Estimation of Subjective Stress in Acute Myocardial Infarction
BACKGROUND and AIMS: Mental stress is considered to be a precipitating factor in acute coronary events. We aimed to assess the association of subjective or ‘perceived’ mental stress with the occurrence of acute coronary events. SETTINGS AND DESIGN: Prospective case-control survey was carried out in a referral teaching hospital. subjects & METHODS: Consecutive patients with acute myocardial infarction and ST elevation on electrocardiogram who were admitted to the Coronary Care Unit of a referral teaching hospital were enrolled in the study as cases. Controls were unmatched and were enrolled from amongst patients with coronary artery disease who did not have recent acute coronary events. Subjective Stress Functional Classification (SS-FC) for the preceding 2-4 weeks was assessed and assigned four grades from I to IV as follows: I - baseline, II - more than usual but not affecting daily routine, III - significantly high stress affecting daily routine and IV - worst stress in life. STATISTICAL ANALYSIS: Proportions of different characteristics were compared using chi-square test with Yates continuity correction. Student’s unpaired t test was applied for mean age. ‘p’ value of < 0.05 was considered statistically significant. RESULTS: SS-FC could be reliably (99%) and easily assessed. Eighty (53%) of the total 150 patients with acute MI reported ‘high’ levels of stress (stress class III and IV). This is in contrast to only 30 (20%) of 150 healthy controls reporting high stress for the same period (p value < 0.001). CONCLUSION: Patients with acute myocardial infarction report a higher subjective mental stress during 2 to 4 weeks preceding the acute coronary event.
The impact of psychological factors in acute coronary events is only now emerging.,,,, Depression following myocardial infarction can influence long-term outcome in a manner and scale comparable to left ventricular (LV) dysfunction. Mental stress can play a vital part in plaque instability and rupture leading to doubling the frequency of acute coronary events.,
Subjective 'stress' perceived by the person can increase adrenergic output, alter the coagulation system, increase blood viscosity and promote the development of arrhythmias.,, These are postulated to contribute to the role played by psychological stress in initiating acute coronary events. Quantification of stress objectively can be done using available scoring systems but cardiologists caring for acutely ill patients are unlikely to undertake these steps in their routine practice.
In any given situation, the stress for an individual will vary dramatically based on prior life experiences, conditioning and coping skills.,, Also, research has indicated that subjective stress is an important factor in determining sympathetic output. Considering the importance of stress in precipitating an acute coronary event, we decided to study the correlation between subjective stress levels and acute coronary events. We hypothesized that physicians and cardiologists caring for acutely ill patients are more likely to address the issue of stress early in the management of cardiac illness, if the tools for assessing stress do not require a lot of time for application and if they do not involve in-depth questionnaires. Hence, instead of attempting to objectively assess stress with traditional scoring systems, we decided to perform and apply a simple functional classification of subjective stress (subjective stress-functional classification, SS-FC) akin to the functional classification provided by the New York Heart Association (NYHA-FC) for heart failure.
The study was conducted in the coronary care unit (CCU) of a large tertiary care teaching hospital after obtaining permission from the Institution's Review Board. Patients admitted to the CCU with acute myocardial infarction showing ST elevation in ECG were consecutively enrolled. Those younger than 20 years, those who were unable to comprehend and/ or react meaningfully were excluded from the study. The patients were informed about the purpose and nature of the study. They were enrolled in the study after obtaining written informed consent. Through direct questioning, the patient's subjective stress level during the 2-4 week period preceding the acute coronary event was assessed. The stress was graded as I to IV using the Subjective Stress Functional Classification (SS-FC): SS-FC I: No perceived mental stress or only basal levels, SS-FC II: More than usual but not affecting daily routine, SS-FC III: Significantly high stress affecting daily routine and SS-FC IV: Worst stress in life, occurrence of major, unexpected or life-changing events.
SS-FC I and II were considered as 'low' stress population while the higher grades were considered as 'high' stress groups. This classification of patients into different stress groups was done by direct patient interview conducted by two investigators independently within 24 hours of CCU admission. This is a novel classification of subjective stress along the familiar lines of NYHA functional classification.
