ECG Blog #462 — Why so Slow ... ?

I was sent the ECG in Figure-1 — told only that the patient was an older adult who reported dizziness with activity.

QUESTIONS:

• What is the rhythm? (HINT: There are at least 4 important findings that should be noted).
•   — Is there AV block?

Figure-1: The initial ECG in today's case. (To improve visualization — I've digitized the original ECG using PMcardio).

MY Thoughts on Today’s CASE:

In general — I favor beginning my assessment of a 12-lead ECG with a long lead rhythm strip by first taking a quick LOOK at the rhythm before proceeding with my interpretation of the 12-lead ECG. As always — I favor the Ps, Qs, 3R Approach (See ECG Blog #185):

• Starting with the long lead II (at the bottom of today’s tracing in Figure-1) — the ventricular rhythm is slow but Regular (ie, with a constant R-R interval of just over 8 large boxes in duration — corresponding to a ventricular Rate just under 40/minute).
• The QRS is narrow in all 12 leads — which defines the rhythm either as supraventricular (ie, arising from at or above the AV Node), or in the Bundle of His (ie, The QRS would be wide if the rhythm originated from outside the conduction system in ventricular myocardium). 
• Regarding P waves — Atrial activity is present, albeit not in the form of P waves. Instead — Figure-2 highlights the presence of a regular “sawtooth” pattern at a rate of ~300/minute (ie, the interval between each sawtooth deflection being approximately 1 large box in duration). Thus, the underlying Rhythm in today’s tracing is AFlutter (Atrial Flutter).

The final parameter in the Ps,Qs,3R Approach — is to assess the 3rd “R” (ie, If P waves or other sign of atrial activity is present — Is this atrial activity Related to neighboring QRS complexes?).

• The most time-efficient way to determine IF one or more P waves are Related to neighboring QRS complexes — is to look in front of each QRS complex, and to ask yourself IF atrial activity manifests a fixed relationship to neighboring QRS complexes.
• No such “fixed” relationship seems to exist in Figure-2 — since the distance between the last “sawtooth” flutter wave and the next QRS complex to appear continually varies. That is, unlike AFlutter with dual-level Wenckebach conduction out of the AV Node (as appears in ECG Blog #243) — the coupling interval between the last atrial deflection before the QRS complex that ends the relative pause is never the same.
• In support of our suspicion that none of the flutter waves in Figure-2 are being conducted to the ventricles — is the regular and very slow rate of the ventricular rhythm (ie, New, untreated AFlutter most often manifests 2:1 AV conduction — with a ventricular rate that is close to 150/minute).

IMPRESSION: The underlying rhythm in today’s case is AFlutter with complete (3rd-degree) AV block, and a very slow escape rhythm at ~40/minute.

• Since the QRS complex is narrow in all 12 leads of this ECG — the escape rhythm originates from either the AV node or the Bundle of His.
• Unless a potentially “fixable” cause of this rhythm can be found (ie, acute ischemia from recent infarction; electrolyte disturbance, use of rate-slowing medication) — the patient will need a pacemaker.
• And, if other causes of this rhythm are ruled out (ie, acute/recent ischemia — rate-slowing medication — severe electrolyte or acid-base disturbance — hypothyroidism — sleep apnea) — then given older age of this patient, the diagnosis will almost certainly be SSS (Sick Sinus Syndrome — See ECG Blog #342).

Figure-2: I’ve labeled regular atrial activity in today’s tracing (RED lines) — that manifests an atrial rate of ~300/minute.

What About the 12-Lead ECG?

Now that we have interpreted the rhythm in today’s tracing — What about the 12-lead ECG?

• The frontal plane Axis in Figure-2 does not make sense! This is because: i) Standard leads I,II,III suggest a nearly vertical axis of at least +80 degrees (equally large positive deflections in leads II and III — with no more than a tiny QRS in lead I ) — whereas this would make the all negative QRS in lead aVF impossible!; — and, ii) QRS morphology in all 3 augmented leads (aVR,aVL,aVF) is all negative and looks nearly identical — which is also impossible given the findings in standard leads I,II,III. Therefore — some form of technical misadventure (ie, lead misplacement) is present — and the ECG should be immediately repeated.
• The chest leads show extremely poor R wave progression (ie, No more than a tiny initial r wave in leads V1,V2 and V3). This suggests that at some point in time — that this patient may have had anteroseptal infarction (which clearly is an important consideration given the rhythm of very slow AFlutter with complete AV block).
• Leads V4,V5,V6 — all show 1 mm of flat ST depression. This strongly suggests ischemia — which could be recent and a contributing (or precipitating) cause of today’s abnormal rhythm.

Unfortunately — I do not have follow-up for this case. Nevertheless, this case provides a wonderful illustration of multiple abnormal findings.

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Acknowledgment: My appreciation for the anonymous submission of today's case.

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Related ECG Blog Posts to Today’s Case:

• ECG Blog #185 — My Ps, Qs, 3R System for Rhythm Interpretation.
• ECG Blog #188 — Reviews how to read and draw Laddergrams (with LINKS to more than 100 laddergram cases — many with step-by-step sequential illustration).

• ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.
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• ECG Blog #164 and ECG Blog #251 —Review of Mobitz I 2nd-Degree AV Block, with detailed discussion of the "Footprints" of Wenckebach.
• ECG Blog #236 — Reviews in our 15-minute Video Pearl #52 how to recognize the 2nd-Degree AV Blocks (including "high-grade" AV block). 
• ECG Blog #186 — Reviews when to suspect 2nd-Degree, Mobitz Type I.
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• ECG Blog #404 — Walks you through a step-by-step approach to this AV block case (with links to a VIDEO of this case, and to Blog #344 for more details).
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• ECG Blog #352 — emphasizes that 1st-degree AV block with a very long PR interval may have hemodynamic consequences.
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• ECG Blog #243 and ECG Blog #347 — Examples of AFlutter with dual-level AV block (Wenckebach) out of the AV Node.