MedSurg 28 – Electrocardiogram

Describe the purpose of an electrocardiogram (ECG).

An electrocardiogram (ECG) provides a graphic representation of cardiac electrical activity, showing how electrical currents are transmitted to the body surface.

Explain how electrodes are used in an ECG procedure.

Electrodes, consisting of a conductive gel on an adhesive pad, are placed on specific sites on the body and connected to an ECG machine or monitor to transmit cardiac electrical currents.

Define the term 'lead' in the context of an ECG.

A lead provides one view of the heart’s electrical activity, and multiple leads can be obtained to give a comprehensive picture of the heart's function.

How does the cardiac axis relate to the lead axis in an ECG?

The relationship between the cardiac axis (direction of electrical current flow in the heart) and the lead axis (imaginary line between positive and negative poles) determines the deflections seen on the ECG pattern.

What does the baseline represent in an ECG reading?

The baseline, or isoelectric line, occurs when there is no current flow in the heart after complete depolarization and repolarization.

Explain the significance of positive and negative deflections in an ECG.

Positive deflections occur above the baseline when the cardiac axis is directed toward the positive pole, while negative deflections occur below the baseline when the cardiac axis moves away from the positive pole.

Describe the standard 12-lead ECG system.

The standard 12-lead ECG consists of 12 leads, with six limb leads placed on the extremities and six chest leads placed on the chest, providing multiple views of the heart's electrical activity.

What are limb leads in an ECG, and how are they configured?

Limb leads are three standard bipolar leads (I, II, and III) that measure electrical activity between two points, with the right arm always negative and the left leg always positive.

How does the 18-lead ECG differ from the standard 12-lead ECG?

The 18-lead ECG adds six leads placed on the right side of the chest to view the right side of the heart, sometimes referred to as a right-sided ECG.

Define unipolar limb leads and provide examples.

Unipolar limb leads consist of a positive electrode only, with examples including aVR, aVL, and aVF, where 'a' means augmented and 'V' denotes a unipolar lead.

Explain the placement of unipolar chest leads in an ECG.

Unipolar chest leads are determined by the placement of the chest electrode, with six leads designated as V leads, providing additional views of the heart's electrical activity.

Describe the placement of the four limb electrodes in a 12-lead ECG.

The four limb electrodes are placed on the extremities: right arm, left arm, right leg, and left leg.

Explain the role of the fifth electrode in a 12-lead ECG.

The fifth electrode, placed on the chest, serves as the positive or exploring electrode and is positioned in one of six designated locations to obtain the desired chest lead.

How does electrode placement affect the accuracy of an ECG?

Accurate and identical electrode placement is crucial for valid comparisons of ECGs taken at different times, especially in patients with chest deformities or large breasts.

What should be done to ensure proper electrode placement in patients with large breasts?

Patients may be asked to move their breasts to ensure proper electrode placement.

Define the importance of removing electrodes after an ECG.

Electrodes should be removed after the ECG to prevent skin breakdown.

What position should a patient be in during a 12-lead ECG?

The patient should be in a semi-reclined position and reminded to remain as still as possible while breathing normally.

Explain the impact of patient movement during an ECG.

Repetitive movement can cause artifacts, leading to inaccurate interpretation of the ECG.

Who is typically responsible for obtaining a 12-lead ECG?

While nurses may be responsible for obtaining 12-lead ECGs, it is more common for trained technicians to perform this task.

What should a technician do if they suspect an abnormality during an ECG?

The technician should notify the nurse or primary health care provider of any suspected abnormality.

Describe the electrode placement for continuous ECG monitoring.

For continuous ECG monitoring, electrodes are placed on the trunk to minimize motion artifacts, with specific placements for the right arm, left arm, right leg, left leg, and one chest lead.

How does skin preparation affect continuous ECG monitoring?

Proper skin preparation, including cleaning and ensuring the area is dry, affects the clarity of ECG recordings by decreasing skin impedance.

What is the role of the nurse in the electrode placement process?

