CR: PBL 1 (ECG and Atrial Fibrillation) Flashcards Preview

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Flashcards in CR: PBL 1 (ECG and Atrial Fibrillation) Deck (37)
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Define cardioversion

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?

Atrial depolarisation


What does a QRS complex represent?

Ventricular depolarisation


What does a T wave represent?

Ventricular repolarisation


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


Define 'automaticity'

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


What is catheter ablation?

Carefully destroys diseased areas of heart by using thin wires through vein into heart --> record electrical activity and energy source transmitted to destroy abnormal tissue (in terms of electricity)


What is a pacemaker?

Battery powered device implanted in chest below collar bone to stop heart beating too slowly (or to regulate)


Are athletes at a greater risk of atrial fibrillation?

Most common arrhythmia in athletes, and are 2-3x more likely to have than ordinary person


Why may athletes be more predisposed to atrial fibrillation than an ordinary person?

Cardiovascular stresses causing structural changes to atrial muscle (involved in abnormal electrical activity, increased firing of ANS nerves may promote disruption OR low level chronic inflammation that accompanies exercise



What does suffering atrial fibrillation increase your risk of?

Stroke, by 4-5x


What are the different types of atrial fibrillation?

Intermittent - intervals of AF
Persistent - in AF for longer than one week
Permanent - always in AF


Which drugs affect heart rate?

Chronotropic - affect the nerves controlling heart or the SAN


Which drugs affect force of heart contraction?

Ionotropic drugs - involved in muscular contraction (depolarisation), especially of cardiac myocytes