- Information
- AI Chat
Basic Cardiac Monitoring
Generalist Nursing Practice IV: Tertiary Care Across the Lifespan (NURS 4889)
Temple University
Recommended for you
Preview text
Basic Cardiac Monitoring:
Normal Electrical Conduction: - SA node (sinoatrial node) - AV node (atrioventricular node) - Conduction - Bundle of His - Right and left bundle branches - Purkinje fibers - Depolarization = stimulation = systole - Repolarization = relaxation = diastole
The Cardiac Conduction System: And its correlation with an ECG - Action potentials spread from SA node to AV node, causing atrial depolarization - Atrial depolarization, seen as the P wave, induces atrial systole - Action potentials spread through the bundle of His, bundle branches and Purkinje fibers, causing ventricular depolarization - Ventricular depolarization, seen as the QRS complex, induces ventricular systole - As actions potentials pass out of the ventricles ventricular diastole is induced - Ventricular repolarization is shown by the T wave
Electrocardiogram Monitoring: - The P wave represents time for the passage of the electrical impulse through the atrium causing atrial depolarization (contraction). - The P-R interval is measured from the beginning of the P wave to the beginning of the QRS complex. It represents the time taken for the impulse to spread through the atria, AV node, and bundle of His; the bundle branches; and Purkinje fibers to a point immediately preceding ventricular contraction. - The QRS complex consists of three distinct waves. The Q wave is the first negative (downward) deflection after the P wave, short and narrow, and not present in several leads. The R wave is the first positive (upward) deflection in the QRS complex, and the S wave is the first negative (downward) deflection after the R wave. The QRS interval is measured from the beginning to the end of the QRS complex. It represents the time taken for depolarization (contraction) of both ventricles (systole). - The ST segment is measured from the S wave of the QRS complex to the beginning of the T wave. It represents the time between ventricular depolarization and repolarization (diastole). It should be isoelectric (flat). - The T wave represents the time for ventricular repolarization. It should be upright. - The Q-T interval is measured from the beginning of the QRS complex to the end of the T wave. It represents the time taken for entire electrical depolarization and repolarization of the ventricles.
Electrocardiogram Monitoring: - Graphic tracing of electrical impulses produced by heart - Waveforms of ECG represent activity of charged ions across membranes of myocardial cells - The electrocardiogram (ECG) is a graphic tracing of the electrical impulses produced in the heart. - The waveforms on the ECG represent electrical activity produced by the movement of ions across the membranes of myocardial cells, representing depolarization and repolarization. - The inside of the cell, when at rest, or in the polarized state, is negative compared with the outside. When a cell or groups of cells are stimulated, the cell membrane changes its permeability. This allows sodium to move rapidly into the cell, making the inside of the cell positive compared with the outside (depolarization). A slower movement of ions across the membrane restores the cell to the polarized state, called repolarization.
12-Lead ECG Lead Placement: - Accurate interpretation of an ECG depends on the correct placement of the leads on the patient.
- A. Limb leads I, II, and III. Leads are located on the extremities. Illustrated are the angles from which these leads view the heart.
- B. Lead placement for limb leads aVR, aVL, and aVF. These unipolar leads use the center of the heart as their negative electrode.
- C. Lead placement for the chest electrodes: V 1 , fourth intercostal space at the right sternal border; V 2 , fourth intercostal space at the left sternal border; V 3 , halfway between V 2 and V 4 ; V 4 , fifth intercostal space at the left midclavicular line; V 5 , fifth intercostal space at the anterior axillary line; V 6 , fifth intercostal space at the midaxillary line.
12-Lead ECG:
- Typically, an ECG consists of 12 leads (or views) of the heart's activity.
- A lead consists of a positive and a negative electrode, with the positive electrode being the "seeing eye." Activity coming toward the positive electrode produces an upward deflection on the EKG paper, and one going away from the seeing eye produces a downward deflection (this is the reason for lead tracings looking different).
- Six of the leads measure electrical forces in the frontal plane. These are bipolar (positive or negative) leads I, II, and III (left column of tracings); and unipolar (positive) leads aVr, aVl, and aVf.
- The remaining six unipolar leads (V 1 through V 6 ) measure the electrical forces in the horizontal plane (precordial leads).
- The 12-lead ECG may show changes suggesting structural changes, conduction disturbances, damage (e., ischemia, infarction), electrolyte imbalance, or drug toxicity. Obtaining 12 ECG views of the heart is also helpful in the assessment of dysrhythmias.
Systematic Approach: Assessment of Cardiac Rhythm - P wave - Atrial rate and rhythm - P-R interval - Ventricular rate and rhythm
- QRS complex
- ST segment
- Q-T interval
- T wave
- When assessing a cardiac rhythm, use a consistent and systematic approach. One such approach includes the following: o 1. Look for the presence of the P wave. Is it upright or inverted? Is there one for every QRS complex or more than one? Are there atrial fibrillatory or flutter waves present? o 2. Evaluate the atrial rhythm. Is it regular or irregular? o 3. Calculate the atrial rate. o 4. Measure the duration of the P-R interval. Is it normal duration or prolonged? o 5. Evaluate the ventricular rhythm. Is it regular or irregular? o 6. Calculate the ventricular rate. o 7. Measure the duration of the QRS complex. Is it normal duration or prolonged? o 8. Assess the ST segment. Is it isoelectric (flat), elevated, or depressed? o 9. Measure the duration of the Q-T interval. Is it normal duration or prolonged? o 10. Note the T wave. Is it upright or inverted?
