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Heart Blocks: A Primer

High grade 2nd degree, 2nd degree Mobitz type 2 and 3rd degree AV blocks require admission for pacemaker placement and/or evaluation. Treatment with Atropine is indicated in bradycardic, symptomatic and/or unstable patients with a 1st or 2nd degree Mobitz type 1 AV block. It is unlikely to be affective in high grade blocks as the block is usually below the AV node. Atropine can still be used as a temporizing measure while setting up for transcutaneous pacing and/or transvenous pacemaker placement in high grade blocks. In symptomatic or unstable bradycardic patients, have the transcutaneous pacer pads placed while simultaneously administering chronotropic agents such as Epinephrine; pacing…

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Articles of Interest

Atrioventricular Block

Atrioventricular (AV) block (often referred to as “heart block”) involves the partial or complete interruption of impulse transmission from the atria to the ventricles. This interruption of impulse transmission results in characteristic ECG findings that differ depending on the subtype of AV block.

Atrioventricular Blocks

First-degree AV block may result from abnormal conduction in the atrium, AV node, or (rarely) in the His bundle and Purkinje fibers. Mobitz type I (Wenckebach) second-degree AV block is almost always located within the AV node, while Mobitz type II second-degree block or advanced heart block is located below the node. Third-degree AV blocks may be proximal (located in the AV node) or distal.

Atrioventricular Blocks – First, Second and Third Degree

Top three reversible causes: Drugs, Ischemia, Electrolytes.

Bradycardia and Pacing

The pacing is usually set to demand (as required) at 70-80 beats per minute starting low (eg. 30 mA) and increasing until electrical capture with established output occurs. In some settings (such as pre-hospital) where there is a concern that electrical artifact may inhibit pacing in the demand mode, it is reasonable to use a fixed (asynchronous) mode.

Conduction abnormalities

This chapter will discuss the syndromes that result in abnormal conduction at every step of the electrical pathway, the aberrations that are manifested in the ECG as a result, and the relevance of each abnormality in a clinical setting. Abnormalities that manifest outside this conduction pathway, congenital and acquired, will also be captured in this chapter.

ECG Pointers: AV Blocks – Part I

AV nodal blocks are defined as delay or interruption in transmission of the electrical impulse between the atria and ventricles. The conduction disturbance can be transient or permanent. They classified based on severity or degree of blockade —the more distal in the conduction system, the more severe block. First-degree and second-degree Mobitz I rarely require pacing.

ECG Pointers: AV blocks – Part II

In Mobitz I block, the AV nodal cells progressively fatigue and then fail producing lengthening PR intervals. In Mobitz II the conduction system suddenly fails to conduct a beat, leaving the PR interval constant prior to sudden failure. For patients with second degree AV block with a ratio of atrial to ventricular conduction of 2:1, the distinction between Mobitz type I and Mobitz type II cannot be made from the surface ECG alone.

Emergency Strategy - How to treat atrioventricular heart block

There are three different forms of atrioventricular block which include first degree AV block, second degree AV block and third degree AV block. First degree AV block causes include myocarditis, toxicity of digoxin, increase vagal tone and acute inferior myocardial infarction. First degree AV block is characterized by delay in AV conduction. In certain cases, first degree AV block, may involve normal heart. None is required in term of management as the patient is mostly asymptomatic. However, ECG may show prolongation of the PR interval more than 0.20 seconds.

Heart blocks: first, second and third degree

These are atrioventricular blocks, arising from some abnormality of conduction between the atria and the ventricle. The PR interval describes this conduction. The PR interval is not just the conduction through the atria- it is also the AV node, the bundle of His and the Purkinje fibers. But, most of the time when this is prolonged, it's the AV node ( in most cases with a PR of 200-300 msec). First degree and Mobitz type 1 are usually AV nodal processes; Mobitz type 2 and third degree heart block are typically due to disease below the AV node.

Management and treatment of AV blocks (AV-block 1, 2 & 3)

Management of AV blocks aims to restore atrioventricular conduction either pharmacologically or by means of artificial pacemakers. Both methods may be used in the acute setting, whereas long-term management only includes pacemaker therapy.

The Heart Block Hat-Trick: A Case of Alternating First-, Second-, and Third-Degree Heart Blocks

Idiopathic third-degree atrioventricular (AV) block in a relatively young patient is an uncommon phenomenon. Even more rare is when the third-degree heart block is alternating with the first- and second-degree AV blocks. In this case, we present a 39-year-old man with varying degrees of AV block, alternating the third-degree, second-degree, and first-degree AV blocks. The patient underwent an extensive workup for underlying etiologies, and results were inconclusive.

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StatPearls

In general, patients that present with first-degree or second-degree Mobitz type 1 AV block do not require treatment. Any provoking medications can be removed, and patients can be monitored on an outpatient basis. However, patients with higher degrees of AV block (Mobitz type 2 AV block, 3rd degree) tend to have severe damage to the conduction system. They are usually at a much greater risk of progressing into asystole, ventricular tachycardia, or sudden cardiac death.

Understanding Atrioventricular Blocks

AV blocks are conduction delays or a complete block of impulses from the atria into the ventricles. AV block may be due to increased vagal tone that may be elicited during sleep, athletic training, pain, or stimulation of the carotid sinus. Damage of the conduction system secondary to hereditary fibrosis or sclerosis of the cardiac skeleton are known as idiopathic progressive cardiac conduction disease. Ischemic heart disease causes 40% of AV blocks.6 AV blocks are also seen in cardiomyopathies, myocarditis, congenital heart diseases, and familial diseases. A plasma potassium concentration above 6.3 mEq/L may also cause AV block. They may be iatrogenic, from medications such as Verapamil, Diltiazem, Amiodarone, and Adenosine, or from cardiac surgeries and catheter ablations for arrhythmias.