Bradyarrhythmias—Conduction System Abnormalities

Usually benign and requires no therapy.

If due to drugs, no need to discontinue.

Because such symptoms as lightheadedness and dizziness are nonspecific and common, especially in older persons, it is essential to exclude other causes before ascribing symptoms to first-degree AVB.

A rare indication for a DDD pacemaker. Shortening the PR interval to 150-200 ms may improve weakness, fatigue, and shortness of breath by restoring optimal AV synchrony. Consider His bundle pacing if the conduction prolongation is at the level of the AVN.

If patient is hospitalized and with refractory low cardiac output, consider temporary AV sequential pacing to improve hemodynamics and symptoms and to determine the benefit of permanent pacing.

No therapy usually required (possible exception if the PR is very long).

May be due to drugs to treat MI (e.g., β-adrenergic blockers, calcium channel blockers, digoxin). If asymptomatic, no medication changes are usually required. If symptomatic or PR very long, consider reducing dosage.

Consider atrial infarction or elevated atrial pressures as the cause and treat appropriately.

No specific therapy.

No need for temporary prophylactic pacing as it does not presage higher degrees of AVB.

If due to a drug, decrease the dose or stop using the drug if it is not essential.

If PR is markedly prolonged (300-400 ms) and hemodynamic compromise is suspected, dual-chamber pacing (at PV or AV interval of 150-200 ms) may improve hemodynamics.

This may be instituted if temporary pacing wires are present after cardiac surgery.

If first-degree AVB appears for the first time after aortic valve surgery, it may indicate damage to the His-Purkinje system (usually associated with left bundle branch block in these cases).

Prolonged PR intervals can cause hemodynamic problems after cardiac surgery since the timing of the “atrial kick” may be more important during this time in which diastolic dysfunction is possible.

Carefully evaluate for the presence of aortic insufficiency, consider TEE.

Acute development of first-degree AVB, especially if it occurs with a new bundle branch block (transient or persistent), is highly suspicious for the presence of a valve ring abscess.

Requires surgical treatment.

Consider TEE.

Transfer patient to a unit with cardiac telemetry (if not already there), as progression to higher levels of AVB can occur.

First-degree AVB is a sign of rheumatic carditis and may presage the development of higher levels of AVB, including complete heart block.

May be an indication for steroids.

If PR is markedly prolonged (> 300 ms), dual-chamber pacing (at PV or AV interval of 150-200 ms) may improve hemodynamics and symptoms.

Ventricles with severe diastolic dysfunction are especially dependent on atrial kick to maximize cardiac output.

If prolongation is at the level of the AV node, consider His bundle pacing.

Treadmill testing will help assess chronotropic competence (if this rhythm is not related to myocardial ischemia), as well as enhance AVN conduction, thereby reducing the degree of Wenckebach block (e.g., from 5:4 to 8:7 or producing first-degree AVB only).

Holter monitoring can assess the degree and level of AVB and the persistence of the problem during activities of daily living and any diurnal variation.

If the QRS duration is wide and Holter monitoring or stress testing suggests infranodal block, an electrophysiology study may help to confirm the level of AVB.

• If block is demonstrated to be intra- or infra-Hisian, permanent pacemaker implantation is reasonable, even in an asymptomatic patient.

• On occasion, intra-Hisian block can be demonstrated in a patient with a narrow, normal-appearing QRS complex by the production of higher degrees of AV block during treadmill testing with the increase in sinus rate.

No therapy.

• If not due to reversible cause (e.g., drugs or transient damage to the AV node from Lyme disease) and the QRS duration is normal, as more advanced or complete heart block rarely develops.

• There may be increased risk of syncope and symptoms in the future.

Some AV nodal blocking drugs (digoxin, β-adrenergic blockers, calcium blockers) may be the cause and should be reduced or stopped if possible, and then only if severe symptomatic bradycardia occurs.

If older or at high risk for structural heart disease, consider an echocardiogram to assess LV function (even if no physical findings are present).

If due to a correctable cause such as AV nodal blocking drugs, stop the drug if possible.

If there is a wide QRS or bundle branch block, it is possible that Wenckebach can be due to block below the AV node (in the His-Purkinje system).

• In this case, permanent pacemaker implantation is indicated.

Acutely, intravenous atropine or oral theophylline usually increases conduction through the AV node.

• These may paradoxically decrease ventricular rate and increase the degree of block if the block is below the bundle of His.

