Sinus Node Responsiveness Index

Parameters:

(1) resting heart rate in beats per minute

(2) logarithm of peak resting serum norepinephrine concentration in pg/mL

sinus node responsiveness index =

= (resting heart rate) / LOG10(peak resting serum norepiphrine)

where:

• The type of logarithm is not specified. Values with LOG10 seemed closer to values in Table 1.

In heart failure the responsiveness index tends to decline from normal.

In heart failure there is decreased sinus node responsiveness to norepinephrine. This may be due to beta-adrenergic downregulation and remodeling of the sinus node associated with heart failure.

This decreased responsiveness may underly the exercise intolerance in heart failure.