A dysrhythmia is any cardiac rhythm other than normal sinus rhythm. Rhythm interpretation requires systematic evaluation of the rate, rhythm, P waves, QRS complexes, P wave-QRS complex
relationship, and PR intervals.
LESSON OUTLINE
In a normal sinus rhythm, the rate is 60 to 100 beats per minute (in an adult),and the rhythm is regular. P waves are present. A P wave precedes each QRS complexes, which has a normal duration (0.04 to .011 seconds). PR intervals are normal (0.12 to 0.20 seconds).
o Sinus bradycardia is similar to normal sinus rhythm, except that the rate is less than 60 beats per minute.
o Sinus tachycardia is similar to normal sinus rhythm, except that the rate is 100 to 180 beats per minute, and the P waves can merge with T waves as the rate increases.
o Sinus arrhythmia is similar to normal sinus rhythm, except that the rate increases with inspiration and decreases with expiration, and the rhythm is slightly irregular.
Premature atrial complexes are ectopic beats initiated by an irritable atrial focus. They usually are transient, but may lead to another atrial dysrhythmia or paroxysmal supraventricular tachycardia.
Atrial fibrillation causes an atrial rate of 400 beats or more per minute. The ventricular rate varies, but the rhythm is irregularly irregular. It produces no P waves, which leads to no P wave-QRS complex relationship and no PR intervals.
Atrial flutter has an atrial rate of 230 to 350 beats per minute, a ventricular rate that varies, and a regular or irregular rhythm. The P waves become saw-toothed flutter (F) waves, and two or more F waves can appear for every QRS complex.
Wandering atrial pacemaker causes a rate of 50 to 100 beats per minute and a regular or slightly irregular rhythm. P waves have at least three different configurations. They precede each QRS complex, but can be obscured by it. The PR interval is variable.
Paroxysmal supraventricular tachycardia has a rate of 100 to 280 beats per minute. The rhythm is regular, but starts and stops. P waves are often distorted and obscured in the QRS complex, which can be normal or wide. PR intervals are short or absent.
A common pre-excitation syndrome, Wolff-Parkinson-White syndrome causes short PR intervals, delta waves, wide QRS complexes, and inverted ST segments and T waves.
Premature junctional complex causes a normal or slow rate and irregular rhythm. P waves can be absent, present before or after the QRS complex, or inverted. PR intervals can be less than 0.12 seconds.
o Junctional escape rhythm has a rate of 40 to 60 beats per minute, accelerated junctional rhythm causes a rate of 60 to 100 beats, and junctional tachycardia causes a higher rate. In all three dysrhythmias, the rhythm is regular. P waves can be absent, present before or after the QRS complex, or inverted. PR intervals can be less than 0.12 seconds.
LESSON OUTLINE
Premature ventricular complexes produce a rate that varies and an irregular rhythm. P waves occur with each sinus beat, but not before premature ventricular complexes. QRS complexes can be normal or wide and bizarre. PR intervals are normal with sinus beats, but not before premature ventricular complexes.
o Idioventricular rhythm causes a rate of 20 to 40 beats per minute and a regular or irregular rhythm. QRS complexes are wide and bizarre, and P waves and PR intervals are absent.
o Ventricular tachycardia is associated with a rate of 100 to 250 beats per minute and a regular rhythm (monomorphic) or irregular rhythm (polymorphic). QRS complexes are wide and bizarre, and P waves and PR intervals are absent.
o Ventricular fibrillation causes the ventricles to quiver, producing a rapid rate and irregular rhythm. P waves, QRS complexes, and PR intervals are absent.
Asystole is the complete absence of ventricular activity and indicates prolonged cardiopulmonary compromise and arrest. Mortality is extremely high.
In pulseless electrical activity, some cardiac activity is present, but no pulse is palpable, requiring basic and advanced life support. This preterminal rhythm can be reversed if the underlying cause is identified and immediately treated. Use the mnemonic for the 6 Hs and 5 Ts to remember possible causes.
In first-degree atrioventricular block, the rate usually is 60 to 100 beats per minute. The rhythm, P waves, and QRS complexes are normal, but PR intervals are prolonged.
o In second-degree atrioventricular block, type I, the PR interval lengthens with each cycle until a QRS complex is dropped. Then the pattern repeats.
o In second-degree atrioventricular block, type II, one or more atrial impulses are not conducted through the atrioventricular node to the ventricles. With this dysrhythmia, P waves outnumber QRS complexes. However, PR intervals remain constant.
o In third-degree atrioventricular block, the atrial rate can be 60 to 100 beats per minute, and the ventricular rate can be below 60 beats per minute. The rhythm is regular. Third-degree atrioventricular block occurs when none of the impulses generated in the sinoatrial node are conducted through the atrioventricular node to the ventricles.
A conduction abnormality, bundle branch block, prevents or delays impulse passage from the bundle of His to the Purkinje fibers. This causes wide, bizarre QRS complexes. Blocks may be rate-related, transient, or permanent.
Long QT syndrome is a conduction abnormality that can be congenital or caused by drugs that prolong the QT interval.
LESSON OUTLINE
A pacemaker can be used to pace the atrium, ventricle, or both. A pacing artifact (spike) appears on an electrocardiogram tracing when the device delivers a pacing stimulus to the heart. Pacemaker malfunctions include failure to pace, failure to capture, and failure to sense.
In pediatric patients, fibrillation, flutter, and atrioventricular blocks rarely occur. These patients are more likely to experience rhythms that are too fast or too slow (for their age) or are absent.