Atrioventricular block, variable

Variables for sinoatrial and atrioventricular nodal tissue only. 0 lso has sodium, calcium, and /3-blocking actions. 

Widening of the QRS complex duration to greater than 100 milliseconds is typical of tricyclic antidepressant and quinidine overdoses (Figure 59-1). The QTC interval may be prolonged to more than 440 milliseconds in many poisonings, including quinidine, tricyclic antidepressants, several newer antidepressants and antipsychotics, lithium, and arsenic (see also http //www.torsades.org/). Variable atrioventricular (AV) block and a variety of atrial and ventricular arrhythmias are common... 

The rate of electrical impulse conduction through different cardiac tissues is variably affected. Thus low doses increase the velocity in the atrium and ventricle but toxic doses decrease velocity, sometimes even producing a block. Digitalis affects the refractory period by shortening it in the atrium, but markedly prolonging it for atrioventricular (AV) transmission. 

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