TEST 1

Basic ECG Concepts Answer Key

1. Heart Anatomy & Blood Flow

• List the three major layers of the heart wall: 1) Endocardium, 2) Myocardium, 3) Epicardium.

• The pericardium is the fibrous sac surrounding the heart.

• The right atrium receives blood from the systemic system (via superior and inferior vena cava).

• The left atrium receives blood from the pulmonary veins.

• The right ventricle pumps blood to the lungs (pulmonary circulation).

• The left ventricle pumps blood to the systemic system.

• Systole is when the heart contracts; diastole is when the heart chambers are filling and the heart is at rest.

• The coronary arteries supply blood to the myocardium.

• The right heart pumps deoxygenated blood to the pulmonary circulation.

• The left heart pumps oxygenated blood to the arterial systemic circulation.

• When the atria contract, an additional 25%25%–30%30% of blood is pushed into the ventricle. This is called the atrial kick.

2. Autonomic Nervous System

• The autonomic nervous system regulates involuntary functions such as blood pressure and heart rate.

• The two major divisions of the ANS are the sympathetic nervous system and the parasympathetic nervous system.

• Sympathetic nerve fibers arise from the thoracic and lumbar regions of the spinal cord.

• The sympathetic nervous system releases norepinephrine.

• Sympathetic stimulation causes increased heart rate, increased conductivity, and increased contractility.

• Parasympathetic fibers arise from the craniosacral (cranial and sacral) regions.

• The parasympathetic nervous system releases acetylcholine.

• The right vagus primarily affects the SA node; the left vagus affects the AV node.

• Parasympathetic stimulation causes decreased heart rate, decreased conductivity, and decreased contractility.

3. Cardiac Cells & Electrophysiology

• The two cardiac cell types are electrical cells and myocardial (mechanical) cells.

• Electrical cells have the properties of automaticity, excitability, and conductivity.

• Myocardial cells have the properties of contractility and extensibility (as well as excitability and conductivity).

• Depolarization is the spread of electrical impulse prior to contraction.

• Repolarization is the return of ions to the resting state.

• The refractory period is divided into the absolute refractory period and the relative refractory period.

• The absolute refractory period begins at the start of the QRS complex and ends at the peak of the T wave.

• During the absolute refractory period, cardiac cells cannot respond to a stimulus, no matter how strong.

• The relative refractory period is also known as the vulnerable period.

• During the relative refractory period, a strong stimulus could cause the cardiac cells to depolarize.

4. Cardiac Conduction System

• The SA node is the physiological pacemaker of the heart.

• The SA node normally beats at 6060–100 bpm100bpm.

• The AV node is referred to as the “gate keeper” of the ventricles.

• The AV node normally beats at 4040–60 bpm60bpm.

• The Bundle of His connects the AV node with the bundle branches.

• The ventricles have an inherent rate of less than 40 bpm40bpm (typically 2020–40 bpm40bpm).

• Complete the conduction pathway: SA node → AV node → Bundle of His → Bundle branches → Purkinje fibers.

5. ECG Paper & Electrical Activity

• The horizontal axis of ECG graph paper measures time.

• The vertical axis measures amplitude (voltage).

• Depolarization is always followed by repolarization (and mechanical contraction).

• An ECG tracing is a record of the electrical activity of the heart.

• Always treat the patient, not the monitor.

• The flat line between waveforms is the isoelectric line.

• A waveform above the isoelectric line has a positive deflection; below the line is a negative deflection.

6. ECG Waveforms & Intervals

• The P wave represents atrial depolarization.

• The P wave is normally smooth, upright, and precedes each QRS complex.

• The PR interval is measured from the beginning of the P wave to the beginning of the QRS complex.

• To calculate the PR interval, count small squares and multiply by 0.04 seconds0.04seconds.

• The normal PR interval is 0.120.12 to 0.20 seconds0.20seconds.

• The QRS complex represents ventricular depolarization.

• The T wave represents ventricular repolarization.

• The QT interval depends on heart rate.

• A slow heart rate produces a longer QT interval; a fast heart rate produces a shorter QT interval.

• The QT interval should be less than half (50%50%) of the R-R interval.

7. Monitoring & Lead Placement

• In a five-lead wire system, the only electrode that requires a change in position is the chest (V) lead.

