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Dizziness and fast pulse rate

  My periods stopped in Feb. of 98 and in July I started to experience dizziness and a feeling of off-balanced,heart palapitations and pressure in my head.I have been to ENT's,had an MRI,CAT scan,hormones checked, worea holtor monitor for 24 hours,and have had my eyes checked.My pulse rate is high constantly with no answers.What could be causing these symptoms? I am very worried.Thanks
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Dear  Linda,
Thank you for your question. There are many causes of tachycardia  (fast heart beat) and they can be divided roughly into sinus (originating from the sinus node or heart's natural pacemaker) and non-sinus tachycardias.  Nonsinus tachycardias are either  supraventricular (coming from the upper chambers of the heart) or ventricular (coming from the lower chambers of the heart).  Supraventricular tachycardias include:  paroxysmal supraventricular tachycardia, atrial flutter, atrial fibrillation and AV nodal tachycardia. Ventricular tachycardias are more serious in nature and are due to a rapid depolarization of  the ventricles.  
Sinus tachycardia is defined as a heart rate of greater than 100 beats per minute originating from the sinus node.  Sinus tachycardia is classified as either appropriate or inappropriate.  There are many causes of appropriate sinus tachycardia such as exercise, anxiety, panic attacks, dehydration, deconditioning, volume loss due to bleeding or other loss of body fluids, hyperthyroidism, electrolyte abnormalities and many other conditions.
Inappropriate sinus tachycardia can only be diagnosed when all causes of appropriate sinus tachycardia have been ruled out.  It is not clear what causes inappropriate sinus tachycardia but possible etiologies are an increase in the rate at which the sinus node depolarizes and an increased sensitivity to adrenaline.  Once the diagnosis has been made by ruling out all of the potential causes of appropriate sinus tachycardia  there are several treatment options.  If the symptoms are not overly concerning no treatment needs to be done.  There is no increase in morbidity or mortality in persons with this condition and they can expect to have a normal life-span.  For persons in whom the symptoms are unbearable medications such as beta blockers or calcium channel blockers can be used, usually with good results.  In the rare person unable to tolerate medical treatment catheter ablation (burning) of the sinus node with insertion of a pacemaker or surgical removal of the sinus node have been used in the past.  Newer techniques are being developed using catheter ablation to modify and not destroy the sinus node thus avoiding the need for a pacemaker.   This procedure is still in it's infancy and should only be undertaken at a major medical center after consultation with an electrophysiologist.
Below are some journal articles that address this topic in depth.  Your local medical library should be able to help you find copies.
Review Articles:
Krahn AD.  Yee R.  Klein GJ.  Morillo C.  Inappropriate sinus tachycardia: evaluation and therapy. Journal of Cardiovascular Electrophysiology.  6(12):1124-8, 1995 Dec.
Inappropriate sinus tachycardia is an ill-defined clinical syndrome characterized by an increased resting heart rate accompanied by an exaggerated response to exercise or stress. It is not associated with underlying structural heart disease. The mechanism may involve a primary abnormality of the sinus node demonstrating enhanced automaticity or, alternatively, a primary autonomic disturbance with increase sympathetic activity and enhanced sinus node beta-adrenergic sensitivity. The diagnosis of inappropriate sinus tachycardia is one of exclusion. It is most common in young females, with a disproportionate number employed in the health care field. Autonomic and electrophysiologic testing may be required in selected individuals to clarify the mechanism and rule out sinus node reentry or right atrial tachycardia. Therapy of inappropriate sinus tachycardia is empiric. Pharmacologic approaches include beta blockers or verapamil. Radiofrequency catheter ablation of the superior portion of the sinus node shows promise as a useful alternative in patients with refractory symptoms.

Sims JM.  Miracle V.  Sinus tachycardia. Nursing.  26(6):49, 1996 Jun.

