Understanding Cardiac Dysrhythmia Interpretation

1. Basic Dysrhythmia Interpretation NURS 108 Spring 2008 Majuvy L. Sulse RN, MSN,CCRN

2. Cardiac Cycle • Systole-simultaneous contraction of ventricles, lasts 0.28 sec • Diastole- ventricular relaxation, lasts 0.52 sec • One cardiac cycle occurs every 0.8 sec

3. Cardiac Cycle • Stroke volume-volume of blood (70cc) pumped out of one ventricle of the heart in a single contraction • Heart rate- number of contractions per minute(60-100bpm • Cardiac output-amount of blood pumped by the left ventricle in 1 minute (4-8L/min) • CO= SV XHR

4. Cardiac Cycle • Preload-degree of myocardial fiber stretch at the end of diastole • Afterload-resistance against which the heart must pump to eject blood through the semilunar valves and into peripheral vessels • STARLING’S Law-the more the muscle fibers are stretched up to a certain point, the more forceful the subsequent contraction will be. • Systemic vascular resistance (impedance)- amount of opposition to blood flow offered by the arterioles, pressure the heart must overcome to open the aortic valve

5. Autonomic Nervous System • Sympathetic-prepares for physical activity-fight or flight response-norepinephrine (Adrenergic nerve endings) • Alpha-vasoconstriction • Beta • Beta 1-increase HR & contractility • Beta 2-bronchial dilation & vasodilation • Parasympathetic-rest & digest function • Acetylcholine (cholinergic nerve endings)

6. Electrophysiologic Properties • Automaticity-ability to generate an electrical impulse spontaneously & repetitively • Excitability-ability to be electrically stimulated or respond to an electrical stimulus • Conductivity-ability to receive an electrical stimulus and transmit to other cardiac cells • Contractility-also rhythmicity is the ability to shorten and cause contraction in response to an electrical stimulus-coordination of contraction to produce a regular heartbeat

7. Major electrolytes that affect Cardiac Function • 3 major cations • K-performs a major function in cardiac depolarization and repolarization • Sodium plays a vital part in myocardial depolarization • Calcium is important in myocardial depolarization and contraction. • Magnesium-acts as transporter for Na & K across cellular membranes. Also plays an important function in muscular contraction

8. Movement of Ions • Resting cardiac cells (Polarization) –inside the cell is negatively charged. K is greater in the cell; Na greater outside the cell (positively charged)-Resting membrane potential • Depolarization (action Potential)-sodium-potassium exchanged pump resulting in positive polarity inside the cell membrane. Myocardial contraction occurs. • Repolarization-recovery or resting phase; positive charges are again on the outside and negative charges in the inside

9. Refractory Periods • Ensures that the muscle is totally relaxed before another action potential occurs • Atrial muscle-0.15 sec • Ventricular muscle-.25-.30 sec

10. Refractory Periods Absolute refractory period-cardiac muscle cannot be depolarized. Corresponds to beginning of QRS to peak of T wave Relative refractory period-cardiac muscles stimulated to contract prematurely if stimulus is stronger than normal. Corresponds with down slope of T wave

11. Cardiac Conduction System

12. Electrical Conduction Pathway • SA node (60-100bpm) • Internodal pathways • AV node ( 40-60bpm) • Bundle of His • Bundle Branches • Purkenje networks (20-40bpm)

13. EKG • ECG/EKG-a graphic representation of cardiac activity • 12 lead-shows electrical activity from 12 different planes of the heart-used as a diagnostic tool rather than a monitoring device • Electrode-adhesive pad that contains conductive gel and designed to be attached to skin • Leads-wires generally color coded. For the EKG to receive a clear picture of electrical impulses, there must be a positive, a negative and a ground. The exact portion of the heart being visualized depends on lead placement

14. EKG Leads • Baseline-isoelectric line-no current flow in the heart; consists of positive, negative deflections or biphasic complex • 3 or 5 lead- used for monitoring the current cardiac activity of patients at risk for cardiac abnormalities • Lead ll or MCL1-modified chest leads mostly used because of ability to visualize P waves. MCL provides a R sided view of the heart. MCL6-L sided view of the heart

15. EKG Leads • Limb leads • Bipolar leads-measures activity between 2 points (I, II, III) • Unipolar leads-positive electrodes only-aVR, aVL, aVF • Chest leads-6 precordial leads