• Three bipolar limb leads form Einthoven's triangle.

• Bipolar leads have a positive and negative pole.

• V1: 4th intercostal space, right sternal border.

• V2: 4th intercostal space, left sternal border.

• V3: placed halfway between V2 and V4.

• V4: 5th intercostal space, left midclavicular line.

• V5: 5th intercostal space, left anterior axillary line.

• V6: 5th intercostal space, left midaxillary line.

8. Troubleshooting

• For artifact, one troubleshooting action is to replace the electrode pads.

• For 60-cycle (AC) interference, check to ensure that the equipment is properly grounded.

• For a wandering baseline, ensure that the electrodes are not placed over bony areas or excessive hair.

9. Key Terms

• Bradycardia means a slow rate; for sinus rhythms, a rate less than 60 bpm60bpm.

• Tachycardia means a fast rate; a rate greater than 100 bpm100bpm.

• Accelerated means faster than the normal pacing rate for a particular center.

Review Questions

1. List the three major layers of the heart wall.

   • Endocardium, Myocardium, Epicardium.

2. Trace the blood flow through the heart and lungs.

   • Superior/Inferior Vena Cava → Right Atrium → Tricuspid Valve → Right Ventricle → Pulmonic Valve → Pulmonary Artery → Lungs (gas exchange) → Pulmonary Veins → Left Atrium → Mitral (Bicuspid) Valve → Left Ventricle → Aortic Valve → Aorta → Systemic Circulation.

3. Differentiate the two types of cardiac cells and their properties.

   • Electrical (Pacemaker) Cells: Specialized cells that generate and conduct electrical impulses. Properties include automaticity, excitability, and conductivity.

   • Myocardial (Mechanical) Cells: Contractile muscle cells that contract in response to electrical stimulation. Properties include contractility and extensibility.

4. State the components of the cardiac conduction system.

   • Sinoatrial (SA) node, Atrioventricular (AV) node, Bundle of His, Right and Left Bundle Branches, and Purkinje Fibers.

5. List and define the key ECG waves in a normal cardiac cycle.

   • P wave: Represents atrial depolarization.

   • QRS complex: Represents ventricular depolarization (and masked atrial repolarization).

   • T wave: Represents ventricular repolarization.

   • U wave: Represents late repolarization of Purkinje fibers or papillary muscles (when visible).

6. Describe how to measure the PR interval, QRS complex, and QT interval.

   • PR Interval: Measured from the start of the P wave to the beginning of the QRS complex (normal range: 0.120.12–0.20 seconds0.20seconds).

   • QRS Complex: Measured from the beginning of the Q wave (or R wave if no Q is present) to the end of the S wave at the J-point (normal range: <0.12 seconds<0.12seconds).

   • QT Interval: Measured from the start of the QRS complex to the end of the T wave (normal: heart rate dependent, typically <0.44 seconds<0.44seconds or less than half the preceding R-R interval).

7. List indications for ECG monitoring.

   • Diagnostic evaluation of dysrhythmias and conduction abnormalities.

   • Identification of myocardial ischemia, injury, or infarction (ACS).

   • Monitoring effects of cardiac medications and electrolyte disturbances.

   • Continuous monitoring during sedation, surgery, emergency transport, or critical care.

8. Describe two types of single-lead monitoring.

   • Lead II: Bipolar lead (RA to LL) that follows the normal conduction axis; ideal for atrial wave (P wave) clarity and overall rhythm analysis.

   • Modified Chest Lead 1 (MCL1): Surrogate for chest lead V1; useful for differentiating bundle branch blocks and ectopic ventricular beats.

9. Describe proper electrode placement for the commonly used leads.

   • Limb Leads: RA (right arm/shoulder), LA (left arm/shoulder), RL (right leg/lower abdomen - ground), LL (left leg/lower abdomen).

   • Precordial Leads: V1 (4th ICS, right sternal border), V2 (4th ICS, left sternal border), V3 (halfway between V2 & V4), V4 (5th ICS, left midclavicular line), V5 (5th ICS, left anterior axillary line), V6 (5th ICS, left midaxillary line).

10. List actions to resolve three common cardiac monitoring problems.

    • Artifact / Motion: Clean skin, replace dried-out electrodes, and advise patient to remain still.

