Heart pump

Determinants of cardiac performance

• Heart rate
• Stroke volume
  * Preload
  * Afterload
  * Contractility

Note:

• Cardiac output not altered by primary changes in heart rate from about 40-50/min to 180/min.
• Beyond this range, CO is rate-dependent.

Force of extrasystole beats

Premature heartbeat is weak, but the beat after the pause is strong because

• Increased filling (acting via Frank-Starling mechanism)
• Increased SR store of Ca2+ available for release
  * postextrasystolic potentiation

Other notes

[WG22:p692]

• Hypocapnia increases cardiac output