Необъяснимая синусовая тахикардия: причины, симптомы и лечение

Syndrome where the sinus heart rate is inexplicably faster than expected
While sinus tachycardia is very common and is the most common type of tachycardia, it is rare to be diagnosed with inappropriate sinus tachycardia as an independent symptom that is not part of a larger condition. Although somewhat rarely diagnosed, IST is viewed by most to be a benign condition in the long term. Symptoms of IST, however, may be distracting and warrant treatment. The heart is a strong muscle and typically can sustain the higher than normal heart rhythm, though monitoring the condition is generally recommended. The mechanism and primary etiology of inappropriate sinus tachycardia has not been fully elucidated. An autoimmune mechanism has been suggested, as several studies have detected autoantibodies that activate beta adrenoreceptors in some patients. The mechanism of the arrhythmia primarily involves the sinus node and peri nodal tissue and does not require the AV node for maintenance. Treatments in the form of pharmacological therapy or catheter ablation are available, but the condition is currently difficult to treat successfully.

Palpitations are the most common symptom in roughly 90% of patients. Other symptoms include chest pain, fatigue, shortness of breath, presyncope, syncope,

The exact cause of Inappropriate sinus tachycardia is still being debated and remains unknown. Several mechanisms have been suggested, including increased sympathetic or decreased parasympathetic drive, increased intrinsic heart rate, dysfunctional neurohormonal modulation, ectopic sinus node activity, and beta adrenergic receptor autoantibodies. Some data show an abnormal response to autonomic stimulation as a result of tissue/cell level changes (intrinsic mechanism), whereas others show a disruption of the autonomic stimulation itself with normal tissues/cell level findings (extrinsic mechanism). It is possible that both mechanistic theories are correct because, despite sharing a single common pathway of sinus tachycardia, individual patients' underlying mechanistic etiologies may differ.

Over 15 electrical currents tightly control the sinus node. The calcium clock and the funny current appear to be the most important currents in regulating sinus node rate. Sinus activation and thus heart rate is regulated further through the autonomic nervous system. At rest, the sinus node is primarily regulated by tonic and phasic parasympathetic activation in normal, healthy individuals. Exercise causes vagal activation, sympathetic activation, and increases in catecholamine levels, which raises sinus rates. Any aspect of regular regulatory processes influencing sinus rate may be compromised in patients with IST.

Inappropriate sinus tachycardia is primarily a diagnosis of exclusion. and hereditary myopathy with lactic acidosis (Larsson–Linderholm syndrome). Sinus tachycardia is a feature of both postural orthostatic tachycardia syndrome and Inappropriate sinus tachycardia. In POTS, there's an abnormal response by the autonomic nervous system when standing up. POTS symptoms are most common when the patient is upright. POTS syndromes and inappropriate sinus tachycardia may overlap, raising the possibility of shared mechanisms. The most common symptoms of POTS are dizziness and, on occasion, syncope, which are also common in IST. Pharmacologic therapy for Inappropriate sinus tachycardia patients should be started gradually, with the goal of lowering HR and improving symptoms. The pharmacologic treatment of IST is empirical, with a trial and error approach typically employed. There are no specific guidelines in place to determine which patients with inappropriate sinus tachycardia should be considered for invasive treatments. Interventions to treat inappropriate sinus tachycardia range from surgical sinus node exclusion to sinus or AV node radiofrequency catheter ablation, which typically is followed by permanent pacemaker implantation and, in recent years, radiofrequency sinus node modification. Several clinical trials have described sinus node modification or ablation in Inappropriate sinus tachycardia. Primary success rates are generally good, however, there is a high rate of symptom recurrence and significant complication rates. These complications include the need for permanent pacing, transient superior vena cava syndrome, and temporary or permanent paralysis of the phrenic nerve. Furthermore, sinus node modification or ablation may not alleviate all IST related symptoms. There is also no consensus on the best approach, which includes modifications or ablation, open chest versus conventional intravascular access, and mapping methods. Finally, there has been no evidence of symptomatic improvement over time.

IST has a generally benign prognosis. One possible reason for a favourable prognosis is that, while IST patients have faster heart rates, their heart rate slows slightly during sleep as well as during various diurnal patterns. Long term consequences are few, but published studies are small, follow up is limited, and populations are varied. Although there have been isolated reports, IST is rarely associated with tachycardia induced cardiomyopathy.

Inappropriate sinus tachycardia, defined as 24 hour average HR > 90 bpm and HR > 100 bpm in a supine or sitting position, has a prevalence of 1.16% in the general population. The epidemiology of Inappropriate sinus tachycardia is not well understood. IST can occur at any age, but it is most common in adolescents and young adults.