Drug therapy for IST has generally been limited to beta blockers, calcium channel blockers, and antiarrhythmic drugs. These are the drugs that have a direct effect on the sinus node, so using them makes sense. But limiting drug use to these agents is a result of the fact that IST is usually diagnosed and treated by cardiologists, who tend not to subscribe to the “generalized autonomic dysfunction” theory of IST. Considering that IST may be one of many dysautonomias opens up the possibility of using several other medications that might be of benefit – these include midodrine, florinef, and the serotonin-reuptake inhibitors.
Beta blockers block the effect of adrenaline on the sinus node, and since patients with IST have an exaggerated response to adrenaline, using beta blockers is logical. Unfortunately, they do not work in all patients.
Calcium blockers and antiarrhythmic drugs have a direct effect on the “firing rate” of the sinus node. But calcium blockers have been only marginally effective in these patients, and antiarrhythmic drugs are not only minimally effective, they expose patients to a relatively high degree of toxicity.
Florinef is a drug that causes sodium retention. Some dysautonomic syndromes – especially POTS and vasovagal syncope – have been shown to be related to decreases in blood volume, and a sodium-retaining drug can increase the blood volume toward normal, and reduce symptoms.
Midodrine causes the tone of the blood vessels to increase, preventing low blood pressure. This drug has proven quite effective in treating vasovagal syncope and in POTS. Whether it is effective in treating IST is unknown, but in some individuals it might be worth a try. (Low blood pressure is a feature seen in many patients with IST.)
Serotonin-reuptake inhibitors (the Prozac family of drugs) are used primarily to treat depression and anxiety, but also have proven useful in treating several of the dysautonomia syndromes. No reports are available using these drugs for IST, but again it might be worth a try.
Often patients’ symptoms can be controlled to a reasonable degree by using a combination of drugs. Such combinations must be administered on a trial-and-error basis, and so require a certain amount of patience, understanding, and trust between the doctor and patient. This is difficult to achieve if the doctor thinks the patient is just nuts. In order to be successfully treated, patients with IST (and the other dysautonomias) must often do a fair amount of doctor shopping.
The important thing about using any drugs in treating IST is this: because IST doesn’t cause death, the only goal in treating this condition is to reduce symptoms. So if the drugs make you feel worse, or have no beneficial effect, there is no reason to take them.
Non-drug therapy.
Increase salt intake. This must be done with the approval of the physician, because it goes against society’s and the medical profession’s prejudice against sodium. But salt increases the blood volume, and to the extent that a reduced blood volume contributes to symptoms, increasing the salt intake might help alleviate symptoms.Sinus node ablation. Cardiologists, especially electrophysiologists, have largely been swayed by the data suggesting that IST is primarily a disorder of the sinus node (as opposed to a more generalized disorder of the autonomic nervous system.) Subscribing to this point of view, as we have noted, has limited their horizons in administering drug therapy. It has also created a certain amount of enthusiasm for using radiofrequency ablation (a technique in which part of the cardiac electrical system is cauterized through a catheter) to modify the function of – or even destroy the function of – the sinus node.
Sinus node ablation has so far achieved only limited success. While IST has been reported as being successfully treated in up to 80% of patients immediately after sinus node ablation, the IST recurs within a few months in the large majority of these patients.
Waiting. One reasonable non-pharmacologic approach to managing IST is to do nothing. While the natural history of this disorder has not been formally documented, it seems likely that IST tends to improve over time in most patients. “Doing nothing” may not be an option in patients who are severely symptomatic, but many patients with IST can tolerate their symptoms once they are assured that they do not have a life-threatening cardiac disorder, once they are told that the problem is likely to improve on its own eventually, and once they are enlightened as to the treatment options.
