Quiz #33: Arterial line traces - Answer

Question:

13-year old patient who underwent repair of coarctation of aorta earlier that day has two arterial lines, right radial & left femoral. According to the reading on the monitor, apparent peak to peak pressure gradient across the coarctation repair site is 37 mmHg.

Question: Based on the traces in each arterial line, is the pressure gradient higher than, lower than or equal to 37 mmHg? Why?

Answer:

The peak to peak pressure gradient is lower than 37 mmHg. Right radial arterial line trace has a “whip”, “fling” or “standing wave” (or as Ashish puts it in sophisticated terms…”distal pulse amplication”) that artificially increases the systolic pressure. Left femoral arterial line has a more rounded peak which is characteristic of a more central arterial line trace. Since the fling or standing wave overestimates the systolic pressure in radial arterial line, gradient of overestimated. Real systolic pressure in right radial arterial line is unfortunately not possible due to technical limitations.

Ashish’s answer: Right radial artery will be higher when compared to the femoral artery BP due to distal pulse amplification. Therefore, the peak to peak pressure gradient across the coarctation site is probably less than 37 mmHg.

Systolic and diastolic arterial blood pressures are higher and lower, respectively, in radial arteries than in the aorta. This phenomenon is known as distal pulse amplification and is due to the characteristics of the vascular tree. Briefly, a pulse waveform entering the aorta is exposed to a sudden impedance change at the capillary level, resulting in a large increment in resistance and producing reflected pulse waveforms. Those waves are added to the following ones, producing higher peaks than the original aortic systolic peak at different distances from the aortic origin. This distal pulse amplification is always present when peripheral vascular resistance is high.

Reference: Peripheral arterial blood pressure monitoring adequately tracks central arterial blood pressure in critically ill patients: an observational study. Mariano Alejandro Mignini, Enrique Piacentini and Arnaldo Dubin.  Critical Care 2006;10:R43.

Quiz #31: Answer

This RA trace was recorded in cath lab under endotracheal general anesthesia.

Question: Which wave is the taller one, a wave or v wave?

Answer: a wave (See labelled images below).

RA pressure trace consists of a, c, v waves and x, y descents.

a – atrial systole (occurs immediately after P wave. Note: electrical activity precedes mechanical activity). Dotted line helps to compare the P wave to the RA waveform.

c – bulging of tricuspid valve “cusps” during onset of ventricular systole. This will appear just after LV pressure trace crosses the atrial wave.

v – venous filling (occurs during atrial diastole which is ventricular systole). Therefore, v wave should coincide with ejection phase of ventricle as shown in LV trace or PA line trace.

(Click on the image to enlarge)

Additional images from the same patient - recorded with LPA pressure in one panel and with LV pressure in the other panel. Label indicates where c wave will be expected.

Quiz #30: EKG and Doppler Trace - Answer

13 yr old girl was transferred to ICU for atrial flutter. Patient is muscle tremors and is neurologically obtunded, thought to be secondary to severe, systemic vasculitis. Figure 1 is an EKG strip from bedside monitor on the floor. Pulse oximeter trace is present in the strip as well.

In order to clarify the diagnosis, Doppler was performed with the cursor placed between mitral valve and aortic valve.

1)      What is the diagnosis?

Sinus rhythm. Muscle tremors causing fib-flutter pattern. In EKG: Hallmark of atrial fibrillation is irregularly-irregular ventricular rate (which is absent here). Also, pulse ox trace is regular and is normal, beat-to-beat. In Doppler trace: There is 1:1 relationship between mitral inflow and aortic outflow.

2)      How would you manage this?

Just get out of the way and let them manage the obtunded state and muscle tremors.

(Click on the image to enlarge)

Quiz #29: CT scan, Vacular anomaly

CT scan images from a 8-mo old boy with stridor, vomiting and weighs 5.6 kg. Figure 1 shows anterior and Left lateral views. Figure 2 shows 3D reconstruction of trachea-bronchial tree (Barium swallow was not performed in this patient).

Questions:

1) What is the arch sidedness?

2) What is the diagnosis?

3) Does the patient need intervention and why?

Answers:

1) Right aortic arch (Arrow in the last image shows indentation in trachea).

2) Double arch with ligamentous (atretic), left arch - creating a vascular ring.

3) Patient needs intervention because the patient is symptomatic and failing to thrive.

A differential interpretation for the diagnosis - Question 2 - is "Right aortic arch with left ductal ligament". Where the anterior end of the ligament is attached will determine the difference. If the ligament is attached to the ascending aorta or a branch of the aorta, it is "double arch". Alternatively, if the ligament is attached to the MPA, it is "right arch with ductal ligament". Dotted line is drawn in the images below to help to make this determination.

Arrow in the last figure indicates the indentation in trachea from right-sided arch. Similar indentation is expected in barium swallow.