bubble_chart Overview

Cardiac A-V block is classified into three types: sinoatrial, atrioventricular, and intraventricular conduction block. Among pediatric conduction blocks, atrioventricular block is the most common. Based on the degree of blockage, it can be divided into grade III: Grade I does not necessarily indicate heart disease, as it can be observed in about 5% of healthy individuals, so its significance should be considered in conjunction with clinical context; Grade II often involves heart disease; Grade III, except for congenital abnormalities in the conduction system, is generally regarded as indicative of severe heart disease.

bubble_chart Clinical Manifestations

In addition to the manifestations of the primary disease, it also presents as:

1. First-degree atrioventricular block: The first heart sound at the apex is often weakened.
2. Second-degree atrioventricular block: Occasionally dizziness, lack of strength, palpitation, and irregular heart rhythm can be detected during auscultation, with dropped beats.
3. Third-degree atrioventricular block: Symptoms include dizziness, lack of strength, palpitation, and shortness of breath after activity. In severe cases, it may lead to a cardio-cerebral syndrome, causing the child to lose consciousness, convulse, or even die. Auscultation reveals a slow but regular heartbeat, often around 40 beats per minute. Acquired cases are mostly caused by organic heart diseases such as myocarditis. Congenital cases can also be seen in children, with a relatively faster ventricular rate (around 40–60 beats per minute). The block may decrease after exercise or drug stimulation.

bubble_chart Auxiliary Examination

Electrocardiogram examination

1. First degree: The P-R interval is prolonged beyond the normal range for each age group. Specifically, >0.14 seconds for those under 1 year old, >0.16 seconds for ages 1–5, >0.18 seconds for ages 5–12, and >0.20 seconds for those over 12 years old.
2. Second degree:
   1. Second degree type I (Wenckebach phenomenon): The block is located in the proximal part of the atrioventricular node, manifested as:
      1. The P-R interval gradually lengthens, but the degree of prolongation progressively decreases, the R-R interval gradually shortens, and eventually a beat is dropped, meaning a P wave is not followed by a QRS complex. The P-R interval then gradually lengthens again, repeating this cycle;
      2. The ratio of P waves to QRS complexes is 3:2, 4:3, 5:4, etc.
   2. Second degree type II (Mobitz type II): The block is located in the distal part of the atrioventricular bundle (bundle branches) and Purkinje fibers, manifested as:
      1. The P-R interval is fixed, but some P waves are not followed by a QRS complex;
      2. The ratio of P waves to QRS complexes may show regular dropping, such as 4:3, 3:2, etc., or irregular dropping.
3. The block in second degree may occur within the atrioventricular bundle or below its branches, with children mostly experiencing the former, manifested as:
   1. The P-P interval and R-R interval are each equal, but the P waves and QRS complexes are unrelated;
   2. The ventricular rate is slower than the atrial rate. The former is often fixed at 40–60 beats per minute, and under exercise or pharmacological stimulation, the degree of block may decrease.

bubble_chart Diagnosis

The causes of atrioventricular block include:

1. various myocarditis and cardiomyopathy;
2. congenital heart diseases such as atrial septal defect, ventricular septal defect, Ebstein's anomaly, etc.;
3. congenital atrioventricular block, mostly third-degree;
4. drug poisoning disease, with digitalis being the most common;
5. electrolyte disturbances such as hypokalemia;
6. increased vagal tone often leading to first-degree or second-degree type I atrioventricular block, etc.

bubble_chart Treatment Measures

(1) Disease Cause Treatment

First-degree and second-degree atrioventricular block are primarily treated by addressing the disease cause. Acute sexually transmitted disease toxic myocarditis-induced %-degree block can be treated with adrenal corticosteroids.

(2) Drug Treatment

For patients with a heart rate below 45 beats per minute or those experiencing chest tightness, lack of strength, or dizziness, medications to accelerate heart rate may be used, such as atropine at a dose of 0.01–0.03 mg/kg, administered subcutaneously or intravenously; or isoproterenol 5–10 mg sublingually, or 0.5 mg added to 100 ml of 5% glucose solution for intravenous drip, with the drip rate adjusted based on efficacy.

(3) Artificial Pacemaker Treatment

For complete atrioventricular block, temporary or permanent pacemaker implantation may be considered depending on the condition. The indications include:

1. Slow ventricular rate at rest, infants <55次/分，兒童<50次/分；
2. those with Adams-Stokes syndrome;
3. those accompanied by heart failure;
4. those with wide and significantly abnormal QRS complexes;
5. those with ventricular arrhythmias.

For cases caused by acute myocarditis, drug poisoning disease, or electrolyte imbalances, temporary pacing may be chosen. Post-cardiac surgery cases may also temporarily use temporary pacing. If the block persists for more than 4 weeks, permanent pacemaker implantation should be considered.