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ECG Basics: Sinus Bradycardia

Sat, 08/13/2016 - 23:56 -- Dawn

Sinus bradycardia.  This strip meets the criteria of:  regular rhythm, rate less than 60 bpm (40 bpm in this case), regular P waves before every QRS.  Sinus bradycardia can have many causes from a completely normal variation to a malfunction of the sinus node.  In some cases, enhanced parasympathetic tone causes sinus bradycardia.  Well-conditioned athletes typically have sinus bradycardia. Treatment depends upon the cause and the patient's response to the rate.  If the rate does not cause hemodynamic impairment, treatment may not be necessary.

Instructors' Collection ECG of the WEEK: Inferior-lateral M.I. With QRS Fragmentation

Sat, 08/13/2016 - 23:33 -- Dawn

SUBTLE ST CHANGES   This ECG was obtained from an 87-year-old man who was experiencing chest pain.  Due to the subtle ST elevation in Leads II, III, aVF, V5, and V6, (inferior- lateral walls) the ECG was transmitted to the hospital by the EMS crew, and the cath lab was activated.  The patient denied previous cardiac history. 

In addition to the subtle ST elevation, there is ST depression in V1 through V4, which represents a reciprocal view of the injury in the inferior-posterior-lateral wall.  Because the anterior wall is superior in its position in the chest, it is opposite the inferior/posterior wall, and can show ST depression when the inferior-posterior area has ST elevation. This ECG was the 6th one done during this EMS call.  Prior to this one, the ST segments were elevated less than 1 mm.  This is a good example of the value of repeat ECGs during an acute event.  

RIGHT VENTRICULAR M.I.?     This ECG was done with V4 placed on the right side, to check for right ventricular M.I., which is a protocol for this EMS agency. When the right coronary artery is the culprit artery (about 80% of IWMIs), RVMI is likely.  In RVMI, we would usually see reciprocal ST depression in Leads I and aVL, but the STE is very subtle here, so the depression would likely be also.  When the culprit artery is the left circumflex artery (<20%), lateral lead ST elevation is more likely, as we see here in V5 and V6. 

WHAT ABOUT RHYTHM?     The rhythm is sinus with PACs.  PACs are considered to be benign in most situations, but in a patient with acute M.I., any dysrhythmia can be concerning. The QT interval, measured as QTc (corrected to a heart rate of 60 bpm), is slightly prolonged at .458 seconds (458 ms).  Over .440 seconds is considered prolonged in men, and over .500 sec. places the patient at increased risk of developing torsades de pointes.  CAD and myocardial ischemia can lead to this modest increase in QTc.

 WHY DO SOME OF THE QRS COMPLEXES HAVE “NOTCHES”?     Of greater importance is the fragmentation of the QRS complexes (fQRS) we see here. Notice the extra notches after the R waves in Leads II and aVF, the notch after the S wave in Lead III, V5 and V6.  This “fragmentation” is a sign of a myocardial scar, and is similar to finding a pathological Q wave on the ECG.  In a patient with a history of coronary artery disease, fQRS is often associated with ventricular dysfunction and congestive heart failure. It can indicate that conditions are favorable for the formation of re-entrant ventricular tachycardia. Fragmented QRS is more likely to appear in the setting of STEMI and NSTEMI, and less likely in unstable angina.

The patient survived post-angioplasty, and we do not know his eventual outcome.  Our thanks to William Bond for providing this ECG.

Coronary Arteries Anterior View Labeled

Click to open: 
Anterior view of coronary arteries

This is an original illustration by Dawn Altman.  It is free for your use in an educational setting.  For other uses, please contact Dawn at [email protected]

 

Question: Does an extreme right axis (backward) always indicate a ventricular rhythm?

Sat, 01/21/2012 - 23:16 -- Dawn

Today's expert is Jason E. Roediger, CCT, CRAT, who is a highly respected Cardiovascular Technician at the Dept. of Veterans Affairs, Hunter Holmes McGuire VA Medical Center in Richmond, VA. He is known for holding numerous certifications in all levels of ECG interpretation, and also for scoring 100% on the Level IV Advanced ECG Board Certification exam that is usually reserved for cardiologists.
 

Answer: Always? No. Usually, Yes.
There are exceptions to several "golden rules" in electrocardiography and this one is not exempt. One of the chronic issues contributing towards widespread confusion in understanding electrical axis is a lack of continuity in terminology. There is no general concensus on how to refer to an axis in the right upper quadrant. Depending on which author you are reading, it has traditionally been known by multiple names: Northwest axis. . . upper right quadrant. . . extreme right axis. . . right superior axis. . . "no-man's-land" (i.e., "N-M-L".). . . etc. Because my first exposure to electrical axis was through Dr. Marriott's textbooks and he prefered to use "N-M-L", I have personally latched on to that particular name as well. Even though some persist in calling it an "extreme left axis" or "far left axis deviation", this practice is frowned upon and discouraged. It's important to note that an axis in "N-M-L" is not synonymous with an "indeterminate" axis which occurs when the QRS is essentially isodiphasic or equphasic in all 6 limb leads and therefore the polarity of the QRS cannot be discerned in leads I and aVF.

Definition: An axis in "N-M-L" is recognized when the QRS complex has a predominantly or wholly negative deflection (i.e., down) in leads I and aVF. The axis is −90 to −180 degrees.

Irregardless of which descriptive name you prefer, in the context of a wide QRS complex tachycardia, this particular axis is highly predictive of ventricular tachycardia and is rarely encountered in "conducted" rhythms however some examples of aberrant SVT have been published with an axis in "N-M-L".

In summary: An axis in "N-M-L" implies (but is not proof of) an apical origin to the rhythm and should make one think of and exclude the possibility of ventricular tachycardia. As a general rule, until it is proven otherwise, assume any wide QRS complex tachycardia is ventricular tachycardia. Even though this one clue carries significant weight in supporting the interpretation of ventricular tachycardia, that conclusion can not be made based solely on this single criteria. This axis is just one of a long list of criteria and should be used in conjunction with all of them as they carry alot of strength when used collectively.
 

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1924:  Willem Einthoven wins the Nobel prize for inventing the electrocardiograph.

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