ECG Flashcards
Describe the basic components of an ECG and their significance in assessing cardiac function.
An electrocardiogram (ECG) records the electrical activity of the heart over time, represented by a series of waves and intervals:
- P wave: This represents atrial depolarization. The P wave shows the electrical activity associated with the contraction of the atria. It is typically upright and rounded. Abnormalities in the P wave can indicate atrial enlargement or atrial arrhythmias.
- QRS complex: This represents ventricular depolarization, where the ventricles contract. A normal QRS complex lasts around 0.06-0.10 seconds. Widened QRS complexes indicate abnormal ventricular conduction, such as bundle branch blocks or ventricular ectopy.
- T wave: This represents ventricular repolarization, where the ventricles recover after contraction. Abnormal T waves (e.g., inverted or peaked) can indicate ischemia or electrolyte imbalances, especially hyperkalemia.
- PR interval: This measures the time taken for the electrical impulse to travel from the atria to the ventricles via the AV node (normally 0.12-0.20 seconds). A prolonged PR interval suggests first-degree heart block, while a shortened PR interval is seen in conditions like Wolff-Parkinson-White syndrome.
- ST segment: This is the flat section between the end of the QRS complex and the beginning of the T wave. Elevation or depression of the ST segment is crucial in diagnosing myocardial ischemia or infarction. ST elevation is seen in acute myocardial infarction (STEMI), while ST depression may indicate ischemia or digoxin toxicity.
- QT interval: It represents the total time taken for both depolarization and repolarization of the ventricles. A prolonged QT interval is a risk factor for arrhythmias like torsades de pointes.
Understanding these basic components helps in identifying a wide range of cardiac abnormalities, from arrhythmias to ischemic heart disease
. Explain the pathophysiological basis of arrhythmias and how they are detected on an ECG.
Arrhythmias are disturbances in the heart’s electrical activity and can be broadly categorized as tachyarrhythmias or bradyarrhythmias. The pathophysiology often involves:
- Abnormal automaticity: Pacemaker cells (e.g., in the SA node) may generate impulses too quickly (e.g., in sinus tachycardia) or too slowly (e.g., in sinus bradycardia). This is often influenced by autonomic nervous system imbalances, ischemia, or electrolyte disturbances.
- Re-entry circuits: These occur when an electrical impulse continues to propagate around a circular pathway, such as in atrial flutter, where a “reentrant” circuit causes rapid atrial depolarizations. Ventricular tachycardia (VT) is another example, where abnormal re-entry in the ventricles leads to rapid contractions.
- Triggered activity: Early after-depolarizations or delayed after-depolarizations (often due to electrolyte imbalances or drug toxicity) lead to spontaneous, extra beats, seen as ectopic beats or premature ventricular complexes (PVCs).
- Conduction blocks: These occur when the normal electrical pathway is interrupted. For instance, AV blocks (e.g., first, second, or third-degree) slow or completely block conduction from atria to ventricles, detectable by prolonged PR intervals or dropped QRS complexes on the ECG.
- ECG detection of arrhythmias: Different arrhythmias present distinct patterns:
- Atrial fibrillation (AF): Characterized by an irregularly irregular rhythm and absence of distinct P waves.
- Ventricular tachycardia (VT): Shows wide QRS complexes (>0.12s) at a rate >100 bpm.
- Supraventricular tachycardia (SVT): Narrow QRS complexes with rapid heart rates (>150 bpm) and usually absent or hidden P waves.
Arrhythmias range from benign to life-threatening, with the ECG providing critical diagnostic information
*Discuss the ECG changes seen in myocardial ischemia and infarction.**
Myocardial ischemia and infarction cause distinct changes on the ECG, and these changes evolve over time:
- Ischemia:
- ST depression and/or T wave inversion indicate subendocardial ischemia (the inner layer of the heart wall). ST depression is seen in conditions like unstable angina or non-ST elevation myocardial infarction (NSTEMI).
- Acute infarction (STEMI):
- ST elevation: In a full-thickness myocardial infarction (STEMI), there is ST segment elevation in leads that correspond to the infarcted area. For example, ST elevation in leads II, III, and aVF suggests an inferior wall infarction.
