EKG Interpretation: Overview and Practice Questions (2025)

An electrocardiogram records the electrical activity of the heart, providing crucial insights into heart rate, rhythm, and potential abnormalities.

Understanding how to read and analyze these waveforms is not only vital for diagnosing conditions such as arrhythmias, myocardial infarctions, and other heart disorders but also for making informed decisions about patient care.

This article will guide you through the fundamentals of EKG interpretation, helping to demystify the complexities of reading EKGs and enhance your clinical confidence.

What is an Electrocardiogram?

An electrocardiogram, or ECG (also known as EKG), is a non-invasive test that records the electrical activity of the heart over a period of time. It provides important information about the heart’s rhythm and function by measuring electrical signals as they travel through the heart.

These electrical signals are responsible for making the heart muscle contract and pump blood. The test is performed using electrodes that are placed on the skin of the chest, arms, and legs. The recorded data is then displayed as a series of waveforms, which represent various phases of the heart’s activity, such as the atrial and ventricular contractions.

An EKG is often used to diagnose various heart conditions, including arrhythmias, heart attacks, and other cardiac abnormalities. It can help healthcare providers evaluate symptoms such as chest pain, dizziness, or shortness of breath. It is also used in routine physical examinations to monitor heart health.

Electrophysiology of the Heart

The electrophysiology of the heart refers to the electrical processes that enable the heart to function as a coordinated pump, maintaining blood circulation throughout the body. This electrical activity starts in specialized cardiac cells that generate and conduct electrical impulses, leading to the rhythmic contraction and relaxation of the heart muscle.

The process begins in the sinoatrial (SA) node, located in the right atrium. Known as the natural pacemaker of the heart, the SA node initiates electrical impulses that spread through the atria, causing them to contract and push blood into the ventricles. These impulses then reach the atrioventricular (AV) node, where there is a slight delay to ensure the ventricles have time to fill with blood.

From the AV node, the electrical signal travels down the bundle of His, which splits into the right and left bundle branches, and continues along the Purkinje fibers that spread throughout the ventricles. This pathway ensures that the ventricles contract in a coordinated manner, propelling blood into the lungs and systemic circulation.

This electrical activity is what is recorded in an electrocardiogram, which captures the waveforms associated with the depolarization and repolarization of the cardiac muscle cells. Depolarization refers to the process that leads to muscle contraction, while repolarization is the process that returns the cells to their resting state, ready for the next impulse.

The heart’s ability to generate and conduct electrical impulses autonomously is known as automaticity, while the orderly sequence of electrical conduction ensures synchronized contractions, known as rhythmicity. Any disruptions in this process can lead to arrhythmias or other cardiac dysfunctions, emphasizing the importance of understanding cardiac electrophysiology in clinical practice.

Components of an Electrocardiogram

An electrocardiogram (EKG/ECG) is composed of two primary components: leads and electrodes. Each plays a crucial role in capturing and displaying the electrical activity of the heart for analysis.

1. Electrodes

Electrodes are sensors that are usually positioned on specific areas of the chest and limbs to provide a comprehensive view of the heart’s electrical activity.

To obtain an accurate reading during an EKG, six standard electrodes must be placed on the patient’s skin in specific locations:

• V1: 4th intercostal space on the right side of the sternum
• V2: 4th intercostal space on the left side of the sternum
• V3: Midway between V2 and V4 on the left side
• V4: 5th intercostal space at the left mid-clavicular line
• V5: Positioned between V4 and V6 on the left side
• V6: 5th intercostal space at the mid-axillary line

Each electrode has an adhesive backing that ensures proper contact with the skin and is connected to the EKG machine. These electrodes capture the electrical signals generated by the heart, allowing the machine to produce a detailed graph of the heart’s electrical activity.

This graph is then analyzed by doctors and medical professionals to assess heart health, detect abnormalities, and guide treatment decisions.

2. Leads

Leads are the visual representations of the heart’s electrical activity as recorded by the electrodes. Each lead provides a different angle or “view” of the heart’s electrical signals, allowing for a thorough analysis of its rhythm and function.

