8-Step Method of ECG Evaluation

Determine rhythm.
- Atrial rhythm:
  - Measure P-P intervals for several cycles.
  - If consistently similar, atrial rhythm is regular.
  - If dissimilar, atrial rhythm is irregular.
- Ventricular rhythm:
  - Measure the intervals between two consecutive R waves in the QRS complexes.
  - If no R wave, use the Q wave or the S wave of consecutive QRS complexes.
  - If R-R intervals are consistently similar, ventricular rhythm is regular.
  - If dissimilar, ventricular rhythm is irregular.
Calculate rate using one of three methods: times-10; 1,500; or sequence.
- Times-10 method
  - Obtain a 6-second strip.
  - Count the number of P waves.
  - Multiply the number of P waves by 10 (ten, 6-second strips equal 1 minute) to calculate the atrial rate.
  - Calculate ventricular rate the same way using R waves.
- 1,500 method (because 1,500 small squares equal 1 minute)
  - Count the number of small squares between identical points on two consecutive P waves.
  - Divide the number by 1,500 to get the atrial rate.
  - Use the same method with two consecutive R waves to calculate the ventricular rate.
- Sequence method
  - Find a P wave that peaks on a heavy black line.
  - Assign these numbers to the next six heavy black lines: 300, 150, 100, 75, 60, and 50.
  - Find the next P wave peak.
  - Estimate the atrial rate based on the number assigned to the nearest heavy black line.
  - Estimate the ventricular rate the same way using the R wave.
Evaluate P wave.
- Determine if a P wave is present for every QRS complex.
- Assess whether it has a normal configuration, size, and shape.
Determine PR interval duration.
- Count the small squares between the start of the P wave and the start of the QRS complex.
- Multiply the number of squares by 0.04 second.
- Determine if the duration is normal (0.12 to 0.20 second, or 3 to 5 small squares) and consistent.
Determine QRS complex duration.
- Measure straight across from the beginning of the QRS complex to the end of the S wave (not just to the peak).
- Count the small squares between the beginning and end of the QRS complex.
- Multiply this number by 0.04 second.
- Determine if the duration is normal (0.06 to 0.12 second); all QRS complexes are the same size and shape, and a complex appears after every P wave.
Evaluate T wave.
- Determine if T waves are present and have a normal shape, normal amplitude, and the same deflection as the QRS complexes.
- Consider whether a P wave could be hidden in a T wave.
Determine QT interval duration.
- Count the small squares between the beginning of the QRS complex and the end of the T wave (where the T wave returns to the baseline).
- Multiply this number by 0.04 second.
- Determine if the duration is normal (0.36 to 0.44 second).
Evaluate other components.
- Make sure that the waveform doesn't reflect problems with the monitor (see pages 28 to 31).
- Note ectopic beats, aberrantly conducted beats, or other abnormalities.
- Check the ST segment for abnormalities.
- Look for a U wave.
- Classify the rhythm strip according to one or all of the following characteristics:
  - Site of origin of the rhythm (sinus node, atria, AV node, or ventricles)
  - Rate (normal [60 to 100 beats/min], bradycardic [less than 60 beats/min], tachycardic [more than 100 beats/min])
  - Rhythm (regular or irregular [flutter, fibrillation, heart block, escape rhythm, other arrhythmias]).

Place the ECG strip on a flat surface.
Position the straight edge of a piece of paper along the strip's baseline.

With the ECG on a flat surface, place one point of the calipers on the peak of the first R wave of two consecutive QRS complexes.

Move the paper up slightly so the straight edge is near the peak of the R wave.
With a pencil, mark the paper at the R waves of two consecutive QRS complexes, as shown below. This is the R-R interval.
Move the paper across the strip lining up the two marks with succeeding R-R intervals. If the distance for each R-R interval is the same, the ventricular rhythm is regular. If the distance varies, the rhythm is irregular.
Use the same method to measure the distance between P waves (the P-P interval) and determine whether the atrial rhythm is regular or irregular.

Adjust the caliper legs so the other point is on the peak of the next R wave, as shown below. This distance is the R-R interval.
Pivot the first point of the calipers toward the third R wave and note whether it falls on the peak of that wave.
Check succeeding R-R intervals in the same way. If they're all the same, the ventricular rhythm is regular. If they vary, the rhythm is irregular.
Using the same method, measure the P-P intervals to determine whether the atrial rhythm is regular or irregular.

Methods of measuring rhythm

Correcting the QT interval

The QT interval is affected by the patient's heart rate. As the heart rate increases, the QT interval decreases; as the heart rate decreases, the QT interval increases. For this reason, evaluating the QT interval based on a standard heart rate of 60 is recommended. This corrected QT interval is known as QTc.

The following formula is used to determine the QTc:

The normal QTc for women is less than 0.45 second and for men is less than 0.43 second. When the QTc is longer than 0.50 second in men or women, torsades de pointes is more likely to develop.

Identifying monitor problems

Abnormal waveforms could indicate monitor problems. This chart reviews commonly encountered problems, their possible causes, and suggested interventions. Remember, however, you should always assess the patient before troubleshooting the equipment.

Waveform	Possible causes	Interventions
*Artifact*(waveform interference)	Seizures, chills, or anxiety Dirty or corroded connections Improper electrode application Short circuit in leadwires or cable Electrical interference from other equipment in the room Static electricity interference from inadequate room humidity	If the patient is having a seizure, notify the doctor and intervene as needed. Keep the patient warm and encourage relaxation. Replace dirty or corroded wires. Check the electrodes and reapply them if needed. Clean the patient's skin well because skin oils and dead skin cells inhibit conduction. Check the electrode gel. If it's dry, apply new electrodes. Replace broken equipment. Make sure all electrical equipment is attached to a common ground. Check all three-prong plugs to make sure no prongs are loose. Notify the biomedical engineering department. Regulate room humidity to 40% if possible.
*False-high-rate alarm*	Gain setting too high, particularly with MCL₁ setting HIGH alarm set too low, or LOW alarm set too high	Assess the patient for evidence of hyperkalemia. Reset gain. Set alarm limits according to the patient's heart rate.
*Weak signals*	Improper electrode application QRS complex too small to register Wire or cable failure	Reapply the electrodes. Reset gain so the height of the complex is more than 1 mV. Try monitoring the patient on another lead. Replace faulty wires or cables.
*Wandering baseline*	Patient restlessness Chest wall movement during respiration Improper electrode application (electrode positioned over bone)	Encourage the patient to relax. Make sure that tension on the cable isn't pulling the electrode away from the patient's body. Reposition improperly placed electrodes.
*Fuzzy baseline*(electrical interference)	Electrical interference from other equipment in the room Improper grounding of the patient's bed Electrode malfunction	Make sure all electrical equipment is attached to a common ground. Check all three-prong plugs to make sure no prongs are loose. Make sure the bed ground is attached to the room's common ground. Replace the electrodes.
*Baseline*(no waveform)	Improper electrode placement (perpendicular to axis of heart) Disconnected electrode Dry electrode gel Wire or cable failure	Reposition improperly placed electrodes. Check if electrodes are disconnected. Check electrode gel. If the gel is dry, apply new electrodes. Replace faulty wires or cables.

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