Describe a "premature ventricular contraction" (PVC).

• A. An early QRS complex originating from the atria
• B. An early QRS complex originating from the ventricles
• C. A normal QRS complex with an altered T wave
• D. A late QRS complex with significant ST depression

Answer: (B)

A premature ventricular contraction (PVC) is defined as an early QRS complex that originates from the ventricles. This means that instead of the heart's electrical impulse starting in the sinoatrial (SA) node and traveling through the atria and then to the ventricles, the impulse in a PVC starts abnormally in the ventricles themselves. As a result, the QRS complex appears wider than normal because the ventricles are contracting prematurely and not following the typical conduction pathway, which involves the atria contracting first.

The presence of PVCs can disrupt the rhythm of the heart, leading to irregular heartbeat sensations and sometimes contributing to other complications depending on their frequency and underlying heart health. Understanding the origin of PVCs is crucial in distinguishing them from other types of premature beats, such as premature atrial contractions (PACs), which would originate from the atria and produce normal QRS complexes. The options that reference other types of QRS complexes, such as a normal QRS with altered T waves or complexes that follow specific ST segment patterns, do not accurately describe the characteristics of PVCs, further highlighting why the option regarding the ventricular origin is the correct response.