Third degree AV block surgery
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. ; Associate Editor(s)-in-Chief: Sara Zand, M.D. Cafer Zorkun, M.D., Ph.D. ; Raviteja Guddeti, M.B.B.S.  Soroush Seifirad, M.D. Qasim Khurshid, M.B.B.S 
Cardiac pacemakers are effective treatments for a variety of cardiac conduction abnormalities and can reestablish adequate circulation by generating appropriate heart rate and cardiac response. Two main factors guide the majority of decisions regarding permanent pacemaker insertion. First is the association of symptoms with arrhythmia, and second is the potential for progression of the rhythm disturbance. Symptoms related to atrioventricular block are determining factor of placing permanent pacemaker, regardless of the level of atrioventricular block. Permanent pacemaker is warranted if the site of atrioventricular block is Infranodal, regardless of the presence or absence of symptoms. Temporary transvenous pacing is used to provide hemodynamic support or back-up pacing to prevent asystole. If atrioventricular block seems to be irreversible, it is better to proceed directly with permanent pacemaker implantation.
- A permanent pacemaker insertion is a minimally invasive procedure.
- The procedure is typically performed in a cardiac catheterization lab or an operating room.
- Transvenous access to the heart chambers under local anesthesia is the preferred technique, most commonly via the subclavian vein, the cephalic vein, or the internal jugular vein or the femoral vein.
- The pacing generator is most commonly placed subcutaneously in the pre-pectoral region.
- Placement of pacemaker leads, surgically via thoracotomy, is rarely used these days.
- Factors associated implantation of permanent pacemaker that should be noticed include:
- Symptoms related to bradycardia ( major determinant)
- Site of atrioventricular block including infranodal atrioventricular block and risk of progression to complete heart block due to unstable ventricular scape rhythm
- Side effects of high burden of right ventricular pacing
- Concomitant systemic disease as a potential risk of atrioventricular block or ventricular arrhythmia
Recommendation for implantation of temporary pacing for bradycardia associated atrioventricular block
|Recommendations for temporary pacing for bradycardia associated atrioventricular block|
|Medical therapy (Class IIa, Level of Evidence B):|
❑ In patients with symptomatic bradycardia associated second or third degree atrioventricular block, refractory to medications, temporary transvenous pacing is recommended to increase heart rate and improve symptoms
- Temporary transvenous pacing is used to provide hemodynamic support or back-up pacing to prevent asystole.
- If atrioventricular block seems to be irreversible, it is better to proceed directly with permanent pacemaker implantation.
- When transvenous pacing wires left in place for a longer duration (>48 hours), the likelihood of complications increases.
- Transcutaneous pacing is used as a short-term bridge to temporary or permanent transvenous pacing or the resolution of bradycardia.
- There is no survival benefit to hospital discharge when transcutaneous pacing is used in the prehospital phase of bradyasystolic cardiac arrest. 
- Due to high capture thresholds and patient discomfort, transcutaneous pacing is poorly tolerated for prolonged use.
Recommendation for placement of permanent pacing
|Recommendations for permanent pacing for chronic management of Bradycardia Attributable to Atrioventricular Block|
|(Class I, Level of Evidence B):|
❑Permanent pacing is recommended in patients with acquired second degree mobitz type2 atrioventricular block, high grade atrioventricular block, third degree atrioventricular block, regardless of symptoms that are not related to reversible causes
|( Class I, Level of Evidence C) :|
❑ Permanent pacing is recommended in patients with permanent atrial fibrillation and symptomatic bradycardia
|(Class IIa, Level of Evidence B)|
❑ In patients with cardiac sarcoidosis and amyloidosis and evidence of mobitz type 2 atrioventricular block, high grade atrioventricular block, third degree atrioventricular block , permanent pacing with additional defibrillator capacity is reasonable if life expectancy>1 year
|(Class IIa, Level of Evidence C)|
|(Class IIb, Level of Evidence C)|
❑ Permanent pacing with additional defibrillator capacity is recommended in patients with neuromuscular disease including myotonic dystrophy type1 with PR interval >240ms , QRS duration >120 ms, fascicular block if life expectancy>1 year
|The above table adopted from 2018 AHA/ACC/HRS Guideline|
- Symptoms related to atrioventricular block are determining factor of placing permanent pacemaker, regardless of the level of atrioventricular block.