The standard 12-lead EKG setup includes:

• Limb Leads: Leads I, II, and III form a triangle (Einthoven’s triangle) and provide views from the frontal plane of the heart.
• Augmented Leads: aVR, aVL, and aVF are unipolar limb leads that also contribute to a frontal plane perspective.
• Precordial Leads: V1 through V6 are positioned across the chest and provide views of the heart from the horizontal plane, offering detailed insight into the anterior, lateral, and posterior aspects of the heart.

Each lead captures electrical activity at a specific angle, highlighting different aspects of the heart’s function. This multi-angle approach is essential for detecting arrhythmias, ischemia, infarction, and other cardiac conditions.

Together, electrodes collect the electrical signals, and leads present those signals as waveforms that healthcare providers can interpret to assess heart health.

EKG Interpretation

EKG interpretation is the systematic analysis of an EKG reading to evaluate the electrical activity of the heart and determine any potential abnormalities. This process requires a step-by-step approach to ensure each aspect of the heart’s electrical pattern is assessed accurately.

Here is an expanded guide to interpreting an EKG:

Step 1: Measure the Atrial and Ventricular Rates

To measure the atrial rate, count the number of P waves (representing atrial depolarization) in one minute. For the ventricular rate, count the number of QRS complexes (representing ventricular depolarization) in one minute.

This step helps establish if the heart rate is within a normal range (60-100 bpm) or if tachycardia or bradycardia is present.

Step 2: Measure the PR Interval

The PR interval represents the time taken for an electrical impulse to travel from the sinoatrial (SA) node to the atrioventricular (AV) node.

It is measured from the beginning of the P wave to the start of the QRS complex and typically lasts between 0.12 to 0.20 seconds (3-5 small boxes on the EKG). A prolonged or shortened PR interval may indicate conduction delays or pre-excitation syndromes.

Step 3: Assess the QRS Complex

The QRS complex reflects the rapid depolarization of the ventricles. Normally, it should be narrow, lasting less than 0.12 seconds (three small boxes).

A prolonged QRS duration suggests abnormalities such as bundle branch blocks or ventricular hypertrophy, which can impede proper conduction through the heart’s electrical pathways.

Step 4: Assess the T Wave

The T wave represents ventricular repolarization. It should be upright (in most leads) and asymmetrical, with a gentle upstroke and a steeper downstroke. Flat, peaked, or inverted T waves can indicate underlying issues such as myocardial ischemia, hyperkalemia, or pericarditis.

Step 5: Assess the ST Segment

The ST segment is the flat section between the end of the QRS complex and the start of the T wave, representing the time between ventricular depolarization and repolarization. It should be level with the baseline.

ST segment elevation or depression may signify acute myocardial infarction, ischemia, or other conditions affecting myocardial perfusion and oxygen delivery.

Step 6: Assess the R-R Interval

The R-R interval measures the time between successive R waves of the QRS complexes, which indicates the regularity of the heartbeat. This interval should be consistent for a regular rhythm.

If the interval exceeds 0.12 seconds or varies significantly, it may indicate an irregular rhythm or a potential heart block, where electrical conduction through the heart is impaired.

Step 7: Assess the Mean QRS Axis

The mean QRS axis refers to the overall direction of electrical activity during ventricular depolarization and is determined by evaluating limb leads. A normal axis falls between 0 and +90 degrees.

Right-axis deviation (greater than +90 degrees) may be seen in conditions such as COPD or right ventricular hypertrophy, while left-axis deviation (between -30 and -90 degrees) can indicate left ventricular hypertrophy or conduction defects like left anterior fascicular block.

Additional Considerations

• P Wave Morphology: Analyze the P wave shape and duration for atrial abnormalities, such as atrial enlargement.
• QT Interval: Measure the QT interval to ensure it is not prolonged, which could predispose the patient to ventricular arrhythmias.

EKG interpretation is an essential diagnostic skill that requires methodical analysis of various components, including the atrial and ventricular rates, PR interval, QRS complex, T wave, ST segment, R-R interval, and mean QRS axis.

