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 ( Vmax) 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, Vmax, 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). Vmax, 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.

Absence of Rgs5 Influences the Spatial and Temporal Fluctuation of Cardiac Repolarization in Mice

AimsThis study investigated the contribution of the regulator of G-protein signaling 5 (Rgs5) knockout to the alteration of the action potential duration (APD) restitution and repolarizing dispersion in ventricle.Methods and ResultsThe effects of Rgs5–/– were investigated by QT variance (QTv) and heart rate variability analysis of Rgs5–/– mice. Monophasic action potential analysis was investigated in isolated Rgs5–/– heart. Rgs5–/– did not promote ventricular remodeling. The 24-h QTv and QT variability index (QTVI) of the Rgs5–/– mice were higher than those of wild-type (WT) mice (P &lt; 0.01). In WT mice, a positive correlation was found between QTv and the standard deviation of all NN intervals (r = 0.62; P &lt; 0.01), but not in Rgs5–/– mice (R = 0.01; P &gt; 0.05). The absence of Rgs5 resulted in a significant prolongation of effective refractory period and APD in isolated ventricle. In addition, compared with WT mice, the knockout of Rgs5 significantly deepened the slope of the APD recovery curve at all 10 sites of the heart (P &lt; 0.01) and increased the spatial dispersions of Smax (COV-Smax) (WT: 0.28 ± 0.03, Rgs5–/–: 0.53 ± 0.08, P &lt; 0.01). Compared with WT heart, Rgs5–/– increased the induced S1–S2 interval at all sites of heart and widened the window of vulnerability of ventricular tachyarrhythmia (P &lt; 0.05).ConclusionOur findings indicate that Rgs5–/– is an important regulator of ventricular tachyarrhythmia in mice by prolonging ventricular repolarization and increasing spatial dispersion in ventricle.

Effects of genetic background, sex, and age on murine atrial electrophysiology

Aims Genetically altered mice are powerful models to investigate mechanisms of atrial arrhythmias, but normal ranges for murine atrial electrophysiology have not been robustly characterized. Methods and results We analyzed results from 221 electrophysiological (EP) studies in isolated, Langendorff-perfused hearts of wildtype mice (114 female, 107 male) from 2.5 to 17.7 months (mean 7 months) with different genetic backgrounds (C57BL/6, FVB/N, MF1, 129/Sv, Swiss agouti). Left atrial monophasic action potential duration (LA-APD), interatrial activation time (IA-AT), and atrial effective refractory period (ERP) were summarized at different pacing cycle lengths (PCLs). Factors influencing atrial electrophysiology including genetic background, sex, and age were determined. LA-APD70 was 18 ± 0.5 ms, atrial ERP was 27 ± 0.8 ms, and IA-AT was 17 ± 0.5 ms at 100 ms PCL. LA-APD was longer with longer PCL (+17% from 80 to 120 ms PCL for APD70), while IA-AT decreased (−7% from 80 to 120 ms PCL). Female sex was associated with longer ERP (+14% vs. males). Genetic background influenced atrial electrophysiology: LA-APD70 (−20% vs. average) and atrial ERP (−25% vs. average) were shorter in Swiss agouti background compared to others. LA-APD70 (+25% vs. average) and IA-AT (+44% vs. average) were longer in 129/Sv mice. Atrial ERP was longer in FVB/N (+34% vs. average) and in younger experimental groups below 6 months of age. Conclusion This work defines normal ranges for murine atrial EP parameters. Genetic background has a profound effect on these parameters, at least of the magnitude as those of sex and age. These results can inform the experimental design and interpretation of murine atrial electrophysiology.

High rate pacing guided by short-term variability of repolarization prevents imminent ventricular arrhythmias autonomically by an ICD

Background The anesthetized, chronic complete atrioventricular block (CAVB) dog model allows reproducible inducibility of Torsade de Pointes (TdP) arrhythmias due to ventricular remodeling and after a challenge with an IKr-blocker. High rate pacing (HRP) prevents ventricular arrhythmias, but has long-term detrimental effects on cardiac function when applied continuously. Temporal dispersion of repolarization, quantified as short-term variability (STV), increases prior to ventricular arrhythmias and has been proposed as a marker to guide HRP. Purpose A proof-of-principle study to show STV determined automatically and in real-time by an ICD can guide HRP to prevent imminent ventricular arrhythmias. Methods Eight CAVB dogs were implanted with an ICD (Medtronic, lead in the right ventricular (RV) apex), with software to automatically determine STV online (STV-ICD). STV was determined from the activation recovery interval (ARI) of 31 consecutive beats with the formula: STV = Σ|ARI(n+1) − ARI(n)|/(N*√2). The CAVB dogs were challenged twice with dofetilide (0.025 mg/kg i.v. in 5 minutes or until the first TdP). In the first experiment, the individual STV-ICD threshold was determined prior to the first arrhythmic event and programmed into the ICD. In a serial experiment, HRP was initiated automatically once the STV-ICD threshold was reached, by gradually increasing the heart rate to 100 bpm. Occurrence of TdPs was monitored for 10 minutes from the start of dofetilide infusion in both experiments. During HRP, STV was measured offline from RV electrograms (EGM) and left ventricular (LV) monophasic action potential durations (MAPD) (STV-offline). Results During the inducibility experiment, 8/8 dogs had repetitive TdPs and STV-ICD increased from 0.96±0.42 to 2.10±1.26 ms* (*p&lt;0.05). During the prevention experiment, all dogs reached the STV threshold. HRP decreased STV-offline from 2.02±1.12 to 0.78±0.28 ms*, which was accompanied by prevention of TdPs in 7/8 dogs* (Figure 1). Conclusion Temporal dispersion of repolarization, quantified as STV, can guide HRP automatically by an ICD to prevent ventricular arrhythmias. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): Dutch Heart Foundation Public Private Partnership

