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 Table of Contents  
ORIGINAL ARTICLE
Year : 2015  |  Volume : 5  |  Issue : 2  |  Page : 73-77

Incidence of electrocardiographic changes indicating myocardial ischemia during cesarean sections under spinal anesthesia


Department of Anaesthesiology and Critical Care, Sarojini Naidu Medical College, Agra, Uttar Pradesh, India

Date of Web Publication11-Sep-2015

Correspondence Address:
Dr. Uma Srivastava
Flat no. 2b2, Bagla Kunj Apartments, Delhi Gate, Agra - 282 002, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2249-4472.165133

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  Abstract 

Objective: Electrocardiographic (ECG) changes and chest symptoms suggestive of myocardial ischemia have been reported in healthy women during cesarean section under regional anesthesia. This study aimed to determine the incidence of ECG changes and find any relation between the changes and subjective chest symptoms, hemodynamic variables, oxytocin, and ephedrine administration.
Materials and Methods: ECG changes were recorded in 237 term parturients during elective cesarean section done under spinal anesthesia. ST-T depression of ≥1 mm and elevation of ≥2 mm for at least 1-min were considered as significant. Timing of hypotension, bradycardia, tachycardia, ECG changes, and chest symptoms were recorded. Pearson correlation coefficient was used to determine the association between ST changes and subjective chest symptoms, hemodynamic variables, oxytocin, or ephedrine administration.
Results: Of 237 patients, 71 (30%) had significant ST-T depression, and 83 (35%) complained of chest symptoms (pressure, squeezing, pain, or dyspnea). Of 71, 42 had chest symptoms. Chest symptoms were also experienced by 30 (18%) patients where no change in ECG was seen (166/237). The changes were more commonly noted at delivery or 3-10 min after oxytocin administration. No correlation was found between ECG changes and chest symptoms, hemodynamic variables, and ephedrine, but there was moderate positive relation with oxytocin.
Conclusion: Chest symptoms and ECG changes consistent with myocardial ischemia were observed in about 1/3 healthy parturients during cesarean section. An association between oxytocin and ECG changes was found in half of the patients. The symptoms were short lived and required no treatment.

Keywords: Cesarean section, electrocardiographic changes, spinal anesthesia


How to cite this article:
Srivastava U, Chauhan N, Gupta V, Singh TK, Kumar A. Incidence of electrocardiographic changes indicating myocardial ischemia during cesarean sections under spinal anesthesia. J Obstet Anaesth Crit Care 2015;5:73-7

How to cite this URL:
Srivastava U, Chauhan N, Gupta V, Singh TK, Kumar A. Incidence of electrocardiographic changes indicating myocardial ischemia during cesarean sections under spinal anesthesia. J Obstet Anaesth Crit Care [serial online] 2015 [cited 2020 Nov 26];5:73-7. Available from: https://www.joacc.com/text.asp?2015/5/2/73/165133


  Introduction Top


Transient electrocardiographic (ECG) changes consistent with myocardial ischemia are not uncommon in healthy women during cesarean delivery under regional anesthesia. It has been reported that 25-60% of women have such findings. [1],[2],[3],[4],[5] Similarly, complaints of chest discomfort usually described as heaviness, pressure, tightening, squeezing and/or frank chest pain, and difficulty in breathing typical of ischemia are also common during cesarean. [1],[2],[6] Various mechanisms have been suggested for the occurrence of chest symptoms but until no definite cause has been identified. Traction on peritoneum, exteriorization of the uterus, cardiac sympathetic block, microemboli in pulmonary circulation, hyperventilation, and oxytocin administration are some of the suggested mechanisms. [2],[3],[5],[7],[8],[9],[10] Palmer et al. (1990). [1] Believed that the association of ECG changes and chest symptoms make it reasonable to speculate that the myocardial injury may be the cause.

The similarity of chest symptoms to myocardial ischemia prompted us to undertake this study on healthy women undergoing elective cesarean section under spinal anesthesia. The aim was to determine the incidence of ischemic changes and to find any correlation between these changes with subjective chest symptoms, hemodynamic changes, and oxytocin administration.


