Control of heart beat
· Contraction of the Heart muscle is SYSTOLE
Relaxation of the Heart muscle is DIASTOLE
Heart rate is normally determined by the pacemaker activity of the sinoatrial node(sa node) located in the right atrium. The sa nodes exibites automaticity firing rate of 100- 115 beats/ min.
To increase above the instinsic rate, there is an an activation of sympathetic nerves innervating the sa nodes so that it increase the flight or fight mechansium.
Blood Pressure
· It is the Pressure in the vessels
· Highest during Ventricular Systole
· Lowest during Ventricular Diastole
· Expressed as Systole: Diastole
· e.g. Dog & cat BP = 120/80
Species Variation – Equine
• Many horses have an arrhythmia called second degree AV block.
It is very common and often goes away with trotting or exercise.
• In second-degree AV block the electrical impulse from the top chamber of the heart (atria) does not conduct to the bottom chamber of the heart (ventricle)
• The AV node malfunctions.
• It is very rare for a horse to have advanced AV heart block that would require pacemaker implantation.
