Paroxysmal tachycardia

Generality

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

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

Attacks of paroxysmal tachycardia vary in duration, from a few seconds to a few hours, or even days. They can occur in healthy individuals, without heart disease or other organic affections. This arrhythmia, in fact, is frequent in infancy and children, but can also arise in subjects subjected to strong emotions or severe physical efforts. The typical symptom of parosisstic tachycardia is a strong palpitation. Much more serious are the cases of paroxysmal tachycardia associated with a heart disorder: the symptoms of palpitation are added to those of dyspnoea, orthopnea and chest pain.

Arrhythmias, what are they?

Before proceeding with the description of sinus tachycardia, it is appropriate to briefly review what cardiac arrhythmias are.
Cardiac arrhythmias are alterations in the normal heartbeat rhythm, also called sinus rhythm as it originates from the sinoatrial node. The sinoatrial node emits impulses for the contraction of the heart and is considered the dominant pathway center, as it is responsible for the normal heartbeat.

The heart rate is expressed in beats per minute and is considered normal if it stabilizes within a range of values ​​between 60 and 100 beats per minute. There are three possible alterations and it is sufficient for one to occur only for an "arrhythmia to arise. They are:

1. Changes in the frequency and regularity of the sinus rhythm. The heart rate may become faster (over 100 beats per minute → tachycardia) or slower (less than 60 beats per minute → bradycardia).
2. The variation of the seat of the dominant marker 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 sinoatrial node is the main one and the others should only serve for the propagation of the impulses it generates.
3. Impulse propagation (or conduction) disturbances.

The pathophysiological mechanisms * underlying these three alterations make it possible to distinguish arrhythmias into two large groups:

1. Arrhythmias mainly due to a modification of automaticity. Arrhythmias with:
   • Changes in the frequency and regularity of the sinus rhythm.
   • Variation of the seat of the dominant marker center.
2. Arrhythmias mainly due to a modification of the conduction (or propagation) of the impulse. 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 muscle contraction spontaneously and involuntarily, that is, without an input coming from the brain.
2. Rhythmicity: it is the ability to neatly transmit impulses of contraction.

* pathophysiology is the study of the changed functions, due to a pathological condition, of a tissue, of an organ or, in general, of an organism

The physiopathological classification is not the only one. We can also consider the site of origin of the disorder and distinguish the arrhythmias in:

1. Sinus arrhythmias. The disturbance concerns the impulse coming from the sinoatrial node. Generally, the frequency changes are gradual.
2. Ectopic arrhythmias. The disorder involves a pathway other than the sinoatrial node. Typically, they arise abruptly.
   The affected areas divide ectopic arrhythmias into:
   • Supraventricular. The disorder affects the atrial area.
   • Atrioventricular, or nodal. The affected area concerns the atrioventricular node.
   • Ventricular. The disorder is located in the ventricular area.

What is paroxysmal tachycardia

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

Paroxysmal tachycardia arises due to a change in the location of the dominant marker center. In fact, the command for the propagation of the cardiac contraction impulse is no longer in the hands of the sinoatrial node, but passes under those of the atrioventricular node. For this reason, it is also called atrioventricular node reentry tachycardia and is classified among ectopic arrhythmias. atrioventricular.
Those associated with paroxysmal tachycardia can be defined as real tachycardic 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 vary in duration, from a few seconds to a few hours or even days; usually, however, they last no more than 2 or 3 minutes. When the attacks exceed 24 hours, it is more correct to attribute them to the so-called persistent ectopic tachycardias.

Causes of paroxysmal tachycardia. Pathophysiology

In most cases, episodes of paroxysmal tachycardia involve healthy individuals without heart disease or other medical conditions. In fact, the tachycardic 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 characteristics of the heart at that age. Infrequent, however, but still possible, are the attacks of paroxysmal tachycardia in pregnant women. . Another particular situation, which still involves women, is that linked to the menstrual cycle: in fact, 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 follows:

1. 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 pathologies, such as hyperthyroidism. In similar circumstances, the reasons for the onset of tachycardia are attributable to an underlying pathological disorder. The most common associated pathologies are:

1. Rheumatic heart disease, i.e. due to a rheumatic disease.
2. Ischemic heart disease.
3. Congenital heart disease.
4. Cardiomyopathies.
5. Vascular diseases of the brain.
6. Hyperthyroidism.
7. Wolff-Parkinson-White syndrome, in children.