  Materials and Methods Top


After the approval from Institutional Review Board and informed written consent, 256 consecutive healthy women requiring elective cesarean section under single shot spinal anesthesia who were older than 18 years were candidates for inclusion in this study. Women with hypertension, valvular heart disease, diabetes, jaundice, asthma, or of American Society of Anesthesiologists grade > II were excluded. All the women were examined 1-day prior to surgery and each patient received tablet ranitidine 150 mg in the night before and on the morning of surgery. Blood pressure (BP), heart rate, and SpO 2 were noted before spinal block, and 12 lead ECG was also obtained. After preloading with 500 ml of Ringer Lactate, spinal block was performed at L2-L4 level with 25 gauge Quincke needle with 2-2.2 ml of 0.5% heavy bupivacaine and 25 µg of fentanyl. Immediately after spinal, patients were placed in supine position with pillow under right buttock. Surgery was allowed after adequate block. Oxygen was administered by Hudson mask at the rate of 4 L/min until delivery and readministered after delivery if needed. After delivery of the placenta, 10 units of oxytocin was given IV slowly (as our obstetric unit protocol). Further doses of oxytocin were available at the request of obstetrician in the form of slow IV infusion for the treatment of persistent uterine atony.

BP was recorded noninvasively every 2 min for first 20 min after spinal and every 15 min thereafter until end of surgery. Hypotension (systolic BP ≤90 mm Hg) was managed by increasing rate of IV infusion and by 6 mg boluses of ephedrine. Heart rate and SpO 2 were monitored continuously. Bradycardia (heart rate <50 bpm) was treated with atropine. ECG (lead II and V5) was monitored continuously until end of surgery. Monitor sounded an alarm when an ischemic event recognized, and anesthetist printed the ECG. Hemodynamic variables, timing of chest symptoms (heaviness, pressure, squeezing, or pain), timing and duration of ST segment changes, and all obstetric events were noted. ECG recordings were analyzed by a cardiologist blind to the patient population for the presence of significant ST-T segment changes. ST segment depression of 1 mm and elevation of 2 mm for at least 1 min duration was considered significant. Intraoperative ECG was compared with baseline tracing.

All statistical calculations were done using SPSS 20.0 for Windows (IBM SPSS Statistics. 20.0). Continuous variables are presented as mean ± standard deviation, and ordinal data are presented as count and percentage. Analysis of variance or Student's t-test was used to compare means. Pearson product-moment coefficient of correlation was used to determine the correlation between ST segment changes and hypotension, tachycardia, bradycardia, oxytocin, and ephedrine use.


  Results Top


The study was done on 256 patients, but data of only 237 patients were analyzed due to protocol deviation such as supplementation needed due to inadequate block, failed spinal, and loss of data.

On the basis of ST segment changes, the patients were distributed in two groups: Those with significant changes (n = 71) and those with no changes (n = 166). The analysis revealed no difference in demographic and other preoperative variables [Table 1]. Risk factors (family history of coronary artery disease) were positive in 14 patients (6 with ST changes and 8 without changes). Postspinal hypotension was noted in 69% (164/237) of patients, and the incidence was not different among two groups of patients [Table 1]. Ephedrine was required in similar proportion in both the groups. No difference existed in the median dose of ephedrine in both groups. Hemodynamic variables are shown in [Table 2]. Mean values at each point during surgery from group of patients, in whom ECG changes were recorded, are compared with group of patients in whom ECG remained unchanged. Mean heart rate was higher at the time of delivery and up to 3-10 min after delivery in patients with ST changes than in those with no ST changes (P < 0.05) [Table 2]. There was no difference in mean systolic and diastolic BP at the time of delivery or later. ST segment depression was evident in 71 of 237 (30%) patients and chest symptoms were experienced by 83/237 (35%) [Table 1]. Squeezing, pressure, and pain were more common symptoms present in over 85% of patients. Complaints of difficulty in breathing and pain in the neck were found in 7 and 8% of patients, respectively. Of these 71, only 42 (59%) had chest symptoms with subsequent ST-T changes. One hundred and sixty-six patients had no ST segment changes and of these, 30 (18%) patients complained of chest discomfort. Patients with ST changes were further analyzed according to time of ST segment changes. The majority of the patients had changes at the time of delivery of baby (24/71) or after oxytocin (43/71) [Table 3]. Chest symptoms were also most often complained at above times [Table 3]. While analyzing the association of various variables (chest symptoms, hemodynamic parameters, oxytocin, or ephedrine administration) to ST segment changes (by Pearson product-moment coefficient of correlation), it was observed that though many patients exhibited symptoms in relation to ST changes, it was not statistically significant [Table 4]. The only significant association was found with oxytocin administration [Table 4]. It was not related to hemodynamic changes or ephedrine. ST segment elevation or T wave inversion was not seen in any patient. Morphology of ST segment depression was mainly horizontal or downsloping. Chest symptoms and ST segment depression were present for 5-20 min and did not require any treatment. The symptoms resolved, and ECG returned to baseline by the end of surgery in all patients.
Table 1: Demographic and other variables (Data are mean ± SD or number and %)


