Cardiovascular System - Cardiac Cycle Flashcards
Describe the electrical events of cardiac cycle
Electrical activity in the heart is strong enough to be detected at the surface of the skin to give an electrocardiogram trace
Sinoatrial node activates automatically, electrical charge from each activation spreads throughout atria along 3 bundles of fibres
This signals atrial muscles to contract producing the P wave of the ECG trace - atrial depolarisation
Spread of current is held up at AV node - give ventricles time to fill up prior to contraction
After AV delay, current spreads down the left side of septum then over to the right activating the heart muscle from apex to base squeezing the blood out very efficiently
This is the QRS trace of ECG
T trace of ECG trace is when the electrical charge in the ventricles return to normal - ventricular repolarisation
What is arrhythmias?
Arrhythmias are abnormal heart rhythms characterized by irregular electrical activity in the heart.
Normally, the heart beats in a regular, coordinated pattern, with electrical signals originating from the sinoatrial (SA) node and propagating through the heart’s conduction system.
However, in arrhythmias, this electrical activity is disrupted, leading to irregular heartbeats or abnormal heart rates.
Arrhythmias can manifest as too fast (tachyarrhythmias), too slow (bradyarrhythmias), or irregular heart rhythms
What are circus movements?
Delay of conduction can cause signal to go in the wrong direction
Atrial, delays, ventricle sequence is interrupted
Controlled in a hazardous way
Causes cardiac arryythmias
What are the different heart sounds produced during the cardiac cycle?
“Lub” sound from closure of AV valves
“Dub” sound from closure of aortic and pulmonary artery valves
A third sound can be heard in some young individuals 1/3 of the way during diastole
Systolic murmurs caused by aortic or pulmonary stenosis or mitral and tricuspid insufficiency
Diastolic murmurs caused by aortic or pulmonary insufficiency or mitral and tricuspid stenosis
Describe the basic cardiac cycle.
Late diastole
Atrial systole
Ventricular systole
Early diastole
Describe late diastole.
Late diastole - AV valves open, blood flows in to the atria and ventricles passively
Describe atrial systole
Atrial systole - atrial contracts, produces P wave in ECG, contraction of muscle around great veins minimises back flow along with inertia of blood
Describe ventricular systole
Isovolumetric contraction- as the ventricles depolarize, pressure within the ventricles rises rapidly, exceeding the pressure in the atria. This rise in pressure causes the closure of the atrioventricular valves, preventing blood from flowing back into the atria.
Ejection phase - semilunar valves (aortic and pulmonary valves) open, allowing blood to be ejected from the ventricles into the pulmonary artery and aorta. Occurs as a result of the pressure gradient between the ventricles and the arterial system
The peak of ventricular pressure during systole is known as the systolic blood pressure, which can be measured clinically by a sphygmomanometer during blood pressure assessment.
C wave of atrial and JV pressures
Describe early diastole
Early diastole is the initial phase of the cardiac cycle, involving the relaxation and filling of the heart chambers following ventricular contraction. Key events during early diastole include isovolumetric relaxation, semilunar valve closure, atrioventricular valve opening, rapid ventricular filling, and atrial contraction. The ventricular myocardium relaxes, causing intraventricular pressure to decrease rapidly. Semilunar valves close, preventing blood backflow from the arteries into the ventricles. Atrioventricular valves open passively, allowing blood to flow from the atria into the relaxed ventricles. The atrial kick, which occurs towards the end of early diastole, contributes 20-30% of ventricular filling, ensuring optimal ventricular preload for the next contraction.
