Regarding the atrioventricular (AV) node and its conduction properties, all of the following are true EXCEPT:

Explanation

## Atrioventricular Node: Anatomy and Conduction Physiology ### Anatomical and Functional Overview **Key Point:** The AV node is located in the triangle of Koch (bounded by the coronary sinus, septal leaflet of the tricuspid valve, and tendon of Todaro) and serves as the critical delay point in the cardiac conduction system. **High-Yield:** The AV node has the **slowest conduction velocity** of all cardiac tissues, not faster than the SA node. This physiologic delay (100–120 ms) is essential for allowing atrial contraction to complete before ventricular depolarization. ### Conduction Hierarchy by Speed ```mermaid flowchart LR A[SA Node<br/>60-100 bpm<br/>Slowest automaticity]:::outcome B[Atrial muscle<br/>~1 m/s]:::outcome C[AV Node<br/>0.02-0.05 m/s<br/>SLOWEST conduction]:::urgent D[His Bundle<br/>1-1.5 m/s]:::action E[Purkinje fibers<br/>2-4 m/s<br/>FASTEST]:::action F[Ventricular muscle<br/>0.3-0.4 m/s]:::outcome A --> B --> C --> D --> E --> F ``` ### Correct Statements | Feature | Details | |---------|----------| | **Location** | Triangle of Koch (right atrium) | | **Boundaries** | Coronary sinus, septal tricuspid leaflet, tendon of Todaro | | **Blood Supply** | AV nodal artery (RCA 90%, LCx 10%) | | **Conduction Velocity** | 0.02–0.05 m/s (SLOWEST in cardiac system) | | **Decremental Conduction** | Yes — impulse slows progressively through the node | | **Physiologic Delay** | 100–120 ms (allows atrial kick before ventricular contraction) | ### Why the Correct Answer is Wrong **Clinical Pearl:** The statement claims the AV node "conducts impulses faster than the sinoatrial node." This is **misleading and incorrect**: - The SA node has a **firing rate** (automaticity) of 60–100 bpm, but this is not the same as conduction velocity. - The AV node has the **slowest conduction velocity** (0.02–0.05 m/s) of all cardiac tissues. - The AV node's slowness is **physiologically essential** — it creates the PR interval delay that allows atrial contraction to complete before ventricular depolarization. **Warning:** Do not confuse **automaticity** (firing rate) with **conduction velocity** (speed of impulse propagation). The SA node fires faster, but the AV node conducts slower. **Mnemonic:** **"AV Node = Slowpoke"** — Remember: AV node is the bottleneck of the conduction system, not a fast conductor. [cite:Gray's Anatomy Ch 3.2; Guyton & Hall 14e Ch 10]