|Year : 2016 | Volume
| Issue : 2 | Page : 125-129
Effect of change in body position on resting electrocardiogram in young healthy adults
Supreet Khare, Anuj Chawala
Department of Physiology, Armed Forces Medical College, Pune, Maharashtra, India
|Date of Web Publication||4-Aug-2016|
Virat Khand, Gomtinagar, Lucknow - 226 010, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
Background: The electrocardiogram (ECG) is recorded in the supine position and values of various parameters are based on calculations made from supine ECG recordings. In certain situations, such as exercise stress testing and evaluation of syncope by the head-up tilt test, the ECG is recorded in the upright position. Thus, it becomes equally important to study and quantify the nature and magnitude of changes seen in the ECG with a change of posture from supine to upright in healthy individuals.
Aim: To study and investigate the effect of a change in body position on the frontal plane on ECG.
Materials and Methods: Thirty healthy adult subjects (15 male and 15 female) in the age group of 18-25 years were included. The ECG was recorded in four body positions, supine, reclining with the trunk flexed at 70°, sitting upright, and standing.
Results: The mean frontal plane QRS axis recorded in the supine and standing positions was comparable. The reclining and sitting ECG show a significant variation of the mean QRS axis as compared to the supine position. The T-wave axis was found to be comparable in the supine and standing positions. The corrected QT (QTc) interval showed a significant change with a change in the body position from supine to standing.
Conclusion: All the subjects showed similar ECG changes, but differences in the magnitude of the changes with change in body position. The change in the QTc interval with standing needs to be explored.
Keywords: Body position, electrocardiogram, posture changes
|How to cite this article:|
Khare S, Chawala A. Effect of change in body position on resting electrocardiogram in young healthy adults. Nig J Cardiol 2016;13:125-9
| Introduction|| |
The electrocardiogram (ECG) is commonly used for studying the electrical activity of the heart. The standard ECG is recorded using an electrocardiograph, which is a galvanometer that records potential differences between two electrodes or between one electrode and a standard reference electrode kept at "zero" potential.  The ECG is the most common investigation carried out to diagnose various conditions of the heart. These clinical conditions can range from primary abnormalities in the electrical conduction system of the heart as seen in heart blocks, abnormal electrical activity as seen in arrhythmias, altered electrical activity in the heart secondary to ischemia of the myocardium, electrolyte abnormalities, effects of drugs and toxins, and other pathological conditions with effects on the heart such as chronic obstructive pulmonary disease, pulmonary embolism, and systemic arterial hypertension. The ECG is also used extensively for monitoring patients, especially in the Intensive Care Unit and emergency room setting and in the operation theaters during surgical procedures. Various diagnostic tests such as exercise stress tests also monitor ECG changes to unmask the underlying cardiac pathologies.
The "standard" ECG is recorded in the supine position and values of various parameters which define normality are based on calculations made from supine ECG recordings. However, in certain situations, such as exercise stress testing and evaluation of syncope by the head-up tilt test, the ECG is recorded in the upright position. The same may also be necessary in patients who cannot assume the supine position due to certain conditions that require them to adopt other postures. An example of the same is patients of pulmonary edema who may benefit from a propped up position recognizing the necessity to examine the effect of body position on ECG, a few studies have been carried out in the past. Most of these studies have focused on comparing the ECG recorded in the supine with the left and right lateral positions in patients being monitored for myocardial ischemia in the intensive care setting.  While this is of great importance and relevance, it is equally important to study and quantify the nature and magnitude of changes seen in the ECG with change of posture from supine to upright in healthy individuals. These changes, if any, would be vital to the interpretation of ECG recorded in the upright position as during exercise stress tests and head-up tilt test for evaluation of syncope. It would also provide an insight into the feasibility of recording the ECG in the seated position in patients being examined in the outpatient department of hospitals. The present study was carried out to describe and quantify the changes in the ECG in terms of the mean electrical axis, amplitude of wave forms, the various intervals and segments on change of posture from supine to upright in healthy adults, and to explore the feasibility of recording ECG in positions other than supine for routine clinical practice.
| Materials and methods|| |
The study was conducted on 30 randomly selected healthy nonsmoking male and female subjects in the age group of 18-25 years.
- Age 18-25 years
- No history of any cardiorespiratory disease in the past.
- History of cardiorespiratory illness in the past
- History of current medication.
Subjects reported to the laboratory between 1500 and 1700 h on the day of the study. It was ensured that all subjects were at least 2 h postprandial.
Recording of electrocardiogram
Subjects were allowed to rest in the supine position for at least 15 min following which the ECG was recorded in the following postures using Philips Page Writer Trim I Cardiograph ECG machine:
ECG was recorded using a standard electrocardiograph. A record of frontal plane leads was obtained (I, II, III, aVR, aVL, and aVF). The sequence of recording of the four ECGs was randomized for subjects to remove any bias.
- Seated upright
- Supine with trunk flexed 70° head up (reclining)
- Standing upright.
Data storage and analysis
The ECGs were analyzed by an individual blinded to the procedure/position of the subject.
