Sinus bradycardia with second degree av block

Heart block is a condition in which the electrical wiring system of the heart does not work properly.  Sometimes it can result in a slow heartbeat that is either regular or irregular. This may cause symptoms.   

Two different types of electrical problems are considered second-degree heart block. With the first type, electrical signals take longer and longer to move from the upper chambers of the heart (atria) to the lower chambers (ventricles). At times, it takes so long that the process does not complete. This results in a missed heartbeat and an irregularity in the pulse.  

With the second type of second-degree heart block, some electrical signals are not relayed from the upper chambers to the lower chambers. Unlike the first type of second-degree heart block, the electrical signals suddenly fail to conduct. This failure to conduct may happen in a very regular pattern and cause missed heartbeats.

What causes second-degree heart block?

Second-degree heart block may develop into a more serious type of heart block. It may cause a sudden loss of consciousness or it may cause the heart to suddenly stop beating.

When a healthy heart beats, an electrical impulse travels through the top chambers of the heart (atria) to the bottom chambers (ventricles). This impulse tells the chambers of the heart to beat and push blood through and out of the heart.

If you have second-degree heart block, the electrical impulses will sometimes not reach the lower chambers of your heart. This can cause your heart to skip beats, leading to an abnormal heart rhythm which affects the flow of oxygen-rich blood to your body and brain. 

What are the types of second-degree heart block?

There are two types of second-degree heart block:

• Second-degree type 1 heart block, also known as Mobitz I.
• Second-degree type 2 heart block, also known as Mobitz II.

If you have second-degree type 1 heart block, or Mobitz I, your heart will skip beats in a regular pattern.  Your body can usually cope well with this, so you won't usually experience any symptoms.

If you have second-degree type 2 heart block, or Mobitz II, your heart will skip beats in an irregular pattern. Your body can't compensate for this and this type of heart block can lead to:

• light-headedness
• dizziness 
• fainting.

Find out more about different types of heart block.

What causes second-degree heart block?

Most people with second-degree heart block have an underlying heart condition like coronary heart disease, cardiomyopathy or congenital heart disease. 

It can also be caused by:

• ageing of the electrical pathways in your heart (so you're more likely to get it if you're older)
• electrolyte imbalances
• some medicines.

What are the tests and treatments for second-degree heart block?

Your doctor might recommend that you have an ECG to diagnose second-degree heart block.

• If you're an adult with second-degree heart block that causes you to have a very slow heart rate, it's likely your doctor will suggest that you have a pacemaker fitted.
• If you have second-degree heart block that was caused by a heart attack, you may just need a temporary pacemaker. If a normal heart rhythm hasn’t returned a few weeks after your heart attack, you might need to have a permanent pacemaker fitted.
• If you're a young person with congenital heart disease with second-degree or third-degree heart block but you don’t have a slow heart rate or any symptoms, you may not need a pacemaker.

Can second degree heart block be cured?

Unless a patient has complete heart block because of medications, most patients who develop second degree heart block will always need a pacemaker.

Second-degree atrioventricular block (AV block) is a disease of the electrical conduction system of the heart. It is a conduction block between the atria and ventricles. The presence of second-degree AV block is diagnosed when one or more (but not all) of the atrial impulses fail to conduct to the ventricles due to impaired conduction. It is classified as a block of the AV node and is categorized in between first-degree (slowed conduction) and third degree blocks (complete block).[1]

Signs and symptoms[edit]

Most people with Wenckebach (Type I Mobitz) do not show symptoms. However, those that do usually display one or more of the following:[2]

• Light-headedness
• Dizziness
• Syncope (fainting)

There are two non-distinct types of second-degree AV block, called Type 1 and Type 2. In both types, a P wave is blocked from initiating a QRS complex; but, in Type 1, there are increasing delays in each cycle before the omission, whereas, in Type 2, there is no such pattern.[3]

Type 1 second-degree heart block is considered a more benign entity than type 2 second-degree heart block [4] with type 1 not having structural changes found on histology.

Both types are named after Woldemar Mobitz.[5][6] Type I is also named for Karel Frederik Wenckebach,[7] and type II is also named for John Hay.[8][9]

Type 1 (Mobitz I/Wenckebach)[edit]

Type 1 Second-degree AV block, also known as Mobitz I or Wenckebach periodicity, is almost always a disease of the AV node. Wenckebach published a paper in 1906 on progressively lengthening PR intervals[10] that was later classified as Type I in Mobitz's 1924 paper.[11] Thus, both "Mobitz type I" and "Wenckebach block" refer to the same pattern and pathophysiology.

