CARDIOLOGY Chapter 13 - Guyton Flashcards
Tachycardia
defined as heart rate >100bpm; caused by increased body temperature, stimulation of the heart by sympathetic nerves, or toxic conditions of the heart
Bradycardia
defined as parasympathetic on heart
What is carotid sinus syndrome?
patients with this have pressure receptors (baroreceptors) in the carotid sinus region of the carotid artery walls that are excessively sensitive, even mild external pressure on the neck elicits a strong baroreceptor reflex, causing intense vagal acetylcholine effects on the heart, including extreme bradycardia
SA Block
impulse from the sinus node is blocked before it enters the atrial muscle, ventricles pick up a new rhythm (AV node) so that the rate of the ventricular QRS-T complex is slowed but not otherwise altered
Bundle of His
means by which impulses ordinarily can pass from the atria into the ventricles
AV Block
ischemia (coronary insufficiency), compression (scar tissue or calcified portions of heart), inflammation (myocarditis), extreme stimulation by vagus nerves (carotid sinus syndrome)
First Degree (Incomplete) AV Block
PR interval > 0.20 sec, delay of conduction from
the atria to the ventricles but not actual blockage of conduction (could be caused by some heart diseases such as acute rheumatic heart disease)
Second Degree AV Block
PR interval increased to 0.25 - 0.45 sec, sometimes the action potential is not strong enough to pass through the bundle so will see dropped beats
Third Degree (Complete) AV Block
complete block of the signal from the atria to ventricles occur and ventricles establish their own rhythm originating in the A-V node or A-V bundle, P waves become dissociated from the
QRS-T complexes (separate rates for atria and ventricles)
Stokes-Adams Syndrome - Ventricular Escape
in some patients with A-V block, the total block comes and goes; each time A-V conduction ceases, the ventricles often do not start their own beating until after a delay of 5 to 30 seconds (overdrive suppression); some part of the Purkinje system beyond the block begins discharging rhythmically at a rate of 15 to 40 times per minute and acting as the pacemaker of the ventricles (ventricular escape)
Why would a person with Stokes-Adams syndrome faint?
Because the brain cannot remain active for more than 4 to 7 seconds without blood supply, most patients faint a few seconds after complete block occurs because the heart does not pump any blood for 5 to 30 seconds, until the ventricles “escape.”
Incomplete Intraventricular Block—Electrical Alternans
blocked impulse conduction in the peripheral ventricular Purkinje system; partial intraventricular block every other heartbeat
What is a premature contraction?
also known as ectopic beat or extrasystole, most premature contractions result from ectopic foci in the heart, which emit abnormal impulses at odd times during the cardiac rhythm
Premature Atrial Contractions
P-R interval is shortened, indicating that the ectopic origin of the beat is in the atria near the A-V node. Also, the interval between the premature contraction and the next succeeding contraction is slightly prolonged (compensatory pause); these are not as serious and can occur in athletes, smoking, lack of sleep, too much coffee, alcoholism
What is pulse deficit?
pulse wave passing to the peripheral arteries after a premature contraction may be so weak that it cannot be felt in the radial artery (decreased stroke volume)