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Table 2: Haemodynamic variables in patients with ECG changes and without ECG changes


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Table 3: Timing of ECG changes and Chest symptoms


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Table 4: Correlation of ECG changes with various variables


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  Discussion Top


This study showed that myocardial ischemia type of ECG changes and subjective chest symptoms were fairly common in women during cesarean section under spinal anesthesia. We could not find any association between maternal hypotension, bradycardia, tachycardia or ephedrine usage, and subsequent findings of ST segment abnormality. But a significant association between oxytocin administration and ST segment changes was found. Hypotension was observed in 69% of women and in most women it occurred within 2-10 min after spinal block while symptoms appeared later.

Chest symptoms suggestive of myocardial ischemia were a common problem experienced by 35% of women. Although not all women who had ECG changes complained of chest symptoms, 42/71 (59%) who did, subsequently had ST depression. Chest symptoms were also experienced by 30/166 (18%) women who did not have any ECG change. Hence, it can be concluded that chest symptoms may not always be associated with ECG changes. Our results confirm the findings of other studies. [2],[3]

The majority of the studies have reported ECG changes suggestive of ischemia after delivery of the baby. [1],[2],[3],[4] Our results agree with them, and incidence reported also concurs with many reports. [2],[3] This time epoch marks the period of highest hemodynamic stress to maternal heart: Rise in preload due to feto-maternal auto-transfusion, use of oxytocic drugs and amniotic, and venous air emboli can occur at this time. [8] They all collectively can lead to transient ECG changes and symptoms similar to myocardial ischemia.

Some studies [3],[7] reported that tachycardia was a significant variable associated with ST changes suggesting the normal rate related changes in ECG. We could not find any relation between tachycardia and ST changes although heart rate was higher at the time of ST depression. In tachycardia, typical J point depression is usually observed unlike horizontal or downsloping depression of ST segment noted in our and other studies. [1],[11]

In this study, we found a significant association between ECG changes and oxytocin administration, a finding reported previously by many investigators. [9],[10],[12] Oxytocin is a vasoactive peptide that is routinely given after delivery whether vaginal or operative to initiate and maintain uterine contraction after placental delivery to prevent excessive bleeding. It is a hormone as well as receptor, and receptors are located in uterus, heart, and large vessels. [13] It has powerful vasoconstrictive effect on umbilical, uterine, and coronary vessels. Coronary artery spasm has been demonstrated after intra-coronary administration in isolated dog heart. [14] Due to direct relaxing effect on systemic vasculature, it reduces systemic vascular resistance that leads to hypotension and reflex tachycardia. [15],[16] The combination of hypotension, tachycardia, and coronary vasoconstriction can cause mismatch between oxygen supply and demand leading to myocardial ischemia even without coexisting coronary artery disease. [9],[17]

The role of ephedrine in possible genesis of ST segment changes and chest symptoms should also be considered. Mathew et al. speculated that beta receptor mediated maternal tachycardia can possibly contribute to ECG changes, but other authors [2],[3],[4] were unable to show any significant relation between peroperative ephedrine and subsequent ST changes. Median doses used to treat hypotension were similar in patients whether they had ECG changes or not. But ECG changes were also noted in women where ephedrine was not used, and statistical analysis also failed to detect any correlation.