17. LIMB LEADS & AUGMENTED LEADS

20. EKG Graph Paper

22. Segments and Intervals

23. Segments and Intervals • P wave-deflection representing atrial depolarization • PR segment-isoelectric line from end of P wave to beginning of QRS-impulse is traveling through the AV node. PR interval-0.12-0.20(time for atrial depolarization-AV node-Purkenje fibers) • QRS complex-ventricular depolarization. QRS duration of 0.04-.10 sec from QRS to J-point • ST segment-early ventricular repolarization from J-point to beginning of T wave. Elevations not more than 1 mm or deflections o.5 mm from isoelectric line • T wave- ventricular repolarization, usually rounded, positive deflection • U wave-smaller polarity as T wave-slow repolarization- not normally seen except in hypokalemia • QT interval-total time for ventricular depolarization and repolarization

24. HR Determination • 6 second method • count QRS complexes in a 6 sec strip x 10 (30 large boxes in 6 sec strip) • P-P or R-R interval method • count number of small blocks in a P- P or R-R interval and divide into 1500 (no. of small blocks in 1 min) • Count the number of large blocks in an interval and divide into 300 (number of large blocks in 1 minute) • Memory method

25. ECG Rhythm Analysis • Analyze P waves- P wave is present. shape is consistent, must be before each QRS • Analyze QRS complex- QRS complex is present & consistent • Determine atrial rhythm or regularity- check regularity by assessing P-P or R-R • Determine ventricular rhythm or regularity-check regularity by assessing R-R • Determine heart rate-use one of the methods • Measure the PR interval-measurement should be constant and should be between 0.12-0.20 • Measure the QRS duration-measurement should be constant and should be between 0.04-0.10 sec • Interpret the rhythm

26. General Rules • First & most important, LOOK at your PATIENT! • Read every strip from left to right • Apply the systematic approach • Avoid shortcuts and assumptions. • Ask and answer each question in the ECG analysis approach

27. Artifacts • Waveforms outside the heart-interference caused by: • Patient movement wandering baseline • Loose or defective electrodes-lost contact with patient’s skin • Improper grounding-in touch with an outside source of electricity • Faulty EKG apparatus Patient assessment is critical

29. Normal Sinus Rhythm SA node generated an impulse that followed a normal pathway, the heart rate falls within the range, atrial & ventricular rhythms are regular, P waves preceded every QRS and QRS is within 0.12sec

30. Sinus Bradycardia SA node fires slower than normal heart rate-less than 60bpm Rhythm is regular P wave upright and same shape PR is constant .12-.20sec QRS-normal <.12sec

31. Sinus Bradycardia • Causes: • Vagal stimulation, MI, hypoxia • Digitalis toxicity • Medication side effects • Normal to athletes • Adverse effects: • Dizziness, weakness, syncope, diaphoresis, pallor, hypotension • Treatment • According to symptoms, atropine to speed up heart rate, pacemaker

32. Sinus Tachycardia SA node fires at a rate faster than normal but conduction pathway is normal. All criteria for interpretation are the same except that the heart rate is faster.

33. Sinus Tachycardia • Causes • Emotionally upset, pain, fever, thyrotoxicosis, hypoxia, hypovolemia, inhibition of vagus nerve, • Caffeine, norepinephrine, theophylline • Adverse effects • Angina, dizziness, hypotension, increased in cardiac workload • Treatment • Treat the cause • Medications may be given- betablockers

34. Sinus Arrhythmia • The only irregular rhythm from the sinus node and has a cyclic pattern that usually corresponds with breathing • Rate- varies with respiratory pattern • Regularity-irregular in a repetitive pattern • P waves-Upright in most leads, same shape and one to each QRS P-P interval is irregular • QRS-<.12 sec • Cause-usually caused by breathing pattern but can also heart disease • Treatment- usually non required

36. Atrial Dysrhythmias • SA node fails to generate an impulse • Atrial nodes or internodal pathways may initiate an impulse and follows the conduction pathway • Dysrhythmias of this type are not lethal • Accessory pathway-irregular muscle connection between atria and ventricles that bypasses the AV node

37. Premature Atrial Contractions • Causes- atria becomes hyper and fire early caused by medications, caffeine, tobacco, hypoxia or heart disease • Adverse effects-if frequent can be a sign of impending heart failure or atrial tachycardia or fibrillation • Treatment-O2, omit caffeine, tobacco or other stimulants. Give digitalis or quinidine, treat heart failure.

