ECG Interpretation Quiz

Cardiology: Dysrhythmias and Basic ECG's

• This is a course about heart rhythm abnormalities and basic electrocardiograms (ECGs).
• The course is for BMS200 students, Week 9.

Learning Outcomes (Page 2, 3)

• Analyze normal ECG characteristics: heart rate, rhythm determination (P-R, QRS, Q-T intervals), and normal waveforms (P, QRS, T waves)
• Describe how triggered activity, abnormal automaticity, and re-entry contribute to common dysrhythmias
• Describe the epidemiology, pathogenesis, clinical features, ECG findings, and prognosis of supraventricular dysrhythmias (atrial fibrillation, atrial flutter, sinus tachycardia, paroxysmal supraventricular tachycardia) and ventricular dysrhythmias(Premature ventricular contraction, idioventricular rhythm, ventricular tachycardia, ventricular fibrillation, torsades de pointes) and conduction block (1st, 2nd, 3rd degree heart block)
• Describe ECG findings typical of cardiac ischemia and relate these to vascular territories.
• Summarize the pharmacologic mechanisms and adverse effects of anti-arrhythmic medications.
• Discuss the role of chronic inflammation and myocardial fibrosis in common dysrhythmias development.

What Do You Think is Happening? (Page 4)

• A new electronic stethoscope can transmit a two-lead ECG to a smartphone.
• The ECG's appearance changes depending on stethoscope placement on the chest.
• A classmate's ECG is shown, indicating possible abnormalities.

Pre-Assessment: Q-T Interval (Page 5)

• The Q-T interval on an ECG represents ventricular repolarization in the heart.

Pre-Assessment: Cardiac Pacemaker (Page 6)

• The area in the heart responsible for initiating the heartbeat is close to the superior vena cava in the right atrium.

Review: Electrocardiogram (ECG) (Page 7, 8, 9)

• An ECG records the electrical activity of the heart by placing electrodes on the skin.
• Wave amplitudes represent the amount of electrical activity in the heart muscle.
• Larger waves indicate greater electrical activity in larger areas of myocardial tissue activation.
• Upward deflections on the ECG indicate electrical impulse movement towards electrodes.
• Downward deflections show movement away.
• Conducting tissues (like the SA node, AV node, and bundle branches) generate less electrical activity than myocardial tissues, making them less noticeable on an ECG.
• ECG primarily reflects the activity of large cardiomyocytes responsible for blood pumping.
• Wave durations (P wave, QRS complex, T wave) signify electrical timing, critical in assessing cardiac health.
• A prolonged QRS complex suggests ventricular conduction delays, and a prolonged QT interval indicates arrhythmia risk.

Review: ECG Measurement (Page 10)

• ECG leads measure the extracellular current moving from depolarized cells to resting (polarized) cells between different areas of the heart.
• ECG only registers significant changes in membrane potential.

Review: ECG Timing (Page 11)

• ECG waves and intervals correlate to heart conduction pathway electrical stimulations.
• The AV delay allows atrial contraction and ventricular filling.

ECG: Amplitude and Vectors (Page 12)

• ECG wave height indicates electrical potential difference intensity between different heart areas.
• Vector length shows the electrical potential difference between two points during depolarization/repolarization.
• Vector direction highlights electrical activity direction through the heart.

Placement of ECG Leads (Page 13, 14)

• ECG leads provide a 3-D view of electrical activity in the heart.
• Coronal views: use leads from the left and right arms and the left leg (to gain a left and right perspective of the heart).
• Precordial leads (cross-section): use leads placed on the chest to gain a front and back/superior and inferior perspective of the heart.
• Bipolar leads compare voltage changes between two chest leads.
• Unipolar (precordial) leads compare voltage changes between a lead and the heart's center region.

ECG: X and Y Axis (Page 15)

• The ECG's x-axis represents time (in seconds).
• The y-axis represents voltage in mV (millivolts).
• Standard ECG grid boxes define voltage and time changes.

Approach to Interpreting ECG (Page 16)

• Determine rate and rhythm, following a systematic approach
• Calculate heart rate and understand rhythm.

Step 2 – Rhythm (Page 17)

• Determine ECG rhythm pattern (regular or irregular) using a rhythm strip, often lead II.
• Assess for presence of abnormal P, QRS, and T waves patterns.
• Identify a normal sinus rhythm, if it is regular or irregular, its pattern, its P waves and QRS ratio etc.

A Normal 12-Lead ECG (Page 18)

• An example of a 12-lead ECG.

Step 3 – Intervals (Page 19,20)

• Evaluate intervals (P-R, QRS, QT) for abnormalities, such as lengthening (prolongation) or shortening (decreasing)
• Recognize possible conduction issues.

