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Paroxysmal tachycardia

Generality

Paroxysmal tachycardia is an arrhythmia characterized by an increase in the frequency and speed of the sudden and abrupt onset heartbeat.

This pathological condition is the result of a change in the dominant marker center location. In fact, the command of the cardiac contraction impulse propagation passes from the sinoatrial node to the atrioventricular node. For this reason, it is also called tachycardia by re-entry of the atrioventricular node and is classified among atrioventricular ectopic arrhythmias.

The attacks of paroxysmal tachycardia have variable duration, from a few seconds to a few hours, or even days. They can occur in healthy individuals without heart disease or other organic diseases. This arrhythmia, in fact, is frequent in early childhood and in children, but can also occur in subjects subjected to strong emotions or severe physical efforts. The typical symptom of parosisist tachycardia is a strong palpitation. Much more serious are the cases of paroxysmal tachycardia associated with a heart disorder: to the symptom of palpitation are added those of dyspnea, orthopnea and chest pain.

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:

  1. 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).
  2. 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 pedestal 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 impulses generated by it.
  3. Impulse propagation (or conduction) disorders.

The pathophysiological mechanisms * that underlie these three alterations allow us to distinguish arrhythmias in two large groups:

  1. 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.
  2. 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).

  1. 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.
  2. 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:

  1. Sinus arrhythmias . The disorder concerns the impulse coming from the atrial sinus node. Generally, frequency alterations are gradual.
  2. Ectopic arrhythmias . The disorder concerns a marker that is different from the atrial sinus node. 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 paroxysmal tachycardia

Paroxysmal tachycardia is an arrhythmia characterized by a sudden and sharp increase in the frequency and speed of the heartbeat. The term paroxysmal indicates precisely the sudden appearance of the arrhythmia, the latter characteristic which distinguishes it from sinus tachycardia.

Paroxysmal tachycardia arises due to a change in the dominant marker center location. In fact, the command of the propagation of the cardiac contraction pulse is no longer in the hands of the atrial sinus node, but passes below those of the atrioventricular node. For this reason, it is also called tachycardia by re-entry of the atrioventricular node and is classified among atrioventricular ectopic arrhythmias.

Those associated with paroxysmal tachycardia can be defined as true tachycardia attacks, characterized by heart rates between 160 and 200 beats per minute. They can occur during the day (standing) or at night (in sleep) and have a variable duration, from a few seconds to a few hours or even days; usually, however, they last for no more than 2 or 3 minutes. When the attacks exceed 24 hours, it is more correct to attribute them to the so-called ectopic persistent tachycardias.

Causes of paroxysmal tachycardia. Pathophysiology

In most cases, episodes of paroxysmal tachycardia concern healthy individuals who do not have cardiac disorders or other diseases. In fact, the tachycardia manifestation often coincides with physical exercise or strong emotions, and ends at the end of these circumstances. Those who are subject to it can suffer an attack even after many days.

Attacks of paroxysmal tachycardia are also frequent during early childhood and in healthy children: the reason lies in the anatomical characters of the heart at that age. On the other hand, the attacks of paroxysmal tachycardia in pregnant women are infrequent, but still possible. Another particular situation, which still involves women, is linked to the menstrual cycle: episodes of paroxysmal tachycardia may occur during menstruation or in the previous week. Thus, the common causes of paroxysmal tachycardia, in the absence of other associated disorders, are summarized as:

  1. Physical exercise.
  2. Anxiety.
  3. Emotion.
  4. Pregnancy.
  5. Period.
  6. Heart of an infant or child.

Quite different is the case of those subjects with heart disease or other organic diseases, such as hyperthyroidism. In such circumstances, the reasons for the onset of tachycardia are attributable to an underlying pathological disorder. The most common associated diseases are:

  1. Rheumatic heart disease, that is due to a rheumatic disease.
  2. Ischemic heart disease.
  3. Congenital heart disease.
  4. Cardiomyopathy.
  5. Cerebral vascular diseases.
  6. Hyperthyroidism.
  7. Wolff-Parkinson-White syndrome, in children.

