The primary reason that an increase in heart rate (100 bpm) detrimental to the client with a myocardial infarction (MI) is that:
A . Stroke volume and blood pressure will drop proportionately
B . Systolic ejection time will decrease, thereby decreasing cardiac output
C . Decreased contractile strength will occur due to decreased filling time
D . Decreased coronary artery perfusion due to decreased diastolic filling time will occur, which will increase ischemic damage to the myocardium
Answer: D
Explanation:
(A) Decreased stroke volume and blood pressure will occur secondary to decreased diastolic filling.
(B) Tachycardia primarily decreases diastole; systolic time changes very little.
(C) Contractility decreases owing to the decreased filling time and decreased time for fiber lengthening.
(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.