By mastering these steps, healthcare providers can identify normal heart function and detect a range of cardiac conditions, from arrhythmias to structural heart disease.

Continuous practice and experience are crucial for enhancing proficiency in EKG interpretation, ultimately leading to better patient outcomes and improved clinical decision-making.

What is Normal Sinus Rhythm?

Normal sinus rhythm is the standard heart rhythm that indicates a healthy heart. It is characterized by a consistent rate between 60 and 100 beats per minute at rest.

Each cardiac cycle has a clear and distinct P wave (indicating atrial depolarization) preceding each QRS complex (representing ventricular depolarization), followed by a T wave (indicating ventricular repolarization). The intervals between these components are regular and within normal limits, such as a PR interval of 0.12 to 0.20 seconds and a QRS duration of less than 0.12 seconds.

Normal sinus rhythm reflects an efficient and coordinated cardiac function, ensuring optimal blood flow throughout the body. Maintaining a normal sinus rhythm is crucial for cardiovascular health, as deviations can indicate arrhythmias or underlying cardiac conditions that may require further evaluation and management.

Types of Arrhythmias

Arrhythmias are irregularities in the heart’s rhythm that can range from harmless to life-threatening. They are typically classified based on the speed, origin, and type of abnormal electrical conduction.

Here are the primary types of arrhythmias:

• Sinus tachycardia
• Sinus bradycardia
• Sinus arrhythmia
• First-degree heart block
• Second-degree heart block
• Third-degree heart block
• Atrial flutter
• Atrial fibrillation
• Ventricular tachycardia
• Ventricular fibrillation
• Asystole

Review this chart and keep reading to learn more about the most common types of arrhythmias that are seen during EKG interpretation.

Sinus Tachycardia

Sinus tachycardia is a type of arrhythmia characterized by an increased heart rate that originates from the sinoatrial (SA) node, which is the natural pacemaker of the heart. In sinus tachycardia, the heart rate exceeds 100 beats per minute but follows a regular rhythm.

This condition can be a normal physiological response to factors such as exercise, stress, anxiety, fever, or dehydration, as it reflects the body’s attempt to increase blood flow to meet higher oxygen and nutrient demands.

However, persistent or inappropriate sinus tachycardia, not related to physical exertion or obvious triggers, may indicate underlying medical issues such as hyperthyroidism, anemia, or cardiac conditions that require further evaluation.

Sinus Bradycardia

Sinus bradycardia is an arrhythmia where the heart rate is slower than normal, typically below 60 beats per minute. This rhythm still originates from the sinoatrial (SA) node and follows a regular pattern, which means the heart’s electrical system is functioning in sequence but at a reduced pace.

Sinus bradycardia can be a normal finding in well-conditioned athletes or during sleep, as their hearts are more efficient at pumping blood.

However, when sinus bradycardia occurs without a clear reason and is accompanied by symptoms such as dizziness, fatigue, or fainting, it could indicate issues like SA node dysfunction, hypothyroidism, or side effects of certain medications. In symptomatic cases, treatment or further evaluation may be necessary to prevent complications.

Sinus Arrhythmia

Sinus arrhythmia occurs when there is irregular spacing between QRS complexes, characterized by R-R intervals that vary by more than 0.12 seconds. This variation is often associated with the breathing cycle, where the heart rate increases during inhalation and decreases during exhalation.

While sinus arrhythmia is most commonly seen in children and young adults and is generally considered a normal finding, it can also occur as a side effect of medications, such as digoxin.

Typically, sinus arrhythmia does not require treatment, as it does not pose a significant risk to heart health. However, if observed in older adults or alongside other cardiac conditions, it may warrant further investigation.

First-Degree Heart Block

First-degree heart block is a type of arrhythmia where there is a delay in the electrical conduction between the atria and the ventricles. This delay is reflected on an EKG as a prolonged PR interval, typically greater than 0.20 seconds.

Although the electrical signal from the sinoatrial (SA) node still reaches the ventricles, it takes longer than usual, causing a delay but not a complete block. First-degree heart block is often asymptomatic and may be found incidentally during routine examinations. It can occur due to high vagal tone, electrolyte imbalances, or as a side effect of certain medications such as beta-blockers or calcium channel blockers.