The nurse determines which lead to select and checks for correct electrode placement, while assistive personnel may apply the electrodes.

What factors can affect the quality of ECG rhythm transmission?

The quality of ECG rhythm transmission can be affected by skin preparation, electrode quality, and ensuring the contact site is free of substances that increase skin impedance.

How should electrodes be attached to ensure effective signal transmission?

Electrodes should be attached to the lead cable and then to the contact site, ensuring the gel is moist and fresh, and the area is free of lotion or other substances.

Describe the function of ECG cables in a critical care unit.

ECG cables can be attached directly to a wall-mounted monitor in a critical care unit, allowing for continuous monitoring of a patient's heart activity while they are restricted to bed rest or sitting in a chair.

Explain the purpose of telemetry systems in ECG monitoring.

Telemetry systems allow ambulatory patients to have their ECG transmitted to a remote monitor via a battery-operated transmitter, enabling freedom of movement without losing transmission.

Define the role of monitor technicians in acute care facilities.

Monitor technicians are responsible for watching a bank of monitors, printing ECG rhythm strips, interpreting rhythms, and reporting significant changes to the nursing staff.

How does the use of telemetry monitors impact nursing assessment?

The use of telemetry monitors increases the need for accurate nursing assessment to initiate appropriate interventions, especially in medical-surgical units.

What are full-disclosure monitors and their benefits?

Full-disclosure monitors continuously store ECG rhythms in memory, allowing healthcare providers to access and print rhythm strips for thorough patient assessment.

Identify the responsibilities of healthcare providers regarding ECG monitoring.

Healthcare providers determine when monitoring can be suspended, such as during showering, and whether monitoring is needed during off-unit testing or transportation.

Discuss the significance of clinical alarms in ECG monitoring.

Clinical alarms associated with continuous ECG monitoring are considered one of the top 10 technology hazards, highlighting the importance of effective monitoring systems.

Describe the process of recording an ECG strip.

An ECG strip is printed on graph paper with standardized measurements, where each small block represents 0.04 seconds, and the speed is set at 25 mm/sec.

Explain the measurement of time on an ECG graph.

Time is measured on the horizontal axis of the ECG graph, with five small blocks representing 0.20 seconds and 30 large blocks representing 6 seconds.

What are the components of a normal ECG complex?

A normal ECG complex consists of a P wave, a QRS complex, a T wave, and possibly a U wave.

Define the segments and intervals found in an ECG.

Segments in an ECG include the PR segment, ST segment, and TP segment, while intervals include the PR interval, QRS duration, and QT interval.

How is the amplitude and duration of ECG waveforms measured?

ECG waveforms are measured in amplitude (voltage) and duration (time), with specific measurements corresponding to the graph's grid.

What is the significance of the vertical lines on ECG graph paper?

Vertical lines on ECG graph paper are usually 15 large blocks apart, representing 3-second segments, aiding in the timing of heart rhythms.

Describe how to estimate the ventricular rate using an ECG monitor.

Count the QRS complexes in a 6-second strip and multiply that number by 10 to estimate the rate for 1 minute.

Explain the significance of the P wave in an ECG.

The P wave represents atrial depolarization and its shape may vary depending on the lead selected.

Define the PR segment in an ECG waveform.

The PR segment is the isoelectric line from the end of the P wave to the beginning of the QRS complex, indicating the delay of the electrical impulse in the AV node.

How is the PR interval measured and what does it represent?

The PR interval is measured from the beginning of the P wave to the end of the PR segment, representing the time for atrial depolarization and impulse travel through the conduction system.

Explain the components of the QRS complex.

The QRS complex represents ventricular depolarization and is measured from the beginning of the Q wave to the end of the S wave.

Describe the significance of the J point in an ECG.

The J point marks the junction where the QRS complex ends and the ST segment begins.

What does the ST segment represent in an ECG?

The ST segment represents early ventricular repolarization.

Define the T wave in the context of an ECG.

The T wave represents ventricular repolarization.

Explain the U wave and its significance in an ECG.

The U wave represents late ventricular repolarization.

