Generality
Ventricular fibrillation is an arrhythmia characterized by rapid, ineffective and irregular contractions of the ventricles. This results in severe impairment of cardiac output, such that ventricular fibrillation is considered to be one of the main causes of cardiac arrest or sudden cardiac death.
The symptoms of atrial fibrillation (palpitation, chest pain, cyanosis, dyspnea and loss of consciousness) arise very quickly, so that the therapeutic intervention, to have a success rate, must be timely. Action must be taken immediately if the patient is to be saved. Emergency treatment consists mainly of cardioversion (or defibrillation). However, alternative therapeutic approaches, such as cardiopulmonary resuscitation, through cardiac massage, and the administration of certain drugs should not be forgotten. As for the diagnostic tests (electrocardiogram, echocardiogram and chest X-ray), ventricular fibrillation has such a rapid course that it does not allow time for an accurate investigation of the causes of the disorder.
NB: to understand some concepts illustrated in the article, it is necessary to know the bases of anatomy and physiology of the heart illustrated in the general article on cardiac arrhythmias.
What is ventricular fibrillation
Ventricular fibrillation is an alteration of the heartbeat at the level of the ventricles, which contract rapidly and in a disorderly fashion. The heart beat and contractions change accordingly, assuming the following characteristics:
- Increased frequency and speed.
- Irregularity and lack of coordination.
- Variable intensity.
- Mechanical ineffectiveness.
The mechanical ineffectiveness arises because the overlapping of numerous contractile impulses does not allow the musculature of the ventricle to respond effectively. In other words, the contraction stimuli, at the time of the systole phase, are so numerous that they do not translate into as many effective and adequate responses. This is due to the fact that the cells of the myocardium, once contracted, need a certain time interval to become receptive again ( refractory time ). This interval of time, identifiable as the diastole phase (ie relaxation of the myocardium), is respected when the heart beats in a regular manner; vice versa, when the rhythm increases dramatically, the time between one impulse and another is so short that it does not determine any concrete cellular response. Furthermore, the desynchronization of the contraction of the various myocardial fibers makes it impossible to develop a ventricular pressure capable of opening the aortic and pulmonary valves and producing systolic range.
All these modifications imposed on the heartbeat compromise the cardiac output caused by the contraction of the ventricle. Cardiac output corresponds to the flow of oxygenated blood that is pumped into the circulation towards the organs and tissues of the human body (including the heart, which receives arterial blood from the coronary arteries that originate in the first section of the aorta). If the blood outflow is insufficient, oxygenation becomes deficient. Consequently, a condition of anoxia is created so that even the heart is gradually less and less oxygenated and capable of performing its contractile function effectively. The final outcome of this situation is the death of the heart, due to acute anoxia, and the consequent arrest of blood circulation . What makes these events even more dramatic is their rapid onset and progression .
Ventricular fibrillation, therefore, is an alteration of the rhythm from the rapid and ominous course, which places it among the most decisive arrhythmias in causing death by cardiac arrest or sudden cardiac death .
80-85% of cardiac deaths are caused by ventricular fibrillation. It has been estimated that, in the western world, it affects 1 person every 1, 000 a year. Males are more affected than women: the ratio is 3: 1.
The incidence of ventricular fibrillation is greater in those individuals aged 50-70 with a pre-existing cardiac ischemia. However, as will be seen shortly, ventricular fibrillation can also occur in the absence of ischemic heart disease, as, for example, in some juvenile and congenital age syndromes.
Causes
The main causes of ventricular fibrillation are:
- Hypoxia due to:
- Coronary.
- Cardiac ischemia.
- Myocarditis.
- valvulopathy
- Metabolic acidosis.
- Hypokalemia.
- Hyperkalemia.
- Hypocalcemia.
- Hypomagnesemia.
- Accidental or surgical heart trauma.
- Electric discharges:
- Alternating currents between 20 and 150 mA.
- Continuous currents between 80 and 600 mA.
- Incorrect or improper drug treatments based on:
- Tricyclic antidepressants.
- Antiarrhythmics.
- Hyperthyroidism.
- Wolff-Parkinson-White syndrome.
- Brugada syndrome.
- Gas poisoning:
- Carbon monoxide (CO).
- Cyclopropane.
- Narcotic poisoning:
- Cocaine.