- Q waves: Pathological Q waves develop as a marker of myocardial necrosis. These waves are wide and deep and suggest an old or completed infarct. For example, significant Q waves in leads V1-V3 can indicate a prior anterior wall infarction.
- T wave inversions: These are often seen after the acute phase of infarction and indicate ongoing ischemia or previous injury.
Recognizing these patterns is critical for the prompt diagnosis and treatment of myocardial ischemia and infarction
Explain the role of the ECG in diagnosing electrolyte disturbances such as hyperkalemia and hypokalemia.
Electrolyte imbalances significantly alter cardiac electrical activity, and the ECG can be a valuable tool for diagnosis:
- Hyperkalemia:
- Peaked T waves are the earliest sign of hyperkalemia. As potassium levels rise, the T waves become tall and narrow.
- Widened QRS complexes develop as hyperkalemia worsens, potentially leading to a sine-wave pattern and eventual cardiac arrest if untreated.
- Flattening or absence of P waves may also occur in severe cases.
- Hypokalemia:
- Flattened or inverted T waves and the presence of U waves are characteristic findings in hypokalemia.
- Prolonged QT interval: This can predispose to torsades de pointes, a life-threatening ventricular arrhythmia.
Both hyperkalemia and hypokalemia require prompt recognition and correction to prevent serious cardiac complications
Describe the ECG findings in various types of heart blocks.**
Heart blocks represent delays or complete interruptions in the conduction system, and different types can be identified by distinct ECG patterns:
- First-degree AV block: Prolongation of the PR interval (>0.20 seconds) without any dropped beats. This often reflects a delay in conduction through the AV node.
- Second-degree AV block (Mobitz I/Wenckebach): The PR interval progressively lengthens until a QRS complex is dropped. This type of block is usually benign and can be seen in athletes or during sleep.
- Second-degree AV block (Mobitz II): There is no progressive lengthening of the PR interval, but sudden, unexpected dropped QRS complexes. Mobitz II is more serious and can progress to complete heart block.
- Third-degree (complete) AV block: There is no conduction between the atria and ventricles, resulting in atrial (P waves) and ventricular (QRS complexes) activity that occurs independently of each other. This requires urgent management, often with a pacemaker
- Eplain the significance of axis deviation on the ECG and its clinical implications.**
The cardiac axis refers to the overall direction of the heart’s electrical depolarization. It is determined by looking at the QRS complex in the frontal leads:
- Normal axis: The QRS complex is positive in both leads I and aVF (between -30° and +90°).
- Left axis deviation (LAD): This occurs when the axis shifts between -30° and -90°. Causes include left ventricular hypertrophy, left bundle branch block, and inferior myocardial infarction.
- Right axis deviation (RAD): Occurs when the axis is shifted between +90° and +180°. Common causes include right ventricular hypertrophy, pulmonary embolism, and chronic lung disease.
Understanding axis deviation helps in diagnosing underlying conditions such as hypertrophy or infarction
7 Discuss the role of ECG in diagnosing and managing congenital heart diseases such as atrial septal defect (ASD) and ventricular septal defect (VSD).
ECG findings in congenital heart diseases often reflect the altered structure and function of the heart:
- Atrial septal defect (ASD):
- The ECG may show right axis deviation and right atrial enlargement. Incomplete right bundle branch block (RBBB) is often seen.
- Ventricular septal defect (VSD):
- The ECG may show signs of left ventricular hypertrophy or biventricular hypertrophy, depending on the size and significance of the defect.
While echocardiography remains the gold standard for diagnosing congenital heart defects, the ECG provides useful supportive information on the impact of these defects on the electrical activity of the heart
Explain the significance of the P wave, QRS complex, and T wave in an ECG, and discuss what abnormalities in each may indicate in terms of cardiac pathology.
