can ANYONE explain how high ca+2 levels change heart rate?

Answer 1

Calcium is involved in cardiac muscle contraction. Essentially the initial depolarization of cardiac muscle activated voltage-gated calcium channels allowing an influx of calcium ions into the cytoplasm of the cardiac muscle cells.

The rise in intracellular calcium allows release of calcium from the Sarcoplasmic Reticulum, further elevating the intracellular calcium concentration.

The high concentration of calcium within the cardiac muscle cell causes a conformational change in the troponin molecule allowing the actin head to bind to the myosin fibre and to execute the power stroke, ratcheting and shortening the muscle fibre (cardiac muscle contraction).

Then calcium is sequestered in the Sarcoplasmic Reticulum and pumped back out of the cell, lowering the calcium level and resetting the conformation of the actin, myosin and troponin.

It is this last bit that is more difficult with hypercalcaemia. This causes a prolongation of the QT interval and makes the heart more vulnerable to a variety of arrhythmias.

In particular there can be an increased risk of R-on-T phenomenon and hence Ventricular Fibrillation.

Answer 2

because your heart's automaticity relies on Sodium, Pottasium and Calcium to work correctly (have the electrical impulses travel correctly); any significant change in the amount of these will change how the electrical impulses flow from the SA node all the way down to the Perkinge Fibers.




^^^^
I'll bet that guy has no idea what any of that means.

Or even what a QT wave is.