n=6 per group): Control group (C group), 35℃ group (H₁ group), 32℃ group (H₂ group). Langendorff isolated heart models were established. After 15 min 37℃ K-H fluid banlanced perfusion, C group continued to perfuse the K-H solution at 37℃ for 30 minutes, H₁ group continued to perfuse the K-H solution at 35℃ for 30 minutes, H₂ group continued to perfuse the K-H solution at 32℃ for 30 minutes. At 15 min of balanced perfusion (T₁), and 30 min of continuous perfusion (T₂), the heart rate,and the MAP in the three layers of the left ventricular anterior wall were recorded, the action potential duration at 50% repolarization (MAPD₅₀), the action potential duration at 90% repolarization (MAPD₉₀) and transmural dispersion of repolarization(TDR) were calculated. At the same time, the occurrence of arrhythmia was recorded. The expression of Kir2.1 protein was measured by Western blot. The average optical density (AOD) and the distribution of Kir2.1 protein were measured by immunohistochemistry in the ventricular tissue measured by electrophysiology. Results: Compared with T₀, the heart rate was decreased, MAPD₅₀ and MAPD₉₀ were prolonged significantly (P＜0.05), and TDR was increased significantly (P＜0.05) in H₁ group, H₂ group at T₁. Compared with C group, the HR was decreased, the MAPD₉₀ was prolonged significantly (P＜0.05), TDR was increased significantly (P＜0.05),the expression and the AOD of Kir2.1 protein were decreased significantly (P＜0.05) in H₁group, H₂group at T₁. Compared with H₁ group, the heart rate of H₂ group was decreased significantly (P＜0.05), MAPD₅₀ and MAPD₉₀ were prolonged significantly (P＜0.05), and TDR was increased significantly (P＜0.05) at T₁. The distribution of Kir2.1 protein in group C was normal, while the distribution of Kir2.1 in H₁ group and H₂ group was disordered. Conclusion: Hypothermia prolonged the ventricular duration of repolarization and increased the dispersion of repolarization. The mechanism is related to the down-regulation the expression of Kir2.1 protein and the disorder of the distribution of Kir2.1 protein.

The Visible Heart® project and methodologies: novel use for studying cardiac monophasic action potentials and evaluating their underlying mechanisms

INTRODUCTION

This review describes the utilization of Visible Heart® methodologies for electrophysiologic studies, specifically in the investigation of monophasic action potential (MAP) recordings, with the aim to facilitate new catheter/device design and development that may lead to earlier diagnosis, treatment, and ultimately a higher quality of life for patients with atrial fibrillation.

AREAS COVERED

We describe the historically proposed mechanisms behind which electrode is responsible for the MAP recording, new catheters for recording these signals, and how Visible Heart methodologies can be utilized to develop and test new technologies for electrophysiologic investigations.

EXPERT OPINION

When compared to traditional electrogram recordings, MAP waveforms provide clinical information vital to the understanding, diagnosis, and treatment of cardiac arrhythmias. New catheters and ablation technologies are routinely being assessed on reanimated large mammalian hearts (swine and human) in our laboratory. These abilities, combined with continued enhancements in imaging modalities and computational systems for electrical mapping, are being applied to the MAP catheter design process. Through this testing we are hopeful that the time from concept to product can be reduced, and that an array of MAP catheters can be placed in the hands of physicians, where they will improve patient outcomes.

Unanesthetized Rodents Demonstrate Insensitivity of QT Interval and Ventricular Refractory Period to Pacing Cycle Length

Aim: The cardiac electrophysiology of mice and rats has been analyzed extensively, often in the context of pathological manipulations. However, the effects of beating rate on the basic electrical properties of the rodent heart remain unclear. Due to technical challenges, reported electrophysiological studies in rodents are mainly from ex vivo preparations or under deep anesthesia, conditions that might be quite far from the normal physiological state. The aim of the current study was to characterize the ventricular rate-adaptation properties of unanesthetized rats and mice.

