Expansion
Chronotropy, inotropy, dromotropy and lusitropy
Expansion
- Chronotropy - heart rate, acting on the sinoatrial node
- Inotropy - force of contraction
- Dromotropy - conduction velocity, mainly at the atrioventricular node
- Lusitropy - rate of relaxation in diastole
Sympathetic stimulation, through beta-1 receptors and cyclic AMP, is positive in all four. It reaches the whole heart: nodes, conducting system and working myocardium.
Parasympathetic (vagal) stimulation, through M2 muscarinic receptors, is negative and acts mainly on the sinoatrial and atrioventricular nodes and the atria, with little direct ventricular innervation. Its effects are therefore chiefly negative chronotropic and dromotropic.
At rest the heart is under dominant vagal tone; the intrinsic rate of the denervated sinoatrial node is about 100 beats per minute, which is why atropine or transplantation raises the resting rate.