February 12, 2016

Mastering ECG interpretation in Telemetry Units # 1

ECG interpretation in telemetry units has been made easier because of the ability to capture, review and print ECG strips at specific time in several simultaneous leads. Here we review the new system (GE telemetry) and how to use/appreciate its built-in functions and master ECG interpretation.
The 2 lead strip

Figure 1 - Anatomy of the 2-lead strip

The typical 2-lead printed strip is a real-time captured strip. This is the strip printed at the start of the shift. So, some of the strips will be "showered" with artifact because we cannot prevent patient activity. Saved telemetry data cannot be printed on this 2-lead strip but can be printed on "FULL DISCLOSURE VIEW".
The anatomy of the strip is labeled (Figure 1). The BOX number is now the TTX # that is documented. This is a unique # for each telemetry box. If a patient is on a different telebox, the central monitor will not receive a signal. 

At the bottom are tiny black lines which are 3-second markers (Figure 2). There are 15 big boxes between markers indicating. One second is equal to 5 big boxes and 1 big box is equal to 0.20 sec or 200 millisecond. So, 15 big boxes multiplied by 0.2 sec is equal to 3 seconds. The 3-seconds marker can be used to compute the heart rate using the 6-second method. Count the number of R waves in 6 seconds and multiply by 10. This is the approximate rate in that strip.

Figure 2 - 3 seconds marker and computing the rate using the 6-second method

In the strip above, there are 9 R waves in the 6-second marker. So the rate is 90.


Figure 3 - Heart rate trend or heart rate histogram

The heart rate trend or heart rate histogram can be printed in the GE system. It is the graphical representation of the heart rate over time.  You can use it to:

1. Check heart rate control
o   in patients with atrial fibrillation who are on drips (diltiazem and amiodarone)
o   patients with anemia will often present with tachycardia. Heart rate often improve after transfusion
o   improvement in heart rate in patients being treated for alcohol withdrawal

2. Check how frequent a tachyarrhythmia is occurring especially in paroxysmal tachyarrhytmias

3. Check how long was the tachyarrhythmia

   4. Marker to print the beginning of a tachyarrhythmia or conversion from sinus rhythm to another arrhythmia and back to sinus rhythm

   5. Check ranges like how low or how high the heart rates in 24 hours

Full disclosure
The full disclosure display is a 1 page 10-seconds strip. It will show all limb leads (I,II, III, aVr, aVL, aVF) and chest lead/s (V1 and/or V6).

Figure 4 - Full disclosure strip

The top portion will show the name, MRN (if it is placed in the system), date, time, heart rate, PVC count, ST analysis of specific lead, and the TTX or box number.

For those used to 2-lead strip, it overwhelming to see so much leads. It will take some time for you to get used to it. Using the full disclosure print-out has a lot of advantages:

1. Catch wrong lead placement
In the strip above (Figure 4), there are Q waves in I and aVL and P waves are inverted. In normal sinus rhythm (Figure 5), the P wave morphology is:
·         Upright P in leads I, II and aVF
·         inverted in aVR
·         P wave is variable in leads III and aVL
·         P wave is upright in leads V4-V6
·         Most often biphasic (positive-negative) in leads V1 and V2

Figure 5 -Normal sinus rhythm in full disclosure (correct lead placement)

So, there is wrong lead placement in Figure 4. Figure 6 is after correcting lead placement.

Figure 6 - Full disclosure after lead placement correction

2. Check simultaneous leads for PQRST contour/morphological differences

Figure 7 - The 3 fates of a PAC (some marked in red arrow)

2.1 - ST distortions due to PAC's
To master ECG interpretation, you have to see more strips and see more leads. Most of the time, the "funky" arrhythmia  behavior can be explained with one phenomenon. The strip above will be most of the time interpreted as sinus rhythm, PAC in bigeminy, PVC and onset of bradycardia. However, if you use full disclosure and compare contour/morphology of PQRST complexes, it is apparent that this strip is sinus rhythm, PAC in bigeminy conducted normally, with aberrancy and non-conducted or it showed the 3 fates of a PAC.

2.2 - Capture fusion beats in VT

Figure 8 - Wide complex tachycardia with no change in QRS direction in the limb leads

In ventricular tachycardia (VT) discrimination, you should think twice to diagnose VT if the direction of the QRS complexes are the same during sinus rhythm. However, in this full disclosure strip (Figure 9), you can clearly see fusion beat (marked with red arrow below). A fusion beat favors VT.

Figure 9 - Fusion beat identified in VT

2.3 - Identifying source of beats

Figure 10 - 2 different shapes of QRS complexes from 2 different sources 

Occasionally, QRS complexes of non-sinus origin will look different. In the strip above (Figure 10), QRS #1-6 are non-sinus in origin (junctional beats) and QRS #7-10 are sinus beats. Even if there is a P wave in QRS #1 but its contour or morphology is the same with QRS #2-6, then QRS #1 is a junctional beat. Difference in QRS morphology is obvious in all leads.


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