Generally, first-degree heart block is considered benign and does not require treatment, but regular monitoring may be recommended to ensure it does not progress to more severe forms of heart block.

Second-Degree Heart Block

Second-degree heart block is an arrhythmia where some of the electrical impulses from the atria fail to reach the ventricles, resulting in intermittent missed beats. This type of heart block is further classified into two subtypes: Type I (Mobitz I or Wenckebach) and Type II (Mobitz II).

• Type I (Mobitz I or Wenckebach): This subtype is characterized by a progressive lengthening of the PR interval until a beat is dropped (i.e., a QRS complex is skipped). This pattern often indicates a temporary and typically benign condition, often associated with high vagal tone or certain medications. Patients may not experience symptoms, but in some cases, they may feel lightheaded or fatigued.
• Type II (Mobitz II): In this subtype, the PR interval remains consistent, but occasional beats are not conducted to the ventricles, resulting in dropped QRS complexes. Mobitz II is more serious than Type I and suggests an issue in the conduction system below the AV node, such as in the bundle of His or bundle branches. It is more likely to cause symptoms like dizziness, fatigue, or syncope and may require a pacemaker for treatment due to its potential to progress to third-degree heart block.

Note: Second-degree heart block requires thorough evaluation to determine the subtype and appropriate management, especially if symptomatic.

Third-Degree Heart Block

Third-degree heart block, also known as complete heart block, is a severe type of arrhythmia where there is a complete absence of electrical conduction between the atria and the ventricles. This means that the atria and ventricles beat independently of each other.

The atria continue to follow the rhythm set by the sinoatrial (SA) node, while the ventricles rely on a secondary pacemaker, such as the atrioventricular (AV) node or the bundle of His, to generate impulses. However, this backup pacing is typically slower and less reliable.

Patients with third-degree heart block often experience significant symptoms such as extreme fatigue, dizziness, syncope (fainting), and shortness of breath due to the reduced efficiency of the heart’s ability to pump blood.

This condition can be life-threatening and requires immediate medical attention. Treatment usually involves the implantation of a pacemaker to restore proper coordination between the atria and ventricles and ensure adequate heart rate and cardiac output.

Atrial Flutter

Atrial flutter is an arrhythmia characterized by a rapid and regular electrical impulse originating in the atria, resulting in a fast heart rate. Unlike atrial fibrillation, where the atrial activity is chaotic and irregular, atrial flutter involves a more organized and repetitive circuit within the atria, typically producing a “sawtooth” pattern on an EKG.

The atrial rate in atrial flutter can range from 240 to 350 beats per minute, with the ventricles responding at a slower, controlled rate depending on the degree of conduction through the AV node (e.g., 2:1 or 3:1 conduction).

Common symptoms of atrial flutter include palpitations, shortness of breath, dizziness, and fatigue. It may occur intermittently (paroxysmal) or persistently and is often associated with conditions such as heart disease, hypertension, or chronic lung disease. Although atrial flutter is less common than atrial fibrillation, it poses similar risks, including an increased likelihood of stroke due to potential blood clot formation in the atria.

Management of atrial flutter typically involves rate control with medications, rhythm conversion using electrical cardioversion, and long-term prevention with antiarrhythmic drugs or catheter ablation. Anticoagulation therapy may also be recommended to reduce the risk of thromboembolic events.

Atrial Fibrillation

Atrial fibrillation (AFib) is an arrhythmia characterized by rapid, irregular electrical impulses in the atria, leading to an uncoordinated and often chaotic heart rhythm. This results in the atria quivering rather than contracting effectively, causing an inconsistent and often rapid ventricular response. On an EKG, AFib is recognized by the absence of distinct P waves and an irregular R-R interval.

AFib can be classified as paroxysmal (occurring sporadically and self-terminating), persistent (lasting more than seven days and requiring intervention to terminate), or permanent (where normal rhythm cannot be restored or maintained). Symptoms may include palpitations, shortness of breath, fatigue, dizziness, and, in some cases, chest pain. However, some individuals with AFib may be asymptomatic.