- Permanent pacemaker is warranted if the site of atrioventricular block is Infranodal, regardless of the presence or absence of symptoms.
- Varied degree of atrioventricular block from first degree atrioventricular block to complete atrioventricular block may develope over the time in neuromuscular disorders such as muscular dystrophies or Kearns-Sayre syndrome.
- Intermittent second-degree or third-degree atrioventricular block on 24-hour ambulatory electrocardiographic monitoring or atrioventricular block on resting ECG was found in 20% of patients with myotonic dystrophy type 1.
- In the presence of atrial fibrillation and slow regular ventricular response and wide QRS and pauses >3 seconds, infranodal atrioventricular block may be suspected. 
- Atrioventricular block may develop by using betablocker for MI or heartfailure and amiodarone and sotalol for atrial fibrillation patients.
- The benefit of using these medications should be balanced over the side effects of right ventricular pacing.
- Atrioventricular block in the setting of cardiac sarcoidosis may resolve by using corticosteroids for 30 days.
- Evidence of prolonged HV interval (>55 ms) despite a narrow QRS was found in AL cardiac amyloidosis.
- Mutations in the lamin A/C gene can present with atrioventricular block, atrial arrhythmias, and ventricular arrhythmia.
- Risk of atrioventricular block and sudden cardiac death may increase in the setting of lamin A/C mutation.
- In one study, the risk of ventricular arrhythmias increased in the presence of first-degree atrioventricular block in lamin A/C mutation.
- Pseudo-pacemaker syndrome may develop in the setting of severe first-degree atrioventricular block with very long PR interval , atrial contraction during the closed atrioventricular valves leading to an increase in wedge pressure and a decrease in cardiac output.
Management of bradycardia or pauses attributable to chronic atrioventricular block algorithm
|Complete heart block (aquired)|
|Permanent pacing (class1)|
|Consider risk for ventricular arrhythmia (class1)|
|Cardiac resynchronization therapy
|His bundle pacing (class2b)|
|The above algorithm adopted from 2018 AHA/ACC/HRS Guideline|
Methods of implantation permanent pacing
- Common side effects of right ventricular pacing include ventricular dysfunction or heart failure symptoms.
- Lower baseline LVEF and a higher percentage of RV pacing may predict RV pacing cardiomyopathy.
- Risk of RV pacing-induced cardiomyopathy increases when RV pacing exceeds 40% or perhaps as low as 20%.
- CRT-P reduced left ventricular end-systolic volume and improved LVEF in comparison with RV pacing in patients with relatively preserved LVEF and LVEF<35%.
- His bundle pacing was associated with a significant decrease in heart failure hospitalizations when ventricular pacing >20% compared with RV pacing.
- Among patients with AF who undergo atrioventricular node ablation to control rapid ventricular rates, implantation of physiologic pacing (CRT or His bundle) was associated with improvement in 6-minute walk distances and quality of life compared with RV pacing.
- In patients with permanent AF when rhythm control is not planned , pacing and sensing of atrium is not recommended.
|Recommendations for permanent pacing techniques and methods for bradycardia associated atrioventricular block|
|(Class I, Level of Evidence A):|
❑ In patients with sinus node dysfunction or atrioventricular block, dual chamber permanent pacing is preferred over single chamber ventricular pacing
|(Class I, Level of Evidence B):|
|(Class IIa, Level of Evidence B):|
❑Cardiac resynchronization therapy or His bundle pacing over right ventricular pacing is recommended in patients with LVEF between 36% -50 % who need more than 40% ventricular pacing
|(Class IIb, Level of Evidence B):|
|(Class III, Level of Evidence C):|
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