High incidence of ECG changes in young healthy pregnant patients compels us to question that can myocardial ischemia occur in the absence of coronary artery disease and are ST changes a valid marker of ischemia? Palmer et al.[1] answer this in affirmation while Mathew et al.[2] negate despite nearly similar results in both the studies. Moran et al.[4] suggested a study of cardiac troponin as a biological marker of ischemia for revaluating ECG changes.

Many authors believe that although the subjective chest symptoms and ECG changes are frequent, they are transient, have no clinical relevance [3],[11],[18] as coronary artery disease is extremely rare in pregnant women [4],[19] with an incidence of 1 in 10,000. [19] Myocardial infarction or ischemia during pregnancy has however been reported over the years. Kulka et al. [20] reviewed 136 cases of myocardial infarction reported during pregnancy and reported that half of the patients had normal coronary vessels. This shows that peri-partum myocardial ischemia/infarction can occur even without evidence of coronary artery disease. [1],[17] Frequent episodes of ST segment depression were reported during continuous Holter monitoring per- and post-operatively with raised troponin T level in small percentage of patients. [4] Several case reports of myocardial ischemia/infarction [17],[21],[22],[23] and cardiac death in pregnant women [24] show that cardiac complication is a risk that must be considered in some parturients. [9] The mechanism that has been proposed to account for this phenomenon include coronary artery spasm, [20] pregnancy associated cardiovascular changes and hypercoagulability, [25] and surges in myocardial oxygen demand. [1] Palmar et al.[1] speculated that increased demand of oxygen by myocardium in pregnant patients along with acute hypervolemia due to prehydration plus auto-transfusion from uterus results in increased end-diastolic volume (pressure) [26] with consequent excessive oxygen demand of myocardium. Concurrently sympathectomy induced a reduction in diastolic pressure and decreased coronary perfusion impairs myocardial oxygen supply. The net effect of increased demand and decreased supply are sufficient to induce cardiac ischemia with subsequent chest symptoms and ECG changes. [1],[9] In the absence of other clear causes, this fact alone may have a significant contribution to reversible ischemic changes. [4] Sudden hypervolemia in normal patients with intact sympathetic nervous system does not lead to increased myocardial oxygen due to reflex venodilatation. [1] Risk factors for coronary artery disease in pregnant patients include family history of the atherosclerotic disease, dyslipidemia, diabetes mellitus, cigarette smoking, and previous use of oral contraceptives. [27]

The etiology of ST segment changes in healthy parturients may also be associated with anxiety states (neuro-circulatory asthenia), vagoregulatory asthenia (hyperdynamic central and peripheral circulation), hyperdynamic heart syndrome, mitral valve prolapsed or autonomic system imbalance. [3]

The design of this study had some deficiencies and limitations. One of the limitations of ECG monitoring when it comes to detect myocardial ischemia is the influence of tachycardia on ST changes. We monitored only two leads and therefore it is likely to have been some loss of sensitivity in the detection of significant changes in some patients. But we monitored lead V5 that is most sensitive in detecting ischemic changes. We could not assess biological markers in the postoperative period to confirm the myocardial injury.

Although the study design does not allow the diagnosis of myocardial ischemia to be made with certainty, given the nature of chest symptoms and ST segment changes, one can speculate that the changes could be ischemic. The exact cause is difficult to define, but the relation to oxytocin cannot be denied. Hence, if indicated, it should be used with caution and preferably as a slow infusion. [9],[28] Further investigations are warranted to determine the association of ECG changes with more objective evidence of myocardial injury. Some case reports of myocardial injury and even cardiac death indicate that cardiovascular complication is a risk that must be addressed in pregnant women. More studies with long-term follow-up are also needed to investigate any impact of intraoperative ECG changes on later life of women in terms of ischemic heart disease.


  Conclusion Top


ST-T segment changes and subjective symptoms commonly occur during cesarean section under spinal anesthesia. The exact cause of these could not be established but in many women they were observed after oxytocin administration.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

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2.
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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]


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1 Pregnancy-Associated Myocardial Infarction (PAMI) Post Elective Caesarean Section
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Heart, Lung and Circulation. 2017; 26: S90
[Pubmed] | [DOI]



 

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