Delayed afterdepolarizations

The answer is c. (Katzung, pp 115-117) Overloading of cell Ca leads to delayed afterdepolarizations. These afterpotentials can interfere with normal conduction by further reducing the resting potential if they regularly reach threshold in the conduction system, an arrhythmia can occur. 

Verapamil can suppress both early and delayed afterdepolarizations and may antagonize slow responses arising in severely depolarized tissue. 

Two forms of abnormal activity, early top) and delayed afterdepolarizations bottom). In both cases, abnormal depolarizations arise during or after a normally evoked action potential. They are therefore often referred to as "triggered" automaticity, ie, they require a normal action potential for their initiation. 

The uncovering of a hidden mechanism of dysrhythmia. For example, antidysrhythmic drugs can cause early or delayed afterdepolarizations, which can result in dysrhythmias. 

Triggered automaticity is also a possible mechanism for abnormal impulse generation. Briefly, triggered automaticity refers to transient membrane depolarizations that occur during repolarization (early after-depolarizations [EADs]) or after repolarization (delayed afterdepolarizations [DADs]) but prior to phase 4 of the action potential. After-depolarizations may be related to abnormal calcium and sodium influx during or just after full cellular repolarization. Experimentally, early after-depolarizations may be precipitated by hypokalemia, type la antiarrhythmic drugs, or slow stimulation rates— any factor that blocks the ion channels (e.g., potassium) responsible... 

ABBREVIATIONS AV, atrioventricular DAD, delayed afterdepolarization DC, direct current HAD, early afterdepolarization WPW, Wolff-Parkinson-White supraventricular tachycardia IV, intra-X venous T, increase -I, decrease , unclear. 

K. Kujala, J. Paavola, A. Lahti, K. Larsson, M. Pekkanen-Mattila, M. Viitasalo, A. M. Lahtinen, L. Toivonen, K. Kontula, H. Swan, CeU model of catecholaminergic polymorphic ventricular tachycardia reveals early and delayed afterdepolarizations. PLoS One 7, e44660 (2012). 

Wang YX, Yao XJ, Tan YH (1994) Effects of berberine on delayed afterdepolarizations in ventricular muscles in vitro and in vivo. J Cardiovasc Pharmacol 23 716-722... 

EADs) occur during the plateau or rapid repolarization phase of the action potential, and these can lead to tachycardias independent of reentrant conduction. It was reported that about 75% of tachycardias initiated early during reperfusion are initiated by a nonreentrant mechanism. It is also well estabhshed that fibrillation can be initiated by EADs. By comparison, delayed afterdepolarizations (DADs) occur following action potential repolarization, and these can trigger premature action potentials and contractions. 

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