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Differential diagnosis?
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Differential diagnosis?

My cardiologist suspects I have IST - testing for pheochromocytoma came back negative but I seem to have recently developed hypertension, does this change the diagnosis of IST, could anything else be at cause?
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3198987_tn?1349078636
No.
I have IST, and pheochromocytoma is just one cause of IST, but mainly its caused by the sinus node being over sensitive to adrenalin. Blood pressure increase is unrelated to IST as far as I'm aware, but I could be wrong about that. Mainly just the heart rate is effect by IST. How fast is your heart rate at rest? at night?, and while you're walking if you dont mind me asking.
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It just seems weird that I've suddenly developed hypertension when I usually used to have hypotension.. Without beta blockers, Walking around I'm generally 130ish, walking up stairs 150 and shower at 180. Also I'm on bisoprolol but this doesn't seem to be lowering my bp? My IST is quite debilitating as I have most of the symptoms of heart failure..
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1756321_tn?1377771734
"IST is a diagnosis of exclusion. Almost always, sinus tachycardia is appropriate. Therefore causes of appropriate sinus tachycardia must first be excluded:

Anemia
Pheochromocytoma
Hyperthyroidism
Volume Depletion
Fever
Anxiety Disorder
Medications
Cardiomyopathy"

"Patients who are being considered for IST must have blood or urine tests to exclude anemia, hyperthyroidism, and pheochromocytoma. Medications can also cause heart racing (hydralazine or other vasodilators, too much thyroid hormone replacement, sympathomimetics for asthma or COPD, anticholinergic medications for irritable bowel syndrome, stimulants prescribed for ADD).

A tilt table test is then required to exclude autonomic disorders that can mimic IST: postural orthostatic tachycardia syndrome (POTS) or orthostatic hypotension. This disorder involves abnormal control of blood pressure, and the fast heart rhythm is necessary because of the hypotension that occurs when the patient stands and blood pools in the veins of the legs. Eventually, an EP study may be required to exclude tachycardias arising from near the sinus node, but not from the sinus node itself (5)."

Excerpts from Heart Racing - Inappropriate sinus tachycardia.
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3198987_tn?1349078636
Well the good news is yours seems to not be as serious as others. Some people who have this have their hearts in the 160-170's just from walking across the room. Also while every patient is different I want to add that I to was put on bisoprolol and it did absolutely nothing for my IST. In fact it seemed to make it worse, much worse. Switched to Atenolol and I've seen really good results.
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