Cardiac performance during pregnancy: serial evaluation using external systolic time intervals

CARDIAC ARRHYTHMIAS DURING PREGNANCY: A CLINICAL APPROACH

Physiologic changes in maternal haemodynamics, hormones and autonomic properties contribute to arrhythmias in pregnancy. While arrhythmias most commonly occur in pregnant women with structural heart disease or those with a history of cardiac arrhythmias, they can also occur de novo in women with no documented cardiac disease.

Maternal left ventricular transverse and long-axis systolic function during pregnancy

OBJECTIVES

Circumferential fiber shortening has been the dominant basis for conventional analysis by echocardiography of left ventricular systolic function during pregnancy. Results in the literature have been conflicting due mainly to the fact that geometric assumptions for the calculation of these indices are made that may not be valid due to changes in left ventricular shape during pregnancy. Left ventricular long-axis displacement is expected to be a useful index of systolic function, independent of the changes in left ventricular geometry. The aim of this study was to compare circumferential to long-axis shortening during left ventricular contraction in pregnant women.

METHODS

This was a cross-sectional study of 125 pregnant women at 9-42 weeks of gestation and 19 non-pregnant female controls. Two-dimensional and M-mode echocardiography of the left ventricle was performed including measurement of left ventricular long-axis displacement and activation time on the lateral, septal, anterior and inferior sides of the mitral annulus. Activation time was assessed as the time from the start of the Q-wave of the electrocardiogram to the onset of left ventricular long-axis shortening.

RESULTS

Mean arterial pressure and activation time decreased during pregnancy, reaching a nadir at about 19 weeks' gestational age of 4% and 13%, respectively, below non-pregnant values; they subsequently increased towards term. Left ventricular long-axis displacement mirrored the changes in mean arterial pressure and activation time and increased with gestational age at all four sites of the atrioventricular plane reaching a peak at about 23 weeks (+ 12% compared to non-pregnant levels). The ejection fraction and fractional shortening remained stable until 30 and 32 weeks, respectively, and then decreased towards term.

CONCLUSION

Changes in left ventricular long-axis performance during pregnancy occur earlier than do measures of transverse function.

Novel real-time R-wave detection algorithm based on the vectorcardiogram for accurate gated magnetic resonance acquisitions

Electrocardiograph (ECG) triggered or gated magnetic resonance methods are used in many imaging applications. Therefore, a reliable trigger signal derived from to the R-wave of the ECG is essential, especially in cardiac imaging. However, currently available methods often fail mainly due to the artifacts in the ECG generated by the MR scanner itself, such as the magnetohydrodynamic effect and gradient switching noise. The purpose this study was to characterize the accuracy of selected R-wave detection algorithms in an MR environment, and to develop novel approaches to eliminate imprecise triggering. Vectorcardiograms (VCG) in 12 healthy volunteers exposed to 1.5 T magnetic field were digitized and used as a reference data set including manually corrected onsets of R-waves. To define the magnetohydrodynamic effect, the VCGs were characterized in time, frequency, and spatial domains. The selected real-time R-wave detection algorithms, and a new "target-distance" VCG-based algorithm were applied either to standard surface leads calculated from the recorded VCG or to the VCG directly. The flow related artifact was higher in amplitude than the R-wave in 28% of the investigated VCGs which yielded up to 9-16%false positive detected QRS complexes for traditional algorithms. The "target-distance" R-wave detection algorithm yielded a score of 100% for detection with 0.2% false positives and was superior to all the other selected methods. Thus, the VCG of subjects exposed to a strong magnetic field can be use to separate the magnetohydrodynamic artifact and the actual R-wave, and markedly improves the trigger accuracy in gated magnetic resonance scans. Magn Reson Med 42:361-370, 1999.

Myocardial infarction during pregnancy: management and outcome of two pregnancies

OBJECTIVE

Each year in the United States approximately 500,000 women die from ischemic heart disease. However, there are < 100 reported cases of myocardial infarction occurring during pregnancy. The current management of these patients is empiric, with pulmonary artery catheterization during labor being frequently reported.

STUDY DESIGN

In the past year we have managed and delivered two such patients, including the first reported case of myocardial infarction with a triplet gestation.

RESULTS

Both patients had clinical and laboratory signs of myocardial infarction and underwent coronary angiography. They subsequently had preeclampsia and were prematurely delivered of viable fetuses. One patient had angina pectoris during labor and was successfully treated with sublingual nitroglycerin. Neither patient suffered reinfarction or heart failure. Invasive hemodynamic monitoring was not used, and the mode of delivery was determined solely on obstetric indications.

CONCLUSION

In pregnant patients with myocardial infarction, invasive central monitoring is unnecessary in patients with good cardiac function and reserve and the mode of delivery should be based on obstetric indications.