Modulating the Infarcted Ventricle’s Refractoriness with an Epicardial Biomaterial

Patients diagnosed with heart failure with reduced ejection fraction (HFrEF) are at increased risk of monomorphic ventricular tachycardia (VT) and ventricular fibrillation. The presence of myocardial fibrosis provides both anatomical and functional barriers that promote arrhythmias in these patients. Propagation of VT in a reentrant circuit depends on the presence of excitable myocardium and the refractoriness of the circuit. We hypothesize that myocardial refractoriness can be modulated surgically in a model of HFrEF, leading to decreased susceptibility to VT.Male Sprague-Dawley rats were infarcted via permanent left coronary artery ligation. At 3 weeks post-infarction, engineered grafts composed of human dermal fibroblasts cultured into a polyglactin-910 biomaterial were implanted onto the epicardium to cover the area of infarction. Three weeks post-graft treatment, all rats underwent a terminal electrophysiologic study to compare monophasic action potential electroanatomic maps and susceptibility to inducible monomorphic VT.HFrEF rats (n=29) demonstrated a longer (p=0.0191) ventricular effective refractory period (ERP) and a greater (p=0.0394) VT inducibility compared with sham (n=7). HFrEF rats treated with the graft (n=12) exhibited no change in capture threshold (p=0.3220), but had a longer ventricular ERP (p=0.0029) compared with HFrEF. No statistically significant change in VT incidence was found between HFrEF rats treated with the graft and untreated HFrEF rats (p=0.0834).Surgical deployment of a fibroblast-containing biomaterial in a rodent ischemic cardiomyopathy model prolonged ventricular ERP as measured by programmed electrical stimulation. This hypothesis-generating study warrants additional studies to further characterize the antiarrhythmic or proarrhythmic effects of this novel surgical therapy.

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.

1272Effect of age, genetic background and experimental conditions on left atrial monophasic action potential duration, effective refractory period and activation time in Langendorff-perfused murine hearts

Funding Acknowledgements Supported by EU [CATCH ME] 633196, British Heart Foundation FS/13/43/30324, AA/18/2/34218 LF, PK, DFG FA413 LF, Studienstiftung to JO. Background Studying cardiac electrophysiology in isolated perfused beating murine hearts is a well-established method. The range of normal values for left atrial action potential durations (LA-APD), activation times (LA-AT) and effective refractory periods (atrial ERP) in murine wildtype (WT) is not well known. Purpose This study aimed to establish reference values for LA-APD, LA-AT and atrial ERP and to identify factors that influence these electrophysiological parameters in wildtype (WT) mice. Method We combined results from isolated beating heart Langendorff experiments carried out in WT between 2005 and 2019 using an octopolar catheter inserted into the right atrium and a monophasic action potential electrode recording from the LA epicardium. Electrophysiological parameters (LA-APD at 50%, 70%, 90% repolarization (APD50, APD70, APD90), LA-AT and atrial ERP) at different pacing cycle lengths (PCL) were summarized. We analyzed effects of PCL, genetic background, age, gender, heart weight to body weight ratio (HW/BW), LA weight to body weight ratio (LAW/BW) as well as coronary flow and temperature as experimental conditions. Results Electrophysiological parameters from 222 isolated hearts (114 female, mean age 6.6 ± 0.25 months, range 2.47-17.7 months) of different backgrounds (77 C57BL/6, 23 FVB/N, 33 MF1, 69 129/Sv and 20 Swiss agouti) were combined. Coronary flow rate, flow temperature and start of isolation to cannulation time were constant experimental conditions over the timespan of experiments. LA-APD was longer while LA-AT decreased with longer PCL throughout all genetic backgrounds (Figure 1A). Genetic background showed strong effects on all electrophysiological parameters. LA activation was delayed in 129/Sv compared to other backgrounds (Figure 1D). LA-APD70 and atrial ERP were significantly shorter in Swiss agouti background compared to others. LA-APD70 was also significantly prolonged in 129/Sv background compared to MF1 (Figure 1C). Atrial ERP was longer in FVB/N compared to other backgrounds. Age effects were compared in groups. Atrial ERP was significantly longer in mice ≤ 3 months compared to all older mice. Atrial ERP was also significantly prolonged (+ 3.4ms, + 13.5%) in female mice compared to males (Figure 1B). Conclusion This dataset summarizes left atrial electrophysiological parameters in the beating mouse heart and can serve as a reference for design and interpretation of electrophysiological experiments in murine models of commonly used genetic backgrounds. We confirm that cycle length, genetic background, age and gender affect atrial electrophysiological parameters. Awareness of these will support successful experimental design. Abstract Figure 1

