tailieunhanh - Ebook The only EKG book you’ll ever need (9/E): Part 2

Part 2 book “The only EKG book you’ll ever need” has contents: Preexcitation syndromes, myocardial ischemia and infarction, finishing touches, putting it all together, how do you get to carnegie hall. | 5. Preexcitation Syndromes For additional ancillary materials related to this chapter. please visit thePoint. In this chapter you will learn: 1 | what happens when electrical current is conducted to the ventricles more rapidly than usual 2 | what an accessory pathway is 3 | that Wolff–Parkinson–White is not the name of a law firm 4 | why accessory pathways predispose to arrhythmias 5 | about the case of Winston T., a preexcitable personality What Is Preexcitation? In the last chapter, we discussed what happens when conduction from the atria to the ventricles is delayed or blocked. This chapter presents the other side of the coin: what happens when the electrical current is conducted to the ventricles more quickly than usual. How can such a thing happen? With normal conduction, the major delay between the atria and the ventricles is in the atrioventricular (AV) node, where the wave of depolarization is held up for about second, long enough for the atria to contract and empty their content of circulating blood into the ventricles. In the preexcitation syndromes, there are accessory pathways by which the current can bypass the AV node and thus arrive at the ventricles without the delay and often ahead of time. A number of different accessory pathways have been discovered. Probably fewer than 1% of individuals possess one of these pathways. There is a decided male preponderance. Accessory pathways may occur in normal healthy hearts as an isolated finding, or they may occur in conjunction with mitral valve prolapse, hypertrophic cardiomyopathies, and various congenital disorders. The most important preexcitation syndrome is Wolff–Parkinson–White (WPW). It is easily diagnosed on the EKG. In WPW, the accessory conduction pathway acts as a short circuit, allowing the atrial wave of depolarization to bypass the AV node and activate the ventricles prematurely. Wolff–Parkinson–White In WPW, the bypass pathway is a discrete aberrant conducting pathway .