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Ch. 34 Care of Patients with Dysrhythmias (M.S.)
Terms in this set (27)
Electrical & Mechanical Systems of the Heart:
- Heart has an electrical conduction system that causes depolarization from cell to cell, (+) to (-).
- Heart also has a Mechanical system "pump" that responds to the electrical stimulus causing muscles to contract and relax.
- The heart is both electrical and mechanical. The two work together in unison. If one system is affected, the other is also affected.
Review of the Conduction System:
• Cardiac dysrhythmias are abnormal rhythms of the heart's electrical system that can affect its ability to effectively pump oxygenated blood throughout the body.
• Dysrhythmias result from disturbances of cardiac electrical impulse formation, conduction, or both and can be life threatening.
• When the heart does not work effectively as a pump, PERFUSION to vital organs and peripheral tissues can be impaired, resulting in organ dysfunction or failure.
• Many diseases, especially coronary artery disease, electrolyte imbalances, changes in oxygenation, and drug toxicity, can cause abnormal heart rhythms.
• To provide collaborative patient-centered care using best practices, a basic understanding of cardiac electrophysiology, the conduction system of the heart, and the principles of electrocardiography are needed by a medical-surgical nurse.
Electrocardiography: automaticity, excitability, conductivity, and contractility
• Specialized cardiac muscle cells possess unique properties: automaticity (the ability of the cardiac cells to generate an electrical impulse spontaneously and repetitively), excitability (the ability of non-pacemaker heart cells to respond to an electrical impulse that begins in pacemaker cells and to depolarize), conductivity (the ability to send an electrical stimulus from cell membrane to cell membrane), and contractility (the ability of atrial and ventricaular muscle cells to shorten their fiber length in response to electrical stimulation, causing sufficent pressure to oush blood forward through the heart; in other words, it is the mechanical activity of the heart).
• The cardiac conduction system specialized cells are responsible for the generation and conduction of electrical impulses that cause atrial and ventricular depolarization (occurs when the normally negative charged cells within the heart muscle develop a positive charge).
• The conduction system consists of the sinoatrial (SA) node, atrioventricular (AV) junctional area, and bundle-branch system.
Cardiac Conduction System:
- Sinoatrial node (P-cells): Electrical impulses 60-100 beats/min; P wave on ECG
- Atrioventricular junction (T-cells): PR segment on ECG; Contraction known as "atrial kick"
- Bundle of His (Purkinje cells): Right bundle branch system; Left bundle branch system
• The electrocardiogram (ECG) provides a graphic representation, or picture, of cardiac electrical activity.
• Some units have full-disclosure monitors, which continuously store ECG rhythms in memory up to a certain amount of time, allowing nurses and health care providers to access and print them for more thorough patient assessment and management.
• Routine strips and changes in rhythm are documented in the patient's record.
• Analysis of an ECG rhythm strip requires a systematic approach using a five-step method facilitated by use of a measurement tool called an ECG caliper.
• The five steps consist of determining the heart rate and the rhythm, analyzing P waves, measuring the PR interval, and measuring the QRS complex duration.
• A lead provides one view of the heart's electrical activity, but multiple leads, or views, can be obtained.
• An 80-lead ECG looks at the heart from 80 views instead of only 12 and gives a 360-degree view of the heart.
• Evaluation of this 80-lead ECG revealed a 15% increase in diagnosing myocardial infarctions, particularly in the posterior wall, which were missed in the 12-lead ECG.
- represents atrial depolarization
- represents the time required for the impulse to travel through the AV node, where it is delayed, and through the Bundle of His, bundle branches, and Purkinje fiber network, just before ventricular depolarization
- represents the time required for atrial depolarization as well as impulse travel through the conduction system and Purkinje fiber network, inclusive of the P wave and PR segment
- it is measured from the beginning of the P wave to the end of the PR segment
- repesents ventricular depolarization and is measured from the beginning of the Q (or R) wave to the end of the S wave
QRS duration (J point):
- represents the junction where the QRS complex ends and the ST segment begins
- represents early ventricular repolarization
- represents ventricular repolarization
- represents late ventricular repolarization
- represents the total time required for ventricular depolarization and repolarization and is measured from the beginning of the QRS complex to the end of the T wave
Electrocardiographic Waveforms 6 second strip:
- Each segment between the dark lines (above the monitor strip) represents 3 seconds when the monitor is set at a speed of 25 mm/sec.