ECG provides a graphical representation of the heart’s electrical activity. Each component of the ECG corresponds to different phases of the cardiac cycle:
- P wave: Represents atrial depolarization. Normally, it is a small, smooth upward deflection. Abnormalities in the P wave can indicate issues with atrial size or conduction. For example, a notched or peaked P wave may suggest atrial enlargement, while an absent P wave can be seen in atrial fibrillation.
- QRS complex: Represents ventricular depolarization. The normal duration is less than 120 ms. Abnormalities in the QRS complex, such as a widened QRS, may suggest bundle branch blocks, ventricular hypertrophy, or ventricular pre-excitation (as seen in Wolff-Parkinson-White syndrome).
- T wave: Represents ventricular repolarization. A tall, peaked T wave is typically seen in hyperkalemia, while flattened or inverted T waves may indicate ischemia or electrolyte disturbances.
Abnormalities in these waves can point to various cardiac conditions like ischemia, arrhythmias, or electrolyte imbalances
Discuss the role of the ECG in the diagnosis of acute coronary syndromes, with emphasis on ST-segment changes, T wave abnormalities, and the development of Q waves.
In acute coronary syndromes (ACS), ECG is essential for diagnosis and triage. There are three main types of ACS: unstable angina, NSTEMI (non-ST elevation myocardial infarction), and STEMI (ST elevation myocardial infarction).
- STEMI: Shows ST-segment elevation in the affected leads, which indicates transmural ischemia (full thickness of the heart wall). These changes appear within minutes to hours and can progress to the development of Q waves.
- NSTEMI: No ST-segment elevation but T wave inversion or ST depression may be seen. These changes suggest subendocardial ischemia (partial thickness).
- Unstable Angina: Similar to NSTEMI, but without the elevation of cardiac biomarkers. T wave inversion or ST depression may be present.
Q waves typically develop hours to days after a myocardial infarction and indicate irreversible damage to the myocardium
Describe the different types of heart block and their ECG manifestations. Include a discussion on first-degree, second-degree (Mobitz type I and II), and third-degree heart blocks.
Heart blocks occur when the electrical signal in the heart is delayed or completely blocked:
- First-degree AV block: Prolonged PR interval (>200 ms) but every P wave is followed by a QRS complex. It is often benign and may not require treatment.
- Second-degree AV block:
- Mobitz Type I (Wenckebach): The PR interval progressively lengthens until a QRS is dropped. This is usually due to reversible causes such as medication.
- Mobitz Type II: A sudden, non-conducted P wave without prior PR lengthening. This is more serious and may require a pacemaker.
- Third-degree (complete) AV block: No relationship between P waves and QRS complexes. The atria and ventricles beat independently. This condition requires urgent intervention with a pacemaker
Explain the pathophysiology behind axis deviation in ECGs and discuss its clinical relevance.
The heart’s electrical axis refers to the general direction of the heart’s electrical depolarization:
- Normal axis: Between -30° and +90°.
- Left axis deviation (LAD): The axis is more negative than -30°, which can occur due to left ventricular hypertrophy (LVH), left bundle branch block (LBBB), or inferior wall myocardial infarction.
- Right axis deviation (RAD): The axis is more positive than +90°, often seen in conditions like right ventricular hypertrophy (RVH), pulmonary embolism, or chronic lung diseases.
Axis deviation helps in diagnosing underlying pathologies such as ventricular hypertrophy or myocardial infarction
Detail how electrolyte imbalances, such as hyperkalemia and hypokalemia, manifest on an ECG and the potential clinical consequences if left untreated.
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Electrolyte imbalances, particularly potassium and calcium, have distinct effects on the ECG:
- Hyperkalemia: Elevated potassium levels cause peaked T waves, shortened QT intervals, and eventually lead to a widened QRS complex and sine wave pattern in severe cases. If untreated, it can lead to fatal arrhythmias.
- Hypokalemia: Causes U waves, T wave flattening, and prolongation of the QT interval. This can predispose to torsades de pointes, a type of polymorphic ventricular tachycardia.
- Hypocalcemia: Prolongs the QT interval, which increases the risk of arrhythmias.