A major concern with AFib is the increased risk of stroke, as the irregular atrial contractions can lead to blood pooling and clot formation. If a clot dislodges, it can travel to the brain and cause a stroke.

Management of AFib focuses on rate and rhythm control and stroke prevention. This may involve medications such as beta-blockers, calcium channel blockers, or antiarrhythmic drugs. Cardioversion (either electrical or pharmacological) is sometimes used to restore normal rhythm. In cases where AFib is persistent or recurrent, catheter ablation may be considered. Anticoagulation therapy, such as warfarin or direct oral anticoagulants (DOACs), is often prescribed to reduce the risk of thromboembolic complications.

Ventricular Tachycardia

Ventricular tachycardia (V-tach) is a serious arrhythmia originating from the ventricles, characterized by a rapid heart rate, typically over 100 beats per minute. V-tach occurs when abnormal electrical signals in the ventricles cause them to contract rapidly and out of sync with the atria. On an EKG, V-tach is identified by wide, regular QRS complexes occurring at a fast rate.

V-tach can be sustained (lasting more than 30 seconds) or non-sustained (lasting less than 30 seconds). Sustained V-tach is particularly dangerous as it can progress to ventricular fibrillation, a life-threatening condition that requires immediate intervention. Symptoms of V-tach may include palpitations, dizziness, chest pain, shortness of breath, and, in severe cases, syncope or sudden cardiac arrest.

V-tach often occurs in individuals with underlying heart conditions, such as ischemic heart disease, cardiomyopathy, or after a heart attack. Other contributing factors can include electrolyte imbalances, congenital heart defects, or the use of certain medications.

Management of V-tach depends on the severity and underlying cause. Acute episodes may require immediate intervention with antiarrhythmic medications or electrical cardioversion. For long-term treatment, options may include implantable cardioverter-defibrillators (ICDs), catheter ablation, or medication to prevent recurrence. Addressing the underlying condition and risk factors is also critical to managing V-tach effectively.

Ventricular Fibrillation

Ventricular fibrillation (VFib) is a life-threatening arrhythmia characterized by rapid, chaotic electrical activity in the ventricles, causing them to quiver rather than contract effectively. This results in the heart being unable to pump blood, leading to a dramatic drop in blood pressure and the cessation of blood flow to vital organs. On an EKG, VFib is seen as an irregular, disorganized pattern without identifiable QRS complexes, P waves, or T waves.

VFib is the most common cause of sudden cardiac arrest and requires immediate medical intervention. Without prompt treatment, VFib can lead to death within minutes. The most effective treatment for VFib is defibrillation, which delivers an electric shock to the heart to reset its electrical activity and restore a normal rhythm. Cardiopulmonary resuscitation (CPR) is also essential to maintain blood circulation until defibrillation can be performed.

Common causes of VFib include underlying heart conditions such as coronary artery disease, a prior heart attack, cardiomyopathy, or electrolyte imbalances. It can also be triggered by severe electrical shock, drowning, or trauma to the heart.

Management after survival of VFib may involve addressing underlying conditions, lifestyle modifications, and the use of an implantable cardioverter-defibrillator (ICD) to monitor and automatically correct abnormal rhythms in the future. Medications such as antiarrhythmic drugs may also be prescribed as part of long-term treatment to prevent recurrence.

Asystole

Asystole, often referred to as “flatline,” is a condition where there is a complete absence of electrical activity in the heart, resulting in no contractions and no blood flow. It is characterized by a flat or nearly flat line on an EKG, with no detectable P waves, QRS complexes, or T waves. Asystole is one of the most severe forms of cardiac arrest and indicates that the heart has ceased to function as a pump.

Asystole can result from severe underlying conditions, such as extensive myocardial damage, prolonged hypoxia, or advanced heart disease. It can also occur due to significant electrolyte imbalances, drug overdose, or severe trauma. Unlike certain arrhythmias like ventricular fibrillation, asystole is not shockable, meaning defibrillation is not effective in restoring cardiac activity.