Methods: An implanted device was chronically implanted in rodents for atrial or ventricular pacing studies. Following recovery from surgery, QT interval was evaluated in rodents exposed to atrial pacing at various frequencies. In addition, the frequency dependence of ventricular refractoriness was tested by conventional ventricular programmed stimulation protocols.

Results: Our findings indicate total absence of conventional rate-adaptation properties for both QT interval and ventricular refractoriness. Using monophasic action potential recordings in isolated mice hearts we could confirm the previously reported shortening of the action potential duration at fast pacing rates. However, we found that this mild shortening did not result in similar decrease of ventricular refractory period.

Conclusion: Our findings indicate that unanesthetized rodents exhibit flat QT interval and ventricular refractory period rate-dependence. This data argue against empirical use of QT interval correction methods in rodent studies. Our new methodology allowing atrial and ventricular pacing of unanesthetized freely moving rodents may facilitate more appropriate utility of these important animal models in the context of cardiac electrophysiology studies.

Pharmacokinetics and electrophysiological effects of sotalol hydrochloride in horses

BACKGROUND

Arrhythmias in horses may require long-term anti-arrhythmic therapy. Unfortunately, oral anti-arrhythmic drugs for use in horses are currently scarce. In human patients and small animals, sotalol, a β-blocker with class III anti-arrhythmic properties, is often used for long-term treatment.

OBJECTIVES

To determine the pharmacokinetics of sotalol at multiple oral dosages in unfasted horses, as well as the effects on electro- and echocardiographic measurements, right atrial and ventricular monophasic action potential (MAP) and effective refractory period (ERP).

STUDY DESIGN

Placebo controlled, double-blinded experiment.

MATERIALS AND METHODS

Six healthy, unfasted Warmblood horses were given either 0, 2, 3 or 4 mg/kg bodyweight (bwt) sotalol orally (PO) twice daily (bid) for 9 days in a randomised cross-over design. Echocardiography and surface electrocardiography were performed and plasma concentrations of sotalol and right atrial and right ventricular MAPs and ERPs were determined at steady-state conditions. Statistical analysis was performed using a repeated measures univariate analysis with post hoc Bonferroni corrections.

RESULTS

Calculated mean steady-state plasma concentrations determined by nonlinear mixed-effect modelling were 287 (range 234-339), 409 (359-458) and 543 (439-646) ng/mL for 2, 3 and 4 mg/kg bwt sotalol PO bid respectively. Sotalol significantly increased the QT interval and ERPs, but, despite increasing plasma concentrations, higher dosages did not result in a progressive increase in QT interval or ERPs. Echocardiographic and other electrocardiographic measurements did not change significantly. MAP durations at 90% repolarisation were not significantly different during sotalol treatment. Besides transient local sweating, no side effects were noted.

MAIN LIMITATIONS

Study size and ad libitum feeding of hay.

CONCLUSIONS

Sotalol at a dose of 2, 3 and 4 mg/kg bwt PO bid increases the QT interval and ERP and might be a useful drug for long-term anti-arrhythmic therapy in horses.

Amyloid beta peptide 22-35 induces a negative inotropic effect on isolated rat hearts

Evidences indicate that deposition of amyloid beta peptides (Aβs) plays an important role in the pathogenesis of Alzheimer disease. Aβs may influence cardiovascular system and ileum contractions. But the effect of amyloid beta peptide 22-35 (Aβ_22-35) on cardiovascular functions and contractions of ileum has not been studied. Therefore, the present study aimed to investigate the possible effects of this peptide on isolated rat heart and ileum smooth muscle. Langendorff-perfused rat heart preparations were established. The hearts were perfused under constant pressure (60 mmHg) with modified Krebs-Henseleit solution. Aβ_22-35 at doses of 1, 10 and 100 nM significantly decreased left ventricular developed pressure (LVDP; an index of cardiac contractility) and maximal rate of pressure development of left ventricle (+dP/dt_max; another index of cardiac contractility). This peptide at doses studied had no significant effect on heart rate, coronary flow, monophasic action potential amplitude (MAPamp), MAP duration at 90% repolarization (MAP₉₀) and ileum contractions. We suggest that Aβ_22-35 exerts a negative inotropism on isolated rat hearts with unchanged heart rate, coronary flow, MAPamp, MAP₉₀ and smooth muscle contractility of ileum.