Plasma and red blood cell beta-endorphin immunoreactivity in normal and complicated pregnancies: gestational age variation

Recent observations suggest that there may be two pools of beta-endorphin-like immunoreactivity in mammalian circulation. One of these pools is present in plasma and the other is detected in association with erythrocytes. Elucidation of an erythrocyte-associated pool may explain some of the wide variability of plasma beta-endorphin levels reported in the literature. We measured beta-endorphin immunoreactivity levels in 85 normal and 33 complicated pregnancies to delineate a possible correlation between gestational age and beta-endorphin immunoreactivity levels in plasma and in erythrocytes. Our results indicate that beta-endorphin immunoreactivity levels in both plasma and erythrocytes vary systematically throughout the gestational period, reaching a peak at 31 to 32 weeks of gestation. Amniotic fluids at midgestation were also analyzed and no correlation was observed between the levels of beta-endorphin immunoreactivity and fetal sex. Compared to normal patients, diabetic patients had significantly lower levels of beta-endorphin immunoreactivity in plasma and higher levels in erythrocytes although the total beta-endorphin immunoreactivity was not statistically different from that in normal subjects. We conclude that (1) the total beta-endorphin immunoreactivity level in whole blood is much higher than that reported in plasma, (2) both plasma- and erythrocyte-associated beta-endorphin immunoreactivity levels vary with gestational age, with a peak level at 24 to 32 weeks of gestation, (3) amniotic fluid beta-endorphin immunoreactivity levels are unrelated to fetal sex, and (4) diabetic patients may have a different distribution of beta-endorphin immunoreactivity pools than normal individuals.

A longitudinal study of cardiovascular dynamic changes throughout pregnancy

Systemic blood pressure (measured with a zero-randomized sphygmomanometer), stroke volume and heart-rate (measured with a Minnesota Impedance Cardiograph), hematocrit, and their derivatives -- cardiac output and peripheral vascular resistance--have been assessed in three groups of subjects. First, a control group of 19 nonpregnant women were matched for age and weight with the subjects in the second group, which consisted of 19 patients who were seen at regular intervals on 12 to 15 occasions from 8 to 11 wk of pregnancy until 6 wk postpartum. The third group consisted of 8 patients seen from before conception, throughout pregnancy and to several months postpartum. Readings were made with the subject in each of six positions: supine, reclining, left and right lateral, left and right tilt. This paper concerns the readings obtained in the left lateral position. The data showed that pulse rate rose throughout pregnancy. Stroke volume and cardiac output rose shortly after conception, the increase over the prepregnancy level being statistically significant by 12 wk. Thereafter both values fell throughout the rest of pregnancy and were below prepregnancy levels by about term, taking some weeks to regain the prepregnancy value. There were irregular fluctuations in the level of systolic blood pressure; diastolic blood pressure fell during the first 16 wk and then rose to reach almost the prepregnancy value by term. Peripheral resistance fell during the first trimester, then increased markedly throughout the remainder of pregnancy.

R--pulse wave timing: a technique for continuous cardiovascular monitoring in obstetrics--preliminary report

A simple, noninvasive technique for continuous cardiovascular monitoring in obstetrics using R--pulse wave timing is described. This preliminary study suggests that different maternal heart rate/R pulse patterns are found in different clinical circumstances. A significant decrease in the R pulse interval occurred in the third trimester in both normal and diabetic women in the left lateral position when compared to the supine position. The R pulse intervals were all prolonged in the standing position in both gravid and nongravid women. During labor R pulse interval usually shortened during uterine contraction. Prolongation of R pulse interval was observed during thiopental injection, hypotension, and excessive bleeding at cesarean section. Exercise testing in healthy male subjects suggested that the change in R pulse interval becomes constant when the oxygen consumption rate reaches a plateau at 100% maximal work load. Further extensive clinical study appears worthwhile since it may add another dimension to cardiovascular monitoring and give an early indication of cardiovascular reserve.

Systolic time intervals in normotensive and hypertensive human pregnancy

Systolic time intervals were measured in 10 nonpregnant, 37 normotensive, and 18 hypertensive pregnant women in both supine and lateral positions. With all the subjects in the supine position, left ventricular ejection time (LVET) was shortened; the pre-ejection period (PEP) lengthened, and the PEP/LVET ratio increased in normotensive late pregnancy compared with the nonpregnant state. Similar alterations in systolic time intervals were observed in hypertensive women in both early and late pregnancy in the supine position. In normotensive women in early pregnancy, alterations in systolic time intervals were inconclusive. When normotensive women in late pregnancy were turned from the supine into the left lateral position, a prolongation of LVET and a decrease in the PEP/LVET ratio were observed. When hypertensive women in late pregnancy adopted the left lateral position, no significant alterations in systolic time intervals occurred. Isovolumetric contraction time (ICT) was prolonged only in the hypertensive pregnant women in the supine position. The study suggests that left ventricular performance is diminished in normotensive women in late pregnancy when supine but improves when they adopt the lateral position. In addition, hypertensive pregnant women show evidence of diminished left ventricular performance which is not improved in late pregnancy by assumption of the left lateral position.