6/14/17. Recognizing and Treating LifeThreatening Arrhythmias. Overview. Why do an ECG?

Transcription

1 6/14/17 Recognizing and Treating LifeThreatening Arrhythmias Sandy Tou, DVM DACVIM (Cardiology & Internal Medicine) Raleigh, NC Overview Brief overview of basic ECG principles ECG diagnosis & treatment Ventricular tachycardia Supraventricular tachycardia Atrioventricular block Atrial fibrillation Why do an ECG? Assess heart rate Investigate an arrhythmia Palpable pulse deficits Workup of known heart disease Evaluate for chamber enlargement Evaluate for conduction disturbance Patient showing clinical signs relatable to heart disease 1

2 What is an ECG? Graphic recording of direction & magnitude of electrical activity generated by depolarization & repolarization of heart Wav es of dep olarization occurs in many directions simultaneously Sum of all depolarization vectors creates an overall net vector Overall vector is detected using 2 surface electrodes of opposite polarity Principles of ECG Each limb lead has a negative (+) and positive (+) electrode or pole Each lead evaluates the heart s depolarization pattern from a single plane Different leads allow you to see the pattern of depolarization from different angles Principles of ECG Lead II is often considered the most useful lead because it approximates depolarization through the normal heart Electrical activity that travels TOWARD (+) pole is POSITIVELY deflected on ECG Electrical activity that travels AWAY from (+) pole is NEGATIVELY deflected on ECG 2

3 Components of the ECG Waves (3 ) P wave = atrial depolarization QRS complex = ventricular depolarization T wave = ventricular repolarization Intervals/segments (3) PR = conduction through AV node QT = ventricular depol & repolarization ST = ventricular quiescence 5Y MC Boxer Collapsed at home during exercise Fully recovered by presentation PE Intermittent premature beats on auscultation Intermittent pulse deficits Boxer Big 4 (PCV/TS/BG/azo) Blood pressure TFAST/AFAST/lung ultrasound Continuous ECG monitoring ECG diagnosis: ventricular tachycardia 3

4 Ventricular tachycardia (VT) Tachycardia (>180 beats/min) Wide and bizarre QRS complexes Absent P waves Reason to Treat VPCs 1. Hemodynamic compromise 2. Rapid couplets and triplets 3. Ventricular tachycardia 4. R-on-T phenomenon 5. Multiform VPCs Acute Management of VT 2 mg/kg IV slow bolus to convert Up to 4 doses Monitor for side effects (nausea, vomiting, seizures) Lower dose in cats! Lidocaine mcg/kg/min to maintain Magnesium chloride 4

5 Chronic Management of VT Assess for an underlying cause First-line oral antiarrhythmic therapy Sotalol 2-3 mg/kg PO q12 hours Mexilitine 5-8 mg/kg PO q8 hours Nutraceuticals Fish oils Magnesium supplementation Causes of VT Cardiac Arrhythmogenic RV cardiomyopathy (ARVC) Dilated cardiomyopathy (DCM) Chronic mitral valve disease Myocarditis/endocarditis Neoplasia Upright VPCs (RV origin) Noncardiac (systemic) disease Splenic tumor Negative VPCs (LV origin) Workup of VT Echocardiogram Abdominal ultrasound Troponin level ARVC genetic test (Boxers) 5

6 Mistaken Identity Accelerated idioventricular rhythm (heart rate not rapid) Bundle branch block (P wave is present) 3Y MC Labrador Retriever Presents after several episodes of syncope PE Paroxysms of tachycardia auscultated II Dev: Speed: 25 mm/sec Limb: 10 mm/mv Chest: 10.0 mm/mv Electrode Off F 60~ Hz PH10 CL P? Regular tachycardia Narrow QRS complexes Abrupt onset/offset R wave alternans (varying R wave height) ECG diagnosis: supraventricular tachycardia 6

7 6/14/17 Supraventricular tachycardia (SVT) Cause Abnormal electrical circuit Congenital accessory pathway Fibrosis/cardiomyopathy Initiated by premature beat SVT Treatment Vagal maneuver Slow conduction through AV node Diltiazem Regular mg/kg PO q8h Extended-release (Dilacor) 3-5 mg/kg PO q12h Slow conduction through accessory pathway Lidocaine Radiofrequency ablation now offered at NCSU Suspect a transient arrhythmia? Holter monitor (24 hour ambulatory ECG) NC State Holter Monitor Service Well-tolerated by most dogs and some cats 7

8 6/14/17 10y MC Cocker Spaniel Collapsed at home during morning walk 4 days of lethargy and exercise intolerance PE Anxious Heart rate 60 beats/min Regular rhythm III/VI left apical holosystolic murmur Mild abdominal distension Slow ventricular rate Fewer QRS complexes than P waves (nonconducted P waves) P waves and QRS complexes are unrelated (no consistent PR interval) Escape rhythm ECG diagnosis: 3 rd degree AV Block 3 rd degree AVB Cause Idiopathic fibrosis of the AV node (most common) Underlying cardiac disease Aortic valve endocarditis Neoplasia Tick-borne disease 8

9 3 rd degree AVB Atropine response test to rule out vagally-mediated block Atropine 0.04 mg/kg SQ, repeat ECG in 30 min Refer through ER service Baseline bloodwork, BP Thoracic radiographs and echocardiogram Temporary pacing if needed Artificial pacemaker implantation ($ ) Dogs with 3 rd and high-grade 2 nd degree AV block (Shrope, 2006) 24% 1 mo 40% 6 mo 75% sudden death 3rd degree AV block is immediately life-threatening in dogs Cats with 3 rd degree AV block (Kellum, 2006) Mean age: 14 years Median HR: 120 bpm (range ) Most had underlying heart disease MST 386 days (range ) 13/21 survived >1 year after diagnosis Survival not affected by heart disease of CHF 3 rd degree AV block is not immediately life threatening in cats 9

10 10y FS German Shepherd Presents for weakness & tachypnea Rising resting RR (>36 breaths/min) Known history of CMVD and CHF CHF well-managed PE Irregular tachyarrhythmia Variable intensity heart sounds ( shoes in the dryer ) Pulse deficits II Irregular tachyarrhythmia (variable R-R intervals) Narrow, upright QRS complexes No visible P waves ECG diagnosis: atrial fibrillation Atrial fibrillation (AF) Significant atrial dilatation is necessary to perpetuate AF Giant breed dogs are the exception Clinical signs may be vague or related to venous congestion Signs of forward (low-output) heart failure Syncope Let hargy/exercise intolerance Development/recurrence of congestive heart failure Left CHF (pulmonary edema) Right CHF (ascites) 10

11 6/14/17 AF Fall in cardiac output Tachycardia results in decreased filling time Loss of AV synchrony Treatment of AF Rate control Optimize heart rate (< bpm in hospital) Treat CHF if present Diltiazem Regular diltiazem mg/kg PO q8h Extended-release diltiazem (Dilacor) 3-5 mg/kg PO q12h Digoxin mg/kg PO q12h Treatment of AF Rhythm control for lone AF Restore AV synchrony Improve cardiac output 11

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