European Journal of Cardiovascular Medicine

Pregnancy is a physiological situation characterized by significant hemodynamic changes that might cause symptoms and signs that resemble cardiovascular diseases. These hemodynamic adjustments often begin in the first trimester and progress to 50% or higher in the second and third trimesters. Hemodynamic alterations include increased blood volume, cardiac output, and reduced systemic vascular resistance (SVR) and vascular reactivity. ^{1 The} heart rate (HR) rises by 25% due to increased adrenergic activity. Preload increases as circulation volume increases, and afterload lowers as SVR decreases, all of which improve cardiac output.²

Pregnancy causes the uterus to expand, which increases the size of the cardiac silhouette. This, along with hemodynamic changes brought on by pregnancy, can cause various changes in the ECG, which should be taken into account when interpreting the ECG to prevent mistakes.^3,4 An electrocardiogram is a visual representation of the summated action potentials produced in the heart muscle using metal electrodes applied to the body and a moving piece of paper⁵. The interpretation of an ECG is an important part of the evaluation of cardiac disease.

Arrhythmias are a common occurrence during pregnancy, affecting both women with structurally normal and defective hearts, with or without pre-existing arrhythmias, and including those with congenital cardiac disorders. ^[6-8] Women with congenital cardiac disease, structural heart disease, and previous arrhythmias have the highest risk of acquiring the condition. ^[6-8] They may, however, experience these symptoms and signs for the first time during pregnancy. ^[7]

Several hemodynamic changes occur during normal pregnancy, such as increased blood volume and cardiac output, decreased systemic vascular resistance (SVR), and blood pressure. Heart rate (HR) rises by 25% as adrenergic activity increases. Preload increases as circulation volume grows, but afterload lowers as SVR drops. ^[9] All of these things improve cardiac output. Hormonal alterations include elevated estrogen, beta-human chorionic gonadotropin, and adrenergic activity. Autonomic activity, particularly sympathetic activity, increases.

Electrocardiographic abnormalities found during pregnancy include sinus tachycardia, left axis deviation, ectopic beats, inverted or flattened 'T' waves, 'Q' waves in lead III, QT interval extension, and PR interval decrease. Therefore, it is very important to understand the cardiovascular modifications during normal pregnancy. This helps to establish a point of comparison when pathological issues emerge during pregnancy.¹⁰ Cardiovascular disorders are the leading indirect cause of maternal mortality overall.¹¹ As a result, the study's goal is to examine changes in cardiac electrical activity across all three trimesters of a normal pregnancy and compare them to non-pregnant women.

OBJECTIVES

1. To study the various electrocardiogram changes in normal pregnant women aged 18-35 years.
2. To detect any deviation from the normal physiologic changes during pregnancy.

Study Design: Institutional-based cross-sectional study.

Study area: The study was conducted in the Department of Physiology and OBG, Government Medical College, Kadapa, Andhra Pradesh.

Study Period: 15 months from January 2017 to June 2018.  

Study population: Subjects attending Antenatal clinics and Non-pregnant subjects attending to female medical O.P. Department in the age group of 18-35 years.

Sample size: The study consisted of a total of 200 subjects. (pregnant – 150 and non–pregnant – 50)

Sampling Technique:  Simple Random technique.

Inclusion Criteria:  

1. Non-pregnant women – included 50 cases in the age group of 18-35 years.
2. Pregnant women – 1st trimester

- 2nd trimester

- 3rd trimester

Exclusion Criteria:  

1. Pregnancy-induced Hypertension
2. Anemias
3. Pregnancy included diabetes (Gastetional diabetes)
4. Pre-eclamptic Toxemia
5. Heart disease complicating pregnancy
6. Associated Medical disorders
7. Patients under medication.

Ethical consideration: Institutional Ethical committee permission was taken before the commencement of the study.

Study tools and Data collection procedure:

INSTRUMENT USED ELECTRO-CARDIOGRAPHIC MACHINE:

The instrument used to record electrocardiographs is Bene Heart R3/Bene Heart R3A. The salient features are –

1. Real-time ECG recording.
2. Built-in rechargeable lithium-ion battery for mains independent use.
3. Printing the ECG on 50-mm paper using a quality thermal printer.
4. Compact design and low weight for portability.
5. Auto power off.
6. DF protection.
7. Lead OFF detection.
8. Thermal paper - In rolls: Roll – 80mm X 20m, 200 pcs
9. Recording system - Thermal printer, 8 dots/mm built-in thermal

recorder, 8 dots/mm – vertical, 32 dots/mm – Horizontal.