Management of asystole involves immediate and aggressive resuscitative efforts, including high-quality cardiopulmonary resuscitation (CPR) and administration of epinephrine. Identifying and treating reversible causes using the “H’s and T’s” mnemonic (e.g., hypoxia, hypothermia, toxins, or thrombosis) is essential to improve the chance of restoring a heartbeat. The prognosis for asystole is generally poor unless reversible causes are rapidly identified and corrected.

What are Premature Ventricular Contractions?

Premature ventricular contractions (PVCs) are a type of arrhythmia characterized by early heartbeats originating from the ventricles rather than the sinoatrial (SA) node. These premature beats disrupt the normal rhythm of the heart and are often felt as a skipped or extra beat, followed by a stronger-than-normal heartbeat as the heart resets itself. On an EKG, PVCs are seen as wide and atypical QRS complexes occurring earlier than the next expected normal beat.

PVCs can occur in healthy individuals without underlying heart disease and may be triggered by factors such as stress, caffeine, nicotine, alcohol, or certain medications. However, frequent or persistent PVCs can be a sign of an underlying heart condition, such as cardiomyopathy, coronary artery disease, or electrolyte imbalances.

While occasional PVCs are often benign and do not require treatment, they can cause palpitations or discomfort. If PVCs are frequent or symptomatic, further evaluation may be needed to assess for structural heart disease or other contributing factors. Management may include lifestyle changes, addressing triggers, or using medications such as beta-blockers or antiarrhythmic drugs in more severe cases.

EKG Interpretation Practice Questions

1. A P-R interval of 0.32 seconds is an indication of what?
It indicates a disturbance in the heart’s conduction system, often suggestive of first-degree heart block.

2. What type of monitor is worn for 24 hours to evaluate the heart’s performance during normal activities?
Holter monitor

3. A patient shows symptoms of a heart attack, and the physician suspects left ventricular involvement. Which EKG leads should you assess?
Leads I, aVL, V5, and V6.

4. What do depressed T waves on an EKG tracing represent?
Myocardial ischemia

5. What causes elevated ST segments on an EKG tracing?
Myocardial infarction and certain cardiac medications.

6. Every small square on the horizontal axis of the EKG grid paper represents how much time?
0.04 seconds

7. How many electrophysiological phases are there in an action potential?
Five phases

8. Where does the electrical impulse of the heart originate in a normal conduction system?
The SA node (sinoatrial node)

9. In which phase of repolarization is there a slow influx of calcium?
Phase 2

10. Stimulation of the parasympathetic system causes what?
A decrease in heart rate and decreased conduction velocity.

11. What does the P wave on an EKG tracing represent?
Atrial depolarization

12. What does the T wave on an EKG tracing represent?
Ventricular repolarization

13. What is excitability?
The ability of cardiac cells to reach their threshold potential and respond to a stimulus.

14. What is the normal P-R interval?
Between 0.12 and 0.20 seconds.

15. What part of the autonomic nervous system can cause an increase in heart rate?
The sympathetic nervous system.

16. How many times can EKG electrodes be used?
Most types are disposable and should only be used once.

17. Two or more waveforms represent what?
A complex

18. What does the term repolarization mean?
The process by which cardiac cells return to their resting membrane potential.

19. What lead is commonly viewed during continuous cardiac monitoring?
Lead II

20. Which electrolytes are primarily involved in the cardiac cycle?
Sodium, calcium, and potassium.

21. Can a 12-lead EKG be used to determine cardiac output?
No, a 12-lead EKG cannot measure cardiac output.

22. What is measured vertically on EKG grid paper?
Voltage

23. What is the duration represented by each large square on EKG paper?
0.20 seconds

24. In which phase can a strong stimulus depolarize cardiac cells?
The relative refractory period.

25. Which leads are considered bipolar leads?
Leads I, II, and III

26. Which leads provide information about the lower surface of the heart?
Leads II, III, and aVF

27. What happens when the cardiac cells are in the resting or polarized state?
In this state, the inside of the cell is negatively charged with potassium (K+), while the outside is positively charged with sodium (Na+).

