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beat (bet)

1. To strike; to throb or pulsate. 2. A stroke, impulse, or pulsation, as of the heart or pulse. 3. Activity of a cardiac chamber produced by catching a stimulus generated elsewhere in the heart. [A.S. beatan]
apex b. the visible and/or palpable pulsation made by the apex of the left ventricle as it strikes the chest wall in systole; normally in the fifth intercostal space, about 10 cm to the left of the median line.
atrial capture b. the cardiac cycle resulting when, after a period of A-V dissociation, the atria regain control of the ventricles; atrial depolarization due to retrograde transmission from a ventricular ectopic beat or an electronically paced ventricular impulse.
atrial fusion b. a b. that occurs when the atria are activated in part by the sinus impulse and in part by an ectopic or retrograde impulse from A-V junction or ventricle.
automatic b. in contrast to forced b., an ectopic b. that arises de novo and is not precipitated by the preceding b.; thus escaped and parasystolic b.'s are automatic.automatic contraction;
combination b. fusion b
coupled b.'s beats (usually premature) that recur at a fixed interval from a preceding (usually normal) beat.
dependent b. forced b
Dressler b. fusion b. interrupting a ventricular tachycardia and producing a normally narrow QRS complex as a result of the fusion of two impulses, one impulse from the ventricular tachycardia and the other from a supraventricular focus; Dressler b.'s strongly support the diagnosis of ventricular tachycardia by interruption of it.
dropped b. a heart b. that fails to appear.
echo b. extrasystole produced by the return of an impulse in the heart retrograde to a focus near its origin which then returns antegradely to produce a second depolorization.
ectopic b. a cardiac b. originating elsewhere than at the sinoatrial node.
escape b. , escaped b. an automatic b., usually arising from the A-V junction or ventricle, occurring after the next expected normal b. has defaulted; it is therefore always a late b., terminating a longer cycle than the normal.escape contraction;
forced b. 1. an extrasystole supposedly precipitated in some way by the preceding normal b. to which it is coupled; 2. an extrasystole caused by artificial stimulation of the heart.dependent b;
fusion b. a b. triggered by more than a single electrical impulse, when the wave fronts coincide to act together on a single final pathway of activity; in the electrocardiogram, the atrial or ventricular complex when either atria or ventricles are activated jointly by two simultaneous or nearly simultaneous invading impulses.combination b., mixed b., summation b;
heart b. a complete cardiac cycle, including spread of the electrical impulse and the consequent mechanical contraction.ictus cordis;
interference b. ventricular capture in forms of A-V dissociation due to interference.
mixed b. fusion b
paired b.'s See bigeminy.
parasystolic b. parasystole
premature b. extrasystole
pseudofusion b. an electrocardiographic representation of a cardiac depolarization produced by superimposition of an ineffectual electronic pacemaker spike upon a QRS-complex originating from a spontaneous focus within the heart; the pacemaker spike is ineffectual because the electronic discharge, which it represents graphically, occurred within the absolute refractory period of the spontaneous beat and is therefore not indicative of pacemaker malfunction.
reciprocal b. See reciprocal rhythm.
retrograde b. a b. occurring as an electrical activation of a portion of a heart chamber cephalad to the chamber of origin, e.g., an atrial b. triggered by an impulse originating in the ventricle.
summation b. fusion b
ventricular fusion b. a fusion b. that occurs when the ventricles are activated partly by the descending sinus or A-V junctional impulse and partly by an ectopic ventricular impulse.


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