Everything you want to know about 2nd degree AV Blocks

Episode 98​

July 15, 2013


​​When is 2nd degree AV block not the same as Mobitz? Here’s everything you want to know about 2nd degree AVB!

 
2nd Degree AV Block

Atrial impulses fail to conducts to the ventrcles. (ie P:QRS >1)

Type I (Mobitz I, Wenckebach)

  • Each atrial impulse has longer and longer conduction time until it fails to conduct to the ventricle.

  • Block usually at level of AV node, producing narrow QRS’s

  • May sometimes also have wide QRS’s in patient’s with pre-existing bundle branch block or intraventricular conduction delay

  • At least 2 consecutive P-QRS complexes demonstrate progressive PR-interval lengthening before a non-conducted P-wave

  • P-P interval remains constant​

Type II (Mobitz II)

  • Some but not all impulses are transmitted to the ventricles WITHOUT progressive PR lengthening.

  • Typically due infranodal block, producing wide QRS’s (can also sometime be narrow!)

  • At least 2 consecutive P-QRS complexes demonstrate constant PR-intervals before the non-conducted P wave

  • P-P interval remains constant

What if there are not any consecutive P-QRS complexes before the non-conducted P?

  • If there is a fixed 2:1 ratio throughout, you can’t tell if the PR-interval is lengthening, hence can’t differentiate between Type I & II

  • Just call it “2nd degree AV block with fixed 2:1 block”

Advanced (high-grade) AV Block

  • P:QRS conduction ratio of is 3:1 or higher

  • Produces extremely slow ventricular rates

  • Can be Mobitz I or II, may be able to differentiate based on width of QRS

Right Bundle Branch Block

3-Step approach to diagnosing AV blocks 

 

Everything you want to know about 2nd degree AV Blocks

Episode 98​

July 15, 2013


​​When is 2nd degree AV block not the same as Mobitz? Here’s everything you want to know about 2nd degree AVB!

 
2nd Degree AV Block

Atrial impulses fail to conducts to the ventrcles. (ie P:QRS >1)

Type I (Mobitz I, Wenckebach)

  • Each atrial impulse has longer and longer conduction time until it fails to conduct to the ventricle.

  • Block usually at level of AV node, producing narrow QRS’s

  • May sometimes also have wide QRS’s in patient’s with pre-existing bundle branch block or intraventricular conduction delay

  • At least 2 consecutive P-QRS complexes demonstrate progressive PR-interval lengthening before a non-conducted P-wave

  • P-P interval remains constant​

Type II (Mobitz II)

  • Some but not all impulses are transmitted to the ventricles WITHOUT progressive PR lengthening.

  • Typically due infranodal block, producing wide QRS’s (can also sometime be narrow!)

  • At least 2 consecutive P-QRS complexes demonstrate constant PR-intervals before the non-conducted P wave

  • P-P interval remains constant

What if there are not any consecutive P-QRS complexes before the non-conducted P?

  • If there is a fixed 2:1 ratio throughout, you can’t tell if the PR-interval is lengthening, hence can’t differentiate between Type I & II

  • Just call it “2nd degree AV block with fixed 2:1 block”

Advanced (high-grade) AV Block

  • P:QRS conduction ratio of is 3:1 or higher

  • Produces extremely slow ventricular rates

  • Can be Mobitz I or II, may be able to differentiate based on width of QRS

 

Have you mastered AV blocks to make sure your patients get the best care possible? If not, check out these previous episodes…

AV blocks & Rabbit ears for RBBB vs. PVC

Right Bundle Branch Block

3-Step approach to diagnosing AV blocks 

 
Review of Wellens Syndrome
Episode 96
July 1, 2013

Wellens Syndrome

  • T-wave abnormality in precordial leads (V2-V3, +/-V4)
  • Specific for obstructed proximal LAD lesion
  • High risk for extensive anterior wall MI and death
  • 2 types
    • Type 1-Deeply symmetric TWI
    • Type 2- Biphasic T waves with terminal TWI. Goes up first, then down (often misdiagnosed as “normal” or “non-specific T-wave abnormality”).

  • ST changes are often absent and patient can be chest pain free
  • Cardiac biomarkers often initially normal
  • Medical management usually ineffective and patients are best treated with PCI, treadmill stress testing may be hazardous.
  • Do not diagnose in the presence of large amplitude QRS complexes
  • When in doubt get serial ECG’s!