The following parameters were studied:
The data were stored on a data sheet created using MS Excel and statistically analyzed using the Student's t-test.
- Mean QRS vector in the frontal plane
- P-wave vector in the frontal plane
- T wave vector in the frontal plane
- Amplitude of P, QRS, and T waves
- ST segment changes
- Corrected QT interval (QTc) - (Bazett's Formula).
| Results|| |
A total of 30 subjects enrolled for the study, which included 15 males and 15 females. All the subjects were healthy and nonsmokers. The following results were recorded.
Effect of body position change on electrical axis
Effect of body position change on the mean QRS axis in the frontal plane
There was a significant change in the mean QRS axis on change of position from supine to reclining and sitting (P = 0.000 and P = 0.002). The mean QRS axis in the standing position was comparable with that in the supine position (P = 0.491).
Effect of body position change on the mean P wave axis in the frontal plane
There was a significant change in the mean P wave axis on change of position from supine to reclining and sitting (P = 0.041, P = 0.030). The mean P wave axis in the standing position was not significantly different from that in the supine position (P = 0.161).
Effect of body position change on the mean T wave axis in the frontal plane
There was a significant change in the mean T wave axis on change of position from supine to reclining and sitting (P = 0.009, P = 0.012). The mean T wave axis in the standing position was not significantly different from that in the supine position (P = 0.453) [Table 1].
Effect of body position on wave amplitudes
Effect of body position change on the mean QRS amplitude in the frontal plane
There was a significant reduction in the mean QRS amplitude on change of position from supine to reclining (P = 0.027). The sitting and standing positions had no significant effect on the mean QRS amplitude compared to the supine value (P = 0.147 and P = 0.266).
Effect of body position change on the mean P wave amplitude in the frontal plane
There was no significant reduction in the mean P wave amplitude on change of position from supine to reclining to sitting to standing (P = 0.055, P = 0.055, and P = 0.500).
Effect of body position change on the mean T-wave amplitude in the frontal plane
There was a significant reduction in the mean T wave amplitude on change of position from supine to reclining and sitting (P = 0.025 and P = 0.048). The T wave amplitude on standing was not significantly different from the supine T wave amplitude (P = 0.500).
Effect of body position change on the mean corrected QT interval
There was a significant increase in the QTc on change of body position from supine to reclining, supine to seated, and from supine to standing (P = 0.010, P = 0.000, and P = 0.000, respectively) [Table 2].
| Discussion|| |
Changes in body position are known to cause changes in the ECG mainly in the electrical axis, QRS amplitude, ST segment, and T wave. These shifts have been attributed to changes in the anatomical orientation of the heart in the chest cavity, changes in lung volume, and change of electrode contact with the skin. Sigler studied the effects of position on the QRS axis and T wave as early as in 1938. 
In another study in 1970, Dougherty examined the isolated effects of anatomical shifts of the heart with changes in the electrical axis.  He concluded that each degree of anatomical shift of the heart coincided with 3° of change in the electrical axis.
Norgard studied the vector cardiogram in 21 subjects for differences in the QRS complex and magnitude of ST-T changes with body position changes.  The results show that both measures are rather sensitive to body position changes, especially to changes to the left lateral position. The authors conclude that automated monitoring algorithms have a limited value as long as these are not used in combination with a detector of body position changes.
Adams and Drew studied this phenomenon in 22 healthy subjects and 18 subjects with heart disease.  The ECG was monitored in the supine, right, and left lateral positions. Seventy percent of their subjects showed changes in the QRS complex morphology with changes in position, while 6 out of the 40 subjects showed ST segment deviations of more than 1 mm. The study concluded that the right and left lateral positions cause significant clinical changes in the ECG and that positional ST segment changes were lesser than reported earlier. In another study on 160 patients admitted to the Coronary Care Unit and undergoing continuous ECG monitoring, it was found that only 14% showed significant changes in the form of QRS axis shifts, ST segment elevations, and T wave inversions with change in body position from supine to left lateral to upright. 
A more recent study on 75 healthy volunteers in whom a standard 12 lead ECG was recorded in three different body positions, supine, semi-recumbent, and upright, found that out of the 75 subjects, 9% showed features of myocardial ischemia on supine ECG, and 12% each on semi-reclined and upright ECG recording. ST segment elevation myocardial infarction pattern was seen in 3% each of recordings in the supine, semi-recumbent, and upright ECG. The authors conclude that changes in body position result in ischemic variations in the standard 12 lead ECG. 
The present study recorded the ECG using frontal plane leads in four different body positions, supine, reclining 70° head-up, sitting upright, and standing in 30 healthy adult subjects with a mean age of 19.7 ± 0.9 years. Fifteen of the subjects were females and 15 were male. Effects of the different body positions on the mean QRS axis, P wave axis, and T wave axis in the frontal plane were analyzed and correlation between anthropometric variables and ECG changes with body position were investigated.