28. When do U waves become present during an EKG complex?
U waves become visible in cases of electrolyte imbalances or heart disease.

29. Which electrodes use the center of the heart as the negative reference point?
Electrodes V1, V3, and V6

30. What is the normal duration for a QRS complex?
0.08–0.12 seconds

31. What leads would be required during continuous EKG monitoring?
Leads I, II, III, and V2

32. What are some benefits of an EKG test?
It is inexpensive, noninvasive, and easy to perform.

33. Why would an EKG test be ordered for a patient?
To investigate symptoms such as chest pain, shortness of breath, dyspnea, weakness, lethargy, or dizziness.

34. What does an EKG measure?
It measures the electrical activity, including repolarization and depolarization, of the heart.

35. What does an EKG not measure?
It does not measure the force of the heart’s contraction.

36. What is the normal pacemaker of the heart?
The SA (sinoatrial) node

37. What is a segment?
A portion of the EKG baseline.

38. What is an interval?
An interval includes at least one wave and the segment that follows.

39. How do you calculate the heart rate on an EKG?
Count the number of large boxes between two R waves and divide 300 by that number.

40. How many seconds does each small square on an EKG represent?
0.04 seconds

41. How many seconds does each large square on an EKG represent?
0.2 seconds

42. What is the rate of the SA node?
60–100 beats per minute

43. What is the rate of the AV node?
40–60 beats per minute

44. What is the rate of the Purkinje fibers?
20–40 beats per minute.

45. What two nerve fibers in the right atrium can alter the heart rate when stimulated?
Sympathetic and parasympathetic nerve fibers.

46. What does the P wave represent?
Atrial depolarization (contraction)

47. What does the QRS complex represent?
Ventricular depolarization and atrial repolarization.

48. What does the T wave represent?
Ventricular repolarization

49. What does the Q wave represent?
The conduction of an impulse down the interventricular septum.

50. What does the U wave represent?
Repolarization of the bundle of His and Purkinje fibers.

51. What is the PR interval?
It is the distance from the beginning of the P wave to the beginning of the QRS complex.

52. What does it mean if the PR interval is prolonged?
It indicates a 1st-degree atrioventricular (AV) block.

53. Which rhythm is commonly associated with acute hypoxemia?
Sinus tachycardia

54. What happens to the P waves and QRS complexes during a third-degree heart block?
There is no association between the P waves and QRS complexes in a third-degree heart block.

55. What is implied by an abnormally long PR interval?
An atrioventricular block

56. Why is there a temporary delay of the electrical impulse at the atrioventricular (AV) node?
To allow the ventricles sufficient time to fill with blood before contraction.

57. What medication is typically used to treat sinus bradycardia?
Atropine

58. What term describes the ability of certain cardiac cells to depolarize without external stimulation?
Automaticity

59. Which EKG abnormality is considered life-threatening?
An elevated ST segment

60. An EKG rhythm strip shows a sawtooth pattern at a rate of 270 beats per minute. What is the likely interpretation?
Atrial flutter

61. What do inverted T waves on an EKG suggest?
Myocardial ischemia

62. What structure normally sets the pace for a healthy heart?
The sinoatrial (SA) node

63. Is atrial flutter considered a life-threatening arrhythmia?
No, it is not typically life-threatening.

64. Is a narrow QRS complex a common characteristic of a premature ventricular complex (PVC)?
No, PVCs usually have a wide QRS complex.

65. Is pericarditis a common cause of ventricular tachycardia?
No, pericarditis is not commonly associated with ventricular tachycardia.

66. In which part of the cardiac conduction system does the electrical impulse travel the fastest?
The Purkinje fibers

67. What medication is most effective for treating premature ventricular contractions (PVCs)?
Lidocaine

68. An EKG showing one P wave for every QRS complex with a PR interval of 0.30 seconds is indicative of what?
First-degree heart block

69. Which wave represents the depolarization of the ventricles?
The QRS complex

70. What is the normal width of a QRS complex?
Not wider than 3 small squares (0.12 seconds).

71. Which waves represent the repolarization of the ventricles?
T waves

72. For what arrhythmia is an electronic pacemaker indicated?
Third-degree heart block

73. What is the normal maximum duration of a P wave?
3 small squares (0.12 seconds).

74. What is an electrocardiogram primarily used for?
To assess a patient with symptoms suggestive of acute myocardial conditions.