    • 60-Cycle AC Interference: Ensure equipment is properly grounded and move other active electrical equipment away from the monitor cable.

    • Wandering Baseline: Clean oily skin, shave excessive hair, and place electrodes over soft tissue/muscle rather than bony prominences

1. Depolarization & Repolarization

• Depolarization is the process of discharging resting cardiac muscle fibers by means of an electrical impulse that stimulates contraction.

• A polarized myocardial cell normally has a net internal charge of −90 mV−90mV.

• During depolarization, the permeability of the cell wall changes to allow sodium (Na+Na+) ions into the cell.

• Calcium (Ca2+Ca2+) ions also enter the cell and help maintain the depolarized state.

• Repolarization begins with the closing of the sodium and calcium channels.

• During repolarization, potassium channels open to allow potassium (K+K+) to leave the cell.

• The sodium-potassium pump helps maintain the polarity of the cell membrane.

2. Cardiac Action Potential

• The cardiac action potential is divided into 55 phases.

• Phase 00 represents cell depolarization and contraction.

• On the ECG, the QRS complex represents Phase 00.

• Phase 22 is also known as the plateau phase.

• The ST segment corresponds to Phase 22.

• The T wave represents Phase 33 of the cardiac action potential.

• Phase 44 is called the resting membrane potential phase.

3. Refractory Periods

• The period from Phase 00 to the middle of Phase 33 is called the absolute refractory period.

• The second half of Phase 33 to the beginning of Phase 44 is called the relative refractory period.

4. The Conduction System

• The dominant pacemaker of the heart is the sinoatrial (SA) node.

• The SA node is located at the junction of the superior vena cava and the right atrium.

• Electrical impulses are delayed in the AV node for about 0.10 seconds0.10seconds.

• The delay in the AV node allows the atria to empty blood into the ventricles.

• Impulses normally pass through the bundle of His into the right and left bundle branches.

• Any conduction system component can act as a pacemaker (latent/backup) if the SA node fails.

• The accessory pathway associated with Wolff-Parkinson-White syndrome is called the bundle of Kent.

5. Autonomic Nervous System & the Heart

• Sympathetic nerves release the neurotransmitter norepinephrine.

• Parasympathetic impulses travel through the vagus nerve.

• Acetylcholine causes the SA node to decrease the heart rate.

• Baroreceptors detect changes in blood pressure.

• Chemoreceptors detect changes in oxygen, carbon dioxide, and pHpH levels.

6. ECG Basics

• The three standard limb leads are Lead I, Lead II, and Lead III.

• The precordial leads are labeled V1 through V6.

• Leads aVR, aVL, and aVF are called augmented limb leads.

• ECG paper moves at a speed of 25 mm/s25mm/s.

• One small box on ECG paper equals 0.04 seconds0.04seconds.

• One large box on ECG paper equals 0.20 seconds0.20seconds.

• The vertical axis of ECG paper represents voltage (amplitude).

7. ECG Components

• The P wave represents atrial depolarization.

• A normal PR interval measures between 0.120.12 and 0.20 seconds0.20seconds.

• The QRS complex represents ventricular depolarization.

• A normal QRS duration is less than 0.12 seconds0.12seconds.

• The J point marks the end of the QRS complex and the beginning of the ST segment.

• The T wave represents ventricular repolarization.

• Tall, peaked T waves may indicate hyperkalemia.

• The QT interval represents all electrical activity of one completed ventricular (cardiac) cycle.

• The R-R interval can be used to calculate heart rate and determine rhythm regularity.

8. Dysrhythmia Interpretation

• The first step in dysrhythmia interpretation is identifying the P, QRS, and T waves.

• A regular rhythm has equal distances between R waves.

• The fastest method for calculating heart rate is the 66-second method.

• To use the 6-second method, count the number of QRS complexes in 6 seconds and multiply by 1010.

• The sequence method is reserved for regular rhythms.

• The 1,500 method is the most accurate method for calculating heart rate.

9. Specific Dysrhythmias

• Normal sinus rhythm has an intrinsic rate of 6060 to 100 beats/minute100beats/minute.

• Sinus bradycardia is defined as a heart rate less than 60 beats/minute60beats/minute.

• Sinus tachycardia is defined as a heart rate greater than 100 beats/minute100beats/minute.

