Sunday, June 27, 2021

ECG Blog #237 (52) — A 70-Year Old with Dizziness

The ECG shown in Figure-1 was obtained from a patient in his 70s — who presented to the ED (Emergency Department) with dizziness.

  • How would you interpret this ECG?
  • And — Is there Complete AV Block?
  • In addition to the interesting rhythm — there are at least 4 other ECG findings that should be commented on. How many of these other findings do you recognize?


Figure-1: ECG obtained from a patient with dizziness (See text).



NOTE: Some readers may prefer at this point to refer to ECG Media PEARL #52 ( = the Video Pearl that appears in ECG Blog #236) — before reading My Thoughts regarding the ECG in Figure-1. This 15-minute ECG Video reviews the types of 2nd-degree AV blocks (as opposed to 3rd-degree AV block).

  • For those wanting review on HOW to read (and/or drawLaddergrams — Please check out my 5-minute ECG Video and other material in ECG Blog #188.





My THOUGHTS on the ECG in Figure-1:

As usual — I find it best to begin by assessing the cardiac rhythm. For clarity — I've added colored arrows in Figure-2, in which I label atrial activity. My sequential thought process for interpreting this tracing was the following:

  • RED arrows in Figure-2 indicate P waves we can definitely see.
  • PINK arrows highlight places where P waves would need to be found IF the atrial rhythm is regular. Although T waves in many of the leads on this 12-lead tracing look more peaked than expected — it is not possible to prove that P waves are hiding under the PINK arrows from this single tracing alone. That said — by far, the most likely explanation for atrial activity is that the atrial rhythm is regular! (It is far less likely for there to be SA node exit block after every third P wave).
  • The QRS is wide (I measure 3 little boxes = 0.12 second in several leads). QRS morphology is consistent with RBBB (Right Bundle Branch Block) because: i) there is a widened and predominantly upright QRS complex in right-sided lead V1; and, ii) there are wide, terminal S waves in lateral leads I and V6.
  • QRS morphology is also consistent with LAHB (Left Anterior HemiBlock) because there is predominant negativity in each of the inferior leads. Therefore — there is bifascicular block (ie, RBBB + LAHB).
  • The PR interval preceding each QRS complex in the long lead II rhythm strip is constant. Therefore — Every third P wave is conducting! Since each QRS complex in this tracing is conducted — the rhythm can not possibly be complete AV block. Instead, the rhythm in Figure-2 represents a "high-grade" form of 2nd-degree Ablock (ie, "high-grade" — because 2 out of every 3 P waves within each group fail to conduct, despite having adequate opportunity to do so).
  • There is marked bradycardia! The atrial rate is approximately 110/minute. Since only 1 out of every 3 P waves is conducted — the ventricular rate is 1/3 the atrial rate, or between ~35-40/minute.

Figure-2: I've labeled atrial activity from Figure-1 with colored arrows (See text).

PEARLs regarding the Rhythm in Figure-2:

The rhythm in Figure-2 most probably represents the Mobitz II form of 2nd-degree AV block because: iConsecutive P waves in each grouping fail to conduct — and that is far less common with Mobitz I 2nd-degree AV block; ii) The QRS complex is wide with morphology consistent with bifascicular block (ie, RBBB/LAHB— whereas the QRS complex most often is narrow with Mobitz I; andiii) It is much more common to see a normal (or relatively normal) PR interval for conducted beats when the rhythm is Mobitz II — because the principal conduction problem lies below the AV node (whereas a long PR interval is a common accompaniment of Mobitz I, in which the level of AV block is at the AV node).

  • That said — we can not conclusively prove that the rhythm in this tracing is Mobitz II, because we never see 2 P waves in a row that conduct with the same PR interval. Therefore, we have not proven that the PR interval would not increase if given a chance to do so.
  • Regardless of whether the conduction disturbance in Figure-2 represents Mobitz II or not — consistent failure of consecutive P waves to conduct (which results in marked bradycardia) suggests that unless a "fixable cause" (ie, medication effect, acute ischemia) is found — that a pacemaker will be needed in this symptomatic patient in his 70s.


ECG Findings that Should be Commented On:

ECG findings that should be specifically noted on the interpretation of this tracing include several that we have already mentioned — which are:

  • High-grade 2nd-degree AV block, with resultant marked bradycardia.
  • Complete RBBB.
  • LAHB (thereforebifascicular block = RBBB/LAHB).


Additional ECG findings that should be specifically noted include:

  • The Q wave in lead V1 — which suggests anteroseptal MI has occurred at some point in time (ie, Simple RBBB should manifest an rSR' complex in lead V1 — but without any Q wave).
  • Low voltage. While not satisfying strict criteria for low voltage (ie, No R wave exceeding 5 mm in any limb lead) — overall voltage in the 12 leads of this tracing appears reduced. The clinical significance of this uncertain from the information available.
  • Flattening of the ST segment in multiple leads (ie, in leads I, II, III; aVL, aVF; V2-thru-V6) — and — taller-than-expected T waves in leads V2-thru-V5. While some of the increase in T wave amplitude could be the result of the hidden P waves — in association with the diffuse ST segment flattening and the Q wave in lead V1, these subtle findings could reflect a recent event — which could be the reason for this patient's severe conduction disturbance!



LADDERGRAM of Today's Case:

My laddergram for today's case is straightforward (Figure-3):

  • One out of every 3 P waves in each grouping is conducted to the ventricles.
  • Since I suspect the conduction disturbance represents the Mobitz II form of 2nd-degree AV block — I did not draw a progressive increase in conduction time within the AV nodal tier, but instead showed simple failed conduction for 2 out of every 3 P waves.



Figure-3: I've labeled P waves that I saw in Figure-1 with colored arrows (See text).


Acknowledgment: My appreciation to Neeraj Sonewane (from Nagpur, India) for allowing me to use this tracing.



Related ECG Blog Posts to Today’s Case: 

  • ECG Blog #236 — Reviews the Types of 2nd-Degree AV Block (as opposed to 3rd-degree AV block). 
  • ECG Blog #188 — Reviews the essentials for reading (and/or drawingLaddergrams, with LINKS to numerous Laddergrams I’ve drawn and discussed in detail in other blog posts. 
  • ECG Blog #203 — Reviews the ECG diagnosis of Axis and Hemiblocks (therefore Bifascicular Blocks) — Check out the 12-minute ECG Video (MP-21) in this post.