RT Book, Section A1 Ferry, David R. SR Print(0) ID 1128943875 T1 Ectopic Arrhythmias and Triggered Activity T2 ECG in 10 Days, 2e YR 2007 FD 2007 PB McGraw-Hill Education PP New York, NY SN 9780071465625 LK accesscardiology.mhmedical.com/content.aspx?aid=1128943875 RD 2024/03/28 AB Ectopy—a disorder of impulse formationMechanisms of ectopic arrhythmiasEctopic arrhythmias require:Default—slowing of the normal dominant sinus pacemaker which allows a slower focus to take control, orUsurpation—an acceleration of a lower pacemaker which takes control by virtue of being faster than the sinus rateDisorders of the sinus node, such as SA arrest, SA exit block, or excessive vagal tone may allow a lower focus to take control by defaultA variety of factors, including digitalis toxicity, hypoxia, electrolyte disturbances, ischemia, or chronic lung disease may stimulate an ectopic focus to accelerate and usurp control from the SA nodeProperties of ectopic arrhythmiasEctopic arrhythmias usually start and stop gradually (non-paroxysmally)They are not usually initiated by a premature beatThey may be somewhat irregularThey are not terminated by vagal maneuvers, although AV block may be increasedAV block of varying degrees is frequently present (particularly if digitalis toxicity is the cause)These arrhythmias are usually quite resistant to treatment with standard class I or III agentsCatheter ablation may be effective if a causative agent cannot be identified or treatedThe major ectopic arrhythmiasWandering atrial pacemakerMechanisms and causesThere are three or more ectopic atrial pacemakersThis arrhythmia is typically seen in young healthy persons, particularly athletesThe etiology is uncertainHeart rate—the heart rate is 60–100 and is usually irregularECG morphology (Day 6-01)There are at least three P wave morphologies with varying PR intervalsThere is usually moderate variation in the heart rateMultifocal atrial tachycardiaMechanisms and causesCaused by multiple ectopic atrial fociChronic lung disease is typically the underlying clinical abnormality, although it can also occur in the setting of hypoxia, electrolyte abnormalities, acid-base disturbances, and ischemia (i.e., frequently in the intensive care setting)ECG morphology (Day 6-02)There are at least three P wave morphologies with varying PR intervalsThe rate is 100–140There is typically 1:1 AV conductionThis arrhythmia is frequently confused with atrial fibrillation; the distinction is an important one since management is usually very differentEctopic atrial rhythmsMechanisms and causesA single ectopic atrial focus accelerates and usurps control from the sinus node, or the sinus node slows down and allows an ectopic focus to appearDigitalis toxicity, electrolyte abnormalities, ischemia, hypoxia, and chronic lung disease are typical causesECG morphology (Day 6-03) (Day 6-04)The P waves are of the same morphology but have an abnormal axis, indicating their ectopic originThe atrial rate may be slightly irregularAV block of varying degrees is sometimes present (particularly if digitalis toxicity is the cause)Atrial tachycardia with AV block should be considered a manifestation of digitalis toxicity until proven otherwise (Day 6-05)The atrial rate in atrial tachycardia is usually 140–200Atrial tachycardia may be confused with atrial flutter, but the latter is usually faster and has the typical saw tooth patternEctopic junctional rhythmsMechanisms and causesA single focus near the AV node accelerates and usurps control from the sinus nodeDigitalis toxicity, electrolyte abnormalities, ischemia, hypoxia, and chronic lung disease are typical causesECG morphology (Day 6-06) DAY 6-01 DAY 6-02 DAY 6-03 DAY 6-04 DAY 6-05 DAY 6-06 If P waves are visible, they demonstrate an abnormal axis and appear slightly before or after the QRS complexJunctional tachycardia (rate ...