The normal heart impulse originates in the sinus node and emits excitation at a certain frequency, which sequentially excites the atria, atrioventricular junction, atrioventricular node, atrioventricular bundle, right and left bundle branches and Purkinje fibers, and finally reaches the ventricular muscle to depolarize the ventricles. If a pacing point in the heart is excited earlier than the sinoatrial node and causes early depolarization of the heart, it is called premature pacing. Depending on the ectopic pacing point, atrial, atrioventricular junctional, and ventricular premature contractions can be classified. Among them, ventricular premature beats are the most common, followed by atrial, and atrioventricular junctional beats are rare.
Premature beats are the most common arrhythmia in pediatric patients, both in healthy children and in those with heart disease. Premature beats have no abnormalities in the electrocardiogram, physical examination of the heart, X-ray and echocardiogram are normal, and usually have no serious consequences.
The following manifestations of premature beats should be taken seriously.
1. frequent premature ventricular contractions.
2. Multiple origin or polymorphic premature contractions.
3. Continuous ventricular premature contractions, paired (2 consecutive ventricular premature contractions) or short bursts of ventricular tachycardia (3-5 consecutive ventricular premature contractions).
4. Non-sustained ventricular tachycardia (6-30 consecutive ventricular premature beats), sustained ventricular tachycardia (≥30 consecutive ventricular premature beats).
5. Concurrent ventricular premature beats.
6. R on T (R on T) phenomenon.
7, Concurrent ECG with.
① other types of premature beats (atrial, junctional zone);
②Different types of conduction block;
(3) other types of arrhythmias;
④Prolonged QT interval;
⑤ Myocardial damage (ST-T changes).
Common concomitant symptoms include palpitations, weakness, dizziness and breath-hold. In severe cases, syncope, heart failure or cardiogenic shock may occur.
A 24-hour ambulatory electrocardiogram is required in children with premature beats. According to the 24-hour ECG, premature ventricular contractions are classified into 6 classes: Class 0: no premature contractions, but occasional premature contractions on endurance auscultation; Class I: occasional, less than 30 beats per hour or less than 1 beat per minute; Class II: frequent, more than 30 beats per hour or more than 6 beats per minute; Class III: polymorphic (polygenic) premature contractions; Class IVA: paired premature ventricular contractions, recurrent; Class IVB: three or more Class IVB: three or more recurrent ventricular premature beats with paroxysmal ventricular tachycardia; Class V: premature QRS waves overlapping the T wave of the previous sinus excitation (Ron T) phenomenon. The higher the grade of premature ventricular contractions in patients with organic heart disease, the greater its clinical significance. However, in patients with non-organic heart disease, the prognosis should not be determined solely on the basis of premature beat classification, but should be analyzed in close clinical context.
Etiology of premature beats: 1.
1. Infections: acute infectious diseases (such as scarlet fever, diphtheria, pertussis, typhoid, etc.) and viral infections (such as adenovirus, B encephalitis, coxsackie virus, etc.) are common.
2. Cardiac diseases: myocarditis, cardiomyopathy, mitral stenosis with left atrial enlargement, constrictive pericarditis with double atrial enlargement, pulmonary heart disease with right atrial enlargement, congenital or acquired long Q-T syndrome, mitral valve prolapse, Kawasaki disease and ischemic heart disease, various causes of heart failure, congenital heart disease, anemic heart disease, plateau heart disease and left ventricular pseudotendinous can be complicated by premature beats.
3. Hypoxic asphyxia, airway obstruction, pulmonary solid disease and anesthesia, etc.
4. Premature beats can be induced by phytodysfunction, vagal or sympathetic excitation, mental factors, emotional tension, excitement, fear, and overexertion; some are related to body position, such as only when lying quietly and flat; swallowing action, stomach fullness, biliary tract infection, urinary tract and other visceral reflexes can cause premature beats; hyperthyroidism, smoking, drinking alcohol or coffee can also induce premature beats.
5. Cardiac catheterization and cardiac surgery can cause premature contractions by direct mechanical stimulation of the heart.
6. The effects of drugs: digitalis, quinidine, procainamide, potassium salts, antimony, adrenergic drugs, acetylcholine, reserpine and anesthetic drugs often indicate toxic reactions when premature beats occur.