Medical professionals help? i have postural ortho static tachycardia syndrome.?

i just got a pacemaker for accelerated junctional rhythm. now my ekg said short pr interval.What is that? can a pacemaker help tachycardia. my heart goes to 200 with excertion or stairs-hills. he put me on midogrin 10 mg. 3x a day.

What is Postural Tachycardia Syndrome?
Postural tachycardia syndrome (POTS) is a disorder characterized by a pulse rate that is too fast when the patient stands. Symptoms include rapid heartbeat, lightheadedness with prolonged standing, headache, chronic fatigue, chest pain, and other nonspecific complaints. Causes of POTS usually are not identified in individual patients. Reversible causes such as low blood volume should be ruled out.
Is there any treatment?
Treatment of POTS depends upon the severity of the symptoms. Individuals with the disorder are usually advised to increase their fluid and salt intake. Body stockings may provide some relief. Drug therapy, with fludrocortisone, beta-blockers, midodrine, or clonidine, can be beneficial. Physical exercise, especially calf muscle resistance training, also may help. Some patients may require and benefit from insertion of a cardiac pacemaker.
An accelerated junctional rhythm (rate >60) is a narrow complex rhythm that often supersedes a clinically bradycardic sinus node rate. The QRS complexes are uniform in shape, and evidence of retrograde P wave activation may or may not be present.
Midodrine (MI-doe-dreen) is a medicine used to treat low blood pressure (hypotension). It works by stimulating nerve endings in blood vessels, causing the blood vessels to tighten. As a result, blood pressure is increased.
Midodrine is an alpha-sympathomimetic drug. It is used to treat hepatorenal syndrome and orthostatic hypotension.It is not given before bedtime to avoid supine hypertension; the last dose of midodrine should be taken at least 3 to 4 hours before bedtime.
Please see the web pages for more details on Postural orthostatic tachycardia syndrome and Midodrine (not midogrin).