Arrhythmias: the alterations of the heart
Arrhythmias: ‘Heartbeat’ and ‘heart thump’ are the two expressions people use to describe the alteration in the rhythm of heartbeats
These are the so-called arrhythmias, which, determined by alterations in the ‘electrical’ component of the heart, give rise to various types of heart rhythm irregularities
They are due, in fact, to disturbances in the formation and/or conduction of the cardiac stimulus, are widespread and can occur both in completely healthy hearts and in the course of all known heart diseases.
Their severity is usually closely related to the underlying heart disease, of which they are an epiphenomenon.
A distinction is made between hyperkinetic arrhythmias, in the presence of accelerated rhythms relative to normal, and hypokinetic, in the opposite condition
Accelerated or tachycardic rhythms can be regular or irregular and range from sinus tachycardia (a heart rate greater than 100 beats per minute), due simply to an accelerated rate of discharge of the control unit deputed to the emission of the stimulus (the sinus node) to tachycardic forms that recognize abnormal and different electrogenetic phenomena.
One of the most frequent arrhythmias, especially in old age, is atrial fibrillation, which is characterized by a total irregularity of the heart rhythm and can complicate, either transiently or stably, the course of the most diverse heart diseases, but can also occur in healthy hearts.
Generally, when extra or less beats are experienced, they are harmless extrasystoles, appearing mainly in times of stress or tension.
In the case of atrial fibrillation, the atria become the site of irregular and chaotic electrical activation, they do not contract well, and the muscle loses the synchronism that is normally achieved and that contributes to the filling of the ventricles.
Of these very large numbers of microstimuli (over 1000 per minute) only a few, fortunately, manage to activate the ventricles, preventing the potential storm of impulses from creating arrhythmias incompatible with life.
If the number of stimuli is not excessive in fact, even if the sequence of beats is irregular, cardiac activity is sufficient to ensure adequate circulation.
Atrial fibrillation may occur suddenly, last a few minutes or a few hours, and cease just as quickly and be unrelated to heart disease.
In other cases it may be chronic, as when the atria are altered (mitral valve stenosis, myocardial sclerosis, hyperthyroidism), and in such cases the goal of therapy is to control ventricular rate to achieve good cardiac function.
A dreaded complication of chronic atrial fibrillation is thrombus formation in the heart cavity with frequent embolic detachment.
The mechanisms that generate arrhythmias in the atria can also occur in the ventricles
Since this is where the real pump function takes place, these arrhythmias are more dangerous.
There are, however, benign ventricular arrhythmias (such as simple ventricular extrasystoles) and they occur when a beat fits earlier than expected into the normal cardiac cycle, altering its cadence and causing the ventricles to contract earlier.
Extrasystole can also occur as a result of trivial excess neurovegetative stimulation as occurs in young, anxious, easily aroused people who often, by their very nature, tend to create a vicious cycle.
Simple ventricular extrasystoles are usually harmless
When the phenomenon is associated with a heart disease, things change: if the sequences exceed 4-5 consecutive beats, ventricular tachycardia is realized, which, if it persists beyond 30 seconds (sustained tachycardia), can prelude ventricular fibrillation, a very serious and rapidly lethal arrhythmia.
Therefore, it is necessary to distinguish well and quickly between benign and dangerous forms and to set up appropriate preventive antiarrhythmic therapy.
Among ‘malignant’ arrhythmias, ventricular fibrillation, which is lightning-fast and unpredictable, is the most common cause of sudden cardiac arrest and sometimes may arise in the early stages of an acute myocardial infarction.
In the event of cardiac arrest, the victim’s life depends on the presence of someone who can understand the severity of the situation, raise the alarm and begin, within 4-6 minutes, cardiopulmonary resuscitation (cardiac massage, artificial respiration, etc.) while waiting for the victim to be connected to the defibrillator, an instrument used for 40 years that provides a life-saving electric shock.
Cardiac arrest presents, in fact, as apparent death
The patient is not breathing; the heart is stopped. For 4 to 6 minutes, however, it can still restart.
Minutes that with good cardiac massage can become as much as 10 or 15.
But for the motor to restart it needs a burst, what doctors call defibrillation.
For the past 20 years, in addition to traditional defibrillators, there has been a portable one, about the size of a 24-hour briefcase, equipped with a computer that can deliver the shock.
In the US and England the briefcase is even used by firemen and policemen, in France it is in many ambulances, in Australia it is on all airplanes.
In Italy only a doctor can decide on the use of the defibrillator.
Hypokinetic arrhythmias include sinus bradycardia and the various types of heart block
Sinus bradycardia is defined as a heart rate below 60 beats per minute when, however, the stimulus is produced at its physiological site, i.e., the sinus node.
In itself, sinus bradycardia is a completely physiological phenomenon especially during sleep and in trained athletes.
Cardiac blocks are due to degenerative processes in the stimulus conduction system, which is slowed or arrested at various levels in its progression from the site of formation to the periphery.
Various types of blockages of varying severity are known, up to advanced blockage, which can result in long pauses in cardiac activity with consequent disturbances in cerebral supply and loss of consciousness (syncope).
Advanced heart blocks now find ideal treatment in the implantation of pacemakers (pacemakers), which excellently and physiologically replace spontaneous cardiac stimulation.
Branch blocks are due to an arrest of the progression of the stimulus along one of the dividing branches of the specific system deputed to conduction.
There are two branches of the conduction bundle (His bundle), the right and the left.
In these cases, unlike in complete blocks, the stimulus equally reaches the periphery and activates the whole heart, albeit with a longer path and in a longer time.
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