38. Premature Atrial Contractions Rate normal Rhythm usually regular except for a PAC P waves shaped differently from a normal P wave or hidden in preceding T wave PR interval .12 to .20sec QRS .12sec similar to underlying rhythm

39. Supraventricular Tachycardia (SVT) • Tachycardia (>150 bpm) originating above the ventricles-SA node, atria, AV nodes • P waves not discernible-hidden in T waves • Paroxysmal-starts & ends abruptly • Causes-same as PAcs • Adverse effects- palpitations, light-headedness, dizziness, shortness of breath, chest pain, fainting =decreased cardiac output • Treatment-vagal maneuvers (cough, bear down), carotid massage, or medications digitalis, calcium channel blockers, beta blockers, Adenosine

40. Supraventricular Tachycardia (SVT) Rate 150-250bpm Rhythm regular P waves not discernible PR not discernible QRS usually less than .10sec

41. Atrial Flutter • Results when one irritable atrial foci fires out regular impulses at a rapid rate that P waves are in a sawtooth pattern • Av node (gatekeepers) cannot depolarize fast enough to keep up, many impulses never get through to ventricles. Conduction ratio is variable-2:1block, 3:1 block or 4:1 block. Slow ventricular response-VR of <60pm; rapid VR >100-150bpm) • Causes-acute MI, CHF, digitalis toxicity, pulmonary embolism, SA node disease, septal defects • Adverse effects-decreased cardiac output • Treatment-digitalis, cardioversion, calcium channel blockers, ablation

42. Atrial Flutter Rate atrial 250-300bpm, ventricles-variable Rhythm regular if conduction ratio is constant, irregular if conduction rate varies P waves replaced by fluttery waves PRnot measurable QRS <.12sec

43. Atrial Fibrillation • Most common atrial dysrhythmia in elderly patients • Multiple atrial impulses from different locations all at the same time (350-600bpm) • Ventricular response maybe rapid (100-150bpm) or slow (< 60bpm) • Causes-maybe chronic MI CHF, valvular heart disease, hyperthyroidism • Adverse effects-decreased cardiac output, blood clots which can cause MI, stroke or clot in the lung • Treatment- Digitalis, quinidine, cardizem, anticoagulant as coumadin, cardioversion

44. Atrial Fibrillation

45. Junctional Rhythms • Arrhythmia originating in AV node • HR= 40-60bpm; accelerated =60-100bpm; junctional= 100-140bpm • P wave-absent, inverted before or after a QRS • PR interval-<.12if P precedes a QRS • QRS <.12sec • Cause-vagal stimulation, hypoxia, ischemia of SA node, MI, digitalis toxicity • Treatment-varies according to type of arrhythmia. Atropine to increase HR, withhold or decrease medication that can slow heart rate

46. Junctional Rhythms

47. Ventricular Dysrhythmias • Ventricles serves as pacemaker • Heart rate significantly reduced (20-40 beats per min • Normal conduction system bypassed • QRS bizarre in appearance & >0.12 sec • P waves absent (buried or hidden in QRS) • Rhythms considered life threatening

48. Premature Ventricular Complexes (PVCs) • A single ectopic (out of place) complex from an irritable site • Indicates increased myocardial irritability • Precursors of more serious lethal rhythms • Cardiac output compromised • Causes • Myocardial ischemia, Emotional stress, increased physical exertion, CHF, electrolyte imbalance, digitalis toxicity or acid base imbalances • Treatment- based on symptoms and causative factors • O2 and antidysrhythmics

49. PVCs • Unifocal-arise from one single site • Multifocal- originate from different sites • Ventricular bigeminy- every other beat is a PVC • Ventricular trigeminy-every third beat is a PVC • Ventricular quadrigeminy- every 4th beat is a PVC • Interpolated- a PVC between two sinus beats • Couplet or repititive PVCs- two PVCs occurring together without a normal complex in between • Salvos-3 or more PVCs in a row (Vtach)

50. Premature Ventricular Contraction (PVC) Unifocal PVCs Multifocal PVCs