Permanent pacemaker implantation is indicated if symptomatic second-degree AVB is not otherwise correctable.

Is often reversed during thrombolysis or angioplasty.

• May also appear for the first time concomitantly with these procedures.

• Transient in nature.

Temporary DDD pacing for the following:

• Persistent low heart rate (< 40 bpm)

• Low cardiac output

• Ischemia

• Refractory hypotension

• Symptoms of lightheadedness and dizziness

Atropine or theophylline may reverse the block but can cause unwanted tachycardia during drug administration.

• These drugs are only rarely indicated except at the time of presentation of the patient.

Atypical AV block is more common in inferior-posterior MIs due to the Bezold-Jarisch reflex and the effect of increased vagal tone on the AV node.

• This is usually transient, and unless there is hemodynamic collapse, there is no need for a temporary pacemaker.

• Rarely is there a need for a permanent pacemaker—this is true even if transient third-degree (complete) AV block occurs, as high degrees of block tend to resolve over 5-7 days.

If the AV block does not resolve but the ventricular rate is > 40 bpm, no therapy is required if patient is asymptomatic.

If the block does not resolve after 7 days and/or ventricular rate < 40 or if patient is symptomatic, a permanent pacemaker is indicated.

Assess drugs given and their need; stop offending drugs that enhance vagal tone, if possible.

If no symptoms, no therapy.

If symptomatic and no reversible causes, provide temporary pacing before surgery.

• Need for permanent pacing can be accomplished in the postoperative setting.

Atropine or isoproterenol may be given to increase AV node conduction if symptomatic or hemodynamically significant.

Rare after CABG but, if it occurs, consider an offending drug or transient ischemia to the AV node.

• No therapy is generally needed.

If associated with wide QRS complex, consider block below the His.

• If it persists, consider an EP study to assess the level of the block.

If patient is asymptomatic and block is above His, no need for permanent pacemaker.

If patient is symptomatic or block is below the His, permanent pacemaker is indicated.

If the block is associated with valve (especially aortic) surgery, consider direct damage to the AV node.

• If persistent, a pacemaker is indicated for symptoms or persistent slow rate (< 40 bpm or no increase in rate with exercise).

Risk for complete heart block and death is significant (approximately 50%).

• A dual-chamber permanent pacemaker is recommended as the pacing system of choice.

Admit the patient for a permanent pacemaker and place on a cardiac monitor.

• In the absence of symptoms or progressive (higher-degree AVB), there is no need for a temporary pacemaker before permanent pacemaker implantation.

Avoid atropine.

Evaluate for the presence of underlying cardiac disease, such as infiltrative processes (e.g., amyloid), or MI.

Dual-chamber permanent pacemaker implantation is indicated.

Admit the patient and place on a cardiac monitor.

If symptomatic or hemodynamically detrimental ventricular bradycardia is present, a temporary pacemaker is indicated if a permanent system cannot be placed expeditiously.

Do not give atropine because this may worsen the AVB and produce a slower ventricular rate.

• Exercise, sinus tachycardia, and catecholamines also can worsen the degree of block by enhancing AV nodal conduction and impinging on the refractory period of the His-Purkinje system.

Place temporary pacemaker.

• Mobitz type II second-degree AVB is associated with a high rate of heart failure in this setting.

• A permanent pacemaker is indicated if the AVB is persistent because the risk of complete heart block is > 50%.

• Long-term prognosis may not be improved.

Avoid the use of antiarrhythmic drugs (including lidocaine) in the absence of a pacemaker, unless there is sustained ventricular tachyarrhythmia, as these drugs may worsen the degree of AVB.

Do not give atropine.

Mobitz type II second-degree AVB has a lower (albeit not known with certainty) incidence in the current early revascularization era but if present or of new onset may improve with time, but this is rare. After being present and persistent, a pacemaker will likely be needed.

Place permanent pacemaker.

• If urgent or emergent surgery, place a temporary pacemaker with the plan for a permanent pacemaker after surgery.

If CABG, epicardial atrial and ventricular wires can be placed, with temporary pacing as standby, until a permanent transvenous pacemaker can be placed.

It is best to place the permanent pacemaker after CABG or other cardiac surgery as leads otherwise tend to dislodge.

If endocarditis, temporary pacemaker until infection resolves and after cardiac surgery.

• Avoid antiarrhythmic drugs and atropine.

If bradycardia, temporary pacing (via epicardial wires, if present, after cardiac surgery).