• Atrial fibrillation is characterized by an irregularly irregular rhythm.

• Atrial flutter produces characteristic sawtooth (flutter) waves.

• Supraventricular tachycardia often has a rate between 150150 and 250 beats/minute250beats/minute.

• Junctional rhythms usually have a rate of 4040 to 60 beats/minute60beats/minute.

• Premature atrial complexes are also known as PACs.

• Multifocal atrial tachycardia is commonly associated with significant pulmonary disease.

• Wolff-Parkinson-White syndrome is characterized by a short PR interval and a delta wave.

10. Bonus Review

• Treat the patient, not the monitor.

• Transcutaneous pacing is abbreviated as TCP.

• Synchronized cardioversion is used to treat hemodynamically unstable tachycardias.

• Adenosine should be administered rapidly and followed with a 20 mL20mL saline flush.

• Vagal maneuvers stimulate parasympathetic (vagal) receptors.

1. Cardiovascular Introduction

1. CVD refers to a group of disorders of the heart and blood vessels.

2. Coronary heart disease (CHD) is a disease of the coronary arteries.

3. Acute Myocardial Infarction (AMI) occurs when sudden narrowing or complete blockage of a coronary artery causes myocardial tissue death.

4. In the United States, one person experiences an AMI about every $40\,\text{seconds}$.

5. Cardiac arrest is the cessation of cardiac mechanical activity.

6. Most out-of-hospital cardiac arrests occur in a home or residence.

2. Anatomy and Physiology Review

2.1 Cardiovascular System

1. The cardiovascular system is composed of the heart and blood vessels.

2. The primary function of the cardiovascular system is to deliver oxygenated blood and nutrients to the cells.

3. The cardiovascular system also delivers hormones and transports waste products.

2.2 Heart Chambers

1. The heart has 4 chambers:

   • Right atrium

   • Right ventricle

   • Left atrium

   • Left ventricle

2. The right atrium receives blood low in oxygen from the superior and inferior vena cava.

3. The left atrium receives oxygenated blood from the lungs through the pulmonary veins.

4. The right ventricle pumps deoxygenated blood to the lungs.

5. The left ventricle pumps oxygenated blood throughout the body.

6. The septum separates the right and left sides of the heart.

   • The interatrial septum separates the right and left atria.

   • The interventricular septum separates the right and left ventricles.

2.3 Functional Pumps of the Heart

1. The right heart is a low-pressure system responsible for pulmonary circulation.

2. The left heart is a high-pressure system responsible for systemic circulation.

2.4 Myocardium and Coronary Arteries

1. The myocardium is the middle layer of the heart wall, composed mostly of thick cardiac muscle tissue, and is responsible for cardiac contraction.

2. The left main coronary artery supplies:

   • Left anterior descending artery

   • Circumflex artery (supplies the anterior wall, apex, and lateral/posterior walls of the ventricle)

3. The right coronary artery supplies:

   • Right atrium

   • Right ventricle

   • Inferior wall of the left ventricle

   • Portions of the conduction system

2.5 Cardiac Cell Properties

Cardiac cells have four important properties:

1. Contractility

2. Automaticity

3. Excitability

4. Conductivity

2.6 Cardiac Conduction System

The cardiac conduction system consists of six parts:

1. SA node

2. AV node

3. Bundle of His

4. Right bundle branch

5. Left bundle branch

6. Purkinje fibers

2.7 Nerve Stimulation

1. Sympathetic stimulation strengthens the force of contractions and increases the heart rate.

2. Parasympathetic stimulation slows the discharge rate of the SA node and slows conduction through the AV node.

3. Patient Assessment

3.1 Primary Survey

1. The normal order of the primary survey is Airway, Breathing, Circulation (ABC).

2. If cardiac arrest is suspected, the order changes to Circulation, Airway, Breathing (CAB).

3.2 History Taking

1. Acute coronary syndromes (ACS) are caused by an abrupt reduction in blood flow through a coronary artery.

2. The three major ACS conditions are:

   • Unstable angina

   • Non-ST segment elevation myocardial infarction (NSTEMI)

   • ST-segment elevation myocardial infarction (STEMI)

3. Common chief complaints in ACS include:

   • Chest pain

   • Dyspnea

   • Diaphoresis

   • Discomfort radiating to arm, jaw, or neck

4. OPQRST stands for:

   • O = Onset

   • P = Provocation

   • Q = Quality

   • R = Region/radiation

   • S = Severity

   • T = Time

5. Dyspnea that is relieved by a change in position is called orthopnea.

6. Sudden nighttime difficulty breathing associated with left ventricular failure (LVF) is called paroxysmal nocturnal dyspnea.