Study of the time-relationship of the mechano-electrical interaction in an animal model of tetralogy of Fallot: implications for the risk assessment of ventricular arrhythmias

OBJECTIVES The long-term outcome of tetralogy of Fallot (TOF) is determined by progressive right ventricular (RV) dysfunction through pulmonary regurgitation (PR) and the risk of malignant arrhythmia. Although mechano-electrical coupling in TOF is well-known, its time effect on the inducibility of arrhythmia remains ill-defined. The goal of this study was to investigate the mechano-electrical properties at different times in animals with chronic PR. METHODS PR was induced by a transannular patch with limited RV scarring in infant pigs. Haemodynamic assessment included biventricular pressure–volume loops after 3 (n = 8) and 6 months (n = 7) compared to controls (n = 5). The electrophysiological study included endocardial monophasic action potential registration, intraventricular conduction velocity and induction of ventricular arrhythmia by burst pacing. RESULTS Progressive RV dilation was achieved at 6 months (RV end-diastolic volume 143 ± 13 ml/m2—RV end-systolic volume 96 ± 7 ml/m2; P &lt; 0.001), in association with depressed RV contractility (preload recruitable stroke work-slope: 19 ± 1 and 11 ± 3 Mw.ml−1.s−1 for control and 6 m; P &lt; 0.001) and left ventricular contractility (preload recruitable stroke work-slope: 60 ± 13 and 40 ± 11 Mw.ml−1.s−1 for control and 6 m; P = 0.005). Concomitant to QRS prolongation, monophasic action potential90-duration and dispersion at the RV and left ventricle were increased at 6 months. Intraventricular conduction was delayed only in the RV at 6 months (1.8 ± 0.2 and 2.4 ± 0.6 m/s for group 6M and the control group; P = 0.035). Sustained ventricular arrhythmias were not inducible. CONCLUSIONS In animals yielding the sequelae of a contemporary operation for TOF, mechano-electrical alterations are progressive and affect predominantly the RV after midterm exposure of PR. Because ventricular arrhythmias were not inducible despite significant RV dilation, the data suggest that the haemodynamic RV deterioration effectively precedes the risk of inducing sustained arrhythmia after TOF repair and opens a window for renewed stratification of contemporary risk factors of ventricular arrhythmias in patients operated on with currently used pulmonary valve- and RV-related techniques.

Generation of Monophasic Action Potentials and Intermediate Forms

ABSTRACTThe Monophasic Action Potential (MAP) is a near replica of the transmembrane potential recorded when an electrode is pushed firmly against cardiac tissue. Despite its many practical uses, the mechanism of MAP signal generation and the reason it is so different from unipolar recordings is not completely known and is a matter of controversy. It is hypothesized that partial depolarization of the cells directly underneath the electrode contributes to the generation of MAP signals. In this paper, we describe a parametric, semi-quantitative method to generate realistic MAP and intermediate forms – multiphasic electrograms different from an ideal MAP – that does not require the partial depolarization hypothesis. The key ideas of our method are the formation of junctional spaces, i.e., electrically isolated pockets between the surface of an electrode and tissue, and the presence of a complex network of passive components that acts as a high-pass filter to distort the signal that reaches the recording amplifier. The passive network is formed by the interaction between the passive tissue properties and the double-layer capacitance of electrodes. We show that it is possible to generate different electrograms by the change of the model parameters and that both the MAP and intermediate forms reside on a continuum of signals. Our model helps to decipher the mechanisms of signal generation and can lead to a better design for electrodes, recording amplifiers, and experimental setups.SIGNIFICANCERecording the Monophasic Action Potential (MAP) is potentially very useful in both experimental and clinical cardiac electrophysiology and can provide valuable information about the repolarization phase of the action potential. However, despite its benefits, it currently has only a small and niche role. The main challenge is the technical difficulties of recording an ideal MAP. Our results provide a better understanding of the mechanisms of the generation of cardiac electrograms and may help to optimize experiments and improve tools to achieve the full potentials of recording the MAP signals.