75. What is a potential serious complication associated with atrial fibrillation?
Atrial thrombi (blood clots).

76. What is the normal duration for the PR interval?
It should not be longer than 0.20 seconds.

77. What structure acts as the heart’s backup pacemaker?
The atrioventricular (AV) node

78. How is voltage represented on EKG paper?
It is measured on the vertical axis.

79. Is an occasional premature ventricular contraction (PVC) a cause for major concern?
No, an occasional PVC is typically not a major concern.

80. What condition is commonly associated with right-axis deviation?
Cor pulmonale

81. What type of medications can lead to a first-degree heart block?
Beta-blockers

82. What is atrial fibrillation?
An arrhythmia characterized by quivering atrial muscle in an erratic pattern, preventing coordinated contraction. True P waves are absent, and the R-R interval may be irregular.

83. What is atrial flutter?
An arrhythmia marked by rapid atrial depolarization due to an ectopic focus, depolarizing at 250-350 beats per minute. The P waves are similar and create a sawtooth pattern. There are often multiple P waves for each QRS complex, with the R-R interval either regular or irregular.

84. What is a first-degree heart block?
An arrhythmia where the PR interval is longer than 0.20 seconds. Each P wave precedes a QRS complex, which typically has a normal configuration. The R-R interval is regular. This condition is common after an AV node injury from a heart attack or due to medications like digoxin or beta blockers.

85. What is a premature ventricular contraction (PVC)?
An irregular rhythm characterized by a unique, wide, and bizarre QRS complex.

86. What is the PR interval?
The time from the start of atrial depolarization to the start of ventricular depolarization.

87. What does the P wave indicate?
It shows the wave of atrial depolarization.

88. What does the QRS complex represent?
It represents the wave of depolarization spreading over the ventricles.

89. What is sinus arrhythmia?
An arrhythmia where the spacing between QRS complexes is irregular, with an R-R interval that varies by more than 0.12 seconds. It may result from the influence of breathing on the heart or medications like digoxin.

90. What is sinus bradycardia?
An arrhythmia where the heart rate is below 60 beats per minute, but the EKG tracing otherwise appears normal.

91. What is sinus tachycardia?
An arrhythmia where the heart rate exceeds 100 beats per minute, but the EKG tracing otherwise appears normal.

92. What are the steps to interpreting an EKG?
(1) Identify the atrial rate, (2) Measure the PR interval, (3) Assess the QRS complex, (4) Evaluate the T wave, (5) Check the ST segment, (6) Identify the R-R interval, and (7) Determine the mean QRS axis.

93. What is the ST segment?
The period between the end of ventricular depolarization and the beginning of repolarization.

94. Which type of heart block is considered the most severe?
Third-degree heart block.

95. What does the T wave represent?
The repolarization of the ventricles.

96. When is an elevated or depressed ST segment typically seen?
During a myocardial infarction, and it should be treated as a potentially life-threatening arrhythmia.

97. Who is responsible for interpreting an EKG?
A physician

98. When is sinus bradycardia considered a clinical problem?
When it leads to a significant drop in blood pressure or causes symptoms.

99. What are the adhesive disks used during an EKG?
Electrodes

100. Why is it important for respiratory therapists to understand EKGs?
To quickly recognize and respond appropriately to serious arrhythmias.

Final Thoughts

Mastering EKG interpretation is a valuable skill that requires attention to detail and a deep understanding of the heart’s electrical patterns.

By familiarizing yourself with the normal and abnormal waveforms, as well as the common findings seen in various cardiac conditions, healthcare providers can improve their diagnostic accuracy and patient outcomes.

As with any medical skill, practice and continued learning are essential for proficiency. Whether you are a student, a respiratory therapist, or a seasoned clinician, refining your EKG interpretation skills will contribute to more efficient and effective care.