tailieunhanh - Ebook ECG workout-Exercises in arrhythmia interpretation (6th edition): Part 2

(BQ) Part 2 book "ECG workout-Exercises in arrhythmia interpretation" presents the following contents: Ventricular arrhythmias and bundle-branch block, pacemakers, posttest. Invite you to consult. | 9 Ventricular arrhythmias and bundle-branch block Overview The three preceding chapters have focused on supraventricular arrhythmias. Supraventricular arrhythmias refer to those rhythms that originate above the bundle branches and include the sinus atrial and junctional rhythms. The electrical impulse produced by supraventricular rhythms follows the normal conduction pathway resulting in simultaneous depolarization of the right and left ventricles. The resulting QRS complex is narrow second or less in duration . Ventricular beats and rhythms Figure 9-1 originate below the bundle of His in a pacemaker site in either the right or left ventricle. When impulses arise in the ventricles the impulse does not enter the normal conduction pathway but travels from cell to cell through the myocardium depolarizing the ventricles asynchronously. Therefore the ventricles are not stimulated simultaneously and the stimulus spreads through the ventricles in an aberrant manner resulting in a wide QRS complex of second or greater. Since ventricular depolarization is abnormal ventricular repolarization will also be abnormal resulting in changes in the ST segments and T waves. The ST segments and T waves will slope in the opposite direction from the main QRS deflection if the ectopic QRS complex is predominantly negative the ST segment is usually elevated and the T wave positive if the ectopic QRS complex is predominantly positive the ST segment is usually depressed and the T wave negative . A P wave is not produced in ventricular rhythms. Ventricular arrhythmias include premature ventricular contractions PVCs ventricular tachycardia VT ventricular fibrillation VF idioventricular rhythm accelerated idioventricular rhythm and ventricular standstill. All of these rhythms are associated with a wide QRS complex except VF and ventricular standstill which do not have QRS complexes . Because the ventricles are the least efficient of the heart s pacemakers most of these rhythms are or