Quiz #23 Answer: Shunt Calculcation (VSD with Eisenmenger)

Answers are in red fonts against the questions.

Scroll down for details of calculation.

Hypothetical case: 32 year old male with VSD and Eisenmenger syndrome. Necessary data are given.

Questions:

1)      What is the overall Qp/Qs?...1.0

2)      Calculate the effective pulmonary blood flow (Qep)….1.17 L/min/m²

3)      Calculate the amount of right to left shunt….0.35 L/min/m²

4)      Calculate the amount of left to right shunting….0.35 L/min/m²

(From Science and Practice of Pediatric Cardiology, 1990 ed. Page 921)

·         O2 content at 100% saturation is 17 g x 1.36 = 23.12 g%.

·         Qp:

=  (0.95 – 0.60) g% = 120/8.0 (x10 to convert to L/min/m2)

= 120/80 = 1.5 L/min/m².

·         Qs:

Qs = 120/23.1 (0.85-0.50) g% = 120/8.0*10 = 1.5 L/min/m².

Qp/Qs = 1.0

·         Effective PBF  (Qep):

Qep – 120/23.1(0.95-0.50) g% = 120/10.4 (x10 to convert to L/min/m²)

= 120/104 = 1.17 L/min/m².

(Both 1.15 and 1.17 are correct depending upon the calculation step at which you round the numbers. 1.15 is more correct than 1.17)!

·         R-L shunt:

(Qp – Qep) = 1.5 – 1.15 = 0.35 L/min/m²

(Pulmonary blood flow includes Qep + R-L shunt via VSD. Therefore, R-L shunt is Qp – Qep)

·         L-R shunt:

(Qs – Qep) = 1.5 – 1.15 = 0.35 L/min/m².

(Systemic blood flow includes Qep + L-R shunt via VSD. Therefore, L-R shunt is Qs – Qep).

Quiz #22: ICU monitor interpretation - Answers

5 month old baby. Postoperative day 1 after closure of membranous VSD. Panel 1 and Panel 2 were recorded few minutes apart.

(Click on the image to enlarge)

1.       What is the arrhythmia in Panel 1?

a.       JET (This patient already on Amiodarone. Therefore, JET rate is lower than usual)

2.       What type of pacing is done in Panel 2?

a.       Atrial pacing

3.       Describe the important difference between the CVP waveform in Panel 1 and Panel 2. What is the reason for the difference?

a.       “Giant” a-waves in Panel 1.

b.      Mechanism: Atrial contraction against closed AV valve. Junctional beat gets transmitted both atrium and ventricle. P wave is embedded inside the QRS. Both atria and ventricles contract at the same time, leading to atrial contraction against a closed AV valve (Ventricular contraction causes AV valves to close).

c.       Giant a-waves vs. Cannon a-waves: Strictly speaking, these two entities are different. In junctional rhythm, “Giant a-waves” are present in every beat. In contrast, “Cannon a-waves” are noted in complete AV block where P wave to QRS relationship is not 1 to 1. Some P wave happen to precede QRS. Therefore, some atrial contractions occur with AV valve open. Only occasional P waves conflict with QRS complexes causing atrial contraction with closed AV valve. Therefore, large a-waves are noted only in some beats…similar to a cannon firing only intermittent. Cannon needs to be packed with gun powder after each firing!

4.       Comment about AV conduction in Panel 2.

a.       Apparently, prolonged PR interval (First degree AV block). “Apparently” because actual measurements are not possible from these images.

5.       Why does arterial line trace have a “flat top”? How will you rectify this issue?

a.       Upper limit of the display-scale for arterial line is set at 90 mmHg. But, systolic BP is 99. This is rectified by either increasing the upper limit of display-scale or “auto adjust” mode on the monitor.

Quiz #21: EKG Answer

Question: What is the EKG diagnosis?

Answer: Wandering pacemaker

Discussion: Wandering pacemaker is characterized by 2-3 P wave morphologies and can be associated with variable PR interval (usually one PR interval length per P wave morphology). Rhythm will follow the background sinus rhythm.

In this patient, baseline rhythm is sinus arrhythmia. Each beat is a sinus beat (P, followed by QRS).

3 different P wave morphologies are noted (inverted, flat, and upright in rhythm strip - lead II). PR interval is 80 ms with inverted P wave and is ~120 ms with upright P wave.

This is not premature atrial contraction - because the complexes are not premature when a different P wave morphology appears!