10. Print width - 40 mm
11. Paper transport speed - 25 or 50mm/sec – 5mm /s, 12.5mm/s, 25mm/sec, 50mm/s
12. ECG recording - Real-time acquisition and printing of selected lead.
13. Filters - Digital linear phase mains interference cum muscle tremor filter (22Hz-3db).
14. Keyboard - Rubber keypad with 7 function keys and 16 LED function indicators height x length x width x 260 mm x 194mm x 56mm
15. Dimension - 325 mm x 210 mm x 90 mm (including handle) (Length x width x height)
16. Weight - < 1.28 Kg.

STANDARD ACCESSORIES:

1. Patient Cable.
2. Earth Cable.
3. Chest electrodes which are six in number.
4. Limb electrodes for the upper and lower limbs.
5. Gel Bottle
6. Paper Roll for recording the ECG
7. Power card (Manual).

Paper Roll Electrocardiographic Sheet:

The electrocardiographic recording paper is divided into small and large squares. The small squares are 1 mm square. The large squares are 5 mm square. The squares form a grid that facilitates the measurement of (i) time parameters (horizontal measurement) and (ii) deflexion amplitudes (vertical measurement). In the clinical context, the electrocardiogram is nearly always conventionally recorded at a paper speed of 25mm per second. At this paper speed, five large squares represent one second, and one large square represents 0.04 or 1/25 of a second. Most graph papers used for the recording of electrocardiograms have a fresh fifteenth large square (three seconds) marked by a vertical line on the upper border. This facilitates the quick assessment of heart rate. 

 Statistical analysis:

Data were entered in an MS Excel spreadsheet and validated and analyzed using SPSS v20. 0. Incidence was calculated from data. Chi-square was used to analyze variables. All the p-values less than 0.05 were considered statistically significant.

TABLE 1: DISTRIBUTION OF AGE GROUP IN DIFFERENT TRIMESTERS OF PREGNANT AND NON-PREGNANT WOMEN

NP: Non-pregnant: FT: First Trimester, MT: Mid Trimester, TT: Third Trimester

TABLE 2: DISTRIBUTION OF HEART RATE IN DIFFERENT TRIMESTERS OF PREGNANT AND NON-PREGNANT WOMEN

TABLE 3: DISTRIBUTION OF PR INTERVAL IN DIFFERENT TRIMESTERS OF PREGNANT AND NON-PREGNANT WOMEN

TABLE 4: DISTRIBUTION OF QRS COMPLEX DURATION IN DIFFERENT TRIMESTERS OF PREGNANT AND NON-PREGNANT WOMEN

TABLE 5: DISTRIBUTION OF QT INTERVAL IN DIFFERENT TRIMESTERS OF PREGNANT AND NON-PREGNANT WOMEN

TABLE 6:  DISTRIBUTION OF QTC INTERVAL IN DIFFERENT TRIMESTERS OF PREGNANT AND NON-PREGNANT WOMEN

TABLE 7: DISTRIBUTION OF T WAVE INVERSION IN V2 IN DIFFERENT TRIMESTERS OF PREGNANT AND NON-PREGNANT WOMEN

TABLE 8: DISTRIBUTION OF T WAVE INVERSION IN LEAD III IN DIFFERENT TRIMESTERS OF PREGNANT AND NON-PREGNANT WOMEN

TABLE 9: DISTRIBUTION OF MEAN QRS AXIS DEVIATION IN DIFFERENT TRIMESTERS OF PREGNANT AND NON-PREGNANT WOMEN

The average age was 26.28 ± 1.29 years with a P value of less than 0.01. This correlates with the study conducted by Beeram Sumalatha et al.¹² which conducted a study with 151 pregnant women. The average age was 23.38 ± 3.49 years. Out of that 12 (7.94%) were in the first trimester, 48 (31.78%) were in the second trimester, and 91 (60.26%) were in the third trimester. The study conducted by Valivety Uma et al.¹³ also showed similar results which support the present study.

