AEMCA Practice Exam

Automaticity refers to the ability of certain heart cells to generate an electrical impulse without external stimulation. Factors that enhance automaticity generally increase the excitability of cardiac cells, making them more likely to initiate spontaneous depolarization.

Increased preload, which is the initial stretching of the cardiac muscle fibers prior to contraction, is not primarily associated with enhancing automaticity. Instead, it relates more to the volume of blood in the ventricles at the end of diastole and the subsequent force of contraction during systole. While preload plays a significant role in the Frank-Starling mechanism and helps improve cardiac output, its influence on automaticity is minimal compared to the other conditions mentioned.

Hypokalemia, myocardial infarction (MI), and digitalis toxicity can all affect automaticity in different ways. For instance, hypokalemia can increase automaticity by altering the resting membrane potential of cardiac cells, making them more prone to spontaneous depolarization. An MI can lead to increased automaticity in ischemic areas of the heart as they may develop ectopic pacemaker activity. Digitalis toxicity can also enhance automaticity by increasing intracellular calcium levels, which facilitates more frequent depolarizations.

Thus, among the conditions presented, increased preload is the least likely to enhance automatic