The pathophysiological explanation of how the conduction of the pulse varies with the occurrence of a paroxysmal tachycardia is somewhat complicated. Therefore, we will limit ourselves to describing some key points. At the origin of the alteration there is an extrasystole, of atrial origin, which is associated with the normal sinus impulse coming from the atrial sinus node. The anomalous association of these two impulses creates disorder through the conduction pathways, placed between atria and ventricles. The outcome of this disorder results in an overlap of multiple contraction pulses that increase the heart rate.

Symptoms

The severity of the symptoms of a paroxysmal tachycardia depends on the association, or not, with the heart and other disorders seen above. In fact, an individual, subjected exclusively to attacks of tachycardia, shows palpitation (or heart disease) and, rarely, dyspnea. Patients suffering from heart disease or cerebral vascular diseases present a much more articulated and serious symptomatology.

The main symptoms, therefore, are:

  1. Palpitation (or heartbeat ). It is the natural consequence of increasing heart rate.
  2. Dyspnea . It is difficult breathing. It occurs, with greater incidence, in patients with cardiopathies, as a malfunction of the heart determines an insufficient flow of oxygenated blood towards the tissues. In other words, the cardiac output is insufficient. This causes the patient to increase the number of breaths to elevate the blood flow pumped into the circulation. This compensatory mechanism, however, does not give the desired results and shortness of breath and wheezing appear, demonstrating the link between the respiratory system and the circulatory system.
  3. Orthopnea . It is dyspnea from lying (lying position). It occurs in individuals with mitral stenosis, whose most severe cases can degenerate into pulmonary edema.
  4. Chest pain due to angina pectoris . It occurs in patients with ischemic heart disease, caused for example by atherosclerosis or aortic stenosis. There is an imbalance between demand (which increases) and supply (which is not enough) of oxygen.
  5. Dizziness, syncope and visual disturbances . There are three manifestations related to cerebral vascular diseases, due to which the flow of oxygenated blood to the brain is lower than normal.

Diagnosis

Accurate diagnosis requires a cardiological examination. The traditional exams, valid for the evaluation of any arrhythmic / tachycardic episode, are:

  1. Wrist measurement.
  2. Electrocardiogram (ECG).
  3. Dynamic electrocardiogram according to Holter.

Wrist measurement . The doctor can draw fundamental information from the evaluation of:

  1. Arterial pulse . It informs about the frequency and regularity of the heart rhythm.
  2. 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 severity and the causes of paroxysmal 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.

Anamnesis, that is, the collection of information by the physician of what the patient describes about tachycardia attacks also plays an important role in the diagnosis. The anamnesis is necessary because, as has been said, paroxysmal tachycardia frequently occurs with episodes that are distant days / weeks from one another, even in those who do not have pathological disorders of another nature. These individuals, unless the tachycardia attack is in place, show a normal ECG trace, making a correct diagnosis impossible.

Therapy

The therapeutic approach is based on the causes that determine paroxysmal tachycardia. In fact, if it is due to particular cardiac disorders, or to other diseases, the possible therapies are pharmacological, electrical and surgical. The most suitable antitachycardia drugs are:

  1. Antiarrhythmics . They are used to normalize the heart rhythm. For example:
    • quinidine
    • Procainamide
    • Disopyrimide
  2. Beta-blockers . They are used to slow down the heart rate. For example:
    • Metoprolol
    • Timolol
  3. 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.

Electric therapy means the possibility of subjecting the heart to electrical stimulation, using a device called a pacemaker, which interrupts the tachycardia attack and normalizes the heart rhythm. Inserted under the skin, at chest level, these devices can be:

  1. Automatic, that is able to recognize tachycardia and deliver the appropriate impulse.
  2. To external control, that is operated by the patient himself in the moment of need.

Pacemakers are also used to replace drug therapy.

The surgical intervention on the heart 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 therapy were implemented, this would not be sufficient to solve the problem.

If, on the other hand, paroxysmal 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. In these cases, in fact, the arrhythmia is exhausted by itself. If, however, it causes some concern, it is useful to know that those who are subject to these attacks can also act to interrupt the tachycardia event. By means of the so-called Valsalva or Muller maneuvers, in fact, it is possible to stop supraventricular tachycardias, including the paroxysmal one, without the administration of drugs. These maneuvers are based on vagal stimulation, that is, of the vagus nerve, and must be given, for the first time, by the doctor, who will instruct the patient on the correct methods of execution.

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