- Additional questions to consider include the following: o 1. What is the dominant or underlying rhythm and/or dysrhythmia? o 2. What is the clinical significance of your findings? o 3. What is the treatment for the particular rhythm?
Normal Pacemaker of Heart - SA node (60–100 beats/minute) - Normal Sinus Rhythm
Secondary Pacemakers - AV node (40–60 beats/minute) - Junctional Rhythm
- His-Purkinje Fibers (20–40 beats/minute)
- Ventricular Rhythm
- Dysrhythmias result from disorders of impulse formation, conduction of impulses, or both.
- The heart has specialized cells in the SA node, atria, AV node, and bundle of His and Purkinje fibers (His- Purkinje system), which can fire (discharge) spontaneously. Normally, the SA node is the pacemaker of the heart. It spontaneously fires 60 to 100 times per minute.
- A secondary pacemaker from another site may fire in two ways. o If the SA node fires more slowly than a secondary pacemaker, the electrical signals from the secondary pacemaker may “escape.” The secondary pacemaker will then fire automatically at its intrinsic rate. These secondary pacemakers may start from the AV node at a rate of 40 to 60 times per minute or the His-Purkinje system at a rate of 20 to 40 times per minute. o Another way that secondary pacemakers can start is when they fire more rapidly than the normal pacemaker of the SA node. Triggered beats (early or late) may come from an ectopic focus or accessory pathway (area outside the normal conduction pathway) in the atria, AV node, or ventricles. This results in a dysrhythmia, which replaces the normal sinus rhythm.
Autonomic Nervous System: Control of Heart Rate - Parasympathetic o Decreases rate of SA node o Slows impulse conduction of AV node
Sympathetic o Increases rate of SA node o Increases impulse conduction of AV node o Increases cardiac contractility
The autonomic nervous system plays an important role in the rate of impulse formation, the speed of conduction, and the strength of cardiac contraction.
The components of the autonomic nervous system that affect the heart are the vagus nerve fibers of the parasympathetic nervous system and nerve fibers of the sympathetic nervous system.
Stimulation of the vagus nerve causes a decreased rate of firing of the SA node and slowed impulse conduction of the AV node.
Stimulation of the sympathetic nerves increases SA node firing, AV node impulse conduction, and cardiac contractility.
Calculating Heart Rate: - Options o Number of QRS complexes in 1 minute o Number of QRS complexes in 6 seconds x 10 o R-R intervals in 6 seconds x 10 o Number of small squares between one R-R interval, and divide this number into 1500 o Number of large squares between one R-R interval, and divide this number into 300 - You can use a variety of methods to calculate the HR from an ECG. - The most accurate way is to count the number of QRS complexes in 1 minute. However, because this method is time consuming, a simpler process is used. - Note that every 3 seconds, a marker appears on the ECG paper. Count the number of R-R intervals in 6 seconds and multiply that number by 10. (An R wave is the first upward [or positive] wave of the QRS complex.) This is the estimated number of beats per minute. - Another method is to count the number of small squares between one R-R interval. Divide this number into 1500 to get the HR. - Last, you can count the number of large squares between one R-R interval and divide this number into 300 to get the HR. - All these methods are most accurate when the rhythm is regular.
Normal Sinus Rhythm: - Sinus node fires 60–100 beats/minute - Rhythm is regular. P wave precedes each QRS complex - P-R interval is normal - QRS complex has a normal shape and duration. - Normal sinus rhythm refers to a rhythm that starts in the SA node at a rate of 60 to 100 times per minute and follows the normal conduction pathway. - Rhythm is regular. The P wave precedes each QRS complex and has a normal shape and duration. The P-R interval is normal, and the QRS complex has a normal shape and duration. - P Wave - Atrial rate and rhythm - PR Interval
- Ventricular rate and rhythm
- QRS complex
- Interpretation
Sinus Bradycardia: HR < 60bpm: - SA node fires at a rate less than 60 beats/minute.
- Caused by vagal inhibition or sympathetic stimulation
- Associated with physiologic and psychologic stressors
- Drugs can increase rate
- The discharge rate from the sinus node increases because of vagal inhibition or sympathetic stimulation.
- Sinus tachycardia is associated with physiologic and psychologic stressors such as exercise, fever, pain, hypotension, hypovolemia, anemia, hypoxia, hypoglycemia, myocardial ischemia, heart failure (HF), hyperthyroidism, anxiety, and fear.
- It can also be an effect of drugs such as epinephrine (EpiPen), norepinephrine (Levophed), atropine (AtroPen), caffeine, theophylline (Theo-Dur), or hydralazine (Apresoline). In addition, many over-the- counter cold remedies have active ingredients (e., pseudoephedrine [Sudafed]) that can cause tachycardia.
- Manifestations o Dizziness o Dyspnea o Hypotension o Angina in patients with CAD
- Treatment o Guided by cause (e., treat pain) o Fluids – IV and/or PO o β-adrenergic blockers
- The clinical significance of sinus tachycardia depends on the patient’s tolerance of the increased HR. The patient may have dizziness, dyspnea, and hypotension due to decreased CO. Increased myocardial oxygen consumption is associated with an increased HR. Angina or an increase in infarction size may accompany sinus tachycardia in patients with coronary artery disease (CAD) or an acute MI.
Basic Cardiac Monitoring
Course: Generalist Nursing Practice IV: Tertiary Care Across the Lifespan (NURS 4889)
University: Temple University
- Discover more from:Generalist Nursing Practice IV: Tertiary Care Across the LifespanNURS 4889Temple University30 Documents
- More from:Generalist Nursing Practice IV: Tertiary Care Across the LifespanNURS 4889Temple University30 Documents