cardio day 2 pt 2

SA Node and Junctional Escape Beats

• SA Node Functionality

  • The SA node normally initiates the heartbeat.
  • If it fails to fire when needed, it can result in various heart rhythms.

• Junctional Escape Beats

  • When the SA node fails, the AV node can take over, firing at a slower rate (typically 40-60 bpm).
  • These beats are termed "junctional escape beats".
  • Opposite of Premature Junctional Complex (PJC) which occurs early in the cycle.

Key Differences Between PJC and Escape Beats:

• PJC: Occurs early; the heart rhythm is essentially normal but early.
• Escape Beats: Occur late due to a pause in SA node firing.

Premature Contractions

• Premature Contractions:

  • These are early beats occurring in cardiac cycles.
  • They result in compensatory pauses after the contraction.

• What Identifies Junctional Beats:

  • Absence of P Waves: Junctional complexes will not have preceding P waves.
  • Heart Rate: Generally ranges from 40-60 bpm for junctional rhythms.

• Identification of Junctional Complexes:

  • Retrograde P Waves: Occur after the QRS complexes, indicating some abnormal impulse conduction.
  • Inversion of P Waves: Sometimes, P waves can flip orientation due to the retrograde conduction.

Aberrant conduction in Premature Junctional Complexes (PJCs)

• Aberrant PJC: If a PJC displays a wide QRS complex, it can be confused with other wide QRS complexes, such as PVCs (Premature Ventricular Contractions).
  • Distinguishing Features:
  • PVCs generally display a wider complex and are often seen with negative deflection in leads where normal complexes are positive.
  • PJCs typically reflect the same direction as sinus complexes.

Escape Rhythms and Complexes

• Junctional Escape Rhythm:

  • If SA node does not fire, junctional escape beat can initiate a series of junctional rhythms (complex or rhythm).
  • Identified when SA node 'wakes up' after a pause.

• Wandering Baseline:

  • Seen during these rhythms may indicate movement or artifact rather than a true physiological change.

• Differentiating Escape Rhythm from Sinus Rhythm:

  • Different morphology in P waves when there's a transition from sinus to junctional rhythm indicates the fail of the SA node.

Bundle Branch Block (BBB) Detection

• Bundle Branch Block Overview:

  • Identified through 12-lead ECG: Wide QRS complexes can indicate a BBB.
  • Importance of V1 Lead: Critical in assessing and determining the presence of BBB.

• Identifying the J Point and QRS:

  • J Point: Intersection of the S wave and the ST segment, crucial for interpreting BBB.
  • QRS Characteristics:
  • Left BBB: QRS deflections move towards the left above the J-point.
  • Right BBB: QRS deflections angle right below J-point.

Atrioventricular (AV) Blocks

• First Degree AV Block:

  • Identified by a prolonged PR interval (>0.20 seconds) with consistent intervals, typically the effect of SA node delay.

• Types of AV Blocks:

  • Second Degree AV Block: Type I (Wenckebach) and Type II (Mobitz).
  • Third Degree AV Block: Complete dissociation between atria and ventricles.
  • Recognition: Look for prolonged PR intervals and varying characteristics of QRS responses related to expected atrial impulses.

Summary of Key Terms

• Compensatory Pause: A pause in heart rhythm typically occurs after a premature contraction.
• P Wave: Represents atrial depolarization on the ECG; its absence or inversion is crucial for junctional recognition.
• QRS Complex: Depicts ventricular depolarization; abnormal width can indicate conduction blocks or arrhythmias.