Assessing the Relative Integrity of Formed Cardiac Linear Lesions by Recording Both Focal Monophasic Action Potentials and Contact Forces: A Technical Brief

The use of therapeutic ablation in patients with atrial fibrillation has become a mainstay in the treatment of this disease, yet often these individuals require multiple procedures. In other words, successful first time treatments are impacted by challenges, including the generation of linear lesions in certain anatomies like the mitral isthmus of the left atrium. Hence, there is a need to find ways to address the presence of unwanted conduction gaps at the time of lesion creation. In this paper, we describe a novel approach to examine conduction gaps, by using a proof of concept device to examine local electrical activation within the cardiac areas of an applied lesion, i.e., to locate gaps in the lesion set. To accomplish this, both epicardial and endocardial linear ablation lines composed of spot lesions with conduction gaps were created in a porcine model. The forces necessary to elicit monophasic action potentials (MAP) were collected from >200 measurements on the epicardium of the right ventricle. Ablations were then performed on the ventricular epicardium and left atrial mitral isthmus endocardially, while recording MAPs. We were able to successfully demonstrate the use of a proof of concept device to identify conduction gaps in linear lesion sets; furthermore, we were able to determine required contact forces to appropriately determine focal electrical changes of the underlying tissues. New catheter designs that incorporate capabilities to record focal MAPs could be employed clinically to better assess a given lesion quality and/or to determine the existence of an undesired conduction gap.

Spatial correlation of action potential duration and diastolic dysfunction in transgenic and drug-induced LQT2 rabbits

BACKGROUND

Enhanced dispersion of action potential duration (APD) is a major contributor to long QT syndrome (LQTS)-related arrhythmias.

OBJECTIVE

To investigate spatial correlations of regional heterogeneities in cardiac repolarization and mechanical function in LQTS.

METHODS

Female transgenic LQTS type 2 (LQT2; n = 11) and wild-type littermate control (LMC) rabbits (n = 9 without E4031 and n = 10 with E4031) were subjected to phase contrast magnetic resonance imaging to assess regional myocardial velocities. In the same rabbits' hearts, monophasic APDs were assessed in corresponding segments.

RESULTS

In LQT2 and E4031-treated rabbits, APD was longer in all left ventricular segments (P < .01) and APD dispersion was greater than that in LMC rabbits (P < .01). In diastole, peak radial velocities (Vr) were reduced in LQT2 and E4031-treated compared to LMC rabbits in LV base and mid (LQT2: -3.36 ± 0.4 cm/s, P < .01; E4031-treated: -3.24 ± 0.6 cm/s, P < .0001; LMC: -4.42 ± 0.5 cm/s), indicating an impaired diastolic function. Regionally heterogeneous diastolic Vr correlated with APD (LQT2: correlation coefficient [CC] 0.38, P = .01; E4031-treated: CC 0.42, P < .05). Time-to-diastolic peak Vr were prolonged in LQT2 rabbits (LQT2: 196.8 ± 2.9 ms, P < .001; E4031-treated: 199.5 ± 2.2 ms, P < .0001, LMC 183.1 ± 1.5), indicating a prolonged contraction duration. Moreover, in transgenic LQT2 rabbits, diastolic time-to-diastolic peak Vr correlated with APD (CC 0.47, P = .001). In systole, peak Vr were reduced in LQT2 and E4031-treated rabbits (P < .01) but longitudinal velocities or ejection fraction did not differ. Finally, random forest machine learning algorithms enabled a differentiation between LQT2, E4031-treated, and LMC rabbits solely based on "mechanical" magnetic resonance imaging data.

