Cardiovascular changes in pregnancy

Physiological changes during pregnancy.

1. CARDIOVASCULAR CHANGES IN PREGNANCY Dr.Nishant K. Thakur MD Obstetrics & Gynaecology

2. ANATOMICAL CHANGES Change in cardiac radiographic outline that occurs in pregnancy. The blue lines represent the relations between the heart and thorax in the non pregnant woman, and the black lines represent the conditions existing in pregnancy. Heart is pushed upward and outward with slight rotation to left due to elevation of the diaphragm consequent to the enlarged uterus.

3. Pregnant women normally have some degree of benign pericardial effusion, which may increase the cardiac silhouette.

4. Abnormal clinical findings: Palpitation Apex beat is shifted to the 4th intercostal space about 2.5 cm outside the midclavicular line. Resting pulse rate increases approximately 10 beats/min. A systolic murmur(apical or pulmonary area-due to decreased blood viscosity and torsion of the great vessels) A continuous hissing murmur (tricuspid area in the left second and third intercostal spaces called the “mammary murmur-due to increased blood flow through the internal mammary vessels)

5. Doppler echocardiography shows an increase in the left ventricular end diastolic diameters The left and right atrial diameters also increase. A third heart sound (S3) due to rapid diastolic filling and rarely a fourth heart sound may be auscultated. ECG reveals normal pattern except evidences of left axis deviation.

6. CARDIAC OUTPUT: CO = SV × HR starts to increase from 5th week of pregnancy and reaches its peak 40–50% at about 30–34 weeks. Thereafter the CO remains static till term. CO is lowest in the sitting or supine position and highest in the right or left lateral or knee chest position. Cardiac output increases further during labor (+50%) and immediately following delivery (+70%) over the pre-labor values.

7. Overall maximum CO is seen immediately after delivery> 2 nd stage of labor> late 1 st stage of labor> 28-32 weeks > early 1 st stage of labor.

8. Affect of maternal posture in hemodynamics

9. MAP also rises. CO returns to pre-labor values by 1 hour following delivery and to the pre-pregnant level by another 4 weeks time. The increase in CO is caused by: Increased blood volume. To meet the additional O2 required due to increased metabolic activity during pregnancy The increase in CO is chiefly affected by increase in stroke volume and increase in pulse rate.

10. BLOOD PRESSURE: Maternal BP (BP = CO × SVR) Systemic vascular resistance (SVR) decreases (–21%) due to smooth muscle relaxing effect of progesterone, NO, prostaglandins or ANP. In spite of the large increase in cardiac output, the maternal BP decreases. Maximum decrease in BP is seen in second trimester. There is overall decrease in diastolic blood pressure (BP) and mean arterial pressure (MAP) by 5–10 mm Hg.

11. Sequential changes in blood pressure throughout pregnancy in supine(blue) and in left lateral recumbent(red) position.

12. VENOUS PRESSURE: Antecubital venous pressure remains unaffected . Femoral venous pressure is markedly raised especially in the later months(It is due to pressure exerted by the gravid uterus on the common iliac veins, more on the right side due to dextrorotation of the uterus). venous pressure is raised from 8–10 cm of water in nonpregnant state to about 25 cm of water during pregnancy in lying down position and to about 80–100 cm of water in standing position.

13. In pregnancy, there is no significant change in CVP, MAP and PCWP although there is increase in blood volume, cardiac output and heart rate. The reasons are: there is significant fall in SVR, pulmonary vascular resistance (PVR) and colloidal osmotic pressure.

14. SUPINE HYPOTENSION SYNDROME (POSTURAL HYPOTENSION): During late pregnancy, the gravid uterus produces a compression effect on the inferior vena cava when the patient is in supine position. This, however, results in opening up of the collateral circulation by means of paravertebral and azygos veins. In some cases (10%), when the collateral circulation fails to open up, the venous return of the heart may be seriously curtailed. This results in production of hypotension, tachycardia and syncope.

15. Uterine blood flow is increased from 50 mL/min in nonpregnant state to about 750 mL near term. In a normal pregnancy, vascular system becomes refractory to angiotensin II, endothelin I and other pressure agents. Pulmonary blood flow (normal 6,000 mL/min) is increased by 2,500 mL/min. Renal blood flow (normal 800 mL) increases by 400 mL/min at 16th week and remains at this level till term. The blood flow through the skin and mucous membranes reaches a maximum of 500 mL/min by 36th week. Heat sensation, sweating or stuffy nose complained by the pregnant women can be explained by the increased blood flow.