Final answer:
High grade AV nodal blocks refer to serious disruptions in the electrical conduction between the heart's chambers, classified into first-degree (delayed conduction), second-degree (intermittent blockage), and third-degree (complete block) with each having different ECG manifestations and clinical significance.
Step-by-step explanation:
High Grade AV Nodal Blocks
High grade AV nodal blocks are serious conditions that involve a disruption in the electrical conduction between the atria and the ventricles of the heart. These blocks are categorized by degrees:
- First-degree AV block signifies a delay in conduction, visible on an ECG as an extended PR interval.
- Second-degree AV block shows an intermittent failure of impulses to pass from the SA node to the AV node, resulting in some P waves on the ECG not followed by a QRS complex.
- Third-degree AV block, or complete heart block, occurs when there is no conduction between the atrial and ventricular activity, leading to complete dissociation of the P wave and QRS complex on ECG readings. In such cases, the AV node may take over as a pacemaker with a reduced rate of 40-60 beats per minute.
Each of these blocks can have significant clinical implications, with the potential for reduced cardiac output and the need for interventions such as a pacemaker to maintain an adequate heart rate.