In addition, patients with coronary artery disease (CAD) who presented to the cardiology outpatient department during the study period for routine follow-up were enrolled as 'controls' after obtaining informed consent. The same SS-FC test used for the study subjects was administered to the controls for the assessment of subjective stress during the preceding 2-4 week period. Proportions of different characteristics were estimated from the sample of the study groups and compared using chi-square test with Yates continuity correction. Student's unpaired t test was applied for mean age. 'P' value of < 0.05 was considered statistically significant.
One hundred and fifty patients with acute myocardial infarction and an equal number of controls were enrolled in the study.
[Table - 1] and [Table - 2] show the number of cases and controls in each level of stress. Eighty (53%) of the 150 patients with acute MI reported high levels of stress. This is in contrast to only 30 (20%) of 150 stable CAD patients reporting high stress for the same period [Figure - 1].
The risk factor profile of the study patients is compared in [Table - 3] after dividing the patients into 'low' stress (stress class I and II) and 'high' stress (class III and IV) groups to eliminate bias due to confounding cardiovascular risk factors. High stress was reported equally among men and women. Occurrence of traditional risk factors was not significantly different between the low and high stress groups although lipid abnormalities were present more often in the high stress groups.
Fifty-three per cent of patients with an acute MI had 'high' stress (SS-FC III, IV) within the month prior to the occurrence of the acute event. On the other hand, only 20% of controls reported 'high' stress. This statistically significant difference confirms the role of elevated stress in the initiation of acute coronary events. Fifteen per cent of patients with acute MI reported 'worst stress' in life (score IV). The proportion of those with score IV in the study group was significantly higher than that in the control group (5 %). The higher incidence of coronary events reported following war and earthquakes is comparable to subjects who reported stress of level IV. Most people who reported this score in our study had recently suffered unexpected financial difficulty or death/ severe illness in the family.
The incidence of traditional risk factors in our study was not significantly different amongst the various stress groups. The average age was lower in the control group and the incidence of risk factors like smoking, hypertension and diabetes was significantly lower among the controls. Nevertheless, among patients with MI, 'low' and 'high' stress groups were well matched for age and traditional risk factors.
Our study did have certain limitations. The patients were assessed only after the index event. It is possible that the patients' reporting of stress may have been influenced by the event. The investigator estimating the stress could not be blinded to the diagnosis. The subjective score is only a comparison with the individual's “baseline” stress levels months or years earlier and it varies as per personality and coping skills. The study did not include performance of objective assessment of stress. Nevertheless, this study underscores the significance of subjective stress in precipitating acute coronary events. We deliberately did not include unstable angina patients in our study primarily to avoid overlap with non-cardiac chest pain syndromes. These non-specific symptoms may occur more often with high mental stress and further confuse our results.
SS-FC is a very simple tool that could be rapidly applied to “semi-quantify” the perceived stress. As it does not involve any questionnaire or psychological examination, SS-FC can be used in acute care settings and at follow-up visits. It is known that survival post-MI can be adversely affected by depression. Patients who persist with high stress and fail to cope adequately may benefit from early referral for psychological evaluation and drug therapy. Adrenergic blockade and prevention of excess pro-coagulant activity are important strategies in the management of patients with coronary heart disease. These strategies may assume greater importance in patients with 'high stress'. Atenolol and sustained release verapamil have shown better results in stressed individuals and may be preferred over other agents in this setting.,
The discussion about mental stress in the acute care setting will result in patients identifying a possible area for future improvement. The development of better coping skills and outlook may help in post-MI recovery. This can be tested by the application of the stress score every few months and following up the patients for occurrence of major adverse cardiac events (MACE).
This scoring of stress excludes 'high-strung' and 'type A' personalities by grading stress only against the individual's baseline. Also, by confining our stress classification to the 2-4 week period before the coronary event, we effectively excluded the subset of people who have developed an adequate 'coping mechanism' which sets in typically by 3 to 6 months following adverse life events. The important role played by subjective stress in initiating coronary events is confirmed by our series.
Application of this tool in a large prospective series can help estimate the relative risk of acute coronary events attributable to subjective stress. It is worth exploring whether treating subjective stress in critically ill cardiac patients with counselling and anti-anxiety medication would reduce the incidence of MACE.
Initial assessment of subjective stress can be rapidly and reliably performed in acute care settings by medical specialists involved in patient care. A significant proportion of patients report 'high' levels of subjective stress in the 2-4 week period preceding acute coronary events. This study confirms the association of subjective stress and acute coronary events.