By Dr. Stefano Casali
Syncope
The etymology of the word comes from the Greek "syn koptein" which means to break, interrupt, cut. From the clinical point of view it is the expression of an alteration of brain functions, generally due to a decrease in cerebral blood flow or to an electrical or metabolic dysfunction that can be the expression of different pathologies, from a benign and insignificant episode, to unexpected death.
Pre-syncope or lipotimia is rather a lesser degree of the same disorder characterized by a feeling of incipient fainting, weakness (asthenia), cold sweating, a sense of nausea, but without complete loss of consciousness and without falling to the ground. Syncope is a fairly frequent event in young subjects (about 5% of hospital admissions and 3% of cases that are visited in an emergency room).
A syncopal episode may occur more frequently:
in young subjects (up to 40-45% in some cases) in which it is often isolated and has a benign meaning;
in elderly subjects, in which it can more easily hide important diseases and have more serious consequences.
The loss of consciousness is an expression of an alteration in brain function, which may be due to various causes:
a sudden reduction or interruption of the blood supply to the brain;
a disturbance in the electrical function of neurons;
a metabolic disorder. Neurons are very sensitive to the lack of energy substrates, particularly a reduction in blood glucose = hypoglycemia.
In relation to the primary causes and the basic mechanism we distinguish three groups of syncopes:
non-cardiovascular, due to other causes (neurogenic, metabolic ...);
cardiovascular, due to an acute decrease or interruption of the blood supply to the brain;
neuromediate, due to vasomotor instability mediated by nerve reflexes.
They can also be classified as:
Indeterminate syncopes: syncopations that at the end of all possible investigations with the means now available do not find a justification, they are very small in number.
Cardiovascular syncope: due to a pathology of the nervous system (neurogenic syncope) eg. generalized epileptic attack (crisis of great evil). In this case the subject falls quickly to the ground in the grip of convulsions, often getting injuries from trauma and bites of the tongue. The recovery of consciousness is slow and often the subject remains asleep. A very similar type of syncope can also be caused by a migraine crisis or a transient ischemic attack (TIA). Or following a sudden reduction in the flow of blood located in a restricted area of the brain (microembolism, spasm of blood vessels) that lasts from several minutes to hours (more frequent in the elderly with atherosclerosis of cerebral vessels or arterial hypertension).
Cardiovascular syncopes: they are quite frequent and are due to a sudden interruption or reduction of the generalized cerebral flow (that is, it involves the whole brain), consequent to a reduction in cardiac output that can be caused by different diseases and mechanisms, in turn divided into two main groups:
- obstruction of blood flow within the heart or major vessels (aorta, pulmonary artery, etc.) as occurs in some valvular diseases (stenosis of the aortic valve or mitral valve), in hypertrophic cardiomyopathies in which the heart muscle (especially the left ventricle) is very hypertrophic and rigid and fills with difficulty. Syncope in these cases occurs during exercise:
- "effortless syncope";
- a cardiac arrhythmia
Cardiac output is the product of stroke volume (amount of blood expelled at each contraction of the left ventricle) for heart rate. Arrhythmias that cause a sudden increase in heart rate ( tachyarrhythmias ) greatly shorten the duration of diastole, hence the filling of the heart. This can reduce stroke volume and consequently cardiac output, causing pre-syncope or syncope. In this case the subject can signal the fact that the loss of knowledge was preceded by a strong palpitation or a sudden acceleration of the beat. A drastic reduction in cardiac output can instead occur in those cases of arrhythmia in which the heart rate falls below the normal heart rate ( bradyarrhythmia ). This happens in the alterations of the atrio-ventricular conduction system and can reach up to the electric asystole (the heart stops). In the trained athlete there is physiological vagotonia = benign arrhythmia that disappears when the individual ceases to train and is not accompanied by symptoms. In some subjects however vagotonia does not cease with dislocation and tends to worsen over time = non-physiological vagotonia.
