Arrhythmias

 

2018 update for the practical doctor

notes by dr Claudio Italiano  


General notions


A cardiac cell presents a difference in membrane potential between the inside that is electronegative and the positive outside. There is therefore a transmembrane potential which, however, undergoes a modification in the course of the cardiac cycle in the sense that some ion pump systems (sodium, potassium, calcium and chlorine) allow the migration of the same and, consequently, cause a change in the polarization of membrane (see ecg  ecg2). In particular during the depolarization of the membrane comes potassium and sodium enters, so that the internal environment of the cell becomes positive and this is to constitute the so-called action potential. It is an expression of ion transfer through the Na-K ATP asi pump. Some cells, however, are able to depolarize automatically, unlike the cells of the common myocardium, and are called "pacemakers". The Breast Node (NS) consists of these cells and as it is equipped with the fastest automatism it controls the cardiac activity, triggering the action potentials in the common myocardium. Thus, through a sodium-calcium exchange, the muscle fiber cells are contracted (hence the use of calcium antagonists in therapy). There are other structures that like the sinus node have automatic activity: among these the atrioventricular node (NAV), which is however equipped with a slower automatism, so it can act as a pacemaker only when the other markers are so to speak " off. " The refractory period, however, is a minimum interval between two action potentials, during which the common myocardium fails to be stimulated. The NAV has a refractory period, therefore, longer, since the frequency of its action potentials is shorter, but its physiological function is important, as we will see, in the supraventricular tachyarrhythmias where an excessive rhythm of the ventricular chambers, causing a poor pump activity, would cause death by cardiovascular collapse.

Arrhythmogenesis

Risultati immagini per cardiac action potentialThe rhythm is normal or sinus when the Nodo del Seno footprint generates in a physiological way its action potentials, acting as main pacemaker (orchestra master!), Proceeding from top to bottom, ie from the atria towards the ventricles, with the right pauses to allow the filling of atria and then of ventricles, while the wave of depolarization reaches the various elements of the specific myocardium and, therefore, the most distal markers; its frequency (of the NS) is in this case between 60-100 b / m; the specific myocardial cells of the placenta have an action potential with a particular appearance (in blue), determined by ionic currents, given the automation function that must have a marker. In phase 0, substances such as adrenaline and acetylcholine of the ortho and parasympathetic system act, which accelerate and slow down the automatism of the myocardial cells of the step marker respectively. Conversely, the cells of the common myocardium present an aspect of the action potential that is represented by the red trace of the figure. They have a phase 0 followed by an action potential that depends on the sodium rapid current; the phase of the plateau (phase 2), is that on which they play their role the stimulators of the orthosympathetic and parasympathetic system. The arrhythmia can be defined as an alteration of the normal automatism and / or of the normal conduction of the electric activity to the other markers. It may happen that, as a result of myocardial pathologies, the discharge of other cells of the myocardium is determined and there will therefore be an "abnormal automatism" or special functional stresses that exalt or depress the activity of the specific myocardium, determining "abnormal automatism". The same happens when myocarditis, myocardosclerosis, drug poisoning, hypoxia cause such stresses to reach a potential threshold that can trigger the action potential and, in this case, the "triggered activity" will take place. If instead of the functional or organic conditions obstruct and block the conduction of electrical impulses to the myocardium, there will be "conduction abnormalities". In this regard, if an impulse is not conducted in a uniform manner, because it encounters tissue that slows down its anterograde progression, once the same has come out of the refractory period, the same impulse can go back give rise to the phenomenon of "re-entry". If vice versa it takes some faster access routes, es. bundle of Kent, we will have the "pre-excitation".

Classification of arrhythmogenesis mechanisms

Impulse training disorders
abnormal automatism
abnormal automatism
triggered activity
Disorders of impulse conduction
slowdown or block
preexcitation
return


Combined disorders
parasystole
Types of arrhythmia and old classification based on kinetics
Below is a graph of the automatic cardiac action potential: Purkinje fibers, phase 0 depolarization, phase 1 early rapid repolarization, phase 2 plateau, phase 3 completion of repolarization, phase 4 diastole:

Some years ago they were classified according to the electrogenic mechanism, the seat and the type and degree, first in HYPOCINETICS and HYPERCHINETICS; the former are with a bradycardial attitude, that is at low frequency, the others include exalted myocardial activity:
depression of automatism. At the NS level: sinus arrest; sinus bradycardia.
conduction depression.

At the level of the sino-atrial junction: block S.A. of 1st, 2nd, 3rd degree

At the level of the NAV, His bundle, branches and fascicles: AV block of 1st, 2nd, 3rd degree
Recently, in the last 10-15 years the old nomenclature, which divided arrhythmias into hyperkinetic and hypokinetic, was abandoned: in fact the word "kinetic" expresses the movement of the walls of the heart and has nothing to do with batmotropism, chronotropism and dromotropism of the heart, that is, the capacity of the myocardium to generate a cardiac pulse in time and to lead it within the myocardium itself.
Today we prefer to speak, rather, not of the force of contraction of the heart and therefore of the kinetics, but to classify otherwise the aritime, for which we will have:
-Bradicardie
-Tachicardie
- Ectopic bactites.
Tachycardias, in their turn, are subdivided into supraventricular and ventricular, and each of these classes has different forms. Bradycardias include sinus bradycardia, sino-atrial block, and atrio-ventricular block. The ectopic beats may be supraventricular (atrial and junctional) or ventricular.

