Systematic cardiac rhythm strip analysis.
Correctly analyzing cardiac rhythms requires utilization of a systematic process (see Table 1). Failure to utilize this process can lead to an incorrect rhythm interpretation. Using a caliper will also improve the accuracy of rhythm analysis. For example, a rhythm that appears to be regular to the naked eye may be found to be irregular when using a caliper.
The first step in analyzing a cardiac rhythm strip is determination of the heart rate. The heart rate indicated at the top of the rhythm strip printout must be verified by the nurse. Cardiac monitors have been known to double the heart rate incorrectly in rhythms with a very elevated T-wave. In addition, most cardiac monitors will include premature ventricular contractions (PVCs) or other abnormal beats when calculating heart rate. The quickest way to verify the heart rate is by counting the number of QRS complexes occurring in a 6-second strip and multiplying this number by ten. A more accurate but time-consuming way to calculate heart rate is to count the number of small boxes between two consecutive R waves and divide that number into 1,500 (Huff, 2006). If there are two rhythms on the same strip (e.g., sinus rhythm and an episode of ventricular tachycardia), the rate of each rhythm should be determined independently.
Determining the regularity of the atrial and ventricular rates is the second step in rhythm analysis. Ventricular regularity is determined by measuring the R-to-R intervals across the entire strip. If an R-to-R interval on the strip varies by more than three small boxes (0.12 seconds), the ventricular rate is considered irregular (Huff, 2006). To determine atrial regularity, the nurse should measure the P-to-P intervals across the entire strip. If a P-to-P interval on the strip varies by more than three small boxes, the atrial rate is considered irregular.
The third step in analyzing a cardiac rhythm strip involves assessment of the P wave. Are the P waves upright in lead II? Are they uniform (all the same shape and size)? Is there a P wave before every QRS complex? Inverted P waves, P waves of varying shapes or sizes, or missing or extra P waves should be noted as they provide important clues to rhythm interpretation (Huff, 2006).
Measurement of the P-R interval is the fourth step in rhythm strip analysis. The P-R interval is measured from the beginning of the P wave to the beginning of the QRS complex. A normal P-R interval measures 0.12-0.20 seconds (3-5 small boxes). The P-R interval reflects depolarization of the atria and the spread of the impulse through the atrioventricular (AV) node. A prolonged P-R interval (greater than 0.20 seconds) indicates a delay in conduction through the atria and/or AV node (Huff, 2006).
Measurement of the QRS duration is the fifth step in analyzing a cardiac rhythm strip. The QRS duration represents ventricular depolarization. The R wave is a positive waveform; the Q wave is a negative waveform following the R wave, and the S wave is a negative waveform
following the R wave. The ORS duration is measured from the beginning of the Q wave to the end of the S wave. The normal QRS duration measures less than 0.12 seconds. A ORS duration measuring 0.12 seconds or greater indicates a delay in conduction through the ventricle. It should be noted that you may not always observe all three waveforms; there may be a Q wave (no R or S), or a R wave (no Q or S), or a combination of Q and R, or R and S waves (see Figure 1) (Huff, 2006).
[FIGURE 1 OMITTED]
Step 6 in cardiac rhythm strip analysis involves examination of the S-T segment. The normal S-T segment begins at the isoelectric line. The P-R segment is used as a baseline from which to evaluate the degree of displacement of the S-T segment from the isoelectric line. S-T segment elevation or depression is considered significant if displacement is 1 mm (one small box) or more above or below the isoelectric line and is seen in two or more leads. ST segment depression can be an indication of myocardial ischemia, ventricular hypertrophy, bundle-branch block, or hypokalemia, or may result from digitalis administration. ST segment elevation can be an indication of acute myocardial injury, pericarditis, coronary vasospasm, ventricular aneurysm, or hyperkalemia (Huff, 2006).
The seventh step in analyzing a rhythm strip is assessment of the T wave. Is the T wave upright or inverted? Is the T wave peaked? Abnormal T waves can indicate myocardial ischemia or infarction, pericarditis, hyperkalemia, ventricular hypertrophy, bundle-branch block, or subarachnoid hemorrhage (Huff, 2006).
The eighth and final step in cardiac rhythm analysis is measurement of the Q-T interval. The Q-T interval represents ventricular activation to recovery and is measured from the beginning of the Q wave to the end of the T wave. A normal Q-T interval should be equal to or less than one-half the distance of the R-to-R interval. A prolonged Q-T interval can be congenital or caused by electrolyte imbalances, hypothermia, myocardial ischemia, or administration of certain anti-arrhythmic or psychotropic agents. A prolonged QT interval places a patient at increased risk for life-threatening dysrhythmias.
After systematically analyzing the rhythm strip, you are ready to begin rhythm interpretation and determination of the clinical significance of the rhythm to your patient. Future columns will provide opportunities to practice the steps of cardiac rhythm analysis and interpretation for actual patient cardiac rhythm strips.
American College of Cardiology. (1991). Position statement: Recommended guidelines for in-hospital cardiac monitoring for detection of arrhythmia. Journal of American College of Cardiology, 18, 1431-1433.
Helms, S., & Adkins, S. (2006). Telemetry and evidence-based practice go hand in hand. Nursing 2006 Critical Care, 1(1), 17-19.
Huff, J. (2006). ECG workout. Philadelphia: Lippincott Williams & Willkins.
Beth Palmer, DNP, RN CMSRN, ANP-BC, ACNS-BC, is a Nurse Practitioner, Community Living Center, Veteran's Affairs San Diego Healthcare System, San Diego, CA; and a MEDSURG Nursing Editorial Board Member.
TABLE 1. Steps in Rhythm Analysis 1. Verify rate 2. Determine atrial/ventricular regularity 3. Assess P waves 4. Measure P-R interval 5. Measure QRS duration 6. Assess S-T segment 7. Evaluate T wave 8. Measure Q-T interval
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|Title Annotation:||Tackling Telemetry|
|Date:||Mar 1, 2011|
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