Wellens, make sure you know about it. These will help…


 
Review of Wellens Syndrome
Episode 96
July 1, 2013

Wellens Syndrome

  • T-wave abnormality in precordial leads (V2-V3, +/-V4)
  • Specific for obstructed proximal LAD lesion
  • High risk for extensive anterior wall MI and death
  • 2 types
    • Type 1-Deeply symmetric TWI
    • Type 2- Biphasic T waves with terminal TWI. Goes up first, then down (often misdiagnosed as “normal” or “non-specific T-wave abnormality”).

  • ST changes are often absent and patient can be chest pain free
  • Cardiac biomarkers often initially normal
  • Medical management usually ineffective and patients are best treated with PCI, treadmill stress testing may be hazardous.
  • Do not diagnose in the presence of large amplitude QRS complexes
  • When in doubt get serial ECG’s!

Wellens, make sure you know about it. These will help…


 
Lumen stenosis and size is not as important as plaque vulnerability 
Episode 95
June 24, 2013

Size isn’t everything! Here’s the most important video of the year! (no joke)

Plaque vulnerability based on 3 major factors

  1. Fibrous cap
  2. Lipid core
  3. Inflammatory cells

Recent stress testing and catheterizations are NOT predictive of new plaque rupture!

  • Small plaques may be more unstable and more prone to rupture
  • Infarct related arteries often have non-obstructing plaque, before rupture and MI
  • Angiography can not distinguish stable vs. unstable plaque composition, and give no information about the fibrous cap or lipid core

Key point: Nothing will risk stratify you to zero! You can’t always rely in the recently negative stress test or “unremarkable” cath.  History of presenting illness is the most important information and should guide your management.


Must read references:

Libby, P. (2013). Mechanisms of Acute Coronary Syndromes and Their Implications for Therapy. New England Journal of Medicine, 368(21), 2004–2013.

 
References:

Virmani, R., Burke, A. P., Farb, A., & Kolodgie, F. D. (2006). Pathology of the Vulnerable Plaque. Journal of the American College of Cardiology, 47(8), C13–C18.


 
Lumen stenosis and size is not as important as plaque vulnerability 
Episode 95
June 24, 2013

Size isn’t everything! Here’s the most important video of the year! (no joke)

Plaque vulnerability based on 3 major factors

  1. Fibrous cap
  2. Lipid core
  3. Inflammatory cells

Recent stress testing and catheterizations are NOT predictive of new plaque rupture!

  • Small plaques may be more unstable and more prone to rupture
  • Infarct related arteries often have non-obstructing plaque, before rupture and MI
  • Angiography can not distinguish stable vs. unstable plaque composition, and give no information about the fibrous cap or lipid core

Key point: Nothing will risk stratify you to zero! You can’t always rely in the recently negative stress test or “unremarkable” cath.  History of presenting illness is the most important information and should guide your management.


Must read references:

Libby, P. (2013). Mechanisms of Acute Coronary Syndromes and Their Implications for Therapy. New England Journal of Medicine, 368(21), 2004–2013.

 
References:

Virmani, R., Burke, A. P., Farb, A., & Kolodgie, F. D. (2006). Pathology of the Vulnerable Plaque. Journal of the American College of Cardiology, 47(8), C13–C18.


 
Scarbossa’s criteria identifies MI in patients with LBBB 
Episode 94
June 17, 2013

Tombstones, checkmarks, and bundles, oh my!

Criteria for left bundle branch block (LBBB)

  • Widened QRS > 0.12 sec in adults
  • Broad notched or slurred R waves in I and V6 WITHOUT Q-waves
  • Broad S waves in V1, V2, V3, may have a small r wave

LBBB causes ST-segment and T wave changes that make the diagnosis of acute MI difficult. Patients with LBBB can be expected to have ST-segment and T waves that are discordant to the direction of the QRS complex. This is expected and referred to as the “rule of appropriate discordance”. In fact, it is very concerning when the QRS complex and the ST-segment are concordant (point in same direction).

You CAN diagnose MI in LBBB, once you understand Sgarbossa’s criteria.

Sgarbossa’s criteria is used to diagnose MI in the setting of a known chronic LBBB. The following 3 ECG criteria can help diagnose AMI in patients with LBBB.

