Guyton Kap. 13- Cardiac Arrhythmias And Ekg

Front 1

Causes of cardiac arrhythmias:

Back 1

1. Abnormal rhythmicity of the pacemaker
2. Shift of the pacemaker from the sinus node to another place in the heart
3. Blocks at different points in the spread of the impulse through the heart
4. Abnormal pathways of impulse transmission through the heart.
5. Spontaneous generation of faulty impulses in almost any part of the heart

Front 2

Relation of fever and heart rate:

Back 2

The heart rate increases about 18 beats/ min for each degree of Celsius increase in temperature, up to a temperature of 40.5 degrees. Beyond this temp heart rate may decrease because of debility of the heart muscle due to the fever

Front 3

Why does fever increase heart rate?

Back 3

Because of increased metabolism of the sinus node

Front 4

Conditions that can decrease or block conduction through AV- bundle:

Back 4

1. Ischemia to AV node or bundle
2. Compression of AV bundle by scar tissue etc
3. Inflammation of AV node or bundle (myocarditis due to diphtheria or rheumatic fever)
4. Extreme vagal stimuli

Front 5

First degree AV- block:

Back 5

Prolonged PR intervall of longer then 0.20 sec. (Delay but not actual blockage)

Front 6

Second degree AV- block:

Back 6

P wave and some dropped "beats" or dropped QRS complexes. When conduction through AV- bundle takes longer then 0.25- 0.45 sec the action potentials are sometimes strong enough to pass through to the ventricles and sometimes not.

Front 7

Third- degree AV- block (complete AV- block):

Back 7

No impulses are conducted from atria to ventricles--> ventricular escape beats. P waves are dissociated from QRS complexes.

Front 8

How long from stop of blood supply to the brain until syncope?

Back 8

4-7 seconds

Front 9

Causes of premature contractions is ectopic foci. Causes of ectopic foci are:

Back 9

1. Local areas of ischemia
2. Small calcified plaques at different point in the heart, which press against the adjacent cardiac muscle so that the fibers become irritated
3. Toxic irritation of the conductive system or cardiac muscle by drugs, nicotine or caffeine.

Front 10

Why is there a pulse deficit in premature contraction?

Back 10

Because the heart contracts ahead of schedule before the ventricles are fully filled

Front 11

Long QT syndrome:

Back 11

Dangerous because of great risk of developing torsade de point arrhythmias. Can be caused by rare mutations in the sodium and potassium channel genes. Or by acquired electrolyte imbalances such as hypo- magnesemia, -kalemia, - calcemia.

Front 12

Paroxysmal Tachycardia:

Back 12

Rapid ectopic beats caused by re- entrant circus movement feedback pathways that set up local repeated self- excitation. Begins suddenly and stops suddenly.

Front 13

Ventricular paroxysmal tachycardia:

Back 13

Significant because it only appears after ischemia (opposed to supraventricular tachycardia which is common and usually not dangerous) and it can cause VF

Front 14

"Re- entry" phenomenon, circus movements:

Back 14

Normally one action potential dies out because the heart muscle cells are in absolute refractory after depolarization. But if the "circuit" are to long or the speed of the action potential is to slow the cells will be out of refractory period and can be stimulated by a re- entry impulse. Or the refractory period might just be greatly shortened---> VF

Front 15

Cause of "long pathway":

Back 15

Dilated heart

Front 16

Cause of decreased rate of conductivity:

Back 16

Blockage of Purkinje system, ischemia, hyperkalemia

Front 17

Causes of shortened refractory period:

Back 17

Drugs such as adrenaline or repetitive electrical stimulation

Front 18

Typical cause of AF:

Back 18

Atrial dilation from heart valve lesions that prevent the atria from emptying properly into the ventricles, or from ventricular failure with excess damming of blood into atria. Dilated atrial walls are ideal conditions for long conductive pathways and slow conduction---> re- entry==> AF

Front 19

EKG in AF:

Back 19

No P waves because of many depolarization waves with different polarity that neutralize each other, or fine high frequency waves.

Front 20

Irregular ventricular rhythm during AF:

Back 20

During AF impulses are conducted to the AV- node rapid and irregular. When one impulse reaches AV- node it takes 0.35 sec until it is repolarized and can take another impulse. But then there is a 0- 0.6 sec interval until next impulse reaches AV- node. (ventricular interval may vary from 0.35 to 0.95 sec)

Front 21

Atrial flutter:

Back 21

Circus movement in atria where the signal travels as a single large wave always in one direction around and around muscle mass--> fast rates (200- 350 beats/ min). Too fast for AV- conduction---> 2:1 or 3:1