There is a significant increase in mean heart rate from 1st trimester to 3rd trimester. There is an increase in heart rate from a mean of 84 ± 13 beats per minute in non-pregnant women, 93± 11 bpm in the 1st trimester, 106 ± 10 bpm in the 2nd trimester and 110 ± 10bpm in the 3rd trimester, with a p-value of less than 0.00001 which correlates with the study of Venkatachalam Madras et al.¹⁴ which conducted a study on 200 women, among them 50 were non-pregnant, 50 women each in 1st, 2nd and 3rd trimester of pregnancy. There is a statistically significant increase in mean heart rate. The mean of 76.01 was seen in non-pregnant women, 82.08 bpm was seen in the 1st trimester, 89.12 bpm in the 2nd trimester and 95.75 bpm in the 3rd trimester respectively. This study also correlates with the study conducted by Palaparthi Lissie et al.¹⁵ A total of 150 subjects were taken (50 control and 100 pregnant women) in the 2nd and 3rd trimester. There was an increase in the heart rate of 87.3 during 2nd trimester and 94.3 in the 3rd trimester with a p-value of less than 0.0001.

Regarding the distribution of PR interval among non-pregnant and three different trimesters of pregnant women, with a mean of 0.14 seconds in the non-pregnant group, 0.125 seconds in the 1st trimester, 0.129 seconds in the 2nd trimester and 0.121 sec in the 3rd-trimester group, with a p-value of 0.016 this is statistically significant. This study correlates with the study of Venkatachalam Madras et al.¹⁴ According to their study, there was a mean value of 0.142 sec in non-pregnant, 0.13 sec in 1st trimester, 0.13 sec in 2nd trimester and 0.124 sec in 3rd trimester with a p-value of 0.0001.

The present study also correlates with the study conducted by Sharad Kole et al.¹⁶ The study included a total of 193 pregnant women and 30 same-aged non-pregnant women taken as controls. Their study showed a mean PR interval of 0.143 ± 0.03 in controls, 0.143 ± 0.02 in 1st trimester, 0.126 ± 0.02 in 2nd trimester and 0.12± 0.01 in 3rd trimester with a p-value of0.000. The present study also correlates with the study conducted by Sonam Choudary et al.¹⁷, which conducted a study on 60 pregnant women in 3rd trimester, which showed a mean value of PR interval as 0.12 ± 0.01 sec in 3rd trimester and a value of 0.14 ± 0.01 sec in controls with a p-value of 0.00.

The distribution of QT interval duration among non-pregnant and three different trimesters of pregnant women, with a mean duration of 0.36 ± 0.03 sec in non-pregnant, 0.33± 0.02 sec in 1st trimester, 0.34 ± 0.02 sec in 2nd trimester and 0.33 ± 0.02 sec in 3rd trimester, with a p-value of less than 0.01. This study correlates with the study conducted by Revathi M et al.¹⁸ which included a total of 90 subjects, 30 were non-pregnant and 60 were pregnant, which included early and late pregnancy. Their study showed a mean QT interval of 0.36 ± 0.01 in the controls, 0.34 ± 0.03 in early pregnancy and 0.33 ± 0.02 in the late pregnancy with a p-value of less than 0.001.

This study also correlates with the study of Sonam Choudary et al.¹⁷ who conducted a study on 60, 3rd trimester pregnant women and 60 non-pregnant women of the same age group. The mean QT interval of the non-pregnant group was 0.35± 0.18 sec and in pregnant women, it was 0.36 ± 0.03 sec with a p-value of 0.03. The present study also correlates with the study conducted by Valivety Uma et al.¹³, they conducted a study on 200 subjects of which 100 were pregnant in the 3rd trimester and 100 were non-pregnant. Their study showed a mean of 0.33± 0.02 in the controls and 0.35 ± 0.04 sec in the 3rd trimester with a p-value of 0.0003.

T- Wave Inversion in Lead III: This is seen in 18 % of the subjects with a p-value of 0.04 which is statistically significant and correlates with the study of Venkatachalam Madras et al.¹⁴, according to a study conducted by a total of 200 women with 50 non-pregnant, 50 pregnant women each in 1st, 2nd and 3rd trimester. T Wave inversion in lead III was found in 20% of the women with a p-value of 0.0001 which was statistically significant.

