Arrhythmias, Cardiac ; diagnosis ; Electrocardiography ; Heart Ventricles ; physiopathology ; Prognosis

The effect of the autonomic nerves on the transmural dispersion of ventricular repolarization (TDR) under acute myocardial ischemia in intact canine was investigated. Using the monophasic action potential (MAP) recording technique, MAPs of the epicardium (Epi), mid-myocardium (Mid) and endocardium (Endo) were recorded simultaneously by specially designed plunge-needle electrodes at the left ventricular free wall under acute myocardial ischemia in 12 open-chest dogs. MAPD90 and TDR among three myocardial layers as well as the incidence of the early afterdepolarization (EAD) before autonomic nervous stimulation and during autonomic nervous stimulation were compared. It was found that 10 min after acute myocardial ischemia, TDR was increased from 55 +/- 8 ms to 86 +/- 15 ms during sympathetic stimulation (P < 0.01). The TDR (53 +/- 9 ms) during parasympathetic stimulation was not significantly different from that of the control (55 +/- 8 ms) (P > 0.05). The EAD was elicited in the Mid of 2 dogs (16%) 10 min after acute myocardial ischemia, but the EAD were elicited in the Mid of 7 dogs (58%) during sympathetic stimulation (P < 0.01). It was concluded that: (1) Sympathetic stimulation can increase the transmural dispersion of repolarization and induce early afterdepolarizations in the Mid under acute myocardial ischemia, which provide the opportunity for the ventricular arrhythmia developing; (2) Parasympathetic stimulation has no significant effect on the transmural dispersion of repolarization under myocardial ischemia.
Action Potentials/physiology ; Autonomic Nervous System/*physiopathology ; Electric Stimulation ; Heart Ventricles/innervation ; Heart Ventricles/*physiology ; Myocardial Ischemia/*physiopathology ; Neuromuscular Junction

OBJECTIVETo observe the action potential duration restitution (APDR) change and potential association with ventricular arrhythmia (VA) in Langendorff-perfused chronic heart failure rabbit hearts.

METHODSMale rabbits were randomly divided into two groups: control (CTL, n=15) group and chronic heart failure (CHF, n=15) group. CHF was induced by injecting isoproterenol (300 µg×kg(-1) ×d(-1)) for 14 days. Four weeks later, cardiac function and structure change of both groups were assessed by echocardiography. In the whole Langendorff-perfused hearts, the monophasic action potential (MAP) and the effective refractory period (ERP) were recorded from left anterior basal ventricle, left anterior free wall, left anterior apex and left posterior basal ventricle, left posterior free wall and left posterior apex, the APD curves were also constructed in both groups; at the six sites of every isolated heart, the programmed electrical stimulation and burst pacing were used to induce action potential duration (APD) alternans and VA, respectively.

RESULTSLeft ventricular ejection was reduced and end-dimension was enlarged in rabbits of CHF group. Compared with the same sites of CTL group, the 90% of MAP duration (MAPD90), the ERP, the max slope (Smax) of APDR curves, the pacing cycle length of inducing the APD alternans and the VAs were significantly increased (all P<0.05) in CHF group; the spatial dispersions of MAPD90, ERP and Smax of APDR curves in CHF group were also greater than in CTL group (all P<0.05).

CONCLUSIONThe ventricular APD alternans might be linked with occurrence of the VA in CHF rabbits. Increase of the Smax from APDR curves and the spatial dispersions of Smax in this CHF model might facilitate the development of ventricular arrhythmia.

Action Potentials ; Animals ; Arrhythmias, Cardiac ; physiopathology ; Electrocardiography ; Heart Failure ; physiopathology ; Heart Ventricles ; physiopathology ; Male ; Rabbits ; Ventricular Fibrillation ; physiopathology

The cardiac inwardly rectifying potassium channel (I(K1)), which is mainly expressed in mammalian atrial and ventricular myocytes, has been considered as the primary conductance controlling the resting potential (RP) and permitting a significant repolarizing current during the terminal phase of action potential. Therefore, I(K1) is highly influential on the RP, and the modulation of I(K1) would likely have profound effects on cardiac excitability and arrhythmogenesis. This article may shed light on the fundamental properties of cardiac I(K1), the mechanisms of inward rectification and I(K1) subunits composition. Furthermore, the article discusses the role of I(K1) in ventricular excitability and arrhythmogenesis and explores the possibility of modulating I(K1) as an antiarrhythmic mechanism. In fact, both blocking and enhancing I(K1) could be antiarrhythmic, but have proarrhythmic potential at the same time. Action potential duration (APD) prolongation has been accepted as an important antiarrhythmic strategy with some evidence in animal models of arrhythmogenesis that I(K1) blockade can prolongate APD and be antiarrhythmic. However, the potential of I(K1) blockade has not resulted in the development of specific I(K1) blockers used clinically. Safety concerns are probably the main reason, and the therapeutic potential for I(K1) blockers seems somewhat small. On the contrary, the up to date reports indicate that moderately activating I(K1) and hyperpolarizing the RP which has been depolarized by pathologic injury are to be feasible and effective to alleviate some kinds of ventricular arrhythmias.
Action Potentials ; Animals ; Arrhythmias, Cardiac ; physiopathology ; Heart ; physiopathology ; Heart Ventricles ; physiopathology ; Membrane Potentials ; Potassium Channels, Inwardly Rectifying ; physiology