In Wenckebach's 1906 paper, his original observations were from increasing delay in contraction of the atria and ventricles that shortened after a brief pause and this was later observed on ECG after Einthoven's invention in 1901 that became the electrocardiogram (ECG). In modern practice, Mobitz I heart block is characterized by progressive prolongation of the PR interval on consecutive beats followed by a blocked P wave (i.e., a dropped QRS complex). After the dropped QRS complex, the PR interval resets and the cycle repeats. This grouped beating was described as "Luciani periods" after Luigi Luciani's work in 1873.[12] The result is a lengthening of the R-R intervals as each subsequent P-wave reaches an increasingly refractory AV node until the impulse fails to conduct, which ultimately results in a blocked QRS complex.[13]

One of the baseline assumptions when determining if an individual has Mobitz I heart block is that the atrial rhythm has to be regular. If the atrial rhythm is not regular, there could be alternative explanations as to why certain P waves do not conduct to the ventricles.[citation needed]

This is almost always a benign condition for which no specific treatment is needed for the rhythm itself. It can be seen in myocardial ischemia, propranolol use, digitalis use, rheumatic fever, and chronically in ischemic heart disease and other structural diseases (amyloidosis, mitral valve prolapse, aortic valve disease, and atrial septal defect). In symptomatic cases, intravenous atropine or isoproterenol may transiently improve conduction.[14]

Type 2 (Mobitz II/Hay)[edit]

Type 2 Second-degree AV block, also known as Mobitz II, is almost always a disease of the distal conduction system (His-Purkinje System).

Mobitz II heart block is characterized on a surface ECG by intermittently non conducted P waves not preceded by PR prolongation and not followed by PR shortening. There is usually a fixed number of non-conducted P waves for every successfully conducted QRS complex, and this ratio is often specified in describing Mobitz II blocks. For example, Mobitz II block in which there are two P waves for every one QRS complex may be referred to as 2:1 Mobitz II block.[15]:181

The medical significance of this type of AV block is that it may progress rapidly to complete heart block, in which no escape rhythm may emerge. In this case, the person may experience a Stokes-Adams attack, cardiac arrest, or sudden cardiac death. The definitive treatment for this form of AV Block is an implanted pacemaker.

The impairment is usually below the AV node.[16] Although the terms infranodal block or infrahisian block are often applied to this disorder, they refer to the anatomic location of the block, whereas Mobitz II refers to an electrocardiographic pattern.

P:QRS ratios[edit]

Because type I Mobitz block occurs in regular cycles, there is always a fixed ratio between the number of P waves and the number of QRS complexes per cycle. This ratio is often specified when describing the block. For example, a Mobitz type I block which has 4 P waves and 3 QRS complexes per cycle may be referred to as 4:3 Mobitz Type I block.[15]:179

Type II Mobitz block also usually occurs with a fixed P:QRS ratio, with a set number of P waves for every successfully elicited QRS.[15]:179 This ratio is also frequently specified in referring to 3:1, 4:1, 5:1, or higher Mobitz type II block. Higher numbers of P waves for every QRS indicate more severe block[15]:181 and ratios of 3:1 and above are also referred to as "High Grade" AV Block[17]e60. Of course, because type II Mobitz block is unstable by nature, it is common for the P:QRS ratio in Mobitz type II block to change over time.[citation needed]

The P:QRS ratio is always of the form X:(X − 1) in type I Mobitz block and of the form X:1 in type 2 Mobitz block because of the nature of the pattern of each. Thus one may leave out the type and refer to 3:1 Mobitz block or 4:3 Mobitz block, for example, without creating ambiguity, except in the case of 2:1 block.[citation needed]

2:1 AV block[edit]

In the case of 2:1 block (2 P waves for every QRS complex) it is impossible to differentiate type I from type II Mobitz block-based solely on the P:QRS ratio or on a pattern of lengthening PR intervals.[15]:182 In this case, a lengthened PR interval with a normal QRS width is most likely indicative of a type I-like pathology, and a normal PR interval with a widened QRS is most likely indicative of a type II-like pathology.[15]:182

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What is sinus bradycardia with AV block?

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What is the treatment for 2nd degree AV block?