- Hypercalcemia: Shortens the QT interval
Explain how ECG findings are used in the diagnosis of ventricular hypertrophy (both left and right). Discuss the voltage criteria for diagnosing left ventricular hypertrophy (LVH) and right ventricular hypertrophy (RVH) and the clinical conditions associated with each.
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ECG is useful in diagnosing both left ventricular hypertrophy (LVH) and right ventricular hypertrophy (RVH):
- Left Ventricular Hypertrophy: Characterized by increased QRS voltage. One commonly used criterion is the Sokolow-Lyon index: if the sum of the S wave in V1 and the R wave in V5 or V6 exceeds 35 mm, LVH is likely. Conditions such as hypertension and aortic stenosis often lead to LVH.
- Right Ventricular Hypertrophy: Seen as tall R waves in V1 and V2, with a rightward shift in the QRS axis (right axis deviation). Conditions like pulmonary hypertension and chronic lung disease contribute to RVH
Analyze the ECG changes associated with atrial fibrillation and ventricular tachycardia. Compare their pathophysiology and discuss their implications in terms of management and prognosis.
- Atrial Fibrillation (AF): On ECG, AF is characterized by an absence of P waves and an irregularly irregular rhythm. There are rapid, chaotic atrial electrical impulses, leading to disorganized atrial activity. AF increases the risk of stroke and is managed with rate control, rhythm control, and anticoagulation.
- Ventricular Tachycardia (VT): VT presents as wide QRS complexes with a regular rhythm. It arises from abnormal electrical signals originating in the ventricles. VT can degenerate into ventricular fibrillation, which is life-threatening and requires immediate intervention.
Both conditions represent significant arrhythmias that require different management approaches, but both are associated with significant morbidity and mortality if untreated
What’s the function of ecg
Electrocardiogram (ECG)
Purpose:
An ECG records the electrical activity of the heart. It captures the heart’s depolarization (when heart cells are activated and contract) and repolarization (when they relax), reflecting the overall electrical activity.
- Electrical potentials of about 1 mV are generated at the body’s surface, which form the familiar P-QRS-T pattern.
- Use of ECG: It is useful for investigating rhythm disturbances, myocardial and pericardial diseases, electrolyte imbalances, and more
What’s the location and placement of a 12 ecg lead
Lead Placement
The standard 12-lead ECG system includes:
- Limb leads: Lie in the frontal plane (Leads I, II, III, aVR, aVL, aVF).
- Precordial (chest) leads: Circle the heart in the transverse plane (V1-V6).
Precordial (Chest) Lead Placement:
- V1: Right sternal border, 4th intercostal space.
- V2: Left sternal border, 4th intercostal space.
- V3: Midway between V2 and V4.
- V4: 5th intercostal space, midclavicular line.
- V5: Anterior axillary line, 5th intercostal space.
- V6: Mid-axillary line, 5th intercostal space
What are the Ecg Waves and Intervals: and meaning
- P wave: Represents atrial depolarization (when the atria contract).
- QRS complex: Represents ventricular depolarization (ventricles contracting).
- T wave: Reflects ventricular repolarization (ventricles relaxing).
- PR interval: Time from the beginning of the P wave to the start of the QRS complex. It indicates the time for the electrical impulse to travel from the atria to the ventricles.
- QT interval: Time from the start of the QRS complex to the end of the T wave. It represents the total time of ventricular activity, including depolarization and repolarization
How do you do ECG Interpretation:
- Look at the rhythm strip: Usually lead V1 or lead I.
- Examine the P waves: Are they similar? Is there a 1:1 relationship between P waves and QRS complexes?
- Check the rhythm: Is it regular or irregular? For example, in atrial fibrillation (AF), _____ waves are absent? , and the rhythm is irregular.
- Calculate the heart rate:
- 300 divided by the number of big squares between R-R intervals (for regular rhythms).
- 1500 divided by the number of small squares between R-R intervals.
- For irregular rhythms, count the number of cardiac cycles in 6 seconds and multiply by 10.
- Assess the axis: The QRS axis represents the direction of the heart’s electrical activity in the frontal plane, usually measured using the QRS complex.