Ebstein malformation is a congenital heart disease characterized pathologically by displacement of the septal leaflet of the tricuspid valve towards the apex of the right ventricle of the heart. Hypoplasia, dysfunction of the right ventricle and tricuspid regurgitation cause an increased volume load of the right heart and result in the clinical manifestations of chest tightness, shortness of breath and fatigue after activities, palpitation, cyanosis and heart failure. We report a case of Ebstein's anomaly with refractory right heart failure and leg ulcers.
Ebstein Anomaly ; Heart Failure ; Heart Ventricles ; physiopathology ; Humans ; Leg Ulcer ; Tricuspid Valve Insufficiency

This study was performed to assess the influence of the cryoinjury on the dynamics of wavefronts and to determine whether they can convert ventricular fibrillation (VF) to ventricular tachycardia (VT) in fibrillating right ventricular (RV) of swines using an optical mapping system. A cryoinjury with a diameter of 12 mm was created on the epicardium of perfused RV of swines (n = 6) and optical mapping were taken from baseline until 10 minutes after the cryoinjury. Out of 35 cryoinjuries, the images were possible to be interpreted in 32. The optical action potential could not be observed in either the cryoinjury or peri-injury sites at 1 and 3 minutes, was observed in only the cryoinjury site at 5 minutes, and recovered in both sites at 10 minutes. The cycle length of the tachycardia was 135.9 +/- 23.6 msec at baseline, 176.2 +/- 79.3 msec at 1 minute, 187.6 +/- 97.9 msec at 3 minutes, 185.5 19.2 msec at 5 minutes, and 152.1 +/- 64.1 msec at 10 minutes. The cycle lengths at 1, 3, and 5 minutes after the cryoinjury were significantly more prolonged than that at baseline (p = 0.001, p = 0.006, p = 0.016). After the cryoinjury, the VF changed to VT in 9 (28.0%), and terminated in 2 (6.3%). These changes were observed mainly within 5 minutes after cryoinjury. The cryoinjury had anti-fibrillatory effects on the tissue with VF. This phenomenon was related to a decreasing mass and stabilizing wavefronts.
Ventricular Fibrillation/*physiopathology ; Tachycardia, Ventricular/*physiopathology ; Swine ; Heart Ventricles/*physiopathology/surgery ; Female ; Disease Models, Animal ; *Cryosurgery ; Animals

In this paper, to analyze the functional influence of ischemia on cardiac cell electrical activity and subsequently on ventricular electrical wave conduction, a human ventricular ischemic model was developed, which took into account three major pathophysiological components of ischemias hyperkalaemia, acidosis, and anoxia. This model simulated the action potential (AP) propagations of endocardial, midmycardial and epicardial cells with different levels of ischemia, and the influence of each factor on cell AP was analyzed. Finally the ECG waveform under ischemia was quantified by using a 2D model of human left ventricular tissue based on the anatomical structure of human heart. The experimental results showed that under ischemia action potential durations (APD) were reduced. In most cases, the larger the size of ischemic region or the more severe the ischemic level, the more dramatic the changes in the amplitude of ST-T wave were observed. For the three components of ischemia, hyperkalaemia was the dominant contributor to ST-T wave changes, which was in agreement with the results obtained on animal models.
Action Potentials ; physiology ; Computer Simulation ; Electrocardiography ; Heart Ventricles ; physiopathology ; Humans ; Hyperkalemia ; physiopathology ; Models, Cardiovascular ; Myocardial Ischemia ; physiopathology

There are many differences between cardiac resynchronization therapy (CRT) and conventional pacing therapy in terms of indications and implant techniques. Generally speaking, CRT requires implanting 3 pacing leads in heart failure patients with ventricular dysynchrony. A left ventricular lead is implanted via intravenous coronary sinus. The pacing site of left ventricle has important influence on therapy response. Sometimes open chest implant or other pacing modes are adopted to compensate the anatomical limitation of coronary sinus and its branches. In addition, the pacing sites and modes of right atrium and right ventricle are also under research to further improve CRT response.
Cardiac Pacing, Artificial ; methods ; Electrodes, Implanted ; Heart Atria ; Heart Failure ; physiopathology ; therapy ; Heart Ventricles ; Humans ; Ventricular Dysfunction, Left ; physiopathology ; Ventricular Dysfunction, Right ; physiopathology

