Arrythmias: Sinus, Supraventricular, and Ventricular EXS 460 Thaler Chapters 3,4,5 Arrythmias Arrythmias of sinus origin Ectopic rhythms Atrial, junctional, and ventricular Conduction blocks Atrioventricular (Chapter 4) Right or left bundle branch (Chapter 4) Pre-excitation excitation Syndromes due to bypass tracts in the atria or AV area (Chapter 5) Electrical Conduction System SA node AV node Bundle of His Purkinjie Fibers 1
Basic ECG Rhythm Terminology normal sinus rhythm (NSR) sinus arrhythmia ectopic beat, ectopy, ectopic pacemaker supraventricular rhythm atrial A-V V nodal (junctional) Ventricular rhythm Escape beat or escape rhythm Identification of the Origin of an Ectopic Beat 1. Is there a P wave? 2. Does a P wave precede each QRS complex? 3. QRS complex width: < 0.10 sec 4. Is the rhythm regular or irregular? Sinus Rhythms Sinus bradycardia heart rate < 60 bts min -1 Sinus tachycardia heart rate > 100 bts min -1 Sinus arrhythmia Is most notably due to effects of breathing. Increased heart rate with inhalation Decreased heart rate with exhalation? Sinus arrest or exit block 2
Mechanisms of Abnormal Electrical Impulse Formation Enhanced automaticity abnormal condition of latent pacemaker cells in which their firing rate is increased beyond their inherent rate Thaler, pg 113 Mechanisms of Abnormal Electrical Impulse Formation (con t) Reentry progression of an electrical impulse is delayed or blocked in one or more segments of the electrical conduction system while being conducted normally through the rest of the conduction system 3
Atrial premature beat P wave is altered in shape compared to other P waves and comes early. QRS complex normal shape and duration Cycle comes early, (i.e. distance between 2 QRS complexes is less than adjacent cardiac cycles) Junctional Premature Beat single ectopic beat that originates in the AV node or Bundle of His area of the condunction system Retrograde P waves immediately preceding the QRS Retrograde P waves immediately following the QRS Absent P waves (buried in the QRS) Goldberger & Goldberger, p 164 4
AV node as a pacemaker Goldberger & Goldberger, p 163 Causes of PAC and PJC Cause Digitalis toxicity Myocardial Infarction Myocardial Ischemia ingestion of caffeine or amphetamines Clinical Significance - Atrial Flutter Regular rhythm with P waves appearing at a rate of 250 to 300 bts min -1 P waves are noted for there saw tooth pattern, and or flutter waves Can be in normal hearts or in those with disease Most likely due to AV block, creating a reentry circuit 5
Atrial Flutter (example) Saw Tooth Regular Ventricular Rhythm Atrial Fibrillation In this rhythm the AV node is bombarded with impulses at a rate of 300 + times per min. P waves are not distinguishable on the ECG, and appear as fibrillation waves or f waves. QRS complexes are irregular in rhythm with normal duration Causes mitral valve or coronary artery disease, long standing hypertension is still the most common cause Atrial Fibrillation (example) Fine fib waves Course fib waves Irregular Ventricular Rhythm 6
Junctional Escape Beat JEB PJC JEB PJC Goldberger & Goldberger, p 163 Junctional Rhythm Rate: 40 to 60 beats/minute (atrial and ventricular) Rhythm: regular atrial and ventricular rhythm P wave: usually inverted, may be upright; may precede, follow or be hidden in the QRS complex; may be absent PR interval: not measurable or less than.20 sec. QRS and T wave : usually normal Junctional Escape Rhythm Goldberger & Goldberger, 1994 7
Junctional Rhythms Causes Digitalis toxicity Inferior wall MI Myocardial Ischemia Increased vagal tone Rheumatic heart disease Valvular disease Organic disease of the SA node Verapamil toxicity Anticholinesterase toxicity May occur immediately after surgery Rate: Paraoxysmal Supraventricular Tachycardia (PSVT) 160 to 240 beats/minute Rhythm: P wave: regular atrial and ventricular usually inverted, may be upright; may precede, follow or be hidden in the QRS complex; may be absent PR interval: : not measurable or less than.12 sec. QRS and T wave : usually normal PSVT (example) Sudden run of 3 or more premature supraventricular (junctional) beats 8
SA Etiology of PSVT 2 most common types of PSVT SA BT AV AV Carotid Massage Can help to diagnose and terminate PSVT Thaler, 99 Thaler, 99 Ventricular Arrythmias Supraventricular area fails to fire, which results in ventricular ectopic beat Premature ventricular contraction (PVC) by far the most common. No visible P wave QRS > 0.12 seconds in length and is bizarre in morphology May be common 9
Types of PVCs Uniform Multiform PVC rhythm patterns Bigeminy PVC occurs every other complex Couplets 2 PVCs in a row Trigeminy Two PVCs for every three complexes Malignant PVC patterns Frequent PVCs Multiform PVCs Runs of consecutive PVCs R on T phenomenon PVC that falls on a T wave PVC during acute MI Thaler, 99 10
Thaler, 99 Ventricular Rhythms Ventricular tachycardia (VTach( VTach) 3 or more PVCs in a row at a rate of 120 to 200 bts min -1 Most likely due to acute infarction and/ or ischemia Ventricular fibrillation (VFib( VFib) Preterminal event in which myocardium is dying No visible P or QRS complexes. Waves appear as fibrillating waves VTach Vfib 11
Torsades de Pointes Type of VT known as twisting of the points. Usually seen in those with prolonged QT intervals caused by Pharmacologic agents Accelerated Idioventricular Rhythm Benign rhythm sometimes seen in acute infarction at a rate of 50 to 100 beats per minute Non-pharmacoligic Treatment Programmed Electrical Stimulation More of a diagnostic procedure to determine origin of the arrhythmia in order to administer proper treatment Recurrent VT or experienced sudden death Can even use catheter ablation to treat the malignant pathway Implantable defibrillators 12
Goldberger & Goldberger, 1994 Goldberger & Goldberger, 1994 A 50 year old man with chest pain for 24 hours 13
Quiz 11/01/01 1. Define Lead I 2. Define Lead V5 3. What does axis tell us about the myocardium? 4. Determine axis for the tracing shown on the overhead 5. How do you determine heart rate using the triplicate method? 14