CONCLUSIONS

The prolongation of APD led to impaired diastolic and systolic function in transgenic and drug-induced LQT2 rabbits. APD correlated with regional diastolic dysfunction, indicating that LQTS is not purely an electrical but an electromechanical disorder.

Renal denervation suppresses ventricular arrhythmias during acute ventricular ischemia in pigs

BACKGROUND

Increased sympathetic activation during acute ventricular ischemia is involved in the occurrence of life-threatening arrhythmias.

OBJECTIVE

To test the effect of sympathetic inhibition by renal denervation (RDN) on ventricular ischemia/reperfusion arrhythmias.

METHODS

Anesthetized pigs, randomized to RDN or SHAM treatment, were subjected to 20 minutes of left anterior descending coronary artery (LAD) occlusion followed by reperfusion. Infarct size, hemodynamics, premature ventricular contractions, and spontaneous ventricular tachyarrhythmias were analyzed. Monophasic action potentials were recorded with an epicardial probe at the ischemic area.

RESULTS

Ventricular ischemia resulted in an acute reduction of blood pressure (-29%) and peak left ventricular pressure rise (-40%), which were not significantly affected by RDN. However, elevation of left ventricular end-diastolic pressure (LVEDP) during LAD ligation was attenuated by RDN (ΔLVEDP: +1.8 ± 0.6 mm Hg vs +9.7 ± 1 mm Hg in the SHAM group; P = .046). Infarct size was not affected by RDN compared to SHAM. RDN significantly reduced spontaneous ventricular extrabeats (160 ± 15/10 min in the RDN group vs 422 ± 36/10 min in the SHAM group; P = .021) without affecting coupling intervals. In 5 of 6 SHAM-treated animals, ventricular fibrillation (VF) occurred during LAD occlusion. By contrast, only 1 of 7 RDN-treated animals experienced VF (P = .029). Beta-receptor blockade by atenolol showed comparable effects. Neither VF nor transient shortening of monophasic action potential duration during reperfusion was inhibited by RDN.

CONCLUSIONS

RDN reduced the occurrence of ventricular arrhythmias/fibrillation and attenuated the rise in LVEDP during left ventricular ischemia without affecting infarct size, changes in ventricular contractility, blood pressure, and reperfusion arrhythmias. Therefore, RDN may protect from ventricular arrhythmias during ischemic events.

A new biomarker--index of cardiac electrophysiological balance (iCEB)--plays an important role in drug-induced cardiac arrhythmias: beyond QT-prolongation and Torsades de Pointes (TdPs)

INTRODUCTION

In the present study, we investigated whether a new biomarker - index of cardiac electrophysiological balance (iCEB=QT/QRS) - could predict drug-induced cardiac arrhythmias (CAs), including ventricular tachycardia/ventricular fibrillation (VT/VF) and Torsades de Pointes (TdPs).

METHODS

The rabbit left ventricular arterially-perfused-wedge was used to investigate whether the simple iCEB measured from the ECG is reflective of the more difficult measurement of λ (effective refractory period×conduction velocity) for predicting CAs induced by a number of drugs.

RESULTS

Dofetilide concentration-dependently increased iCEB and λ, predicting potential risk of drug-induced incidence of early afterdepolarizations (EADs) starting at 0.01μM. Digoxin (1 and 5μM), encainide (5 and 20μM) and propoxyphene (10 and 100μM) markedly reduced both iCEB and λ, predicting their ability to induce non-TdP-like VT/VF. At 10μM, both NS1643 and levcromakalim significantly decreased λ and iCEB, which was preceded with presence of non-TdP-like VT/VF. Isoprenaline (0.05 to 0.5μM) significantly reduced both λ and iCEB, which was associated with a high incidence of non-TdP-like VT/VF in most preparations. Other biomarkers (i.e. transmural dispersion of T-wave and instability of the QT interval) predicted only dofetilide-induced long QT and EADs, but did not predict drug-induced risk of non-TdP-like VT/VF.