- To estimate the ventricular rate, count the QRS complexes in a 6-second strip and then multiply that number by 10 to estimate the rate for 1 minute.
ECG Rhythm Analysis: Determining HR: Normal, Tachycardia, Bradycardia
- 60-100 bpm Normal
- Greater than 100 bpm: Tachycardia
- Less than 60 bpm: Bradycardia
ECG Rhythm Analysis: Determining Heart Rhythm
- check the regularity of the atrial rhythm by assessing the PP intervals, placing one caliper point on a P wave and placing the other point on the precise spot on the next P wave; then move the caliper point from P wave to P wave to determine the regularity of the rhythm; P waves of a different shape create an irregularity; a slight irregularity of no more than 3 small blocks is considered essentially regular if the P waves are all of the same shape
- check the regularity of the ventricular rhythm by assessing the RR intervals, placing one caliper point on a portion of the QRS complex and the other point on the precise spot of the next QRS complex; then move the caliper from QRS complex to QRS complex along the entire strip to determine the regularity of the rhythm; QRS complexes of a different shape create an irregularity; a slight irregularity of no more than 3 small blocks between interval is considered essentially regular if the QRS complexes are all of the same shape
ECG Rhythm Analysis: Analyze P waves
1. Are P waves present?
2. Are the P waves occurring regularly?
3. Is there one P wave for each QRS complex?
4. Are the P waves smooth, round, and upright in appearance, or are they inverted?
5. Do all the P waves look similar?
ECG Rhythm Analysis: Measure PR interval
- place one caliper point at the beginning of the P wave and the other point at the end of the PR segment; the PR interval normally measures between 0.12 and 0.20 second; this should be constant throughout the strip
1. Are PR intervals greater than 0.20 second?
2. Are PR intervals less than 0.12 second?
3. Are PR intervals constant across the ECG strip?
ECG Rhythm Analysis: Measure QRS duration
- place one caliper point at the beginning of the QRS complex and the other at the J point, where the QRS complex ends and the ST segment begins; the QRS duration normally measures between 0.04 and 0.10 second; the measurement should be constant throughout the strip
1. Are QRS intervals less than or greater than 0.12 second?
2. Are the QRS complexes similar in appearance across teh ECG paper?
ECG Rhythm Analysis: Examine the ST segment
- the normal ST segment begins at the isoelectric line; ST elevation or depression is significant if displacement is 1 mm (one small box) or more above or below the line and is seen in two or more leads
ECG Rhythm Analysis: Assess the T wave
- note the shape and height of the T wave for peaking or inversion
ECG Rhythm Analysis: Measure the QT interval
- a normal QT interval should be equal to or less than one-half the distance of the R-to-R interval
• Sinus arrhythmia is a variant of NSR resulting from changes in intrathoracic pressure during breathing.
• Sinus arrhythmia has all the characteristics of NSR except for its irregularity.
o The PP and RR intervals vary, with the difference between the shortest and the longest intervals being greater than 0.12 second.
- The normal increase in HR that occurs during inspiration; this is more accelerated in children than in adults
- Sinus referes to the natural pacemaker of the heart which is called the SA node; Arrhythmia mean abnormal heart rhythm
Normal Sinus Rhythm (NSR):
• Normal sinus rhythm (NSR) is the rhythm originating from the SA node (dominant pacemaker) that meets these ECG criteria:
o Rate: Atrial and ventricular rates of 60 to 100 beats/min
o Rhythm: Atrial and ventricular rhythms regular
o P waves: Present, consistent configuration, one P wave before each QRS complex
o PR interval: 0.12 to 0.20 second and constant
o QRS duration: 0.04 to 0.10 second and constant
- Most common dysrhythmia seen in clinical practice.
- The atrial "Quiver" (irregular heartbeat) can cause blood to pool and possible thrombus formation (Blood clots); stroke; heart failure; and other heart-related complications
- Drug Therapy: Warfarin (Coumadin) or Xa (Factor 10a) drugs (Xarelto)
- Monitor patients for complications.
- Offer periods of rest/exercise for c/o fatigue.
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