What electrolyte inactivates troponin and allows actin and myosin to form a bridge enabling fibers to contract?

Choice A rationale

Checking vitamin K levels doesn't directly monitor warfarin's effect.

Choice B rationale

PTT and aPTT assess heparin, not warfarin.

Choice C rationale

INR specifically measures warfarin's effectiveness and safety.

Choice D rationale

Platelet levels don't monitor the anticoagulant effect of warfarin.

Choice A rationale

Cardiac glycosides are not known for increasing heart rate. Instead, they tend to decrease heart rate by enhancing vagal tone and increasing the refractory period of the atrioventricular node, which helps in controlling heart rate, especially in atrial fibrillation.

Choice B rationale

Cardiac glycosides actually increase the force of myocardial contractions. They inhibit the sodium-potassium ATPase pump, which leads to an increase in intracellular sodium and calcium levels in the myocardial cells, thus increasing the force of contraction.

Choice C rationale

Cardiac glycosides do not significantly decrease conduction velocity. They primarily affect the contractility and heart rate but their influence on conduction velocity is relatively mild.

Choice D rationale

Cardiac glycosides improve renal blood flow and increase urine output by increasing the cardiac output and reducing the activation of the renin-angiotensin-aldosterone system. This helps in relieving symptoms of heart failure.