7. Cardiac causes of syncope include dysrhythmias, myocardial infarction (MI), and cardiovascular disease (CVD).

8. Palpitations are sensations of abnormally fast or irregular heartbeats.

9. Fatigue is common in patients with impaired cardiac function.

10. Patients may also report:

    • Feelings of impending doom

    • Nausea or vomiting

    • Hypoxia or poor perfusion

3.3 Medications

Examples of common cardiac medications:

1. Antiarrhythmics: Lidocaine, Procainamide

2. Anticoagulants: Warfarin

3. ACE Inhibitors: Enalapril, Captopril

4. Beta-blockers: Atenolol

5. Diuretics: Furosemide

6. Vasodilators: Nitroglycerin

3.4 Medical History

Patients should be evaluated for a history of:

1. Hypertension

2. Myocardial infarction (MI)

3. Coronary artery disease (CAD)

4. Congestive heart failure (CHF)

5. Diabetes mellitus

6. Hyperlipidemia

7. Stroke

3.5 Secondary Assessment

1. Pale, mottled, or cyanotic skin may indicate poor tissue perfusion.

2. Flushed, warm skin may indicate fever.

3. Jugular venous pressure is assessed by observing the height of the distended fluid column in the jugular vein.

4. During chest inspection, look for:

   • Surgical scars

   • Transdermal nitroglycerin (NTG) patches

   • Pacemaker or implanted defibrillator

   • Chest enlargement

5. Crackles or wheezes may indicate left ventricular failure with pulmonary edema.

6. Bilateral pitting edema may indicate right ventricular failure.

7. One-sided pitting edema may suggest an occlusion in a major vein.

8. Common monitoring devices include:

   • $12$-lead ECG monitor

   • Pulse oximeter

   • Non-invasive blood pressure (NIBP) monitor

   • End-tidal $CO_2$ ($ETCO_2$) monitor

3.6 Pulse and Blood Pressure Findings

1. A pulse deficit is the difference between the apical pulse and the peripheral pulse.

2. Pulsus paradoxus occurs when systolic blood pressure falls more than $10\,\text{mmHg}$ during inspiration.

3. Pulsus alternans may indicate severe ventricular failure.

4. Normal systolic blood pressure (SBP) is less than $120\,\text{mmHg}$.

5. Normal diastolic blood pressure (DBP) is less than $80\,\text{mmHg}$.

6. Stage 2 hypertension is defined as:

   • SBP of $140\,\text{mmHg}$ or higher

   • DBP of $90\,\text{mmHg}$ or higher

7. An SBP lower than $90\,\text{mmHg}$ may indicate hypotension or shock.

8. Narrowed pulse pressure may be seen in hypovolemia, cardiogenic shock, and aortic stenosis.

3.7 Assessment of Heart Sounds

S1

1. S1 occurs when the tricuspid and mitral valves close.

2. Decreased S1 sounds may indicate:

   • Severe left ventricular dysfunction

   • Heart failure

   • Obesity

   • Emphysema

S2

1. S2 occurs when the pulmonic and aortic valves close.

2. S2 sounds may be louder in patients with chronic high blood pressure or pulmonary hypertension.

3. Decreased S2 sounds may indicate hypotension.

S3 and S4

1. S3 is commonly associated with ventricular failure.

2. S4 may be associated with ventricular hypertrophy and possible myocardial infarction.

3.8 Heart Murmurs

A murmur is caused by turbulent blood flow through the valves. Causes include:

1. Increased blood flow across a normal valve

2. Flow across an irregular or constricted valve

3. Blood flow into an enlarged heart chamber

4. Backward blood flow through a compromised valve

3.9 Reassessment

1. Reassessment should be performed on the way to the hospital.

2. Notify the receiving facility of:

   • Historical findings

   • Physical exam findings

   • Cardiac monitoring or $12$-lead ECG findings