Learning Objectives 🎯

• 💡 Define 1st and 2nd-degree AV blocks.
• 📝 Identify 1st and 2nd-degree AV blocks on an ECG.
• 🩺 Differentiate between Mobitz Type I (Wenckebach) and Mobitz Type II 2nd-degree AV blocks.
• 🤔 Explain the clinical significance of AV blocks.
• ✅ Understand the causes of AV blocks.

Step-by-Step Content 📝

What are AV Blocks? 🤔

AV blocks occur when the electrical impulse from the atria to the ventricles is delayed or completely blocked. This disruption in conduction can result in various ECG patterns.

1st-Degree AV Block 🕰️

Definition: 1st-degree AV block is characterized by a prolonged PR interval (greater than 0.20 seconds or one large box on the ECG paper). It signifies a delay in conduction through the AV node but every atrial impulse eventually reaches the ventricles.

ECG Characteristics:

• Prolonged PR interval (> 0.20 seconds)
• Each P wave is followed by a QRS complex.

Clinical Significance: Usually asymptomatic and often requires no treatment. However, it may indicate underlying heart disease.

2nd-Degree AV Block 💔

Definition: 2nd-degree AV block occurs when some atrial impulses are blocked from reaching the ventricles. This results in some P waves not being followed by a QRS complex.

There are two main types of 2nd-degree AV block:

Mobitz Type I (Wenckebach) 📉

ECG Characteristics:

• Progressive lengthening of the PR interval until a QRS complex is dropped (P wave not followed by a QRS).
• The PR interval after the dropped beat is usually shorter.
• Often occurs in a repeating pattern.

Mnemonic: “Longer, longer, longer, drop! Then you have a Wenckebach.”

Clinical Significance: Usually benign and transient. May be caused by medications or increased vagal tone.

Mobitz Type II ⬆️⬇️

ECG Characteristics:

• PR interval remains constant before the dropped QRS complex.
• Sudden, unexpected failure of conduction.
• More likely to progress to complete heart block (3rd-degree AV block).

Clinical Significance: More serious than Mobitz Type I. Often indicates structural heart disease and may require a pacemaker.

Example ECGs 📈

Let’s look at some examples:

• 1st-Degree AV Block: Find an ECG strip with a PR interval consistently longer than 0.20 seconds.
• Mobitz Type I: Look for the progressive PR interval lengthening followed by a dropped beat.
• Mobitz Type II: Identify an ECG with a constant PR interval followed by a suddenly dropped QRS.

Clinical Significance Summary 🩺

• 1st-degree AV block: Usually asymptomatic.
• 2nd-degree AV block (Mobitz Type I): Usually benign.
• 2nd-degree AV block (Mobitz Type II): Potentially serious and may require intervention.

Causes of AV Blocks 💔

AV blocks can be caused by various factors, including:

• Medications (e.g., beta-blockers, calcium channel blockers)
• Ischemic heart disease
• Infections (e.g., Lyme disease)
• Structural heart disease
• Age-related degeneration

Quiz Time ❓

1. Which of the following defines a 1st-degree AV block?
   A. Dropped QRS complexes
   B. Prolonged QRS duration
   C. Prolonged PR interval (Correct)
   D. Absent P waves
2. In Mobitz Type I (Wenckebach), what happens to the PR interval?
   A. Remains constant
   B. Progressively shortens
   C. Progressively lengthens (Correct)
   D. Disappears entirely
3. Which type of 2nd-degree AV block is more likely to progress to complete heart block?
   A. Mobitz Type I
   B. Mobitz Type II (Correct)
   C. Both equally
   D. Neither
4. A patient presents with a PR interval of 0.24 seconds on their ECG. What type of AV block is this?
   A. Normal ECG
   B. 1st-degree AV block (Correct)
   C. 2nd-degree AV block
   D. 3rd-degree AV block
5. Which of the following medications can cause AV blocks?
   A. Aspirin
   B. Beta-blockers (Correct)
   C. Antacids
   D. Vitamins

Summary 📝

Today, we covered 1st and 2nd-degree AV blocks. Remember the key ECG characteristics of each type, especially the difference between Mobitz Type I and Mobitz Type II. Understanding these blocks is essential for accurate ECG interpretation and patient management. 🎉

Review and Practice 📚

Review your notes and practice identifying AV blocks on ECG strips. Focus on measuring the PR interval and observing any patterns in the ECG. Look for ECG examples online or in textbooks.

Next Day Preview 🚀

Tomorrow, we will conquer the final AV Block – 3rd Degree (Complete Heart Block) ⚕️.