Atrioventricular Block: Causes

Pathogenesis (disease development)

The pathogenesis of AV block is most often (50%), as in sick sinus syndrome (sinus node disease), of chronic degenerative origin; this involves slowly progressive fibrosis (abnormal proliferation of connective tissue) of the excitation guidance system (ELS). The second most common cause of AV block is ischemic-related (reduced blood flow) (40%), either due to ischemic cardiomyopathy (heart muscle disease) or acute coronary syndrome (ACS; spectrum of cardiovascular diseases caused by occlusion or high-grade narrowing of a coronary vessel). Various causes lead to a more or less severe failure of the sinus node (= primary pacemaker center of the heart), with the result that the AV node (atrioventricular node; secondary pacemaker center of the heart) must step in as a replacement pacemaker. This can cause a threatening drop in the heart’s pumping capacity. In 1st degree AV block, there is delayed conduction of excitation. [1st degree AV block. PQ time > 0.20 seconds (200 ms)]In 2nd degree AV block, two types are distinguished.

  • Mobitz I type (Wenckebach block): in this case, there is intermittent interruption of excitation conduction with prior prolongation of PQ time.
  • Type Mobitz II (Mobitz block): absence of a ventricular action on atrial excitation without prior prolongation of the PQ interval; in this case, only every 2nd, 3rd, or 4th atrial action can also be regularly transmitted to the ventricle (2:1 or 3:1 or 4:1 block) [prognosis: unfavorable; indication for the installation of a permanent pacemaker].

In 3rd degree AV block, there is a complete interruption of excitation conduction between the atrium (atrium) and ventricle (ventricle). This leads to a complete dissociation of atrial and ventricular rhythm. [Indication for placement of a permanent pacemaker: AV block III° (permanent/permanent or frequently intermittent/interrupting)].

Note: Patients with a HV interval s= 70 ms have a significantly higher incidence of IL and III degree AV block than those with normal HV time. The HV interval indicates the time between excitation of the His bundle (His spike) and the first ventricular excitation in the lead.A HV interval of >70 msec indicates pacing.

Etiology (Causes)

Biographic Causes

  • Genetic burden – congenital (inherited) defect.
  • Age – older age (hazard ratio per 5-year intercept: 1.34).

Behavioral causes

  • Physical activity
    • Athletes (increased parasympathetic tone; usually AV block of I. Grade or mildly pronounced AV block II. Degree)
  • Sleep (increased parasympathetic tone; usually AV block of I. Degree or a weakly pronounced AV block II. Degree)

Disease-related causes

  • Acute coronary syndrome (ACS; spectrum of cardiovascular disease caused by occlusion or high-grade narrowing of a coronary artery).
  • Acute rheumatic fever – inflammatory rheumatic systemic disease of the skin, heart, joints, and brain; secondary disease following infection with group A β-hemolytic streptococci.
  • Chronic heart failure (cardiac insufficiency) (hazard ratio 3.33).
  • Hypertension (high blood pressure) – systolic blood pressure (hazard ratio 1.22).
  • Ischemic cardiomyopathy (heart muscle disease associated with reduced blood flow to the heart muscle).
  • Coronary spasm – spasm of the coronary arteries; spontaneous in Prinzmetal’s angina (synonym: Variant angina or vasospastic angina), which is angina pectoris with and without coronary stenosis, furthermore, mechanically through the catheter tip, that is, an induced coronary spasm during coronary angiography (radiological procedure that uses contrast agents to visualize the lumen (interior) of the coronary arteries (arteries that surround the heart in a wreath shape and supply the heart muscle with blood)).
  • Lenègre disease – congenital degenerative disease of the excitation conduction system of the heart. The acquired form due to mechanical injury is called Lev disease.
  • Lev disease – degenerative disease of the excitation conduction system of the heart.
  • Lyme disease with cardiac involvement (carditis/Lyme carditis; AV block) – infectious disease transmitted by ticks; complication can occur within days to months after a tick bite; rate of carditis in Europe is approximately 1%.
  • Mononucleosis (synonyms: Pfeiffer’s glandular fever, infectious mononucleosis, mononucleosis infectiosa, monocytic angina or kissing disease, (Student’s) kissing disease, called) – common viral disease caused by the Epstein-Barr virus; this affects lymph nodes, but can also affect the liver, spleen and heart.
  • Myocardial infarction (heart attack) (hazard ratio 3.54).
  • Myocarditis (inflammation of the heart muscle)
  • Neoplasia (malignant tissue neoplasms).
  • Sarcoidosis (synonyms: Boeck’s disease; Schaumann-Besnier’s disease) – systemic disease of connective tissue with granuloma formation (skin, lungs and lymph nodes).

Laboratory diagnoses – laboratory parameters considered independent risk factors.

Medications

Operations

  • Ethanol ablation of the ventricular septum (transcoronary ablation of septal hypertrophy, TASH) for hypertrophic obstructive cardiomyopathy.
  • Cardiac surgery
  • Implantation of a device that can apply pressure to the AV node region
  • Interventional aortic valve replacement (“transcatheter aortic valve implantation,” TAVI).
  • Catheter ablation of AV nodal re-entrant tachycardia (AVNRT; risk 0.2% to 0.5%).