tailieunhanh - Ebook Basic electrocardiography: Part 2

(BQ) Part 2 book "Basic electrocardiography" presents the following contents: Atrioventricular (AV) block, bundle branch blocks and hemiblocks, chamber enlargement, arrhythmias. Invite you to consult. | Atrioventricular AV Block 4 There are three types of atrioventricular AV node block first-degree second-degree and third-degree. These are sometimes abbreviated 1 2 and 3 respectively Table . These abbreviations should not be confused with primary secondary and tertiary which can carry the same annotation. While AV block may be a transient phenomenon . associated with ischemia infarction or drug intoxication the block may be permanent. First-degree AV block is simply a prolongation of the PR interval above the normal range . s Fig. . At slow heart rates the normal PR interval may extend up to s but for simplicity it is reasonable to read any prolongation of the PR interval over s as first-degree AV block and simply keep in mind that slight prolongations at slow heart rates are of little clinical consequence. In fact first-degree AV block is essentially a benign condition and is very unlikely to be associated with progression to a higher degree of AV block 1 . Second-degree AV block is of two subtypes Mobitz I and Mobitz II. Mobitz I is also commonly known as Wenckebach block. In Mobitz I Wenckebach there is gradual prolongation of the PR interval duration until finally one P wave is not conducted through the AV node to the ventricles Fig. . As a consequence a P wave is not followed by a QRS complex. Following the dropped beat the missing QRS after a P wave the PR interval is once again relatively short and then gradually prolongs again until another beat is dropped and the cycle recurs. The length of the cycle . the number of conducted beats before the nonconducted beat may vary. The extent of block is given in a ratio with the number of atrial beats observed in the cycle followed by a colon and then the number of ventricular beats in the cycle. For Mobitz I the number of atrial beats in the cycle is always just one greater than the number of ventricular beats . 3 2 4 3 . This repetitive prolongation of PR intervals until a P