Generality
Sinus tachycardia is an arrhythmia characterized by an increase in the frequency and speed of the sinus rhythm, ie the heartbeat imposed by the atrial sinus node. Sinus tachycardia is the most common form of tachycardia and often does NOT represent an alarming episode. In fact, similar arrhythmic manifestations can be the normal consequence of physical exercises or of a strong emotion, physiological events at the end of which the cardiac rhythm returns to normal. Therefore, no specific treatments are needed. Episodes of sinus tachycardia are common in fever, but disappear when the body temperature is normal. Very different is the case of sinus tachycardias due to stable and serious diseases, such as heart disease or anemia.
Arrhythmias, what are they?
Before proceeding with the description of sinus tachycardia, it is advisable to briefly review what are cardiac arrhythmias.
Cardiac arrhythmias are alterations of the normal heartbeat rhythm, also called sinus rhythm as it originates from the atrial sinus node . The atrial sinus node emits the impulses for the contraction of the heart and is considered the dominant marker-center, as responsible for the normality of the heartbeat.
The heart rate is expressed in beats per minute and is considered normal if it stabilizes in a range of values between 60 and 100 beats per minute. There are three possible alterations and it is sufficient if one is present only because an arrhythmia occurs. They are:
- Changes in the frequency and regularity of sinus rhythm. Heart rate can become faster (over 100 beats per minute → tachycardia) or slower (less than 60 beats per minute → bradycardia).
- The variation of the center of the dominant pedestal center, that is the point of origin of the primary impulse that determines the cardiac muscle contraction. The marker centers are more than one in the heart, but the atrial sine node is the main one and the others should serve only for the propagation of the contraction pulses generated by it.
- Impulse propagation (or conduction) disorders.
The pathophysiological mechanisms * that underlie these three alterations allow us to distinguish arrhythmias in two large groups:
- Arrhythmias mainly due to a modification of the automaticity . Arrhythmias with:
- Changes in the frequency and regularity of sinus rhythm.
- Variation of the dominant marker center location.
- Arrhythmias mainly due to a modification of the conduction (or propagation) of the pulse. Arrhythmias with:
- Impulse propagation disorders.
Automaticity, together with rhythmicity, are two unique properties of some muscle cells that make up the myocardium (the heart muscle).
- Automaticity: it is the ability to form impulses of muscular contraction in a spontaneous and involuntary way, that is without an input coming from the brain.
- Rhythmicity: is the ability to transmit contraction pulses in an orderly manner.
The classification on a pathophysiological basis is not the only one. We can also consider the site of origin of the disorder and distinguish arrhythmias in:
- Sinus arrhythmias . The disorder concerns the impulse coming from the atrial sinus node. Generally, frequency alterations are gradual. This is the case, for example, of sinus tachycardia.
- Ectopic arrhythmias . The disorder concerns a marker that is different from the atrial sinus node; this is the case, for example, of paroxysmal tachycardia. Generally, they arise abruptly.
The affected areas divide the ectopic arrhythmias into:
- Supraventricular. The disorder affects the atrial area.
- Atrioventricular, or nodal. The affected area concerns the atrioventricular node.
- Ventricular. The disorder is displaced in the ventricular area.
What is sinus tachycardia
Sinus tachycardia (from the Greek ταχύς, velocity, and καρδία, heart) is an arrhythmia characterized by an increase in the frequency and speed of normal heart rhythm (alteration # 1). The term sinus indicates the atrial sinus node as the site of origin of the arrhythmic disorder.
Sinus tachycardia is the most frequent arrhythmic form and, usually, it is not an alarming episode. In fact, it is commonly observed in childhood, adolescence and in response to transient situations that require a greater demand for oxygen from the tissues, such as exercise, emotions, pregnancy and even fever. To satisfy the highest oxygen demand, you need a superior cardiac output (blood flow). To increase cardiac output, the body increases the frequency of the heartbeat, generating tachycardia.
Thus, a concise outline of what happens during sinus tachycardia is:
- Higher oxygen demand →
- Increased heart rate (tachycardia) →
- Increased cardiac output →
- Greater amount of oxygenated blood to the tissues
Causes of sinus tachycardia
The causes, or factors, of sinus tachycardia are different. They differ based on the severity and transience of conditions that require more oxygen.
NON-serious transient circumstances, capable of causing sinus tachycardia, are distinguished in physiological stimuli and pathophysiological stimuli.
Physiological stimuli
- Physical exercise.
- Emotion.
- Pregnancy.
- Anxiety.
Pathophysiological stimuli
- Temperature.
- Hyperthyroidism.
- Pheochromocytoma.
A sinus tachycardia can also be attributed to non-transient pathological conditions, much more serious than a simple fever, such as:
- Anemia.