How is the QT interval defined and measured?

The QT interval represents the total time for ventricular depolarization and repolarization, measured from the beginning of the QRS complex to the end of the T wave.

Describe the characteristics of the Q wave in the QRS complex.

The Q wave is the first negative deflection and may not be present in all leads; when present, it represents initial ventricular septal depolarization.

What does an abnormal Q wave indicate in an ECG?

An abnormal Q wave may indicate myocardial necrosis (cell death).

Explain the variability of the R wave in the QRS complex.

The R wave is the first positive deflection and its size may vary, being small, large, or absent depending on the lead.

Define the S wave in the context of the QRS complex.

The S wave is a negative deflection following the R wave and is not present in all leads.

How is the QRS duration measured and what does it represent?

The QRS duration is measured from the beginning of the QRS complex to the J point, representing the time required for depolarization of both ventricles.

Describe the relationship between the shape of the P wave and the origin of the electrical impulse.

The shape of the P wave is consistent when the impulse is generated from the SA node; if generated from an ectopic focus, the shape changes.

What is the normal range for the PR interval?

The normal PR interval measures from 0.12 to 0.20 seconds (five small blocks).

Describe the ST segment in an ECG.

The ST segment is normally an isoelectric line that represents early ventricular repolarization, occurring from the J point to the beginning of the T wave.

Explain how the length of the ST segment can vary.

The length of the ST segment can vary with changes in heart rate, administration of medications, and electrolyte disturbances.

Define the T wave in an ECG.

The T wave follows the ST segment and represents ventricular repolarization; it is usually positive, rounded, and slightly asymmetric.

How can T waves change in appearance?

T waves may become tall and peaked, inverted, or flat due to myocardial ischemia, potassium or calcium imbalances, medications, or autonomic nervous system effects.

What is the U wave and when is it typically seen?

The U wave, when present, follows the T wave and may result from slow repolarization of ventricular Purkinje fibers; it is generally smaller and of the same polarity as the T wave.

Explain the significance of an abnormal U wave.

An abnormal U wave may suggest an electrolyte abnormality, particularly hypokalemia, or other disturbances.

Describe the QT interval and its importance.

The QT interval represents the total time required for ventricular depolarization and repolarization, measured from the beginning of the Q wave to the end of the T wave.

How does the QT interval vary?

The QT interval varies with the patient’s age and gender and changes with heart rate, lengthening with slower rates and shortening with faster rates.

What can prolong the QT interval?

The QT interval may be prolonged by certain medications, electrolyte disturbances, or subarachnoid hemorrhage.

What is torsades de pointes?

Torsades de pointes is a unique type of ventricular tachycardia that can result from a prolonged QT interval.

Define artifact in the context of ECG monitoring.

Artifact is interference seen on the monitor or rhythm strip, which may appear as a wandering or fuzzy baseline, caused by patient movement, loose electrodes, or faulty equipment.

How can artifacts affect ECG interpretation?

Some artifacts can mimic lethal dysrhythmias, such as ventricular tachycardia or ventricular fibrillation, necessitating careful patient assessment to differentiate them from actual lethal rhythms.

Describe the first step in ECG rhythm analysis.

The first step is to determine the heart rate, commonly using the 6-second strip method, which involves counting the number of QRS complexes in 6 seconds and multiplying by 10.

What is considered a normal heart rate?

Normal heart rates fall between 60 and 100 beats per minute.

Define bradycardia and tachycardia.

Bradycardia is a heart rate less than 60 beats per minute, while tachycardia is a heart rate greater than 100 beats per minute.

How can current monitoring systems assist in heart rate assessment?

Current monitoring systems display a continuous heart rate and print it on the ECG strip, but caution is needed to confirm the rate by assessing the patient directly.

What is the second step in ECG rhythm analysis?

The second step is to determine the heart rhythm by assessing for atrial and/or ventricular regularity, identifying whether the rhythms are regular or irregular.

Describe the types of irregular rhythms.

Irregular rhythms can be classified as regularly irregular, occasionally irregular, or irregularly irregular.

