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ATRIO –VENTRICULAR BLOCK (AVB)

AV block, or heart block, exists when conduction of the stimulus from the atria to the ventricle through the AV node is slowed or blocked.The AV block may be transient ,intermittent ,or permanent .It may be incomplete or complete. Atrioventricular BlocksImpulse is delayed within the AVnode, bundle of His or His-Purkinjesystem.

HEART

CORONARY VASCULATURE

A heart block can be a blockage at any level of the electrical conduction system of the heart.

Types of heart block

AV nodal block

Intraatrial block

SA nodal blocks

Bundle branch blocks

Intraventricular block

TYPES ACCORDING TO SEVERITY• First degree AV block• Second degree AV block

–Type I second degree AV block (Mobitz I) / Wenckebach block

–Type 2 second degree AV block (Mobitz II)

• Third degree AV block (Complete heart block)

FIRST DEGREE HEART BLOCK(Ⅰ゜AVB)

I゜AVB is prolongation of the atrio-

ventricular conduction time and is also

referred to as first degree A-V block.

The electrical impulse moves through the AV node

more slowly than normal

Heart rate and rhythm are normal

Generally, no treatment is necessary for first-degree heart block.

• ECG: Prolonged P-R interval:

• longer than 0.20sec in adults and >0.22s in old adults.

• PR Interval > 0.2 seconds (>5 small sq) but constant The difference of P-R interval between two times is more than 0.04 second.

SECOND-DEGREE HEART BLOCK

SECOND-DEGREE HEART BLOCK

Some signals from the atria don't

reach the ventricles

Causes "dropped beats

There are two types: Type I second-degree heart block, or Mobitz Type

I, or Wenckebach's AV block Type II second-degree heart block, or Mobitz

Type II

Mobitz Type I, or Wenckebach's AV block

• Electrical impulses are delayed more and more with each heartbeat until a beat is skipped

• Level of block is at AV node

• ECG:(1) The P-R interval

becomes longer and longer

(2) RHYTHM: irregular

3:2 CONDUCTION RATIO

Mobitz Type II Failure of conduction of one or more sinus beats to the ventricle More serious An abnormally slow heartbeat may resultLevel of block is below AV nodeThere is a fixed numerical relationship between atrial and ventricular impulses,which may be 2:1 or 3:1 or 4:1

Mobitz Type II

MOBITZ TYPE I MOBITZ TYPE II

•PR interval lengthens;Preceding the pause is longer than that after the pause

•Level of block: is at AV node

•QRS - Normal

•PR interval consant;Preceding the pause is same as that after the pause

•Level of block: is below AV node

•QRS -wide

THIRD-DEGREE OR COMPLETE HEART

BLOCK!• Heart's electrical signal doesn't pass from the upper to the lower chambers.

• This can precipitate VT/VF• Ventricles end up producing their own electrical signals (called the escape rhythm)

• Some part of conducting system will take over as pacemaker

• The escape pacemaker can be in the AV node Or it can be in the His bundle or even distal to it

• It usually results in a very slow heartbeat (bradycardia) and can cause a heart attack.

LEVEL OF BLOCK

•At AV nodal – Junctional rhythm with narrow QRS complex

•At His-Purkinje level - Ventricular escape rhythm with wide QRS

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•ECG:• Atrial rate : normal• Ventriuclar rate : less than 45bpm• P wave: dissociated from QRS• There is no P-R to QRS relationship• QRS : normal/ wide• Regular P-P interval .Rugular R-R interval

SUMMARY :1º : Prolongation of PR Interval 2º : Mobitz I – Increasing PR Interval until dropped beat is seen Mobitz II – Constant PR Interval with more P waves to QRS 2 : 1 – Constant PR Interval with more P waves to QRS 3º : Complete pathological block at the AV node Complete dissociation between P waves

CAUSES• Can be either congenital or acquired

– autoimmune diseases• Causes of acquired complete heart block

include the following:• Drugs or toxins

– Beta-blockers– Calcium channel blockers– Digoxin or other cardiac glycosides

Causes ctd.....

