Neurally Mediated Syncope

Neurally Mediated Syncope (NMS) is a complex and poorly understood process by which patients become very lightheaded, or may lose consciousness. It is currently undergoing a great deal of investigation by cardiologists and neurologists throughout the world. It is also termed neurocardiogenic dysfunction and vasovagal syncope. It has also been termed postural orthostatic tachycardia syndrome (POTS) by some neurologists.

In our current understanding, NMS may represent an exaggerated normal response, or may occur as a result of an acquired autonomic (nervous system) problem. Because of the extreme complexity of this multi-organ process, current medical research has been unable to identify specific defects which, in turn, would lead to uniform and effective therapy.

A patient with NMS develops symptoms in the upright (standing or sitting) position. abrupt symptoms, such as a loss of consciousness, are rare. The vast majority of patients have gradual (seconds to minutes) worsening of lightheadedness and weakness without vertigo (the sensation that a room is spinning). This progresses to nausea and/or sweating, and is frequently associated with anxiety and palpitations.

If these symptoms are not acted upon by the patient lying down, they may experience a fading sensation associated with sight or hearing loss. Patients frequently report that their vision becomes tunneled, noting that it sounds as though the people next to them seem a “long way off.”

Finally, this will progress to a loss of consciousness. Often, however, patients are able to let themselves down to a couch or the ground without injuring themselves. On rare occasions, the patient may be observed to have brief, seizure-like, hand or arm activity, which is associated with a brief but dramatic drop in blood pressure.

Once having passed out, or having “aborted” a developing spell by lying down (preferably with the legs elevated), patients rapidly gain consciousness, being aroused and fully aware of their surroundings within seconds. Normally, after 5-10 minutes, patients can resume normal activity, and rarely feel “washed out.”

Syncope symptoms sometimes begin with the adolescent growth spurt. they may be related to the onset of menstruation for girls (women may experience worsening of spells on a monthly basis, possibly related to hormonal changes). Scientists believe this may develop as a result of an acute autonomic neuropathy, which may follow a viral infection, and may be seen in patients with other neuropathies or nerve diseases involving their arms and legs, and disease processes such as diabetes and amyloidosis. It can be seen in patients with mitral valve prolapse, a situation where patients have a floppy or redundant heart valve. Spells may be relieved with pregnancy or weight gain. NMS can also be aggravated with central blood volume reduction such as with acute viral gastroenteritis, after excessive vomiting, significant bleeding or after a lengthy illness with bed rest causing deconditioning.

Overeating and dehydration, stress or sudden excitement can precipitate these spells. Intake of plenty of water and salt, avoidance of long warm baths, hot tubs, saunas, and prolonged exercise is recommended for patients with frequent spells. Moderation of activity causing these aggravations may need to be individualized for patients with infrequent spells.

Certain drugs, prescribed or over-the-counter, may aggravate this condition. Some of these may include blood pressure medications, which can aggravate the tendency toward NMS by blocking neurovascular reflexes. Various diuretics (water pills), antihistamines, cough and cold medications, certain antidepressants and anticholinergic agents may also aggravate this situation.

In general, spells begin with reduced venous return of blood to the heart due to volume contraction or loss, or to preferential venous pooling. This may be aggravated by venous disease or prolonged upright posturing. Blood return to the heart is pumped first to the lungs and then to the body. If the decrease in venous return develops, thereby causing a slight drop in the systemic blood pressure, reflexes are activated that cause heart rate and the blood pressure to rise, and the force of contraction to increase. This heart “overactivity” increases, thereby triggering special heart nerves (“C” fibers), which detect mechanical overactivity to the heart, yielding a decrease in blood pressure and slowing the heart rate, leading to symptoms of NMS.

Therapy revolves around common sense measure that may alleviate or lessen the symptoms, as well as medications. Rarely, pacing therapy (implantable permanent pacemaker) may help alleviate symptoms. In general, therapy works toward preventing spell development or initiation, but does not “cure” the problem.

Evaluation of patients with symptoms thought possibly to be due to NMS include the physical examination and history. The history may be the most important aspect of the evaluation. Screening blood tests and an echocardiogram (heart ultrasound) are performed. Occasionally a heart (event) monitor may be used to correlate heart rate and symptoms. Tilt table testing has, however, emerged as the best means to examine a patient’s susceptibility to syncope.

During tilt table testing, the patient is placed on a flat, supportive table that allows rotation from a flat (supine) to mostly upright position. An IV line is placed to allow administration of testing medications or fluids. Frequent blood pressure measurements and continuous EKG monitoring recordings are made. Baseline measurements are taken in the supine position and during the upright portion of the testing procedure. Observations for the development of symptoms and associated blood pressure or heart rate changes are made.

The patient is asked to relate their symptoms, noting any weakness, shortness of breath, chest pain, lightheadedness or nausea. Infusion of isoproterenol (a drug used to slightly increase heart rate) may be given to potentiate symptoms. Intravenous beta blockers may be given prior to repeat tilt to assess this medication’s value in preventing recurrence of symptoms. Should a significant blood pressure or heart rate decrease occur during the upright tilt, the tilt table will be promptly lowered to a supine position and the patient observed closely as they recover promptly. Future examinations may also incorporate autonomic nervous system testing utilizing non-invasive tests. The tilt test is not always predictive; a negative test may not mean the patient does not have NMS. Certainly the history, combined with the information gained from the tilt test and other tests, should be factored together.

Medications given in an attempt to prevent recurrent spells are “active” at various levels of this complicated reflex. Medications may serve to increase the return of blood to the heart, decrease the reactive increase in the activity of the heart that would otherwise initiate the reflex, or increase peripheral artery pressure. These medications include lopressor, tenormin, disopyramide, fluodrocortisone, theophylline, and midadrine. You will be given a medication with explanation and side effects on the particular drug you are taking. In general, these medications are well tolerated and provide improvement in patients with a pattern of recurrent spells.

Neurally mediated syncope do’s & don’t’s

DO:

·        add salt to your foods, particularly in hot weather. (if you have a past history of congestive heart failure, check with your physician.)

·        drink extra fluids.

·        know the brand name and chemical (generic) name of your medication.

·        take you medication at prescribed times.

·        when traveling, stop every few hours and get out and walk around to improve your circulation.

·        warm up with easy stretching exercises at the beginning of an exercise program.

·        avoid exercise that makes you hold your breath, grunt or bear down.

·        call us with any problems.

DON'T:

·        get dehydrated – drink plenty of fluids.

·        get up too quickly from bed or chairs. rise slowly.

·        get overtired. be sure to take breaks during long periods of physical exercise.

·        skip your medications just because you are feeling well.

·        stop taking your medications without talking to your physician.

·        consume caffeine.

·        consume alcohol in extreme heat, or in a warm environment such as a hot tub.

These lists are not meant to be all-inclusive. Should you have any further questions regarding neurally mediated syncope, or about the symptoms or evaluations outlined above, please feel free to contact Iowa Heart Center’s arrhythmia services department for further information.