ABSTRACT
The T wave in a surface electrocardiogram (ECG) indicates the diastolic phase in the cardiac cycle. Even though the cellular basis of T-wave morphology in surface ECG remains unclear in clinical cardiology, the morphology may be determined by the transmural voltage gradient during the repolarization period that underlies the changes in the T wave and QT interval. The heterogeneous distribution of electrophysiological activity across the heart is essential for normal cardiac function. However, excessive heterogeneity may contribute to arrhythmogenesis and sudden cardiac death. This paper will provide an overview of T wave genesis and the contribution to action potential duration (APD), in which ion channels are involved in the repolarization period, with special emphasis on K+ channels involved in phase 3 repolarization. These channels are primarily Kv11.1 (hERG1), Kv7.1 (KCNQ1), and Kir2.1 (KCNJ2), which are the α-subunits responsible for conducting I(Kr), I(Ks), and I(K1). Changes in the T wave and QT interval that are affected by both functional loss and gain of these currents are associated with various arrhythmogenic diseases. This review also briefly discusses arrhythmogenesis in diseases that are manifested by changes in the T wave and QT interval.
Subject(s)
Action Potentials , Cardiology , Death, Sudden, Cardiac , Electrocardiography , Heart , Ion Channels , Population CharacteristicsABSTRACT
AIM: To investigate the effects of myocardial remodeling of aged left atrium (LA) on atrial ar-rhythmogenesis in rabbits .METHODS:The male New Zealand rabbits were divided into young LA and aged LA groups . By observing the changes of monophasic action potential ( MAP) and burst-pacing in LA of the rabbits in vivo, the main cardioelectrophysiological parameters such as resting membrane potential ( RMP) , action potential amplitude ( APA) , ma-ximum rise veloctiy of action potential (dv/dtmax), plateau potential and action potential duration at 30%, 50%and 90%( APD30 , APD50 and APD90 ) , as well as the inducibility and duration of atrial arrhythmias were recorded .L-type calcium current (ICa,L) was analyzed via whole-cell patch-clamp technique in enzymatically dissociated single rabbit LA myocytes . The myocardial collagen content was quantified after Masson staining , and the ultrastructure of the LA cells was observed under scanning electron microscope .The expression of Cav 1.2 in LA tissue of the 2 groups was detected by Western blot . RESULTS:Compared with young LA group , dv/dtmax and plateau potential were significantly decreased , APD30 and APD50 were shortened, and APD90 was notably prolongated in aged LA group (P<0.01).The inducibility or duration of atrial arrhythmias was severely increased or prolongated in aged LA group (P<0.01).With voltage clamp model, the den-sity of ICa,L in aged LA group was significantly decreased , and current-voltage curve was notably moved upward compared with young LA group.When the clamp potential was +20 mV, the density of ICa,L was notably modified from (11.72 ± 1.39) pA/pF in young LA group to (6.08 ±0.98) pA/pF in aged LA group ( P<0.01).Compared with young LA group, the protein level of collagen was significantly increased (P<0.01), and the arrange of atrial myocytes was irregular in LA of rabbits in aged LA group .The atrial myocytes of the LA wall in aged LA group exhibited abnormal ultrastructural alterations , such as karyopyknosis , irregular and swelling mitochondria with the presence of vacuoles , and mild and severe sarcomere degeneration .Compared with those in LA tissues of young rabbits , the expression levels of Cav 1.2 in the LA tis-sues of aged rabbits were severely reduced (P<0.01), and had a significant positive correlation with the reduction of ICa,L (r=0.83, P<0.01).CONCLUSION:The pathophysiological characteristics of aged LA are significantly altered , and might contribute to vulnerability and susceptibility of occurrence of atrial fibillation in aged rabbits .The mechanisms might completely attribute to the notable reduction of ICa,L , abnormal alterations of ultrastructures and obvious decrease in the ex-pression of Cav1.2 in the aged LA of aged rabbits .
ABSTRACT
La interacción constante del organismo humano con diferentes sustancias, que incluso en muchas ocasiones se consideran inofensivas, tiene un alto impacto sobre todos los sistemas, siendo el cardiovascular uno de los más afectados. Por lo tanto, es vital reconocer los mecanismos por los cuales estas sustancias ejercen su efecto tóxico sobre este sistema, bien sea afectando la estabilidad de membrana y la función contráctil o generando disfunción de organelos intracelulares y estrés oxidativo. Numerosos estudios han descubierto efectos lesivos de sustancias, como la clozapina y las catecolaminas, que han tenido amplio uso durante largos años. En la actualidad aún se realizan investigaciones que buscan esclarecer los mecanismos cardiotóxicos de medicamentos de formulación común, entre ellos antineoplásicos y anti-inflamatorios no esteroideos (AINE), así como de sustancias de uso habitual que causan adicción, tales como alcohol, cocaína y cocaetileno, su metabolito activo.
The constant interaction of the human body with different substances that are even in many cases considered harmless has a high impact on all systems, being the cardiovascular system one of the most affected. Therefore, it is vital to recognize the mechanisms by which these substances exert their toxic effect on this system, either affecting the membrane stability and the contractile function, or generating intracellular organelles dysfunction and oxidative stress. Numerous studies have found that drugs which have been widely used for many years such as clozapine and catecholamines, have harmful effects. Research is still being done seeking to clarify the cardiotoxic mechanisms of drugs commonly formulated, including anticancer and non steroidal anti-inflammatory drugs (NSAIDs), as well as commonly used substances that cause addiction, such as alcohol, cocaine and cocaethylene, its active metabolite.