Effects of thoracic epidural anesthesia with and without autonomic nervous system blockade on cardiac monophasic action potentials and effective refractoriness in awake dogs.
ABSTRACT The effects of thoracic epidural anesthesia (TEA) on myocardial repolarization and arrhythmogenicity are only incompletely understood. This is primarily because of the lack of appropriate experimental models. In most of the studies performed thus far, TEA was used in anesthetized animals. Baseline anesthesia itself may have modified the effects of TEA. This study investigates right atrial and ventricular repolarization by recording monophasic action potentials after TEA in awake dogs. The authors hypothesized that an antiarrhythmic role of TEA exists, which may be related to a direct effect of TEA on myocardial repolarization.
The hypothesis was tested in an in vivo canine model, in which atrial and ventricular myocardial action potential duration and refractoriness are recorded by means of monophasic action potential catheters.
Thoracic epidural anesthesia significantly increased ventricular monophasic action potential duration for cycle lengths shorter than 350 ms. Changes in monophasic action potential duration were paralleled by a concomitant prolongation of effective refractory period (ERP) at higher rates so that the ratio of ERP to action potential duration was unaffected.
This model helps to study the role of TEA on ventricular repolarization and arrhythmogenicity. Because lengthening of repolarization and prolongation of refractoriness may, in some circumstances, be antiarrhythmic, TEA may be protective against generation of ventricular arrhythmias mediated, e.g., by increased sympathetic tone. The results also imply that the beneficial role of TEA might be stronger at the ventricular site as compared with the atrium. At atrial sites there was only a trend toward prolongation of repolarization even at short cycle lengths.
Article: The physiological effects of thoracic epidural anesthesia and analgesia on the cardiovascular, respiratory and gastrointestinal systems.[show abstract] [hide abstract]
ABSTRACT: Studies of regional anesthesia are increasing in popularity not only for the purpose of technical advancement, but also to better understand the effects of neural deafferentation on the function of various organs. Thoracic epidural anesthesia (TEA) is one of the most versatile and widely utilized neural deafferentation techniques. The aim of this article is to critically review published data regarding the most relevant effects of TEA on the cardiovascular, respiratory and gastrointestinal systems. In the cardiovascular system, TEA modifies the electrical activity of the heart in addition to ventricular function and wall motion. Improvements in regional blood flow and a reduction of the major determinants of cardiac oxygen consumption lead to less severity of the ischemic injury. Although TEA negatively affects the performance of intercostal muscles, it spares diaphragmatic function and, when it is limited to the first five thoracic segments, affects pulmonary volumes to a lesser extent. TEA can be safely used in patients with compromised respiration. Splanchnic sympathetic block is achieved when thoracic fibers from T5 to T12 are affected in a dose-dependent manner. Improved gastrointestinal blood flow and motility are clear in animals, and in clinical studies, TEA has been shown to improve recovery after major abdominal surgery. TEA thus presents a powerful tool available to anesthesiologists for perioperative intervention, but its use alone cannot prevent postoperative morbidity and mortality. It is therefore necessary to address its use in the context of multimodal intervention.Minerva anestesiologica 11/2008; 74(10):549-63. · 2.66 Impact Factor