Flashcards in CR: PBL 1 (ECG and Atrial Fibrillation) Deck (37)
Use of electric shock to convert dangerous, rapid fluttering of heart beat to its normal rhythm
Define atrial fibrillation
Irregularity of heart beat caused by involuntary contractions of small areas of heart muscle walls
Describe the ECG of someone in atrial fibrillation
No P wave, no identifiable PR interval, normal QRS complex
What are heart palpitations?
Sensation where a person is aware of an irregular, hard or rapid heart beat
What is cardiovascular disease?
Any disease of the heart or blood vessels e.g. Atherosclerosis, CHD and peripheral vascular disease
What is systolic blood pressure?
Blood pressure during contraction of the ventricles
What is diastolic blood pressure?
Minimum level of blood pressure measured between heart contractions
What is rivaroxaban?
An oral anticoagulant
What does a P wave represent?
What does a QRS complex represent?
What does a T wave represent?
What does the PR interval represent?
Activation of AVN, bundle of His and Purkinje fibres
How can you calculate ventricular rate from ECG?
Duration between R waves (RR interval)
How can you calculate atrial rate from an ECG?
Duration between P waves (PP interval)
How do atrial and ventricular rates differ in atrial fibrillation?
Atrial rate >360bpm whereas ventricular rate 60-150bpm
Why are blood tests used in the diagnosis of atrial fibrillation?
To check for factors which may have led to AF such as hyperthyroidism or electrolyte imbalance
How can hyperthyroidism lead to greater risk of atrial fibrillation?
Thyroid hormone contributes to arrhythmogenic activity by altering electro physiological characteristics of atrial myocytes by shortening the duration of atrial depolarisation
How can blood tests diagnosis cardiac failure?
Pro-brain natriuretic peptide is released in higher than normal levels (PNP)
Where is the SAN located?
Lateral to the junction where the superior vena cava enters the atrium
What is the function of the AVN?
Initiate wave of excitation in the ventricles following atrial contraction as the septum blocks the AVN impulse from being transmitted directly to ventricles
Ability to depolarise spontaneously
What percentage of ventricular filling is done by atrial contraction at rest and during exercise?
Rest = 10%
Exercise = 40%
Why would atrial fibrillation limit exercise capacity?
Because atrial systole effectively doesn't occur and therefore there is poor ventricular filling leading to poor stroke volume which is insufficient to supply the active muscles and therefore this will lead to quick fatigue and lactic acid build up (cramp)
Why are patients with atrial fibrillation placed on anticoagulants?
AF increases chance of stroke due to slow blood flow (pooling) which increases the likelihood of clots forming and therefore anti coagulants are used to prevent clot formation and reduce stroke likelihood, or may be used prior to cardioversion (also increases risk of stroke)
What is atrial fibrillation?
Atria are experiencing chaotic external signals from the SAN meaning the AVN is bombarded with impulses trying to get through the septum and therefore this causes an irregular ventricular rate also
Explain why irregular radial pulse is a sign of atrial fibrillation
The pulse is too weak as a result of low blood volume being pumped per unit of time
Explain why low blood pressure is a sign of atrial fibrillation
There is a smaller volume of blood being pumped in systole (stroke volume) and therefore the blood pressure decreases
Describe the normal clotting cascade
1) Blood exposed to collagen
2) Factor XII activated --> XIIa
3) Factor XIIa activates factor (with HMW kininogen) XI --> XIa
4) Factor XIa binds calcium and activates factor IX --> IXa
5) Platelets release PF3 and thrombin activates factor VIII --> VIIIa
6) Xa factor (help of PF3) joins VIIIa to form factor X activating factor (tense)
7) Tenase activates X --> Xa (prothrombinase)
8) Tenase binds to Ca2+, Xa and prothrombin --> thrombin
9) Thrombin: Factor XIII --> XIIIa and binds to fibrinogen --> fibrin
10) Fibrin activated by XIIIa --> cross-linking --> clot formed
Describe how the anticoagulant rivaroxaban works
Inhibits free and bound (to prothrombinase complex) factor Xa to stop production of thrombin