The pathophysiological explanation of how the impulse conduction varies upon the occurrence of a paroxysmal tachycardia is somewhat complicated. Therefore, we will limit ourselves to describing some key points. associates with the normal sinus impulse coming from the sinoatrial node. The anomalous association of these two impulses creates disorder through the conduction pathways, located between the atria and the ventricles. The outcome of this disorder translates into an overlapping of several contraction impulses that increase the heart rate.

Symptoms

The severity of the symptoms of a paroxysmal tachycardia depends on the "association, or not, with the cardiac and other disorders seen above" indeed. In fact, an individual, subject only to tachycardia attacks, shows palpitation (or heartbeat) and, rarely, dyspnea. Patients suffering from heart disease or cerebral vascular diseases, on the other hand, present a much more complex and serious symptomatology.
The main symptoms, therefore, are:

1. Palpitation (or heartbeat). It is the natural consequence of the increased heart rate.
2. Dyspnea. It is difficult breathing. It occurs, with greater incidence, in patients with heart disease, as a malfunction of the heart determines an insufficient flow of oxygenated blood towards the tissues. In other words, cardiac output is insufficient. This causes the patient to increase the number of breaths to increase the blood flow pumped into the circulation. This compensatory mechanism, however, does not give the desired results and shortness of breath and labored breathing appear, demonstrating the link between the respiratory system and the circulatory system.
3. Orthopnea. It is dyspnea when lying down (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 the demand (which increases) and the supply (which is not sufficient) of oxygen.
5. Vertigo, syncope and visual disturbances. These are three manifestations linked to cerebral vascular diseases, due to which the flow of oxygenated blood to the brain is less than normal.

Diagnosis

An accurate diagnosis requires a cardiological visit. Traditional tests, valid for the evaluation of any arrhythmic / tachycardic episode, are:

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

Pulse measurement. The physician can draw basic information from the evaluation of:

1. Arterial pulse. It informs about the frequency and regularity of the heart rhythm.
2. Jugular venous pulse. Its rating reflects atrial activity. It is generally useful for understanding the type of tachycardia present.

Electrocardiogram (ECG). It is the instrumental examination indicated to evaluate the course of the electrical activity of the heart. On the basis of the resulting traces, the doctor can estimate the severity and causes of paroxysmal tachycardia.

Dynamic electrocardiogram according to Holter. It is a normal ECG, with the advantageous difference that the monitoring lasts for 24-48 hours, without preventing the patient from carrying out normal activities of daily life. It is useful when tachycardia episodes are sporadic and unpredictable.

Anamnesis, that is the collection of information by the doctor, of what the patient describes about tachycardic attacks, also plays an important role in the diagnosis. The anamnesis is necessary because, as we have said, paroxysmal tachycardia frequently arises with episodes that are days / weeks apart, even in those who do not have pathological disorders of any other nature. These individuals, unless the tachycardia attack is in progress, 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 other pathologies, the possible therapies are pharmacological, electrical and surgical. The most suitable antitachycardia drugs are:

1. Antiarrhythmics. They serve to normalize the heart rhythm. For instance:
   • Quinidine
   • Procainamide
   • Disopyramide
2. Beta blockers. They are used to slow down the heart rate. For instance:
   • Metoprolol
   • Timolol
3. Calcium channel blockers. They are used to slow down the heart rate. For instance:
   • Diltiazem
   • Verapamil

The route of administration is both oral and parenteral.
By electrical therapy we mean the possibility of subjecting the heart to electrical stimulation, using a device called a pacemaker, which interrupts the tachycardic attack and normalizes the heart rhythm. Inserted under the skin, at the thoracic level, these devices can be:

1. Automatic, ie capable of recognizing tachycardia and delivering the appropriate pulse.
2. Externally controlled, i.e. operated by the patient himself in the moment of need.

Pacemakers are also used as a substitute for drug therapy.

Heart surgery depends on the particular heart disease linked to the tachycardic episode.
It should be noted that, in these circumstances, tachycardia is a symptom of heart disease; therefore, surgery aims to cure, first of all, heart disease and, as a consequence, also the associated arrhythmic disorder. In fact, if antitachycardia drug therapy alone 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 manifests itself as a sporadic episode after a run, or a strong emotion, no particular therapeutic measures are required. In these cases, in fact, the arrhythmia ends on its own. If, however, it should cause some concern, it is useful to know that those subject to these attacks can also act in such a way as to interrupt the tachycardic 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, ie 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.