Bradycardias

The 1st block indicates delay, the 2nd intermittent interruption, the 3rd complete interruption of conduction +. The block of the second degree includes the subdivision in I and II type depending on whether the conduction progressively deteriorates, before the block or rather it stops abruptly. The first type realizes the Wenckenbach phenomenon in which the block of the impulse is usually preceded for 3-5 cycles by a progressive lengthening of the conduction time; in the 2nd degree block an impulse can be blocked on a regular basis, every pulse, every two, every three, etc.

Etiopathogenesis

Functional causes can cause blocking, e.g. vagal hypertonia, sleep, digitalis effect, beta blockers, obstructive jaundice, intracranial hypertension. Organic causes: sclerodegenerative processes, myocarditis, tumors, Lenègre's disease, Lev's disease ..

Symptomatology

The subject may feel palpitation, vertigo, angina pectoris, breath suspension, cerebral hypoxia due to pump failure that goes under the name of MAS or Morgagni-Adams-Stokes syndrome, with sudden syncope.Immagine correlata

Electrocardiographic findings

a) Simusale bradycardia, sinus P waves, rhythmic frequencies below 60 b / m;
b) Sinus arrhythmia, sinus P waves separated by progressively longer cycles, influenced by vagal tone;
c) Sinus stop, when one or more sinus P is missing from the path for a time corresponding to the multiple of the sinus cycle.
d) Block Seno-Atrial or BSA, 1st degree where any consideration obviously missing, of 2nd degree with Wenckebach phenomenon: it is characterized by gradual shortening of the P cycle, followed by the QRS, until a pause in which 'is P Atrial. 2nd grade II, where there are pauses without P and QRS;
e) Atrio-Ventricular Block, means altered conduction of the pulse from the atria to the ventricles by slowing or blocking at the level of the sinus node or NAV, bundle of His, bundle branches and subdivisions.
It can be 1 °, 2 °, 3 °.
The BAV of degree 1, is recognized to the ECG because the measure between the wave P and Q, that is the tract PQ is greater than 0,20 sec (> 4 small squares on the ECG) and is based on the NAV;
The 2nd degree BAV can be type I, that is, with periodisms by Luciani Wenckbach, ie the Ps are always constant but the PQ trait lengthens progressively until one or more Ps are followed by QRS.
BAV of the 2nd degree, type II, occurs when the P cycle is constant, but at every 2.3, 4 cycles, a P is not followed by the QRS.
The 3rd degree BAV occurs when there is an electrical independence between the atrial and ventricular chambers, whatever the rhythm.

Tachycardias

They are classified according to type, location, degree of synchronization and electrogenic mechanism. The seat may be supraventricular and ventricular, referring to the bifurcation of His beam. The electrical activity can be synchronized, partially or totally desynchronized.

Supraventricular tachyarrhythmias

1) with synchronized electrical activity.
paroxysmal tachycardias
atrial flutter
sinus tachycardia
atrial tachycardia
accelerated idiomatic rhythm
2) partially de-synchronized electrical activity
chaotic atrial arrhythmia
atrial fibrilloflutter

3) to totally desynchronized activity
atrial fibrillation

 

Ventricular tachyarrhythmias

1) with synchronized electrical activity
common ventricular tachycardia
bidirectional ventricular tachycardia
Slow ventricular tachycardia
Iterative ventricular tachycardia
2) with a partial synchronized activity
tip twist
ventricular flutter
3) totally de-synchronized electrical activity
ventricular fibrillation

Etiopathogenesis

In general hyperkinetic arrhythmias originate due to re-entry phenomena of tiny portions of tissues, microcircuits or whole cardiac chambers may be involved, such as re-entry macrocircuits. The presence of numerous and small return circuits exists in totally de-synchronized activity, e.g. atrial fibrillation. Situations that can trigger these arrhythmias are the use of coffee, smoking, stress (stay calm and take life with philosophy!).

Symptomatology

It can vary from the sensation of palpitation, like the fluttering of wings in the chest, the breathlessness and the sensation of a throat knot, up to the retrosternal constriction of angina, accompanying these forms to polyuria, ie emission of pale, abundant and diluted urine.