DISCUSSION

Our data from 7 reference drugs of known pro-arrhythmic effects suggests that 1) this non-invasive iCEB predicts potential risk of drug-induced CAs beyond long QT and TdP; 2) iCEB is more useful than the current biomarkers (i.e. transmural dispersion and instability) in predicting potential risks for drug-induced non-TdP-like VT/VF.

Alternans in genetically modified langendorff-perfused murine hearts modeling catecholaminergic polymorphic ventricular tachycardia

The relationship between alternans and arrhythmogenicity was studied in genetically modified murine hearts modeling catecholaminergic polymorphic ventricular tachycardia (CPVT) during Langendorff perfusion, before and after treatment with catecholamines and a β-adrenergic antagonist. Heterozygous (RyR2^p/s) and homozygous (RyR2^s/s) RyR2-P2328S hearts, and wild-type (WT) controls, were studied before and after treatment with epinephrine (100 nM and 1 μM) and propranolol (100 nM). Monophasic action potential recordings demonstrated significantly greater incidences of arrhythmia in RyR2^p/s and RyR2^s/s hearts as compared to WTs. Arrhythmogenicity in RyR2^s/s hearts was associated with alternans, particularly at short baseline cycle lengths. Both phenomena were significantly accentuated by treatment with epinephrine and significantly diminished by treatment with propranolol, in full agreement with clinical expectations. These changes took place, however, despite an absence of changes in mean action potential durations, ventricular effective refractory periods or restitution curve characteristics. Furthermore pooled data from all hearts in which arrhythmia occurred demonstrated significantly greater alternans magnitudes, but similar restitution curve slopes, to hearts that did not demonstrate arrhythmia. These findings thus further validate the RyR2-P2328S murine heart as a model for human CPVT, confirming an alternans phenotype in common with murine genetic models of the Brugada syndrome and the congenital long-QT syndrome type 3. In contrast to these latter similarities, however, this report demonstrates the dissociation of alternans from changes in the properties of restitution curves for the first time in a murine model of a human arrhythmic syndrome.

A rabbit Langendorff heart proarrhythmia model: predictive value for clinical identification of Torsades de Pointes

BACKGROUND AND PURPOSE

The rabbit isolated Langendorff heart model (SCREENIT) was used to investigate the proarrhythmic potential of a range of marketed drugs or drugs intended for market. These data were used to validate the SCREENIT model against clinical outcomes.

EXPERIMENTAL APPROACH

Fifty-five drugs, 3 replicates and 2 controls were tested in a blinded manner. Proarrhythmia variables included a 10% change in MAPD(60), triangulation, instability and reverse frequency-dependence of the MAP. Early after-depolarisations, ventricular tachycardia, TdP and ventricular fibrillation were noted. Data are reported at nominal concentrations relative to EFTPC(max). Proarrhythmic scores were assigned to each drug and each drug category.

KEY RESULTS

Category 1 and 2 drugs have the highest number of proarrhythmia variables and overt proarrhythmia while Category 5 drugs have the lowest, at every margin. At 30-fold the EFTPC(max), the mean proarrhythmic scores are: Category 1, 101+/-24; Category 2, 101+/-14; Category 3, 72+/-20; Category 4, 59+/-16 and Category 5, 22+/-9 points. Only drugs in Category 5 have mean proarrhythmic scores, below 30-fold, that remain within the Safety Zone.

CONCLUSIONS AND IMPLICATIONS

A 30-fold margin between effects and EFTPC(max) is sufficiently stringent to provide confidence to proceed with a new chemical entity, without incurring the risk of eliminating potentially beneficial drugs. The model is particularly useful where compounds have small margins between the hERG IC(50) and predicted EFTPC(max). These data suggest this is a robust and reliable assay that can add value to an integrated QT/TdP risk assessment.