As can be seen, the causes are numerous and each has specific characteristics. Treating them in detail is not the purpose of this article. However, a brief parenthesis will be devoted to why certain phenomena, such as hypoxia, electrolyte imbalances, improper intake of drugs, electrical discharges, etc., cause the onset of ventricular fibrillation. In all these circumstances, an ionic / electrolyte imbalance is created over and above the membranes that make up myocardial cells; imbalance that compromises the passage of the contractile impulse. The importance of the correct distribution of ions with charge (positive or negative), such as calcium, potassium, magnesium, etc., is fundamental for transmitting the contraction signal, which is an electrical signal . If this balance fails, the cells no longer function adequately and, in the specific case, they contract with very high frequencies and in an irregular way.
Finally, the cases of ventricular fibrillation in healthy individuals should not be forgotten. We talk about idiopathic ventricular fibrillation, because the causes are not known. The onset is of a paroxysmal nature: therefore, it is sudden and spontaneous.
Symptoms
The typical symptoms of ventricular fibrillation arise very quickly and are consequential to one another. They are:
- Dyspnoea.
- Loss of knowledge.
- Chest pain.
- Pulsating.
- Stop of circulation
- Fatigue sensation.
- Cyanosis.
Due to the gravity of the situation that is created, the timeliness in identifying and understanding the symptoms is fundamental to save the life of the individual affected by ventricular fibrillation.
Diagnosis
In most cases, the rapidity with which the arrhythmic disorder evolves and the consequent need for immediate intervention leaves no time to make a complete diagnosis. However, there may be some warning signs due to an initial myocardial infarction.
Possible diagnostic tests are:
- Electrocardiogram.
- Echocardiography.
- Chest x-ray.
- Coronary angiography.
Electrocardiogram . It is the instrumental examination indicated to evaluate the progress of the electrical activity of the heart. In the case of a ventricular fibrillation, the trace shows rapid and irregular oscillations, with an unmistakable appearance. They are the prelude to the arrest of any cardiac activity. If one encounters a myocardial infarction in the initial phase, by means of ECG, ventricular extrasystoles can be identified, which serve as premonitory clinical signs of a ventricular fibrillation.
Echocardiography . Taking advantage of the ultrasound emission, this non-invasive investigation shows the fundamental elements of the heart: atria, ventricles and valves. The evaluation of the heart allows to verify the presence of valvular anomalies or some other cardiac malformation.
Chest x-ray . It is a clinical investigation useful in providing information on the relationship between heart and lungs. Pulmonary thrombosis, for example, may be associated with ventricular fibrillation events.
Coronary angiography . This is an invasive examination, aimed at assessing the health status of the coronary system. An estimate of the level of coronary occlusion and a timely intervention, able to free the blocked vessels, can avoid the occurrence of a ventricular fibrillation. A catheter is used which acts as a probe to track the obstructed site. Then we act to free this area. This is a delicate operation, because there is a risk of damaging the coronary vessels crossed by the catheter.
Therapy
The therapeutic intervention must be timely, since the evolution of the effects induced by fibrillation is very rapid and dramatic. You have a few minutes, no more than five. In the event of cardiac arrest, different practices can be used:
- Cardioversion or defibrillation . Through a special equipment, an electric discharge is infused to reset and restore the sinus heart rhythm. The discharge is applied by means of two plates placed on the patient's chest. The current instruments are so efficient that they can reveal the progress of ventricular fibrillation and, consequently, apply the right discharge required. In other words, they adjust themselves as needed. These are semiautomatic or automatic defibrillators, which can also be used by non-medical personnel.
- Cardiopulmonary resuscitation (CPR) . If you do not have a defibrillator and there is no time to get it, you must act with CPR. It is a cardiorespiratory action replacing the natural one, practiced in order to pump blood circulating towards the lungs, brain and other organs. It is carried out through the practice of mouth to mouth breathing and cardiac massage.
- Antiarrhythmic drugs . They serve as a support to the previous treatments just described. They have the function of keeping the heart rhythm normal even when it has succeeded in restoring cardiac activity consistent with life. The most used drugs are amiodarone and lidocaine.
Prognosis
As has been said several times, the timeliness of intervention is fundamental to save the patient's life and safeguard the non-oxygenated organs at the time of cardiac arrest. Acting in time gives ample opportunity for survival.
The success of the intervention depends very much on the causes that triggered ventricular fibrillation. If, for example, the patient's heart is suffering from severe heart disease, it may be more difficult to restore cardiac activity.
