Quiz 40: Reason for bradycardia

Called to evaluate a term, 1-day old baby for “bradycardia” (~90 bpm). EKG is given. (Clue: V1 rhythm strip provides best wave forms to evaluate).

Question: (i) What is the cause of this relative “bradycardia” in this baby? (ii) Explain why AV block is not the primary diagnosis?

Answer:

(i) Cause for “Bradycardia” is non-conducted atrial ectopies. There is an atrial ectopy after each QRS (arrows in the figure below) that is not conducted. This is a “physiologic” block because atrial ectopy is too early for the AV node to conduct. Further, the atrial ectopy depolarizes and resets the SA node (as opposed to ventricular ectopy that usually does not). Therefore, SA node fires somewhat later than usual after an atrial ectopy leading to overall slowing of heart rate.

(ii) AV block is not the primary diagnosis because the "block" is secondary to the early timing of the atrial ectopy. AV block is a physiologic event in this situation - not a block at all.

(Unfortunately, the T waves are flat leading to some confusion in recognizing the atrial ectopies).

(Click on the image to enlarge) Arrows indicate "blocked atrial ectopies"

Quiz #39: Where is the catheter?

Two sets of images are given (PA and Lateral views in each set, from the same angiogram before and during contrast injection) obtained during pre-Glenn catheterization in this patient with Tricuspid Atresia.

Questions & Answers:

1) Trace the catheter course.

Answer: IVC-RA-ASD-LA-MV-LV-VSD-RV

2) Where do you think is the tip of the catheter?

Answer: RV

3) Using the second set of images, comment on great arteries relationship? (Normal relationship or not?).

Answer: Normally-related great arteries.

4) Bonus question: Based on the above observations, what classification type of tricuspid atresia is this?

Answer: Type 1b (Tricuspid Atresia with normally-related great arteries, Small VSD and PS). See the last image for classification of Tricuspid atresia.

(Click on the image to enlarge)

(Click on the image to enlarge)

(From Moss & Adams 5^th ed. 1995. Chapter 61: Tricuspid Atresia by Dr. Rosenthal A, Dick, McD II. p 903.)

Quiz #38: EKG Answer

Question: 5-month old with Down Syndrome. 2nd Postoperative day after surgical closure of large inlet VSD. What is the diagnosis?

Answer: Wenckebach phenomenon (2nd Degree, Mobitz type 1 AV block).

Discussion:

1) There are ventricular ectopies (escape beats) after the non-conducted P waves (Large, dark arrows). These beats have confused some responders.

2) "Grouping of beats" as seen here is a feature of Wenckebach phenomenon and is helpful in gestalt recognition.

3) Remember: Shortest PR interval should be seen in the beat that immediately follows the non-conducted beat. This will help to differentiate other rhythms (e.g. 3rd degree AV block with coincidental appearance to Wenckebach, for a short time). If you look at a longer strip of EKG, 3rd AV block with betray itself.

(Click on the image to enlarge)

Quiz #37: Echo Quiz Answer

4-hr old baby with cyanosis. The following is part of the echocardiogram.

Questions:

1) What do you observe?

Answer: ASD/PFO with exclusive right to left shunting.

2) Provide at least 3 differential diagnoses for this observation.

Answer: (i) Persistent pulmonary hypertension of newborn (aka. Persistent fetal circulation), (ii) Tricuspid Atresia, (iii) TAPVR, (iv) Pulmonary Atresia with Intact ventricular septum, (v) Any condition with pulmonary hypertension in a newborn, e.g. Ebtein's anomaly with pulmonary hypertension, etc.

Quiz #36: EKG

Answer: Complete AV block

(Click on the image to enlarge)

Quiz #35: EKG - Answer

Question: 8-year old boy was referred for chest pain. What is the diagnosis?

Answer: WPW syndrome

Short PR interval and Delta wave are noted. Delta wave is somewhat atypical in appearance - as though it is a wide QRS complex. Nevertheless, it is Delta wave.

If you are interested in locating the accessory pathway, you may refer to the answer to Quiz #5. I think, it is left-sided pathway.

(Click on the image to enlarge)

Quiz #34 - Temporary Pacemaker

6 month old infant s/p AV septal defect repair. 3^rd postoperative day. Underlying rhythm was 3^rd degree AV block & probable sinus node dysfunction. The rhythm strip was printed to evaluate the temporary pacemaker.

Questions: (Answers are in red-color fonts)

What mode is being used? ….DDD

Comment about Atrial pacing, Atrial sensing and Ventricular pacing?

a.       Is the pacemaker atrial pacing properly? (Yes/No) …No (No P wave after atrial pacing spikes “AP”)

b.      Is the pacemaker atrial sensing properly? (Yes/No) …Yes (When there is a native P wave, no atrial pacing spike. Atrial sensing “AS” properly)

c.       Is the pacemaker ventricular pacing properly? (Yes/No) …Yes (QRS complex follows every ventricular pacing spike “VP”)