The mean QRS duration distribution with a mean of 0.08 ± 0.01 in the non-pregnant group, 0.07 ± 0.008 in 1st trimester, 0.08 ± 0.009 in 2nd trimester, 0.07 ± 0.008 in 3rd trimester with a p-value of0.30 which is not statistically significant with the studies conducted. Valivety Uma et al.¹³ conducted similar studies, which showed the p values of QRS duration as 0.68, which was not statistically significant. The studies by Sumalatha B. et al.¹² also showed the results of QRS duration which was not statistically significant in all three trimesters of pregnancy. The studies conducted by Sonam Choudary et al.¹⁷ also showed the mean QRS duration in the third trimester as 0.08 ± 0.16 sec. and 0.08 ± 0.00 sec. in controls with a p-value of 0.06 which was not statistically significant. The studies conducted by Palaparthi Lissie et al.¹⁵ included a total of 150 subjects of which 50 were controls and 100 were pregnant women aged between 20- 30 years. Their studies showed a mean value of 0.08 ± 0.01 in the 2nd trimester and 0.08 ± 0.01 in the 3rd trimester with a p-value of1.00 which was statistically insignificant. My studies also correlate with their studies.

The   T wave inversion in V2 was seen in 26% of the subjects in the non-pregnant group, it was seen in 28% of the pregnant women in 1st trimester, 32% of pregnant women in 2nd trimester and 44% of pregnant women in 3rd trimester with a p-value of<0.217 which is statistically not significant. Similar studies were conducted by Venkachalam Madras et al.¹⁴ who showed a value of 4% of T wave in version in V2 in non-pregnant women, 20% of pregnant women in 1st trimester, 24% of pregnant women in 2nd trimester and 40% in the 3rd trimester with a p-value of0.0008 in the 1st trimester, 0.0001 in the 2nd trimester and 0.0001 in the 3rd trimester. The present study does not correlate with their study.

T wave in the version in lead III was seen in 12% of non-pregnant women, 18% of pregnant women in 1st trimester, 33% of pregnant women in 2nd trimester, 40% of pregnant women in 3rd trimester, with a p-value of0.048 which was statistically significant and correlates with the study conducted by Venkachalam Madras et al.¹⁴ Here 2% of the non-pregnant women showed the T wave in the version in the lead III, 18% of pregnant women in 1st trimester, 20% of pregnant women in 2nd trimester and 20% of pregnant women in 3rd trimester, with a p-value of 0.0002 in the 1st trimester, 0.0001 in the 2nd trimester and 0.0001 in the 3rd trimester. The present study correlates with the above study.

Regarding the distribution of QRS axis deviation in non-pregnant women and different trimesters of pregnant women, QRS axis deviation is not seen in control non-pregnant women. The deviation is not present even during the 1st & 2nd trimesters but during the 3rd trimester, there was a left axis deviation in 18 (36%) subjects out of 50 pregnant women, with a p-value of less than 0.01 which is statistically significant and correlates with the studies conducted by Venkatachalam Madras et al.¹⁴ who studied a group consisting of 200 subjects of which 50 were non pregnant women and 150 were pregnant with 50 subjects each in the three trimesters. The mean values were 64.4 ± 5.6 in non-pregnant women, 60.7 ± 3.4 with a p-value of0.0001 in the 1st trimester, 56.2±1.1 with a p-value of0.0001 in the 2nd trimester and 45.2±12.4 with a p-value of 0.0001 in the 3rd trimester. The present study correlates with the above study. Similar studies were conducted by Valivety Uma et al.¹³ Who included a study group of 200 subjects aged between 18 -35 years and 100 pregnant women in 3rd trimester. Their study showed mean values of 45.64 ± 15.51 in the controls and 51±17.9 with a p-value of 0.04. The present study correlates with the above study. Similar studies were conducted by Sonam Choudary et al.¹⁷ who showed a mean value of 36.68 ± 21.44 in the 3rd trimester, and 66.45 ± 12.80 in the controls with a p-value of 0.00. The present study correlates with the above studies.

From our study, it can be concluded that ECG alterations found during pregnancy include sinus tachycardia, left axis deviation, ectopic beats, inverted or flattened T-waves, and Q-waves in lead ll. The QT interval may increase during pregnancy. A prolonged QT interval may result in serious cardiac arrhythmias that cause syncope or death.

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