The primary reason that an increase in heart rate (100 bpm) detrimental to the client with a myocardial infarction (MI) is that:

Question

Options

• AStroke volume and blood pressure will drop proportionately
• BSystolic ejection time will decrease, thereby decreasing cardiac output
• CDecreased contractile strength will occur due to decreased filling time
• DDecreased coronary artery perfusion due to decreased diastolic filling time will occur, which will

• A
  13% (4)
• B
  39% (12)
• C
  6% (2)
• D
  42% (13)

Explanation

(A) Decreased stroke volume and blood pressure will occur secondary to decreased diastolic (B) Tachycardia primarily decreases diastole; systolic time changes very little. (C) Contractility decreases owing to the decreased filling time and decreased time for fiber (D) Decreased O2 supply due to decreased time for filling of the coronary arteries increases ischemia and infarct size. Tachycardia primarily robs the heart of diastolic time, which is the primary time for coronary artery filling.

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