Step 4 – Waves (Page 21)

• Examine the wave forms for position, shape, and size deviations.
• Look for additional waves that aren't normally present in a healthy heart rhythm.

Step 4 - Q Waves (Page 22)

• The presence of specific Q-wave abnormalities strongly indicates a past or current Myocardial Infarction (MI).

Step 4 - ST Segments (Page 23)

• ST segment analysis helps to identify myocardial ischemia (ST elevation or depression).
• Significant ST segment changes may indicate myocardial infarction.

ST Depression and ST Elevation (Page 24)

• Clinical causes (e.g. underlying MI) of ST segment depression and ST elevation are summarized.

Step 4 - T Waves (Page 25)

• Abnormal T-wave morphologies can indicate potential underlying cardiac issues (ischemia or electrolyte imbalances).

Step 4 - P Waves (Page 26)

• P-wave abnormalities can imply atrial fibrillation or other atrial problems or hypertrophy).
• P-wave patterns and atrial enlargement are connected to the shape of the P-waves and the atrial load.

General Pathophysiology of Dysrhythmias (Pages 27, 28, 29, 30)

• Re-entry: Involves a slower conduction in a heart region with an abnormal electrical pathway, causing a repeating circuit of electrical activation in abnormal areas of the heart.
• Ectopic Foci or Abnormal Automaticity: Abnormal electrical signals originating from cells that are not normally involved in heart's rhythm.
• Triggered Activity: Uncommon cardiac rhythm abnormality. The electrical system abnormally re-activates tissues prematurely or improperly.
• In these conditions, abnormalities in the heart's electrical pathways or tissues contribute to irregular heartbeats.

Supraventricular Dysrhythmias (Page 32, 35, 36, 37, 38)

• Atrial Fibrillation (AF): Irregular heart rhythms, with no distinguishable P-wave pattern.
• Atrial Flutter: Irregular, fast heart rhythm caused by a rapid circuit (re-entry) in the atria. Has fixed flutter waves with no isoelectric line between QRS structures.
• Sinus Tachycardia: Fast heart rate initiated by the normal pacemaker (sinus node), generally due to physiological responses to exertion/stress.
• Paroxysmal Supraventricular Tachycardia (PSVT): Intermittent rapid heart rhythm originating from the AV node or atria and terminating suddenly, or having a fast heart rate (150-250 bpm).

Ventricular Dysrhythmias (Pages 39, 40, 41, 42, 43, 44, 45, 46)

• Premature Ventricular Contractions (PVCs): Premature ventricular contractions that can occur alone or in a group.
• Idioventricular Rhythm: A slow heartbeat that arises from the ventricular tissue instead of the normal pacemaker (SA node).
• Ventricular Tachycardia (VT): Fast heart rate arising from a ventricular (non-normal) pacemaker (ventricular). Involves 3 or more consecutive PVC's
• Ventricular Fibrillation: Irregular and uncoordinated heartbeat (rapid rate) originating from the ventricles, often fatal if not treated immediately (CPR or defibrillator).
• Torsades de pointes: A form of ventricular tachycardia characterized by a "twisting" pattern on an ECG, often associated with prolonged QT intervals (a QT interval longer than 500ms).

Conduction Block (Pages 47, 48, 49, 50, 51, 52, 53, 54)

• First-degree AV block: A slight delay between atrial and ventricular contractions.
• Second-degree AV block: A more significant delay in or dropping of some of the ventricular contractions. Includes Mobitz type I and II delays
• Third-degree AV block: Complete breakdown of communication between the atria and the ventricles; separate contraction patterns in atria and ventricles; this is often treated with a pacemaker

Cardiac Ischemia and ECG (Page 55)

• ECG changes in myocardial ischemia, including inverted T waves and ST segment elevation, are discussed.

Anti-Arrhythmic Mechanism of Action (Page 56, 57)

• Various classes of anti-arrhythmic drugs and their mechanisms on different cell channels.
• The effect of anti-arrhythmics on the depolarization and repolarization phases of the cardiac cycle are discussed

Premature Ventricular Contraction (PVC): Case (page 58)

• A case study of a premature ventricular contraction (PVC) is presented.
• The case involves a new electronic stethoscope with an attached ECG.
• The abnormalities are demonstrated through the case example.

Pre-Assessment: Q-T Interval (Page 59)

• The Q-T interval on an ECG represents ventricular repolarization in the heart.

Pre-Assessment: Cardiac Pacemaker (Page 60)

• The area in the heart responsible for initiating the heartbeat is close to the superior vena cava in the right atrium.

Test your knowledge on ECG interpretation with this quiz. Explore questions related to P-R intervals, QRS duration, QT intervals, and the morphology of waves. Perfect for students learning about cardiac physiology.