How can you check the regularity of the atrial rhythm?

Assess the PP intervals by placing one caliper point on a P wave and the other on the next P wave, then move the caliper along the strip to determine the rhythm's regularity.

Explain the significance of ectopic waves in P waves.

Ectopic waves create irregularity in the rhythm as they do not regularly align with other P waves.

Define what constitutes a regular PP interval.

A slight irregularity in the PP intervals, varying no more than three small blocks, is considered regular if all P waves are of the same shape.

How does intrathoracic pressure affect PP intervals?

Changes in intrathoracic pressure during the respiratory cycle can cause slight irregularities in the PP intervals.

Describe the process for checking the regularity of the ventricular rhythm.

Assess the RR intervals by placing one caliper point on a QRS complex and the other on the next QRS complex, then move the caliper along the strip.

What indicates an irregularity in QRS complexes?

QRS complexes of a different shape create an irregularity and do not regularly align with other QRS complexes.

Define a regular RR interval.

A slight irregularity of no more than three small blocks between intervals is considered regular if all QRS complexes are of the same shape.

Analyze the P waves for consistency. What should be checked?

Check that the P wave shape is consistent, indicating atrial depolarization from one focus, and ensure there is one P wave before each QRS complex.

What does it indicate if there are more P waves than QRS complexes?

It indicates that a dysrhythmia exists.

How should the PR interval be measured?

Place one caliper point at the beginning of the P wave and the other at the end of the PR segment.

What questions should be considered when analyzing the PR interval?

Consider if PR intervals are greater than 0.20 seconds, less than 0.12 seconds, and if they are constant across the ECG strip.

How is the QRS duration measured?

Place one caliper point at the beginning of the QRS complex and the other at the J point where the QRS complex ends.

What is the normal range for QRS duration?

The QRS duration normally measures between 0.06 and 0.10 seconds.

What does a narrow QRS indicate?

A narrow QRS (0.11 seconds or less) indicates that the impulse was not formed in the ventricles and is referred to as supraventricular.

Describe the significance of a wide QRS complex in an ECG.

A wide QRS complex (greater than 0.11 seconds) indicates that the impulse may originate from the ventricles or from supraventricular sources with aberrant conduction.

Explain the importance of examining the ST segment in an ECG.

The ST segment should begin at the isoelectric line; significant elevation or depression (1 mm or more) in two or more leads may indicate conditions like myocardial infarction, pericarditis, or hyperkalemia.

How can abnormal T waves be interpreted in an ECG analysis?

Abnormal T waves, such as peaking or inversion, may indicate issues like myocardial infarction or ventricular hypertrophy.

Define the normal QT interval in relation to the RR interval.

A normal QT interval should be equal to or less than half the distance of the RR interval.

Do the steps for interpreting cardiac rhythms include evaluating QRS intervals?

Yes, evaluating whether QRS intervals are less than or greater than 0.11 seconds is part of the interpretation process.

Explain the characteristics of normal sinus rhythm (NSR).

Normal sinus rhythm (NSR) features an atrial and ventricular rate of 60 to 100 beats/min, regular rhythms, present P waves before each QRS complex, a PR interval of 0.12 to 0.20 seconds, and a QRS duration of 0.06 to 0.11 seconds.

Describe sinus arrhythmia and its characteristics.

Sinus arrhythmia is a variant of NSR characterized by irregular rhythms due to changes in intrathoracic pressure during breathing, with PP and RR intervals varying by more than 0.12 seconds.

How does sinus arrhythmia differ from normal sinus rhythm?

Sinus arrhythmia has all the characteristics of NSR except for its irregularity, with variations in PP and RR intervals.

What factors can cause sinus arrhythmias aside from respiratory changes?

Sinus arrhythmias can also be caused by nonrespiratory factors such as medications like digoxin or morphine, which enhance vagal tone.

Assess the role of the sinoatrial (SA) node in cardiac rhythms.

The sinoatrial (SA) node is the dominant pacemaker of the heart, originating the normal sinus rhythm (NSR).