In this study we performed Tissue Doppler Imaging (TDI), two-dimensional speckle tracking imaging (2D- STI) and three-dimensional speckle tracking imaging (3D-STI) on enrolled healthy, overweight and obese groups (34 subjects in each group), respectively, to analyze cardiac structure and its function. Compared with healthy group, global longitudinal strain (GLS), global circumferential strain (GCS), global area strain(GAS) and global radial strain (GRS) decreased progressively (P < 0.05). The ratio of early diastolic mitral inflow velocity to global early diastolic strain rate of left ventricle (E/e'sr) (r = 0.466, P < 0.001), GLS (r = 0.502, P < 0. 001), GCS (r = 0.426, P < 0.001), GAS (r = 0.535, P < 0.001) and GRS (r = -0.554, P < 0.001) were correlated with body mass index (BMI). E/e'sr (r = 0.37, P = 0.003), GLS (r = 0.455, P < 0.001), GCS (r = 0.282, P = 0.02), GAS (r = 0.412, P < 0.001) and GRS (r = -0.471, P < 0.001) were correlated with free fatty acid (FFA). Stepwise multiple linear regression revealed that BMI was independently correlated with E/e'sr, GLS, GCS, GAS and GRS. Waist to hip ratio (WHR) was independently correlated with GLS, GCS, GAS and GRS. FFA was independently correlated with E/e'sr (P < 0.05). The study showed that cardiac structure changed and impaired left ventricular global systolic and diastolic function in overweight and obes population. Moreover, BMI, WHR and FFA may be independent influence factors of cardiac function in overweight and obese population.
Body Mass Index ; Case-Control Studies ; Echocardiography, Three-Dimensional ; Heart ; physiopathology ; Heart Ventricles ; physiopathology ; Humans ; Linear Models ; Obesity ; physiopathology ; Overweight ; physiopathology ; Reproducibility of Results ; Ventricular Function, Left

In order to verify the hypothesis that left ventricular epicardial (LV-Epi) pacing and biventricular (BiV) pacing unavoidably influence the myocardial electrophysiological characters and may result in high risk of malignant ventricular arrhythmia, we calculated, in both normal mongrel dogs and dog models with rapid-right-ventricular-pacing induced dilated cardiomyopathy congestive heart failure (DCM-CHF), the monophasic action potential duration (MAPD) and the transmural dispersion of repolarization (TDR) in intracardiac electrogram together with the QT interval and T(peak)-T(end) (T(p(-T(e)) interval in surface electrocardiogram (ECG) during LV-Epi and BiV pacing, compared with those during right ventricular endocardial (RV-Endo) pacing. To prepare the DCM-CHF dog model, rapid right ventricular pacing (250 bpm) was performed for 23.6+/-2.57 days to the dog. All the normal and DCM-CHF dogs were given radio frequency catheter ablation (RFCA) to His bundle with the guide of X-ray fluoroscopy. After the RFCA procedures, the animals were under the situation of complete atrioventricular block so that the canine heart rates could be voluntarily controlled in the following experiments. After a thoracotomy, ECG and monophasic action potentials (MAP) of subendocardial, subepicardial and mid-layer myocardium were recorded synchronously in 8 normal and 5 DCM-CHF dogs during pacing from endocardium of RV apex (RV-Endo), epicardium of LV anterior wall (LV-Epi) and simultaneously both of the above (biventricular, BiV), the later was similar to the ventricular resynchronization therapy to congestive heart failure patients in clinic. The Tp-Te) meant the interval from the peak to the end of T wave, which was a representative index of TDR in surface ECG. The TDR was defined as the difference between the longest and the shortest MAPD of subendocardial, subepicardial and mid-layer myocardium. Our results showed that in normal dogs, pacing participating of LV (LV-Epi, BiV) prolonged MAPD of all the three layers of the myocardium (P<0.05) with the character that mid-layer MAPD was the longest and subepicardial MAPD was the shortest following subendocardial MAPD. At the same time, TDR prolonged from 26.75 ms at RV-Endo pacing to 37.54 ms at BiV pacing and to 47.16 ms at LV-Epi pacing (P<0.001). Meanwhile in surface ECG, BiV and LV-Epi pacing resulted in a longer Tp-Te) interval compared with RV-Endo pacing (P<0.01), without parallel QT interval prolongation. Furthermore, all the DCM-CHF model dogs showed manifestations of congestive heart failure and enlargement of left ventricles. Based on the lengthening of mid-layer MAPD from 257.35 ms to 276.30 ms (P<0.0001) and increase of TDR from 27.58 ms to 33.80 ms (P equals;0.002) in DCM-CHF model due to the structural disorders of myocardium compared with the normal dog, LV-Epi and BiV pacing also led to the effect of prolonging MAPD of three layers of the myocardium and enlarging TDR. From these results we make the conclusions that prolongation of MAPD of subendocardial, subepicardial and mid-layer myocardium and increase in TDR during pacing participating of LV (LV-Epi, BiV) may contribute to the formation of unidirectional block and reentry, which play roles or at least are the high risk factors in the development of malignant ventricular arrhythmia, especially in case of structural disorders of myocardium. These findings must be considered seriously when ventricular resynchronization therapy is performed to congestive heart failure patients.
Action Potentials ; Animals ; Bundle-Branch Block ; complications ; physiopathology ; Cardiomyopathy, Dilated ; complications ; physiopathology ; Dogs ; Female ; Heart Conduction System ; physiopathology ; Heart Failure ; etiology ; physiopathology ; Heart Ventricles ; physiopathology ; Male ; Torsades de Pointes ; physiopathology ; Ventricular Dysfunction, Left ; physiopathology ; Ventricular Function, Left