What is the current American Heart Association (AHA) term for a heart rhythm that progressively widens and then drops a beat?

Type I Second-Degree AV Block (Wenckebach) is the Current AHA Term for Progressive QRS Widening Before a Dropped Beat

The current American Heart Association (AHA) term for a heart rhythm that progressively widens and then drops a beat is Type I second-degree atrioventricular (AV) block, also known as Mobitz type I or Wenckebach phenomenon.

Characteristics of Type I Second-Degree AV Block

• Type I second-degree AV block is characterized by progressive prolongation of the PR interval before a nonconducted beat (dropped beat) and a shorter PR interval after the blocked beat 1
• This creates the pattern of progressively widening PR intervals until a beat is dropped, followed by the cycle repeating 1
• The block typically occurs at the level of the AV node, though it can occasionally occur at the His-Purkinje level 1
• It is usually associated with a narrow QRS complex, though wide QRS complexes can occur if there is concurrent bundle branch block or if the block is infranodal 1, 2

Differentiating from Other Types of AV Block

• Type II second-degree AV block (Mobitz type II) is characterized by fixed PR intervals before and after blocked beats without progressive prolongation 1
• Type II block is usually associated with a wide QRS complex and is almost always located below the AV node (infranodal) 1, 2
• 2:1 AV block cannot be classified as either Type I or Type II based on ECG appearance alone, as there is only one PR interval to examine before the blocked P wave 3
• Advanced second-degree AV block refers to blocking of 2 or more consecutive P waves with some conducted beats 1
• Third-degree AV block (complete heart block) is defined as complete absence of AV conduction 1

Clinical Significance and Management

• Type I second-degree AV block is generally considered more benign than Type II block 4, 2
• Progression to complete heart block is less common with Type I than with Type II block 4
• Pacemaker implantation recommendations for Type I block depend on symptoms and other factors:
  • Not indicated for asymptomatic patients 1
  • Reasonable for symptomatic bradycardia 1
  • May be considered in minimally symptomatic patients with heart rate <40 bpm while awake 1

Common Pitfalls in Diagnosis

• Atypical forms of Wenckebach (Type I) AV block may be misinterpreted as Mobitz Type II when a series of PR intervals appear constant before the block 2
• Nonconducted premature atrial contractions and atrial tachycardia with block can mimic second-degree AV block 4
• Vagal surges can cause simultaneous sinus slowing and AV nodal block that resembles Type II block 2
• Concealed His bundle or ventricular extrasystoles may mimic both Wenckebach and Type II AV block (pseudo-AV block) 2

Understanding the correct classification of AV blocks is essential for appropriate clinical decision-making, as the prognosis and treatment differ significantly between types.