Sinus tachycardia: what it is and how to treat it
Sinus tachycardia is the most common heart rhythm disturbance found in clinical practice
The medical term sinus tachycardia encompasses a heterogeneous group of disorders including:
- sinus tachycardia secondary to psychophysical stress
- sinus tachycardia secondary to other pathologies,
- orthostatic sinus tachycardia (Postural Orthostatic Tachycardia Syndrome – POTS), characterised by the presence of sinus tachycardia when standing upright
- inappropriate sinus tachycardia, where there is an alteration of the physiological regulatory mechanisms of the chronotropic response.
The clinical and symptomatological overlap of these disorders sometimes makes a correct differential diagnosis difficult.
Postural Orthostatic Tachycardia
Postural Orthostatic Tachycardia is characterised by an intolerance to standing that manifests with changes in posture.
After changing from supine to upright position, there is an increase in frequency of 30 bpm over baseline or heart rate of 120 bpm for at least 10 minutes, without associated orthostatic hypotension.
The condition can then be diagnosed with the Tilt Up Test.
Inappropriate sinus tachycardia
Inappropriate sinus tachycardia is a syndrome in which the sinus heart rate is higher than it should be: the resting heart rate can exceed 100 bpm and minimal physical exertion increases it rapidly and significantly.
Patients have daytime heart rates above 100 bpm, unrelated to physiological increased demand, with 24-hour averages around 90 bpm, and heart rates that normalise at night.
In inappropriate sinus tachycardia, the acceleration of the heart rate for minimal effort is excessive and its recovery is very slow and does not reduce to normal levels.
The origin of the rhythm is always the physiological one, i.e. from the sinoatrial node, and therefore on the electrocardiogram the P waves have morphology and axis superimposed on those of the normal sinus rhythm.
What are the symptoms of sinus tachycardia?
It occurs most frequently in the female sex, generally between the second and fifth decades.
The symptom pattern is varied and the mode of presentation may be constant or intermittent.
Among the most frequent symptoms are
- easy fatigability,
- exercise intolerance,
Usually the diagnosis is not accidental, but patients come to the doctor’s observation due to the appearance of one or more symptoms.
Diagnosis: what tests should be performed?
Instrumental tests such as: electrocardiogram, cardiac Holter (preferably 12-lead), echocardiogram, and some haematochemical and hormonal tests are essential for a correct diagnosis.
The diagnosis of IST is a diagnosis by exclusion and can therefore only be made in the presence of a prolonged and recurrent sinus tachycardia that cannot be explained in any other way.
Before a diagnosis of Inappropriate Sinus Tachycardia is made, other conditions such as postural orthostatic tachycardia and appropriate-secondary sinus tachycardia must be excluded in association with other causes, including those listed below anticholinergics, catecholamines, alcohol, anaemia, antiasthiacs, meta-amphetamines, cocaine, caffeine, marijuana, dehydration, fever, anxiety, panic attacks, pain, myocardial ischaemia, pulmonary embolism, valvulopathies, physical activity, pneumothorax, pericarditis, myocarditis, hyperthyroidism, hyperglycaemia, hypovolaemia, anaemia, hyperpyrexia, infections, hypoxaemia, pheochromocytoma.
Treatment: how is sinus tachycardia treated?
Inappropriate sinus tachycardia is treated with lifestyle changes and increased aerobic physical activity, combined with:
- Beta-blocking drugs (particularly metoprolol and atenolol) which are effective in reducing the frequency, although they are sometimes not tolerated due to the onset of arterial hypotension.
- Ivabradine, an If-current antagonist, is effective in significantly reducing heart rate without any influence on blood pressure and improved exercise endurance.
The use of calcium antagonists is controversial and their efficacy is questionable.
Finally, let us mention transcatheter ablation: some patients do not respond to single or multi-drug therapy. In these patients it is useful to perform transcatheter ablation of sinus tachycardia.
The interventional procedure is aimed at modulating the activity of the sinoatrial node, which thus reduces its intrinsic frequency.