This project, like many science fair projects, is the product of curiosity. A desire to know more about the supposed link between a prolonged QT interval and Sudden Infant Death Syndrome (Ioakeimidis, 2017) created a study with the intent to improve protocol for QT interval measurements in adult women. This was done by identifying the most accurate lead to use for QT interval measurements. A QT interval, an interval measured from a heartbeat displayed on a test known as an electrocardiogram (EKG), can be a predictor of fatal arrhythmias when prolonged. An electrocardiograph is the graphed results of an electrocardiogram. However, the leads used to record the heartbeat often provide twelve different measurements of the true QT interval. Which lead should be used for normal EKGs from adult (defined here as women between 18 and 50 years of age) women? Research provided answers to similar queries, such as which lead should be used when measuring QT interval length in subjects with cardiac diseases (Davey, 2000) and produced a basis on which this project was built. However, no research regarding the effect of lead choice on the accuracy of QT interval measurements in normal electrocardiograms (EKGs) from adult women could be located. This project attempts to find the answer to the question, which lead provides the most accurate measurement of QT interval length in EKGs from adult women? Many hours were spent measuring and examining fifty EKGs from patients that fit within the specified demographic. Data analysis finally provided an answer that would not only satisfy innate curiosity but one which could help to prevent arrhythmias in adult women, maybe even saving lives. This study answered a question and
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provided an incredible educational experience in regards to the mechanisms of electrocardiograms and the human heart.
Purpose
To improve current protocol for measuring QT interval length in normal electrocardiograms from women between 18 and 50 years of age by identifying the most accurate lead for QT interval measurements through regression analysis.
Procedure
1. Open an electrocardiogram from a woman between 18 and 50 years of age reported as
normal and recorded electronically within the last year at a single health care institution.
2. Blind confidential patient information.
3. Using an electronic caliper, find the location to begin the measurement of the QT interval on
the first lead. The starting point of the caliper should intersect with the commencement of the
QRS complex.
4. Adjust the end point of the caliper to the intersection of the descending limb of the T wave
with the isoelectric line on the electrocardiograph. (Goldenberg, 2006)
5. Record the measurement.
6. Repeat steps 1-5 for each of the remaining eleven leads.
7. Find the mean of all twelve measurements, round the mean to the nearest millisecond.
8. Repeat steps 1-7 for each electrocardiograph.
Results
The purpose of this study was to discover which of the twelve leads from a standard
12-lead electrocardiogram (I, II, III, aVF, aVL, aVR, V1, V2, V3, V4, V5, V6) would provide the
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most accurate measurement of QT interval length on normal EKGs from adult women. By comparing measurements from
0.5
0.45
0.4
0.35
0.3
Figure 1.1
Correlation Between Lead V6 QT and Mean QT
each lead on an EKG to the mean QT on the same EKG, accuracy can be judged. Relationships between the sets of values (QT by lead to mean QT across all leads) were examined for each lead. Using Pearson’s formula to obtain the correlation coefficient, measurements were analyzed, and graphs were created for each of
r = 0.98994
0.3 0.35
0.4 0.45 0.5 Lead V6 QT (seconds)
the twelve leads.
Lead V6 had the
highest correlation coefficient between itself and the mean QT. Measurements obtained from Lead V6 had a correlation coefficient of 0.98994 when compared to mean QT
April 16th, 2018
Correlation Between Lead II QT and Mean QT
0.5
0.45
0.4
0.35
0.3
r = 0.98984
0.3 0.35 0.4
0.45 0.5
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Figure 1.2
Lead II QT (seconds) Jana Steyn : Between The Q & T
Mean QT (seconds)
Mean QT (seconds)
0.5
0.45
0.4
0.35
0.3
Correlation Between Lead V2 QT and Mean QT
0.4 0.45 0.5 Lead V2 QT (seconds)
measurements. This lead outperformed all other leads in accurately measuring QT interval length. (Fig. 1.1)
Lead V6 was followed by lead II with a correlation coefficient of 0.98984 . Current protocol dictates that lead II should be used for QT
r = 0.98976
0.3 0.35
Figure 1.3
interval measurements. (Salvi, 2012) (Fig. 1.2)
Finally, lead V2 also provided a surprisingly accurate measurement. Coming in with a
correlation coefficient of 0.98976, it was the third most accurate lead overall. (Fig. 1.3)
All individual lead measurements were analyzed against the mean QT from the same
electrocardiograph. The lead that related most closely to the mean QT (highest correlation coefficient) was deemed most accurate. The results concluded that the most accurate lead was lead V6, followed by II and V2, respectively.
Conclusion
The results of this study provided some insightful information. Standard protocol dictates that lead II should be used to obtain QT interval measurements. (Salvi, 2012) Based on this protocol, a fair assumption could be made to assume that measurements from lead II would prove to be most accurate. Although lead II was proven to be an accurate source of QT interval measurements, this study has shown that lead V6 would be a more precise alternative. A small
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Mean QT (seconds)
change such as the lead used to measure QT interval length could have an incredible impact on the accuracy of measurements. Using a more accurate lead may offer a valuable tool to screen for long QT syndrome (LQTS) and likely contribute to the prevention of fatalities associated with sudden cardiac death as well as other arrhythmias. Based solely on the results of this small-scale study, switching to use of lead V6 for QT interval measurements could have a profound impact on the accuracy of QT interval measurements on normal EKGs from adult women between 18 and 50 years of age.
No significant issues were encountered while gathering or interpreting data for this study. However, applying the procedure to electrocardiographs with shaky baselines required more effort to obtain an accurate measurement. In these cases, a ruler was needed to judge the end of the T wave.
Along with the emergence of handheld EKG technology, validation of a single lead QT measurement might impact the validity of mass screening programs for LQTS, providing a possible direction for future research. Information from this study could be used to validate measurements from these handheld devices.
Acknowledgments
This project could not have been possible without the support of many individuals and organizations. First of all, I would like to thank Royal Inland Hospital for generously providing my source of data. Secondly, I would like to thank my science teacher, Ms. Katie Smylie, for all of her help and patience. Finally, I am grateful to my mother for supporting me, and my father for mentoring me and answering all my confusing questions. I am greatly indebted to the people mentioned above.