Second-degree heart block

Grade 2 heart block is a sudden or progressive delay in the time it takes for an electrical signal to travel through the atria that sets the rhythm of heart muscle contraction.

Epidemiology

The lack of large studies prevents experts from objectively assessing the prevalence of grade 2 heart block. Although it is known that about 3% of cases of such a conduction disorder are associated with structural diseases of the heart, including valve abnormalities, congenital defects of the septa between the heart chambers, and hypertrophic cardiomyopathies.

Causes 2nd-degree heart block

Cardiologists consider atrial ventricular block or atrioventricular block to be a 2nd degree heart block.(AV block) of the 2nd degree, in which the electrical impulse from the upper chambers of the heart (atria) to the lower chambers (ventricles) passes through the atrioventricular node (a cluster of conducting cardiomyocytes on the septum between the atria) intermittently, i.e., there are abnormalities in the conduction system of the heart.

The most common causes of this disorder are related to:

• conduction system damage as a result of myocardial infarction - postinfarction cardiosclerosis;
• coronary heart disease;
• chronic heart failure and cardiomyopathies;
• myocarditis or rheumocarditis;
• Electrolyte imbalance due to hyperkalemia; [1]
• hyperthyroidism;
• Lenegre's disease, an idiopathic fibrosis of the cardiac conduction system;
• constant intake of drugs that slow down the conduction of electrical impulses of the heart, including cardiac glycosides (digoxin), beta-blockers, calcium channel blockers, antiarrhythmic and sedatives, diuretics and lithium preparations.

However, such heart block can also occur without cardiac diseases: against the background of physical exertion in trained athletes, for more details see: "The heart block can occur without cardiac diseases". - Sports heart

Some cases of heart block may be congenital, but most cases of heart block develop after birth.

Heart rhythm disorders in children and heart block of the 2nd degree in a child etiologically can be associated with congenital heart defects (valve defects or interventricular septal defects) (defects of valves, interatrial or interventricular septum), cardiac complications of diphtheria (diphtheria myocarditis), cardiac-type behavioral dystonia (VSD), Brugada syndrome.

Risk factors

First of all, the likelihood of heart block is higher in the elderly. Other risk factors are:

• a wide range of cardiovascular diseases of acute and chronic course;
• structural abnormalities of the heart (many of which are congenital);
• chronic elevation of BP;
• diabetes;
• Autoimmune diseases (sarcoidosis, systemic lupus erythematosus, etc.);
• acute rheumatic fever;
• collagen vascular disorders (systemic vasculitis, etc.);
• heart tumors;
• overactive vagus nerve.

Pathogenesis

In the pathogenesis of 2nd degree heart block, a condition in which electrical signals are delayed in reaching the ventricles, such a key moment as the delay of the next atrial impulse plays an important role.

This may be a gradual slowing of the conduction of electrical impulses through the atria to the atrial-ventricular junction - the AV node (which provides signal transmission between the atria and ventricles) and atrial contraction, which during electrocardiography (ECG) is displayed as prolongation of the PQ interval. In this case, conduction of the excitation signal within the ventricle (which displays a ventricular QRS complex) is not recorded and there is a prolapse of one or two ventricular complexes with the formation of a pause between contractions of the heart chambers.

As a result, the heart beats in a slow rhythm or with skipped beats, which disrupts the rhythmic pumping function of the heart muscle.

Symptoms 2nd-degree heart block

At the 2nd degree of heart block, the first signs may be manifested by frequent dizziness. But this condition is of two types, each of which has its own symptomatology.

The first type is Mobitz type 1 grade 2 heart block (called Wenckebach heart block), which may not cause any symptoms at all.

The second type of 2nd degree AV blockade is Mobitz type 2, which occurs at the level of the bundle of Hiss or the legs of the bundle of Hiss. [2] This type can also be asymptomatic, and the most common symptoms include: dizziness, weakness, pre-fainting and fainting, sensation of skipping heartbeats, chest pain, difficulty breathing or shortness of breath, and nausea. [3] That is, the symptomatology of bradycardia develops.

More information in the materials:

• Heart rhythm and conduction disorder: symptoms and diagnosis
• Hiss bundle branch blockade: causes, symptoms, diagnosis, treatment

Complications and consequences

What are the dangers of developing 2nd degree heart block? In Mobitz type 2 blockade, there is a high probability of its progression to complete AV blockade, in which the slowing of the heart rhythm leads to a decrease in cardiac output. Hemodynamic disturbance and creates a serious problem with the maintenance of the systemic blood supply in the form of Morgagni-Adams-Stokes syndrome.

Bradycardia with HR <40 beats/min is fraught with sudden cardiac arrest.

Diagnostics 2nd-degree heart block

Only instrumental diagnostics can detect heart block and determine its type. For more information - Instrumental methods of heart examination

Laboratory tests, particularly blood tests (biochemical, for electrolytes, creatinine, cholesterol, rheumatoid factor, etc.) are necessary to determine the cause of cardiac conduction disturbance.

And differential diagnosis is carried out in order to distinguish atrial-ventricular block from sinoatrial block and myocardial infarction, congenital from drug-induced, etc.

Treatment 2nd-degree heart block

Asymptomatic grade 2 AV block does not require any specific therapy outside of hospitalization. If the patient is symptomatic, standard cardiac support techniques for bradycardia are used, including the use of atropine and transdermal, transvenous or endocardial pacing.

When indicated, beta-adrenomimetics (Adrenaline, Isoprenaline) are used.

Treatment of Mobitz type 2 blockade includes transvenous stimulation prior to pacemaker surgery or catheter ablation. [4]

Grade 2 heart block: what is contraindicated. Drugs that affect the electrical conductivity of the heart (as mentioned above) are contraindicated. In cases of Mobitz type 1 blockade - in the absence of other heart problems - restrictions on physical activity are minimal, and patients can swim or ride a bicycle. In any case, a cardiologist should be consulted.

Mobitz type 2 degree AV blockade indicates a serious conduction disturbance in the Hiss-Purkinje system and is an irreversible condition in which physical activity must be reduced to avoid serious consequences.

How to eat for 2nd degree heart block? It is necessary healthy diet, and in the presence of cardiac pathologies may be recommended heart disease diet.

Prevention

As a preventive measure, experts recommend adhering to a healthy lifestyle and treating underlying diseases that can lead to rhythm and conduction disorders of the heart.

Forecast

The prognosis for Mobitz type 1 blockade is favorable, but for Mobitz type 2, it depends on the cause, the presence of complications and the work of implanted pacemakers. And in these cases - with pronounced heart problems - for patients of conscription age, 2nd degree heart block and the army are incompatible.

List of studies related to the study of grade 2 heart block

1. "Anorexia nervosa and second-degree atrioventricular block (Type I)". Authors: T. Bravender, R. Kanter, N. Zucker. Year: 2006.
2. "Second-degree atrioventricular block: a reappraisal." Authors: S. Barold, D. Hayes. Year: 2001.
3. "[Definitions of second degree atrioventricular block. An exercise in logic in clinical electrocardiography]."" Authors: S. Barold, S. Garrigue, P. Jaïs, M. Hocini, M. Haïssaguerre, J. Clémenty. Year: 2000.
4. "Second degree atrioventricular block: type I or type II?" Author: F. Duru. Year: 2007.
5. "Second-Degree Atrioventricular Blocks: Taking It Easy." Authors: F. Patani, Francesca Troiano, J. Ricciotti. Year: 2018.

Literature

• Shlyakhto, E. V. Cardiology: national guide / ed. By E. V. Shlyakhto. - 2nd ed., revision and supplement. - Moscow: GEOTAR-Media, 2021