A decrease in the slope of phase 4 depolarization in the sinoatrial node would directly result in which of the following physiological changes?

• A Increased contractility
• B Increased heart rate
• C Prolonged PR interval
• D Decreased heart rate ✓

Explanation

Phase 4 depolarization determines the time required for the SA node to reach threshold. D decreased slope means it takes longer to reach threshold, resulting in a slower heart rate. The PR interval is determined by AV nodal conduction, and contractility is determined by intracellular calcium, not the slope of phase 4.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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