Cardiac Arrythmias Flashcards
What is tachycardia?
Fast heart rate; it is caused by increased body temperature, stimulation by sympathetic nerves or toxic conditions of the heart.
What is endogenously mediated tachycardia?
fast heart beat that is a result of exercise. Can include increased heart rate and cardiac output; filling time is reduced, but stroke volume does not fall.
Why does stroke volume not fall during exercise?
the systolic interval is reduced, and more blood is filled during the diastole. Less is stored in the veins and more in the heart (and therefore, more is pumped).
What is brachycardia?
A slow heart rate. It is caused by excercise, vagal stimulation or baroreceptors in carotid sinus syndrome.
What are spillover signals?
signals from the medulla (inspiratory expiratory) that increase and decrease the number of impulses transmitted through sympathetic and vagus nerves to the heart.
What is a sinoatrial block?
When the impulse from the sinus node is blocked before it enters the atrial muscles.
What are characteristics of sinoatrial block?
NO P WAVE; no last third of diastole, new rhythm picked up in the AV node.
What is an atrioventricular block?
Block by of the AV node; impulses cannot pass from the atria to the ventricles.
What causes an atrioventricular block?
ischmeia of AV node, compression of AV bundle, inflammation of AV node, stimulation by vagus nerve
What is a first degree AV block?
prolonged PR interval ( > 20 sec)
What is a second degree AV block?
prolonged PR interval ( 20 - 45 sec), QRST wave is missing, 2:1 rhythmn.
What is a complete AV block?
When the AV signal is completely blocked. Ventricles establish their own signal at the AV node, and ventricles may not beat for 5 to 30 seconds.
What is Stokes-Adams syndrome caused by?
Complete AV block and lack of blood for 5 to 30 seoncds; occurs to lack of blood to the brain until the ventricles beat again.
What is a partial intraventricular block?
electrical alternans; an alternation in the AMPLITUDE of P waves, QRS complexes or T waves casued by blockages of impulses in the Purkinje fibers.
What are premature contractions?
contractions that occur before they should. They are caused by ectopic foci such as ischemias, calcified plaques or irriation of the conduction system or nodes.
What is paroxysmal tachycardia?
Tachycardia caused by rapid, rhythmical discharges of impluses that spread in all directions throughout the heart. They begin and end suddenly.
When does ventricular fibrillation occur?
When there are abnormal cardiac impulses in the ventricular muscle mass; no coordinated contraction of muscles occurs and heart does not contract enough to pump blood.
Why do the normal depolarization waves die out during fibrillation?
The heart muscle that has already contracted is in the refractory period and cannot respond to being stimulated by the existing depolarization waves.
What does fibrillation occur as a result of?
circus movements
What are circus movements?
three different conditions that cause the impulse to travel around the circle.
What are the three circus movements?
pathway around ventricle is too long, length of pathway is constant but velocity of conduction slows down; refractory period is greatly shortened.
If the pathway around the ventricles is too long, what occurs?
the muscle is no longer in the refractory period and undergo another repolarization (this would usually not occur)
What causes the conduction velocity of the impulse to slow down?
blockage of the purkinje system, ischemia or high potassium levels.
What causes the refractory period of the muscle to be shortened?
drugs (epinephrine, repetitive electrical stimulation)
