Mechanism of 'inappropriate' sinus tachycardia. Role of sympathovagal balance.

Abstract

BACKGROUND "Inappropriate" sinus tachycardia (IST) is an uncommon and poorly defined atrial tachycardia characterized by inappropriate tachycardia and exaggerated acceleration of heart rate with "normal" P wave. The mechanism of this tachycardia is unknown. The purpose of the present study was to determine the role of autonomic balance in the genesis of IST. METHODS AND RESULTS Six female patients aged 23 to 38 years with IST and 10 age- and sex-matched control subjects were assessed with the following autonomic function tests: (1) sympathovagal balance to the sinus node assessed by calculating the LF/HF (low frequency/high frequency) ratio using power spectral analysis both in the supine position and after 10 minutes of head-up tilt to 60 degrees, (2) cardiovagal reflex assessed by cold face test (CFT), (3) beta-adrenergic sensitivity as determined by calculating isoproterenol dose-response curves and isoproterenol chronotropic dose 25 (CD25), and (4) intrinsic heart rate (IHR) assessed after autonomic blockade with atropine 0.04 mg/kg and propranolol 0.2 mg/kg administered as an intravenous bolus. No significant differences in the LF/HF ratio both in the supine position (2.8 +/- 0.3 versus 2.6 +/- 0.4) and during upright tilt (8.7 +/- 1.3 versus 8.5 +/- 0.5) were observed between control subjects and IST patients. Cardiovagal response to CFT was markedly depressed in all patients (6.3% IST patients versus 24.2% control subjects, P < .001). beta-Adrenergic hypersensitivity to isoproterenol was noted in all patients (mean CD25, 0.29 +/- 0.10 microgram IST patients versus 1.27 +/- 0.4 microgram control subjects; P < .001), and high IHR was noted in all cases. The patients were treated with high doses of beta-blockers with adequate short-term control. Radiofrequency catheter ablation of the sinus node area was performed in one drug-refractory patient. CONCLUSIONS These findings suggest that the mechanism leading to IST is related to a primary sinus node abnormality characterized by a high IHR, depressed efferent cardiovagal reflex, and beta-adrenergic hypersensitivity.

Unexplained preoperative tachycardia: is it an important issue?

“…La tachycardie sinusale est associée à une augmentation de la sensibilité à la stimulation ß-adrénergique selon un déplacement vers la droite de la courbe dose-réponse à l'isoprotérénol. 3 La tachycardie sinusale est appropriée ou non (disproportionnée aux demandes). Inappropriée, elle est continue ou temporaire.…”

“…Inappropriée, elle est continue ou temporaire. 3 Survenant surtout chez les jeunes femmes, elle se manifeste par des palpitations légères ou une tachycardie incapacitante incessante.…”

“…Sinus tachycardia is associated with an increased sensitivity to ß-adrenergic stimulation with a shift to the left of the dose-response curve to isoproterenol. 3 Sinus tachycardia can be appropriate or inappropriate (out of proportion with demands). Inappropriate sinus tachycardia can be continuous or temporary.…”

“…Inappropriate sinus tachycardia can be continuous or temporary. 3 It occurs mostly in young females resulting in mild palpitations or incapacitating incessant tachycardia.…”

Síndromes de disfunción autonómica asociados con intolerancia ortostática.

“…Se han documentado, además, respuestas exageradas al reto con isoproterenol y norepinefrina sérica >600 ng/ml. En estos pacientes, el diagnóstico diferencial con la taquicardia sinusal inapropiada (TSI) es difícil y se basa en las características de las respuestas a las pruebas de función autonómica, especialmente la presencia de un aumento del automatismo del nodo sinusal, que es diagnóstico de la TSI y que no ha sido descrito en los pacientes con STOP (20). Esta diferenciación es importante debido a la posibilidad de establecer diagnósticos equivocados como el de TSI, situación en la cual pueden terminar en modificación del nodo sinusal bajo radiofrecuencia y que, después de una aparente eliminación exitosa de la taquicardia, persista la intolerancia ortostática severa.…”