Articles Concerning Catheter Treatment Options.
Lee RJ.  Kalman JM.  Fitzpatrick AP.  Epstein LM.  Fisher WG.  Olgin JE.  Lesh MD.  Scheinman MM. Radiofrequency catheter modification of the sinus node for "inappropriate" sinus tachycardia. Circulation.  92(10):2919-28, 1995 Nov 15.
BACKGROUND: Radiofrequency catheter ablation is the treatment of choice for patients with paroxysmal supraventricular tachycardias refractory to medical therapy. However, in symptomatic patients with inappropriate sinus tachycardia resistant to drug therapy, catheter ablation of the His' bundle with permanent pacemaker insertion is currently applied. We evaluated the safety and efficacy of radiofrequency modification of the sinus node as alternative therapy for patients with inappropriate sinus tachycardia. METHODS AND RESULTS: Sixteen patients with disabling episodes of inappropriate sinus tachycardia refractory to drug therapy (4.2 +/- 0.3 drug trials) underwent either total sinus node ablation or sinus node modification. The region of the sinus node was identified as the region of earliest atrial activation in sinus rhythm during electrophysiological study. This region was further defined by use of intracardiac echocardiography (ICE) in 9 patients, in whom it was found that an ablation catheter could be guided reliably and maintained on the crista terminalis. Radiofrequency energy was delivered during tachycardia between either a standard 4-mm or custom 10-mm thermistor-imbedded catheter tip and a skin patch. Total sinus node ablation was performed successfully in all 4 patients in whom it was attempted and was characterized by a junctional escape rhythm. Sinus node modification was successfully achieved in all 12 patients in whom it was attempted and was characterized by a 25% reduction in the sinus heart rate. For the group as a whole, exercise stress testing after ablation revealed a gradual chronotropic response, with a significant reduction in maximal heart rate (132.8 +/- 6.5 versus 179.5 +/- 3.6 beats per minute [bpm]; P < .001) without evidence of an exaggerated heart rate response to a light workload (103.0 +/- 4.1 versus 139.5 +/- 3.5 bpm; P < .001). Twenty-four-hour ambulatory ECG monitoring revealed a significant decrease in maximal heart rate and mean heart rate after ablation (167.2 +/- 2.6 versus 96.7 +/- 5.0 bpm, P < .001, and 125.6 +/- 5.0 versus 54.1 +/- 5.3 bpm, P < .001, respectively). There was a significant decrease in the number of applications of radiofrequency energy required in patients undergoing modification of the sinus node when guided by ICE compared with fluoroscopy alone (3.6 +/- 0.8 versus 10.4 +/- 2.1; P < .01) as well as a decrease in fluoroscopy time (33.0 +/- 9.5 versus 58.5 +/- 8.4 minutes). After a mean follow-up period of 20.5 +/- 0.3 months, there were no recurrences of inappropriate sinus tachycardia in patients who underwent a total sinus node ablation. However, 2 patients who had a total sinus node ablation subsequently required permanent pacing because of symptomatic pauses, and 1 patient developed an ectopic atrial tachycardia. After a mean follow-up of 7.1 +/- 1.7 months, there were two recurrences of inappropriate sinus tachycardia in patients who underwent sinus node modification. However, no significant bradycardia or pauses were observed. Complications encountered during the study included 1 patient who developed transient right diaphragmatic paralysis and another patient who developed transient superior vena cava syndrome. CONCLUSIONS: Sinus node modification is feasible in humans and should be considered as an alternative to complete atrioventricular junctional ablation for patients with disabling inappropriate sinus tachycardia refractory to medical management. Sinus node modification may be aided by ICE.
Jayaprakash S.  Sparks PB.  Vohra J.  Inappropriate sinus tachycardia (IST): management by radiofrequency modification of sinus node.  Australian & New Zealand Journal of Medicine.  27(4):391-7, 1997 Aug.
BACKGROUND: Inappropriate sinus tachycardia (IST) is a rare form of supraventricular arrhythmia. It can cause disabling symptoms and may be refractory to medical treatment. In symptomatic drug refractory patients, sinus node excision or total ablation of the sinus node with permanent pacemaker implantation was the only therapeutic option. Recently, radiofrequency (RF) modification of the sinus node has been reported to be an effective treatment for this condition. AIM: To present our experience with sinus node modification using RF energy in the management of IST. METHODS: Between 1989 to 1996 three patients (two females and one male), aged 28-36 years were diagnosed with symptomatic IST. All had failed multiple drugs and hence underwent sinus node modification using RF. In the first two patients, the site of RF application was guided by anatomical landmarks using fluoroscopy to localise the presumed most superior portion of the crista terminalis and also the earliest site of atrial activation. In the third patient, a 20 pole electrode catheter was used to map the crista terminalis and guide the ablation. Success was defined by 20-30% reduction in the heart rate with normal atrial activation sequence after ablation. RESULTS: The three patients described here had IST by clinical, electrocardiographic and electrophysiological criteria and were refractory to multiple antiarrhythmic drugs. The number of RF applications were 11, 15, and three applied at the site of earliest atrial activation for the control of heart rates. Patient 3 had a early recurrence at one month and underwent repeat sinus node modification (five RF applications). All three patients who underwent RF modification of the sinus node had a successful outcome. The procedure was uncomplicated and the patients remain asymptomatic during follow up (20, 12 and three months) with satisfactory control of heart rate, although one patient requires atenolol which was previously ineffective. CONCLUSIONS: RF modification of the sinus node is feasible and effective for IST, and should be the treatment of choice in patients refractory to medical therapy.
Surgical treatment  (Only as a last resort)
Esmailzadeh B.  Bernat R.  Winkler K.  Meybehm M.  Pfeiffer D.  Kirchhoff PG.  Surgical excision of the sinus node in a patient with inappropriate sinus tachycardia.  Journal of Thoracic & Cardiovascular Surgery.  114(5):861-4, 1997 Nov.
Information provided in the heart forum is for general purposes only.  Only your physician can provide specific diagnoses and therapies.  Please feel free to write back with additional questions.
If you would like to make an appointment at the Cleveland Clinic Heart Center, please call 1-800-CCF-CARE or inquire online by using the Heart Center website at www.ccf.org/heartcenter.  The Heart Center website contains a directory of the cardiology staff that can be used to select the physician best suited to address your cardiac problem.

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