• coronary artery disease• Profound hypervagotonicity• MI - anterior wall MI• Cardiomyopathy• Sclerosis (Aortic) • Acute rheumatic fever• Metabolic disturbances, Eg, severe

hyperkalemia

•PATHOPHYSIOLOGY

• Duration of the escape QRS complex depends on the site of the block and the site of the escape rhythm pacemaker.

• Pacemakers above the His bundle produce a narrow QRS complex escape rhythm, while those at or below the His bundle produce a wide QRS complex.

• When the block is at the level of the AV node, the escape rhythm generally arises from a junctional pacemaker with a rate of 45-60 beats per minute. Patients with a junctional pacemaker frequently are hemodynamically stable and their heart rate increases in response to exercise and atropine.

• When the block is below the AV node, the escape rhythm arises from the His bundle or the bundle-branch Purkinje system at rates less than 45 beats per minute. These patients generally are hemodynamically unstable and their heart rate is unresponsive to exercise and atropine.

SIGNS AND SYMPTOMS

• Bradycardia• Chest pressure or pain• Fainting, also known as

 syncope• Fatigue• Lightheadedness or dizziness• Palpitations, which can be skipping,

fluttering or pounding in the chest• Shortness of breath

• In patients with concomitant myocardial ischemia or infarction,–Chest pressure or pain–Dyspnea–nausea or vomiting–Signs of anxiety such as agitation or unease–Diaphoresis–Pale complexion–Tachypnea

• Patients may have signs of hypoperfusion–Altered mental status–seizures, caused by not enough oxygen getting to the

brain–Hypotension–Lethargy–Chest pain–.

• Stokes Adams syndrome

–A condition involving sudden fainting which usually lasts for less than a minute and may include seizures. Before the attack the patient becomes pale and during recovery the patient often feels hot and flushed. The fainting occurs when there is a lack of oxygen to the brain due to heart rhythm problems involving slowing of the heart. The condition has a high mortality ratewithout treatment which often involves a pacemakeror medication

Symptoms of Stokes Adams syndrome• Fainting• Blackouts• Sudden loss of consciousness• Fainting when seated - several other types of fainting rarely

occur when seated• Recurrent attacks of fainting

DIAGNOSES

Laboratory StudiesSerum electrolytes levelsDigoxin level Lyme titers Cardiac enzymes a complete blood count

12-lead electrocardiogram Imaging Studies

A chest radiograph If myocarditis or a pericardial effusion is

a concern, an echocardiogram should be performed• angiogram

TREATMENTEmergency department care• Administering oxygen, maintenance of an

intravenous line, frequent monitoring of blood pressures, and continuous cardiac monitoring.

• Anti-ischemic therapy • Transcutaneous pacemaker • Transvenous pacemaker• Arrange for permanent pacemaker insertion

MEDICATIONS

Catecholamines

Anticholinergic agents

Antiarrhythmic drugs

Antidotes

Medications

• Anticholinergic agentsThese agents improve conduction through the AV node by

reducing vagal tone via muscarinic receptor blockade.• CatecholaminesThese agents improve hemodynamics by acting on the

beta-adrenergic receptors to increase the heart rate and contractility, and by acting on the alpha-adrenergic receptors to increase the systemic vascular resistance.

• Sympathomimetic agentsThese agents act on beta-adrenergic receptors and increase

heart rate and contractility• Digoxin immune Fab (Digibind)

WHAT IS A PACEMAKER?

•

The Pacemaker is a battery-powered implantable devices that function to electrically stimulate the heart to contract and thus to pump blood through out the body. These devices are used to help patients with very slow heart beats. A regular pacemaker weighs about an ounce, band has and area of 30cm2. 

DIFFERENT KINDS OF PACEMAKER.