P wave
How do you do
Axis Determination (Isoelectric/Equiphasic Approach):
- Find the transitional lead: The lead where the QRS complex has equal positive and negative components (i.e., isoelectric).
- Use the hexaxial reference system to find the lead that is perpendicular (90°) to the transitional lead. This will indicate the QRS axis.
By thoroughly understanding the placement of ECG leads, interpreting the P-QRS-T waves, and utilizing methods such as axis determination, an ECG can help diagnose a variety of cardiac issues, from rhythm disorders to myocardial infarctions.
P wave meaning and which leas is it best seen and it’s xteristic
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P Wave
- Duration: The P wave represents atrial depolarization (contraction of the atria). It’s best observed in leads II and V1.
- In Lead II, the normal height should be <2.5 mm, and the duration (width) should be <3 small squares (3 mm = 0.12 s).
- In Lead V1, the P wave can be positive, negative, or biphasic. The positive terminal (right atrium) should be <1.5 mm, and the negative terminal (left atrium) should be <1 mm.
PR interval normal range and it’s abnormalities indicates
PR Interval
- Normal Range: 0.12 - 0.22 seconds (3-5 small squares).
- A prolonged PR interval suggests a delay in AV conduction and can indicate conditions like:
- First-degree heart block.
- Ischemic heart disease (IHD).
- Acute rheumatic myocarditis.
- Lyme disease.
- Electrolyte abnormalities like hypokalemia.
- Drug effects: digoxin, beta-blockers, calcium channel blockers (CCBs).
- Second-degree AV block Mobitz Type 1 (Wenckebach): The PR interval progressively lengthens until a beat is dropped (one atrial impulse fails to reach the ventricles).
What’s qrs complex?
And it’s increase and decrease might indicate?
QRS Complex
- Duration: Should be ≤0.10 seconds (2.5 small squares). It reflects ventricular depolarization (ventricular contraction).
- Low Voltage Complexes (QRS <5 mm in limb leads or <10 mm in chest leads) could indicate:
- Obesity.
- Chronic obstructive pulmonary disease (COPD).
- Pericardial effusion.
- Dilated cardiomyopathy (DCM).
- High Voltage Complexes can indicate:
- Left ventricular hypertrophy (LVH):
- R wave in V5 or V6 >25 mm.
- S wave in V1 or V2 >25 mm.
- Sokolow-Lyon criteria: S in V1 + R in V5/V6 > 35 mm.
- Cornell criteria: S in V3 + R in aVL > 28 mm in men, >20 mm in women.
- Right ventricular hypertrophy (RVH):
- R wave in V1 or V2 >7 mm.
- R/S ratio in V1 or V2 >1.
Premature Ventricular Contraction (PVC)
- A PVC represents an early depolarization of the ventricles, producing a wide and abnormal QRS complex, often without a preceding P wave.
What’s q wave and it’s features
What’s the feature of abnormal q wave and what it indicates
Q Waves
- Normal Q waves are small and indicate septal depolarization.
- Abnormal Q waves:
- > 2 mm deep, >1 mm wide, or >25% of the R wave amplitude.
- Causes of abnormal Q waves include myocardial infarction (MI) (especially transmural MI), hypertrophic cardiomyopathy (HCM), left bundle branch block (LBBB), and pulmonary embolism (PE).
ST segment means
It’s elevation signifies?
ST Segment
- The ST segment represents the time between ventricular depolarization and repolarization.
- ST elevation: Typically signifies myocardial injury (e.g., acute MI).
- Anterior MI: Leads V1-V5.
- Septal MI: Leads V1-V2.
- Lateral MI: Leads I, aVL, V5-V6.
- Inferior MI: Leads II, III, aVF.
- Posterior MI: Leads V7-V9.
- Right ventricular MI: Leads V1, V4R.
- Reciprocal changes can appear in opposite leads. For example, inferior MI (ST elevation in leads II, III, aVF) shows reciprocal ST depression in leads I and aVL.
Pericarditis: Generalized ST elevation across multiple leads, not localized to a specific coronary artery territory like an MI.