Electrocardiographic findings
Supraventricular tachyarrhythmias
a) Sinus tachycardia, ie exaltation of the NS automatism, with frequencies of 100-130 b / m; that is, sequences of P followed by narrow QRS, sometimes with BAV of 2 ° of type I; it can depend on stress, emotions, drugs, fever, hypoxemia.
b) idiogunctional rhythm, is characterized by retrograde waves P negative ie in D2, D3 AVF and QRS equal;
c) atrial tachycardia, ie abnormal automatism, at the level of the atrial myocardium, then P ectopic and blockade of 2 ° 2: 1, 2: 3; it differs from the flutter due to the lower frequency of atrial waves;
d) paroxysmal tachycardias

breast-atrial, that is, with a duct of re-entry between the sinus node and the atrial myocardium at frequencies of 100-120 with waves P almost similar to those of sinus, of short duration;

common, of the NAV, only QRS complexes, with P celate and frequency of 140-200 b / m;

paroxysmal tachycardia from accessory fascicle, to freq, 180-250 b / m, to narrow QRS complexes and Pectopic waves;
e) atrial flutter, a macro-indentation expression involving the atria, hence "saw-tooth" F waves, evident as "serrated" oscillations in D2-D3 aVF; BAV 2 ° 1: 1 or 2: 1 appears
f) atrial fibrillation, classical arrhythmia very frequent in the elderly; can be chronically stabilized or paroxysmal, loss of effective atrial contraction can cause problems if associated conditions of mitral stenosis, mitral insufficiency, myocardial hypertrophy exist. It is characterized by desynchronized QRS complexes and small "f" atrial fibrillation waves, with the disappearance of sinus P waves and BAV 2 °, the QRS are narrow, irregularly spaced;
g) fibrillo-flutter, is almost similar to atrial fibrillation from which it differs for the more regular waves;
h) Wolf-Parkinson-White syndrome, is characterized by the presence of accessory conduction pathways, represented by fascicles of tissue similar to the ordinary myocardium or to the fibers of Purkinje, called bundles of Kent; at the ecg there will be a pre-excitation of the ventricles expressed by a short PQ and a Delta wave in front of the QRS, with a wide and aberrant QRS.

Ventricular tachyarrhythmias (TV)

These are alterations of the rhythm that arise distally to the bifurcation of the beam of His, due to disorder of conduction automatism, or to an accelerated idioventricular rhythm or to re-entry circuits; they can be "unsupported" if the phenomenon lasts 15-60 sec, or "sustained" for longer episodes; can occur during myocardial infarction, due to outbreaks of left ventricular aneurysm, myocarditis, etc. We can have benign TV, slow TV or iterative and malignant TV, poor, for example common TV, ventricular flutter, ventricular fibrillation, which is basically a stopping of cardiac activity.
Electrocardiographic findings
a) Common TV, a poor prognosis because it is associated with ventricular fibrillation. at frequency 150-250 b / m;
b) iterative, benign TV with non sustained episodes, at a frequency lower than 150 b / m;
c) Slow TV, or accelerated idioventricular rhythm, frequency of 50-110;
d) tip torsion, due to the characteristic ecg, bizarre appearance, with apexes of "torsion-peak" ventricolograms as if the polarity were inverted;
e) bidirectional ventricular tachycardia, with opposite polarity complexes;
f) ventricular flutter, at ventricolograms with wide and regular oscillations, even at a frequency of 250 b / m;
g) Ventricular fibrillation, with a poor prognosis, which is an expression of disionia, ischemia, with ecg with wide, irregular, aberrant oscillations, therefore extreme electrical instability.

Therapy


It is highly specialized; the common man who runs into the subject with severe arrhythmias or cardiac arrest requires knowledge of resuscitation maneuvers; It consists of:
-Punch to precordio, that is to the sternum of the patient to deliver electricity, in case of mechanical asitolia (heart that does not contract)
- cardiac massage, consists in placing the two hands together, the first one in fist and the other on it and in massaging at about 60 beats per minute the breastbone, compressing with energy; in the meantime it is indispensable, where the subject does not breathe or is cyanotic,
- mouth to mouth breathing, hyperextending the subject's head (ie turning the head backwards) close the nostrils and blow into the mouth at least 20 times a minute, observing if the chest is stretched by insufflation of the lungs
- while a person calls 118.
Specific therapy: atropine, sympathomimetics, steroids, anxiolites, digitalis, electric electroconversion, lidocaine, etc.
The ectopic beats

Under normal conditions, the heart rhythm is governed by the sinoatrial node, which is the natural pacemaker of the heart and, at regular intervals, emits electrical impulses that depolarize the whole myocardium. In particular conditions the activation of the heart, or even part of it, may depend on an impulse that originates in a different place from the sinoatrial node; in such cases the impulse is called ectopic and the beating that results is an ectopic heartbeat. The emission of an ectopic impulse can be "anticipated" compared to the moment in which the basic rhythm complex is expected; in such cases, premature beats are generated, also called extrasystoles.

LInk on topic:

La malattia del nodo del seno, aritmie ipocinetiche
I blocchi atrio-ventricolari
Le aritmie da causa extracardiaca
Extrasistoli ventricolari, pericolose aritmie
La fibrillazione atriale, una aritmia stupida e pericolosa.
La fibrillazione atriale, tipi e terapia


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