What factor contributes to the occurrence of premature ventricular contractions (PVCs)?

• A. Low blood pressure
• B. Increased myocardial irritability
• C. Decreased heart rate variability
• D. Increased parasympathetic activity

Answer: (B)

Premature ventricular contractions (PVCs) are extra, abnormal heartbeats that arise from the ventricles. Increased myocardial irritability is a key factor contributing to the occurrence of PVCs. When the myocardial tissue is more excitable or irritable, it can lead to abnormal electrical impulses that trigger these premature contractions. This irritability can be influenced by various factors such as electrolyte imbalances, ischemia, or increased sympathetic nervous system activity which heighten the responsiveness of the myocardial cells to stimuli, making them more likely to fire prematurely.

In contrast, options like low blood pressure, decreased heart rate variability, and increased parasympathetic activity are generally not directly linked to the development of PVCs. Low blood pressure could indicate other underlying issues but does not directly cause PVCs. Decreased heart rate variability often suggests a more stable state of heart rhythm, which would reduce, rather than increase, the likelihood of PVCs. Increased parasympathetic activity typically leads to a decrease in heart rate and can promote regular heartbeats rather than provoke ectopic activity in the ventricles.