cardio question

[marktwain]

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if automaticity/positive chronotropism is a function of sodium ions, why is a supraventricular tachycardia stopped by calcium channel blockers and not sodium channel blockers???
I am well aware that the calcium channel blocker robs the atrial musculature of the needed calcium for contraction, but why not rob the source of the automaticity of its ions?

 

[nkhan]

If I recall, phase 4 of SA node curve is I-f which is spontaneously depolarizing sodium channels but phase 0 (the actual upstroke of the AP) is mediated by calcium channels. So I'm guessing it won't stop the sodium currents, but it will block the AP's from occurring. Remember this is just the opposite in cardiac muscle (not the SA/AV node etc) in which calcium channels open in phase 2 and cause a plateau with K+ channels effluxing as well, whereas phase 0 (the upstrake) is sodium mediated.

 

[marktwain]

I appreciate your timely explanation, FA also shows that Class 1C sodium channel blockers are used in intractable SVT. This and your explanation has put my earth back on its axis.
Thanks Mr Khan👍