1. STE ≥ 1mm concordant with QRS deflection in any single lead (odds ratios for AMI of 25.2!)

2. STD ≥ 1mm in V1, V2, OR V3 that is concordant. Does NOT need to be in contiguous leads (odds ratios for AMI of 6.0)

3. Discordant STE ≥ 5mm (lower specificity) or STE >20% of size of QRS.


Everything you nees to know about Scarbossa…
Scarbossa’s criteria identifies MI in patients with LBBB 
Episode 94
June 17, 2013

Tombstones, checkmarks, and bundles, oh my!

Criteria for left bundle branch block (LBBB)

  • Widened QRS > 0.12 sec in adults
  • Broad notched or slurred R waves in I and V6 WITHOUT Q-waves
  • Broad S waves in V1, V2, V3, may have a small r wave

LBBB causes ST-segment and T wave changes that make the diagnosis of acute MI difficult. Patients with LBBB can be expected to have ST-segment and T waves that are discordant to the direction of the QRS complex. This is expected and referred to as the “rule of appropriate discordance”. In fact, it is very concerning when the QRS complex and the ST-segment are concordant (point in same direction).

You CAN diagnose MI in LBBB, once you understand Sgarbossa’s criteria.

Sgarbossa’s criteria is used to diagnose MI in the setting of a known chronic LBBB. The following 3 ECG criteria can help diagnose AMI in patients with LBBB.

1. STE ≥ 1mm concordant with QRS deflection in any single lead (odds ratios for AMI of 25.2!)

2. STD ≥ 1mm in V1, V2, OR V3 that is concordant. Does NOT need to be in contiguous leads (odds ratios for AMI of 6.0)

3. Discordant STE ≥ 5mm (lower specificity) or STE >20% of size of QRS.


Everything you nees to know about Scarbossa…
  ECG findings in Thoracic Aortic Dissection
Episode 93
June 10, 2013

Just a simple inferior STEMI? Don’t be too sure….

About 4-8% of Thoracic Aortic Dissection’s (TAD)
will present with ECG signs of STEMI
  • Usually inferior ST-elevation or diffuse ischemia with ST-depression
  • Typical for inferior STEMI’s to have reciprocal changes in leads I & aVL
  • Consider posterior and right ventricular extension of infarction with inferior STEMI
  • Not all chest pain (CP) = ACS, don’t forget to consider TAD
    • CP + new neurological SSx → TAD
    • CP + new diastolic murmur → TAD
    • CP + new renal failure → TAD
    • CP + new ischemic extremities → TAD
    • Remember that TAD can dissect backward and cause hemorrhagic pericardial effusions…careful with that heparin gtt!


  ECG findings in Thoracic Aortic Dissection
Episode 93
June 10, 2013

Just a simple inferior STEMI? Don’t be too sure….

About 4-8% of Thoracic Aortic Dissection’s (TAD)
will present with ECG signs of STEMI
  • Usually inferior ST-elevation or diffuse ischemia with ST-depression
  • Typical for inferior STEMI’s to have reciprocal changes in leads I & aVL
  • Consider posterior and right ventricular extension of infarction with inferior STEMI
  • Not all chest pain (CP) = ACS, don’t forget to consider TAD
    • CP + new neurological SSx → TAD
    • CP + new diastolic murmur → TAD
    • CP + new renal failure → TAD
    • CP + new ischemic extremities → TAD
    • Remember that TAD can dissect backward and cause hemorrhagic pericardial effusions…careful with that heparin gtt!


Digoxin Toxicity & AV block: Will IV calcium cause “stone heart”?
Episode 91
May 28, 2013
Digoxin Toxicity & AV block: Will IV calcium cause “stone heart”?
Episode 91
May 28, 2013

Potassium, digoxin, calcium, AVBs, stone heart…so much to discuss this week!

  • When considering AV blocks, always pay attention to the PR segments to help distinguish between Mobitz I, Mobitz II, & AVD/CHB.
  • Hyperkalemia can cause just about anything, including AV blocks!
  • Calcium in probably safe in digoxin toxicity.
  • Levine et al. in their retrospective review of 129 patients who had digoxin toxicity, found that IV calcium did not seem to cause malignant dysrhythmias or increase mortality. They found no support for the historical belief that calcium is contraindicated for these hyperkalemic patients.
  Impressive Syndrome
  Impressive Syndrome
Episode 90
May 21, 2013

Impressive horses, syphilis, and strokes…all in 14 minutes!
 
Hyperkalemia is the syphilis of electrocardiography. It is the great imitator!
 