What’s qt interval
It’s normal range for both male and female
QT Interval
- Corrected QT interval (QTc): The QT interval represents the duration of ventricular depolarization and repolarization.
- Normal QTc:
- Males: ≤0.44 seconds.
- Females: ≤0.46 seconds.
What are the formulas used in correcting QT interval?
- Bazett’s formula: Corrects the QT interval for heart rate using the formula:
QTc=QT/√R-R
- Fridericia’s formula: Another method to correct the QT interval, especially for faster heart rates:
QTc= QT/3√R−R
The ECG (Electrocardiogram) measures the heart’s electrical activity, which can reveal a variety of heart conditions by analyzing different intervals and waveforms. Here’s a breakdown of the key parameters, waveforms, and related conditions:
- P wave duration: Normally ≤ 0.12s (3 small squares).
- Best seen in Lead II and Lead V1.
- In Lead II: Height < 2.5mm; width < 0.12s.
- In Lead V1: Biphasic, where the positive portion represents the right atrium and the negative portion represents the left atrium.
- PR interval duration: Normal range is 0.12-0.22s.
- Prolonged PR interval (>0.20s): Seen in conditions like:
- First-degree heart block (HB)
- Ischemic heart disease (IHD)
- Acute rheumatic myocarditis
- Lyme disease
- Hypokalemia
- Drug-induced (Digoxin, beta blockers, etc.)
- Mobitz Type 1 (Wenckebach): Progressive prolongation of PR interval followed by a dropped QRS complex.
- QRS duration: Normally ≤ 0.10s.
- QRS abnormalities:
- Low voltage: Amplitude < 5mm in limb leads or < 10mm in chest leads, seen in conditions like obesity, COPD, pericardial effusion, dilated cardiomyopathy (DCM).
- High voltage: Increased amplitude, suggesting left or right ventricular hypertrophy (LVH/RVH).
- LVH:
- R wave in V5 or V6 > 25mm.
- S wave in V1 or V2 > 25mm.
- S V1/V2 + R V5/V6 > 35mm (Sokolow Lyon Criteria).
- Cornell Criteria: S in V3 + R in aVL > 28mm (men) or > 20mm (women).
- RVH:
- R wave in V1/V2 > 7mm.
- R/S ratio in V1/V2 > 1.
- QT duration: Normal range 320-440ms (8-11 small squares).
- Prolonged QT: Can be caused by:
- Ischemic heart disease (IHD), myocarditis, dilated cardiomyopathy (DCM).
- Electrolyte imbalances: ↓ K+, ↓ Mg2+, ↓ Ca2+.
- Drugs: Tricyclic antidepressants, antiarrhythmics.
- Congenital long QT syndromes.
- Shortened QT: Occurs in hyperkalemia, hypercalcemia, hyperthermia, or acidosis.
- T wave amplitude:
- Normally ≤ 5mm in limb leads and ≤ 10mm in chest leads.
- Tall T waves: Seen in acute myocardial infarction (MI) and hyperkalemia.
- Small T waves: Associated with hypokalemia, pulmonary embolism (PE), and hypothyroidism.
- Inverted T waves:
- Can be normal in leads aVR, V1-V2 (young individuals), or V3 (in black individuals).
- Pathological inversion can be seen in ischemia, ventricular strain, Digoxin toxicity, cardiomyopathies, bundle branch block (BBB), pericarditis, pulmonary embolism, and subarachnoid hemorrhage
ST Segment:
- The ST segment represents the interval between ventricular depolarization and repolarization.
- ST elevation indicates acute myocardial infarction (MI) and can help localize the infarct.
- Anterior MI: Elevation in V1-V5.
- Inferior MI: Elevation in leads II, III, aVF.
- Posterior MI: Elevation in V7-V9 with reciprocal changes in V1-V3.
- Pericarditis: Diffuse ST elevation across multiple leads.
Bundle Branch Blocks:
- Left Bundle Branch Block (LBBB) and Right Bundle Branch Block (RBBB):
In complete block the QRS complex is?
What about incomplete block?
- Complete block: QRS duration > 0.12s.
- Incomplete block: QRS duration 0.10-0.12s.
