Focus on Dysrhythmias Relates to Chapter 36 Nursing

Focus on Dysrhythmias (Relates to Chapter 36, “Nursing Management: Dysrhythmias, ” in the textbook) Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc.

Dysrhythmias Abnormal cardiac rhythms are termed dysrhythmias. Prompt assessment of dysrhythmias and the patient’s response to the rhythm is critical. Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 2

Properties of Cardiac Cells Automaticity Excitability Conductivity Contractility Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 3

Conduction System of the Heart Fig. 32 -4. A, Conduction system of the heart. AV, Atrioventricular; SA, sinoatrial. B, The normal electrocardiogram (ECG) pattern. The P wave represents depolarization of the atria. The QRS complex indicates depolarization of the ventricles. The T wave represents repolarization of the ventricles. The U wave, if present, may represent repolarization of the Purkinje fibers or it may be associated with hypokalemia. The PR, QRS, and QT intervals reflect the length of time it takes for the impulse to travel from one area of the heart to another. Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 4

Nervous System Control of the Heart Autonomic nervous system controls: • Rate of impulse formation • Speed of conduction • Strength of contraction Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 5

Nervous System Control of the Heart Parasympathetic nervous system Vagus nerve • Decreases rate • Slows impulse conduction • Decreases force of contraction Sympathetic nervous system • Increases rate • Increases force of contraction Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 6

Electrocardiogram Monitoring Graphic tracing of electrical impulses produced by the heart Waveforms of ECG represent activity of charged ions across membranes of myocardial cells. Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 7

Phases of Cardiac Action Potential Fig. 36 -1. Phases of the cardiac action potential. The electric potential, measured in millivolts (m. V), is indicated along the vertical axis of the graph. Time, measured in seconds (sec), is indicated along the horizontal axis. There are five phases of the action potential, labeled as phase 0 through phase 4. Each phase represents a particular electrical event or combination of electrical events. Phase 0 is the upstroke of rapid depolarization and corresponds with ventricular contraction. Phases 1, 2, and 3 represent repolarization. Phase 4 is known as complete repolarization (or the polarized state) and corresponds to diastole. TP, Threshold membrane potential; RP, resting membrane potential. Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 8

Lead Placement Fig. 36 -4. A, Lead placement for MCL, using a three-lead system. B, Lead placement for V 1 or V 6 using a five-lead system. C, Typical electrocardiogram tracing in lead MCL 1. C, Chest; LA, left arm; LL, left leg; MCL, modified chest lead; RA, right arm; RL, right leg. Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 9

ECG Paper Rhythm strip provides documentation of patient’s rhythm. Allows for measurement of complexes and intervals Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 10

Assessment of a cardiac rhythm Heart rate ( 60 – 100) Is there a P wave before each QRS Is PR ( 0. 06 -0. 12 sec) and QRS ( 0. 08 – 0. 20 sec) intervals WNL Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc.

Assessment of Cardiac Rhythm Fig. 36 -5. Time and voltage on the electrocardiogram; 6 -second strip. Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 12

Calculating HR Count • The number of QRS complexes in 1 minute • The R-R intervals in 6 seconds, and multiply by 10 • Number of small squares between one R-R interval, and divide this number into 1500 • Number of large squares between one R-R interval, and divide this number into 300 Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 13

Assessment of Cardiac Rhythm Fig. 36 -6. When the rhythm is regular, heart rate can be determined at a glance. The estimated heart rate is 70. Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 14

Patient Preparation Clip excessive hair on chest wall. Rub skin with dry gauze. May need to use alcohol for oily skin Apply electrical conductive gel. Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 15

Artifact Fig. 36 -7. Artifact. A, Muscle tremor. B, Loose electrodes. Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 16

Telemetry Monitoring Observation of HR and rhythm at a distant site Two types • Centralized monitoring system • Sophisticated alarm system alerts when it detects dysrhythmias, ischemia, or infarction. Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 17

Normal Sinus Rhythm Sinus node fires 60 to 100 bpm. Follows normal conduction pattern Fig. 36 -8. Normal sinus rhythm in lead II. Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 18

Normal Electrical Pattern Fig. 36 -9. The electrocardiogram complex as seen in a normal sinus rhythm. 1, P wave; 2, PR interval; 3, QRS complex; 4, ST segment; 5, T wave; 6, QT interval. Isoelectric (flat) line represents the absence of electrical activity in the cardiac cells. (See Table 36 -2 for timing of intervals. ) Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 19

Sinus Bradycardia Sinus node fires <60 bpm. Normal rhythm in aerobically trained athletes and during sleep Fig. 36 -11. A, Sinus bradycardia. Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 20

Sinus Bradycardia Clinical associations • Occurs in response to Carotid sinus massage Hypothermia Increased vagal tone Administration of parasympathomimetic drugs Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 21

Sinus Bradycardia Clinical associations • Occurs in disease states Hypothyroidism Increased intracranial pressure Obstructive jaundice Inferior wall MI Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 22

Sinus Bradycardia Clinical significance • Dependent on symptoms Hypotension Pale, cool skin Weakness Angina Dizziness or syncope Confusion or disorientation Shortness of breath Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 23

Sinus Bradycardia Treatment • Atropine • Pacemaker may be required. Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 24

Sinus Tachycardia Discharge rate from the sinus node is increased as a result of vagal inhibition and is >100 bpm. Fig. 36 -11. B, Sinus tachycardia. Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 25

Sinus Tachycardia Clinical associations • Associated with physiologic stressors Exercise Pain Hypovolemia Myocardial ischemia Heart failure (HF) Fever Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 26

Sinus Tachycardia Clinical significance • Dizziness and hypotension due to decreased CO • Increased myocardial oxygen consumption may lead to angina. Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 27

Sinus Tachycardia Treatment • Determined by underlying cause -adrenergic blockers to reduce HR and myocardial oxygen consumption Antipyretics to treat fever Analgesics to treat pain Copyright © 2011, 2007 by Mosby, Inc. , an affiliate of Elsevier Inc. 28