The mean frontal plane QRS axis recorded in the supine and standing positions was comparable and no notable effect of a change in body position was noticed. The standing position is expected to result in a rightward shift of the QRS axis due to descent of the diaphragm and change in the anatomical position of the heart. Sigler noticed shifts in the mean QRS axis in only 20 of the 31 subjects studied, implying that a fairly large number of subjects may not demonstrate QRS axis shits on change of position from supine to standing.  Interestingly, it has also been reported that QRS axis shifts often do not correspond to anatomical shifts of the heart. From a clinical perspective, this finding indicates that ECG recordings in the standing position, as during exercise stress testing, may not be very different from supine ECGs in terms of the mean QRS axis. A similar conclusion was reached by Madias in a study on 10 healthy volunteers. 
The reclining and sitting ECGs show significant variation of the mean QRS axis as compared to the supine position and implies that such recordings may lead to spurious interpretation. Interestingly, the QRS axis in the sitting position was found to be relatively leftward placed compared to the standing position, though both the positions were accompanied by an upright trunk. A possible factor that might account for this difference may be the difference in position of the diaphragm and the role of the musculature of the anterior abdominal wall. Another possibility might be differences in the preload of the heart in the two positions. Analysis of the anthropometric data suggests that the waist circumference appears to have a bearing on the orientation of the QRS axis, especially in the reclining and seated position. A greater waist circumference appears to be related to a more leftward oriented QRS axis. This finding is interesting and merits further exploration. The correlation of body mass index (BMI) and mean QRS axis orientation is also interesting. A raised BMI appears to be associated with a relatively leftward oriented mean QRS axis.
P wave axis
The P wave axis in the standing and supine position were not significantly different, though the reclining and seated position caused significant changes in the orientation of the P wave axis compared to the supine position. P wave axis shifts are known to be larger, more variable, and poorly correlated with QRS axis shifts. It has been suggested that since the atria are tethered to the great vessels, the freedom of movement is relatively less as compared to the ventricles, which may account for a lack of correlation with shifts of the QRS axis.  In addition, Boineau et al., have reported that the location of the sinus node pacemaker shifts with changes in the heart rate.  Since body position changes from supine to upright are associated with changes in heart rate, this fact may also influence the P wave axis. An additional fact that needs to be borne in mind is that since the P waves are of relatively lower amplitude compared to the QRS complex, calculation errors are more likely when calculating P wave axes. In terms of correlation with anthropometric variables, the P wave axis appears to have no correlation with the standing height in any of the body positions studied. Correlations between the chest and abdominal circumference and P wave axis in different body positions were also inconsistent. Greater waist circumference appears to favor a rightward orientation of the P wave axis in contrast to a leftward orientation of the QRS axis. The significance of this association is not readily apparent and requires confirmation.
T wave axis
The T wave axis is usually similarly directed as the mean QRS axis and is generally not interpreted in isolation, but in association with the QRS axis. The T wave axis was found to be comparable in the supine and standing positions. The effect of anthropometric variables on the T wave axis was found to be inconsistent. Posture has been thought to result in changes in cardiac repolarization. However, this conclusion has been made on the basis of measurement of the QT interval, and effect of body position on T wave axis has not been studied in detail. It is likely that in the event of their emergence, a significant correlation between anthropometric variables such as the waist circumference and mean QRS axis, the possibility of there being similar changes with the T wave axis would also exist.
There was no significant difference in the P, QRS, and T wave amplitudes between the supine and standing position. This is consistent with earlier reports and only reinforces the fact that standing ECG recordings can be safely done for monitoring patients during exercise stress tests. Wave amplitudes during the reclining and sitting positions were significantly different from the supine value. This may lead to misinterpretation of the ECG and should be avoided.
Corrected QT interval
The QTc interval (Bazett's) showed a significant change with a change in body position from supine to standing. This change in body position is associated with a compensatory tachycardia leading to a shortening of the QT interval. However, when corrected for heart rate using the Bazett's formula, the QTc was not found to remain the same with change in body position. This seems to suggest alterations in cardiac repolarization with a change in posture from supine to standing. A similar finding has been reported by Williams et al., who have also suggested that this simple measurement may be a useful tool to evaluate drug-induced QT alterations.  This fact needs to be kept in mind when interpreting standing ECG recordings. Whether such alterations in cardiac repolarization can explain the observed changes in the T wave axis with change in body position need to be explored.
| Conclusion|| |
A change in the body position from supine to sitting and standing results in changes in the ECG. These changes manifest in changes in the mean QRS, P wave, and T wave axis recorded in the frontal plane as well as changes in the amplitude of the P, QRS, and T wave forms. ECG recordings in the supine and standing positions are comparable with insignificant differences. The ECG recorded in the reclining and sitting position is significantly different from the supine and standing ECG and should not be used for clinical purposes. The QTc interval shows a significant increase in the standing position compared to the supine position and suggests changes in cardiac repolarization with assumption of the standing position.
The authors thank the Technical Department of Armed Forces Medical College.
Financial support and sponsorship
Funded by Indian Council of Medical Research.
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]