  • Hyperkalemia can cause STE and mimic STEMI’s & is the most rapid killer in DKA
  • Renal patients with systemic complaints should get an ECG and hyperkalemia should be considered
  • Bizarre Rhythm? Wide QRS? Think Tox/metabolic…get Calcium & Bicarb ready!
  • Hyperkalemic periodic paralysis, aka. Impressive Syndrome - Inherited autosomal dominant condition that affects Na+ channels in muscle and the ability to regulate K+ in the blood. 


 
  T-wave changes of severe hypokalemia
  T-wave changes of severe hypokalemia
Episode 89
May 13, 2013

 
Ever heard of “Reverse-Wellens syndrome” ? Watch this to learn about this dangerous Wellens syndrome mimic.
“Reverse-Wellens” waves deflect downward before going up & are seen in cases of severe hypokalemia that produce U-waves. See below…

Compare this to Wellens waves that may also be biphasic, but deflect upward before going down!
What anatomical distribution of ischemia is associated with the ECG changes of Wellens Syndrome? Review Wellens by watching the videos below!  

Review these previous episodes and master Wellens syndrome…

 
  When STE in aVR = Left main coronary artery stenosis
Episode 88
May 6, 2013

aVR - the forgotten 12th lead

  • BEWARE OF STE in aVR for patients with acute coronary syndromes
  • STE in aVR with other ischemic findings on ECG is BAD! (LMCA occlusion, proximal LAD occlusion, or triple vessel disease)
  • In the setting of ACS, STE in aVR…
    • + STE in avL = LMCA occlusion
    • + STE in V1 = LMCA or proximal LAD occlusion
    • STE in avR > STE V1 = LMCA occlusion
    • ST-elevation in aVR not applicable in setting of SVT or in asymptomatic patients without ischemic symptoms
  • aVR STE > 1.0mm should make you worry
  • LMCA occlusion may require CABG, so avoid drugs like clopidogrel
  • 70% mortality without immediate PCI
  • Medical therapy including lytics does not improve mortality
  • Emergent PCI may decrease mortality to 40%
  • Time delay to PCI is the only predictor of survival
  • STE of aVR in very tachycardic rhythms (i.e. SVT), and in the setting of severe hypertension and LVH may be a normal variant or have no clinical significance.

Learn more about the forgotten lead, aVR! This episode is loaded with important references you can share with your cardiologist as needed…

References:
 
 
 
 
 
 
 
 
  When STE in aVR = Left main coronary artery stenosis
Episode 88
May 6, 2013

aVR - the forgotten 12th lead

  • BEWARE OF STE in aVR for patients with acute coronary syndromes
  • STE in aVR with other ischemic findings on ECG is BAD! (LMCA occlusion, proximal LAD occlusion, or triple vessel disease)
  • In the setting of ACS, STE in aVR…
    • + STE in avL = LMCA occlusion
    • + STE in V1 = LMCA or proximal LAD occlusion
    • STE in avR > STE V1 = LMCA occlusion
    • ST-elevation in aVR not applicable in setting of SVT or in asymptomatic patients without ischemic symptoms
  • aVR STE > 1.0mm should make you worry
  • LMCA occlusion may require CABG, so avoid drugs like clopidogrel
  • 70% mortality without immediate PCI
  • Medical therapy including lytics does not improve mortality
  • Emergent PCI may decrease mortality to 40%
  • Time delay to PCI is the only predictor of survival
  • STE of aVR in very tachycardic rhythms (i.e. SVT), and in the setting of severe hypertension and LVH may be a normal variant or have no clinical significance.

Learn more about the forgotten lead, aVR! This episode is loaded with important references you can share with your cardiologist as needed…

References:
 
 
 
 
 
 
 
 
  Dangers of  “Non-specific ST-segment abnormalities” ​
  Dangers of  “Non-specific ST-segment abnormalities” ​
Episode 87
April 29, 2013

 
 
When in doubt, order serial ECG!
Get good at ECG’s and you will save lives!
 
  • ST-segment depression or elevation <1mm are typically interpreted as “Non-specific ST-segment abnormalities” by the ECG machine. Ischemia causes dynamic ECG changes, and this can be an early sign of MI.
  • Beware of STE in aVR! STE in aVR with other ischemic findings is BAD! (LMCA occlusion, proximal LAD occlusion, or triple vessel disease)
 

Learn more about the forgotten lead, aVR! This episode is loaded with important references you can share with your cardiologist as needed…