•There are many different sorts of pacemaker. I will tell you about some of them. A single-chamber pacemaker has one lead while a dual-chamber has two leads. Dual chamber pacemakers have two leads: one in the atrium and one in the ventricle. Dual-chamber pacemakers are more complex and sophisticated than single-chamber pacemakers. A dual chamber pacemaker can receive signal from both the ventricle and the atrium. It can also coordinate the signals and contractions of the atria and the ventricles to help the heart beat more efficiently. There is an external pacemaker for people with small abnormalities in their heart rhythm. The body normally has a pacemaker when you are born but some peoples stop working so that is where the man made pacemaker comes in. Pacemaker systems are often implanted under local anaesthesia in a cardiac catheterization laboratory. Implantation of a pacemaker is considered a minor procedure. Some hospitals with electrophysiology laboratories implant pacemakers there. A pacemaker is implanted just below the collarbone in a procedure that takes about two hours. Each pacemaker can last up to around ten years without a change. 

A bipolar circuit

A unipolar circuit

Pacing sites• Temporary transvenous pacemaker

– involves a pulse generator, which is externally connected to 2 electrode wires, threaded through a large vein (generally the subclavian or internal jugular) into either the right atrium or the right ventricle.These wires directly contact the endocardium within the heart .

• Temporary epicardial pacemaker– involves directly stimulating the epicardium. This type of

pacing is initiated after cardiac surgery.Postoperatively, electrodes are lightly sutured to the epicardium before the thorax is closed. These pacing wires are pulled through the skin and secured to the external chest wall, ready for attachment to a temporary pacing generator as needed

Temporary Dual Chamber Sequential

Pacing Box Temporary Single Chamber Pacing Box

Base Level Pacing Controls

ON and OFF• The device is turned on by

pressing the ON key. The device is turned off by pressing the ON and OFF keys simultaneously.

RATE• This dial is used to set the rate, in

pulse per minute [ppm]), at which pacing pulses are delivered. It allows continuous adjustment of the rate from 30 to 180 min-1 (ppm)

Base Level Pacing Controls ctd….

OUTPUT• This dial is used to set the amplitude, in

milliamperes (mA), of the pacing pulse. It allows continuous adjustment of the stimulus current amplitude from 0.1 to 20 mA. If both the atrium and the ventricle are paced, a separate output

setting is required for each chamber.• The output amount is the level of energy

delivered by the pulse generator to the heart to initiate depolarization.

• Output is then slowly increased until

capture is obtained .

.

SENSITIVITY

• Sensing merely refers to the ability of the generator to detect and recognize the impulses the myocardial tissue is generating on its own.

• This dial is used to enable and adjust the sensitivity, in millivolts (mV), of the sensing circuitry. When enabled, the sensitivity can be adjusted from 0.5 to 20 mV. Initially

set at about 2 to 5 mv.• To synchronize the beats, the

generator first analyzes the intrinsic

rhythm and then stimulates the heart only as needed.

• The most common cause of failure to sense is displacement of the electrode.

Repositioning the patient on his or her left side may improve contact between the electrode and the myocardium. If the response is still inadequate, then the sensitivity must be increased.

This increase is accomplished by turning down the millivoltage, allowing the generator to detect beats that occur at lower millivolt levels. Conversely, if the pacemaker is detecting beats that are not actually occurring

(inappropriate sensing), then the sensitivity threshold must be increased to block out artifact. This increase is accomplished by turning up the millivoltage

CAPTURE

Electrical capture, the ability of the electrical impulse to initiate a cardiac response, is detected by examining an electrocardiogram.

Capture is both an electrical and a mechanical event.

Electrical capture is indicated by a pacer spike followed by a corresponding P wave or QRS complex, depending on which chamber is being paced .If the atrium is paced, the spike appears before the P wave. If the ventricle is paced, the spike occurs before the QRS complex

Failure to capture occurs when a pacer spike is present but is not followed by a corresponding waveform (P wave or QRS complex)

• Atrial pacer–a pacer spike (Ap) followed by a corresponding P wave.

• ventricular pacer• pacer spike (Vp) followed by a corresponding, widened QRS complex.

NURSING DIAGNOSIS

• Acute pain related to an imbalance in oxygen supply & demand.

• Decreased cardiac output related to myocardial ischemia.

• Knowledge deficit related to unfamiliarity with the procedure.

• Anxiety related to surgical procedure.

• Activity intolerance related to decreased cardiac output.

• Sleep pattern disturbance related to environmental changes

• Constipation related to decreased activity level of patient.