- Arterial hypotension.
- Shock.
- Pulmonary embolism.
- Myocardial ischemia.
- Heart failure.
They are different pathological circumstances, but at the base of which there are two common symptoms:
- Decreased tissue oxygenation.
- Decrease in cardiac output.
To compensate for these decreases, the heart responds by increasing the heart rate, thus generating episodes of tachycardia. The mechanism is reminiscent of that induced by physiological (physical exercise) and physiopathological (fever) stimuli, but there is a substantial difference: the transient nature of the conditions in which the patient finds himself. In the case of fever, in fact, tachycardia spontaneously disappears when the fever itself is exhausted. Therefore, no antiarrhythmic treatment is required. The same goes for an emotion and for a physical exercise: at the end of these, the beat resumes the normal sinus rhythm. A myocardial ischemia, on the other hand, is a much more serious and stable pathological circumstance, so much so that the complications it causes require pharmacological and surgical interventions of a certain importance. Only after successful treatment, the problem of sinus tachycardia is resolved.
Finally, episodes of sinus tachycardia may also occur at rest, in the absence of a request for superior oxygen. The responsible agents are:
- Drugs (eg atropine and catecholamines).
- Alcohol.
- Nicotine.
- Caffeine.
Symptoms
The typical symptoms, which characterize sinus tachycardia, depend on their association or otherwise with the other pathologies described in the previous chapter. In other words, the symptomatology is all the more critical and articulated in its manifestations, the more worrying and advanced are the pathological states of an individual suffering from tachycardia. A list of the main symptoms, from the least severe (but always present) to the most serious, is the following:
- Cardiopalmus (or palpitation). It is the natural consequence of the increased heart rate. It is observed in all subjects affected by sinus tachycardia, both healthy and cardiopathic.
- Anxiety. It is linked to heart-pounding.
- Dyspnea (or shortness of breath). It is difficult breathing. The onset mechanism is a demonstration of the link between the respiratory system and the circulatory system. In fact, the greater demand for oxygen by the tissues, both in transient and in severe and stable conditions, obliges the individual to increase the number of breaths to increase the cardiac output. However, especially in severe pathological circumstances, this response does not compensate for the demand for oxygen, resulting in the sensation of shortness of breath and wheezing.
- Chest pain, under the sternum. It is associated with heart disease.
Diagnosis
Accurate diagnosis requires a cardiological examination. The traditional exams, valid for the evaluation of any arrhythmic / tachycardic episode, are:
- Wrist measurement.
- Electrocardiogram (ECG).
- Dynamic electrocardiogram according to Holter.
Wrist measurement . The doctor can draw fundamental information from the evaluation of:
- Arterial pulse . Informs about heart rate and regularity.
- Jugular venous pulse . Its assessment reflects atrial activity. It is useful, in general, to understand the type of tachycardia present.
Electrocardiogram (ECG) . It is the instrumental examination indicated to evaluate the progress of the electrical activity of the heart. Based on the traces that result, the doctor can estimate the extent and severity of sinus tachycardia.
Dynamic electrocardiogram according to Holter . This is a normal ECG, with the very advantageous difference that monitoring lasts for 24-48 hours, without preventing the patient from performing normal daily activities. It is useful if the tachycardia episodes are sporadic and unpredictable.
Therapy
The therapeutic approach is based on the causes that determine sinus tachycardia. In fact, if it is due to particular cardiac disorders, or to other pathologies, the therapy to be adopted is both pharmacological and surgical. The most suitable antitachycardia drugs are:
- Antiarrhythmics . They are used to normalize the heart rhythm. For example:
- quinidine
- Procainamide
- Disopyrimide
- Beta-blockers . They are used to slow down the heart rate. For example:
- Metoprolol
- Timolol
- Calcium channel blockers . They are used to slow down the heart rate. For example:
- Diltiazem
- Verapamil
The route of administration is both oral and parenteral.
Surgical intervention depends on the particular cardiopathy linked to the tachycardia episode.
It should be pointed out that, in these circumstances, tachycardia is a symptom of heart disease; therefore, surgery aims at treating, first of all, heart disease and, as a consequence, also the associated arrhythmic disorder. In fact, if only antitachycardia drug treatment were implemented, this would not be sufficient to solve the problem.
If, on the other hand, sinus tachycardia occurs in healthy subjects, without heart problems, and is manifested as a sporadic episode after a run, or a strong emotion, no particular therapeutic precautions are required. This arrhythmia, in fact, is exhausted on its own and its gradual onset, not abrupt, raises less concern than a paroxysmal tachycardia, for example, sudden and sudden appearance. Sometimes, if the cause of sinus tachycardia depends on excessive caffeine intake, a correction of the doses taken may be sufficient to resolve the disorder.