Temporary Mobitz type II AV block may resolve after cardiac surgery.

• It may be due to trauma near the His-Purkinje system (e.g., with aortic valve surgery, where left bundle branch block is a not infrequent accompaniment).

Persistent (e.g., more than 3-5 days) Mobitz type II block will require permanent pacing.

No antiarrhythmic drugs should be given unless an adequate backup ventricular pacing is available.

Endocarditis with abscess near the septum can destroy the His-Purkinje system.

• Despite surgical repair, permanent pacing will likely be required.

For patients having tricuspid valve replacement, an endocardial lead can occasionally be placed across a porcine bioprosthesis without producing tricuspid regurgitation but should be avoided if there is a mechanical valve.

• Tricuspid valve repair (e.g., annuloplasty) should not pose a problem in positioning a right ventricular lead.

If asymptomatic, evaluate (Holter monitor and exercise test for ventricular rates and diurnal variation) but no therapy.

Exercise testing may be required to help to elicit the site of block: if AV nodal, the AV conduction ratio will increase from 2:1 to 3:2 or higher.

If the AVB is intra-His or infra-Hisian, a higher degree of AV block will occur.

As AV nodal block may be due to a drug (e.g., digitalis, β-adrenergic blockers, calcium channel blockers, amiodarone), these drugs should be discontinued, if possible.

EP study with His bundle recording can help to determine the level of block, although this is rarely necessary in patients with AV nodal block.

In most cases, if observed over a period of time, 2:1 AV block will change to Mobitz type I or II second-degree AVB, allowing the site of block to be further characterized.

Atropine or isoproterenol can improve AV nodal conduction and may be useful as diagnostic maneuvers.

Block in the AV node is usually benign, but if it leads to asystole more than 3 seconds or complete heart block with escape rates of < 40 per minute with symptoms in awake patients, permanent pacing is indicated.

Hemodynamic instability or symptomatic bradycardia with 2:1 AVB that is not reversible is an indication for permanent cardiac pacing.

If hemodynamically unstable, temporary pacing.

Infranodal block is suspected if bundle branch block is present, but even then the block can be in the AV node. May need EP study with His bundle recordings to clarify.

Observe long rhythm strips, including Holter monitoring, if feasible.

Attempt carotid massage and/or assess the effects of atropine or exercise to help determine level of block.

On rare occasions, it may be prudent to apply transcutaneous pacing electrodes.

If block is in the His-Purkinje system, a dual-chamber permanent pacemaker is indicated.

Electrophysiology study to evaluate the level of the block, although this rarely needs to be performed.

If block is intra-His or below, a permanent pacemaker is indicated.

If anterior infarction is evident, block is likely in the His-Purkinje system.

Temporary pacing should be performed; this is often accomplished at the time of percutaneous revascularization procedures.

• Because more than 90% of patients recover with 1:1 AV conduction, generally within a few days, permanent pacing should be considered only if the block is persistent.

If inferior infarction is evident, the block is likely in the AVN.

• Temporary pacing should be performed only if the patient is symptomatic or hemodynamically compromised and can be accomplished expeditiously, without delaying revascularization procedures.

• Otherwise, intravenous atropine, together with rapid revascularization, is expected to resolve the block.

• There is usually no need for a permanent pacemaker because the block almost always resolves.

Perform provocative maneuvers or prolonged observation to define the site of the AVB.

If block is in the AVN, consider discontinuing drugs that may be initiating or maintaining the problem.

• An exception might be the patient with coronary artery disease in whom perioperative β-blockade has morbidity and mortality advantages.

For cardiac surgery, epicardial pacing wires provide an opportunity for temporary AV sequential pacing if HR < 40 bpm or if there is:

• Hemodynamic instability due to low heart rate

• AV dyssynchrony

• Symptoms

For noncardiac surgery and level of the block in the His-Purkinje system, temporary (if surgery emergent) or permanent (if surgery urgent or elective) pacing.

Level of block needs to be determined.

• Even if in the His-Purkinje system, in the first few days after cardiac surgery (e.g., CABG or valve surgery), it may resolve post-op.

• AV block is often due to trauma to AV node or His bundle, and reversibility generally occurs; recovery, however, may not be robust if the block is in the His-Purkinje system.

If related to endocarditis or aortic valve surgery and block is in the His-Purkinje system, resolution is unlikely and permanent pacing will usually be required.