Myocardial infarction is decreased or complete stoppage of blood to a part of the heart muscles. The commonest cause being disease in the coronary artery (1). In 2021,

cardiovascular deaths accounted for 20.5 million deaths worldwide. There are more than half a billion people who are affected by cardiovascular diseases in the whole world. Worldwide, one-third of the deaths are due to non-communicable diseases. These include high blood pressure, unhealthy diet, high cholesterol, diabetes, air pollution, obesity, tobacco use, kidney disease, physical inactivity, harmful use of alcohol and stress (2). Non-communicable diseases like diabetes, systemic hypertension, hypercholesterolemia and metabolic syndrome attribute to cardiovascular diseases (CVD).

The 65th World Health Assembly raised to act on NCD deaths and fixed a target of 25% reduction in the premature deaths due to the non-communicable diseases by 2025 (3,4). The Disability Adjusted Life Years (DALY) due to cardiovascular diseases namely ischemic heart disease was 2.9% in 1990 and increased to 6.6% in 2016 in India.

We have planned to reduce pre-mature deaths due to non-communicable diseases by one-third in 2030 in lieu of the goals set in the Sustainable Development Goals (5,6). In India, THE prevalence of the same disease is reported in younger age groups as compared to the western World. Obstruction in the right coronary artery or the left circumflex artery which is a branch of left coronary artery is the most common cause of inferior wall myocardial infarction (IWMI) (7).

In ST elevation myocardial infarction (STEMI) chest pain is the most common presentation. “Acute Coronary Syndrome” is known as the acute chest pain arising from the heart (8). The STEMI diagnosis is dependent on the time taken to reach hospitals for Primary Percutaneous Coronary Intervention (PPCI). As per guidelines, the time delay limit in hospitals with PPCI is 60 minutes. Those who should be shifted from home or hospitals without PPCI is 120 minutes. When time limit is prolonged, it is advised to start fibrinolytic therapy within 10 minutes from the diagnosis of STEMI (9).

Evidences from published literature suggests that right ventricular function indices like Tricuspid Annular Plane Systolic Excursion (TAPSE), Myocardial Performance Index by Tissue Doppler imaging (MPI_TSI) and peak systolic velocity (Sm) are consistent to prove proximal stenosis of RCA in IWMI (10,11).

Majority of the Indian population live in rural regions and the rural urban distribution is 68.8% in rural areas and 31,2% in urban areas (12). the European Society of Cardiology’s guideline of 120 minutes for PPCI is a difficult one for most of the Indian population. The electrocardiogram for patients with inferior wall myocardial infarction portrays ST elevation in lead II, III and aVF. This displays minor changes depending on the occluded artery (8).

There is less evidence on the trends of echocardiogram in our geographical setting. There are evidences involving single or a few diagnostic parameters. Hence our study is done with the objective

1. To assess Echocardiographic parameters of right ventricle in proximal RCA lesion in patients with IWMI
2. To predict the significance of associated parameters in predicting IWMI patients with proximal RCA lesion at the very beginning.

We did a cross-sectional study in patients attending Cardiology Department, Government Medical College, Namakkal which is a tertiary care Hospital with symptoms suggestive of coronary artery syndrome with inferior wall myocardial infarction. The population of Namakkal District is 17,26,601. Convenience sampling was followed.

The patients who came to the hospital were diagnosed with Electrocardiogram (ECG).  If the arrived in less than 12 hours of infarction, we initiated thrombolysis. ECHO was done within 12 hours of patient arrival to the hospital. Coronary angiography was done 10 to 14 days post fibrinolysis. Patients were classified into proximal RCA lesion and non- proximal RCA lesion groups based on the reported findings. The study was done for eight months from July 2022 to February 2023. We evaluated the clinical characteristics of the patients. The echocardiographic parameters were also included for tabulation.

Inclusion Criteria: 1. significant RCA lesion at coronary angiography and good echocardiographic window 2.  Patients with IWMI with or without right ventricle myocardial infarction.

Exclusion Criteria: 1. candidates for primary PCI or patients with hemodynamic instability. 2. Those with significant LAD, LCX, Diffuse RCA lesion or multivessel disease. 3. Those with previous MI, cor-pulmonale, atrial fibrillation or significant valvular lesion. 4. Those with poor echo window were excluded.

Ethics Clearance: The ethics clearance was obtained from the institutional ethics committee (IEC) after clearance from the institutional scientific review committee (IRB). Information sheet was given to all the study participants and written informed consent was taken from them.

Statistical Analysis: Data was entered in MS Excel and analysis was done using SPSS 22.0.1 software (SPSS Inc., Chicago, Illinois, USA). Mean and standard deviation was used for continuous variables. Number & proportion were used for categorical variables. Alpha error was fixed as 5%. Confidence interval of 95% was used. The test of significance used for comparison were student “t” test and chi-square test.

Table 1: Patient characteristics of the patients with proximal and non-proximal right coronary artery lesion in inferior wall myocardial infarction at Department of Cardiology, Government Medical College, Namakkal.

Among the two arms, the proximal RCA lesion had 41 patients while the non-proximal RCA lesion had 36 patients. The smokers had non-proximal lesion compared to non-smokers who had proximal lesion in Right Coronary Artery and this difference is statistically significant.

Table 2: Echocardiographic parameters of the patients with proximal and non-proximal right coronary artery lesion in inferior wall myocardial infarction at Department of Cardiology, Government Medical College, Namakkal.

The peak myocardial systolic velocity (9.74±0.92 Vs 10.64 ± 1.4) and the ejection time (223±5.4 Vs 265±21.6) shows statistically significant difference between the two comparison groups.   The patients in the proximal lesion RCA group (84±8.9, 80±7.5, 0.64±0.09) have more IVRT, IVCT and MPI as compared to those in the non-proximal lesion RCA group (65±5.1, 64±7.8, 0.39±0.15) which is statistically significant.

This deals with identification of the diseased artery and initiating appropriate management to protect it from complications. The RCA is divided into three parts namely proximal, mid and distal divisions. We have categorized both mid and distal divisions as non-proximal and compared it with the proximal. The branches from the proximal part of the right coronary artery supplies the infundibulum of the right ventricle and the SA node. The marginal branch of mid RCA is used as a marker in angioplasty to identify the inferior border of the heart. The posterior descending artery and the right posterolateral artery are distal terminal branches which branch off at the crux cordis. This is a landmark in angiography (13). We will discuss the complications based on the branch providing blood supply and the level of the occlusion identified by coronary angiography.

The results of the study showed that non-smokers had more proximal lesion 31 (75.6%) in the right coronary artery as compared to smokers 10 (24.4%) which is

statistically significant. Peak systolic velocity Sm (9.74 Vs 10.64) and ejection time (223 Vs 265) were less in the proximal group while isovolumic relaxation time (84 Vs 65), isovolumic contraction time (80 Vs 64) and myocardial performance index (0.64 Vs 0.39) were more in the proximal group and the difference is statistically significant.

STEMI in the precordial chest leads help us judge the artery of concern. The occlusion of both the left anterior descending and the proximal right coronary artery show ST elevation in V1 to V3 chest leads. Patients might present with chest pain and ventricular fibrillation with STEMI in V1 to V3 and V4R in ECG. Normally, ST elevation in inferior leads is seen in RCA occlusion. There is a possibility of atrial fibrillation as well as ventricular fibrillation in myocardial infarction. Normal left ventricle ejection fraction and slight right ventricle dilatation is visualized in ECHO. Coronary angiography which is the gold standard choice needs to be done to confirm the particular arterial occlusion. PCI needs to be done to relieve the symptoms (14).

We reported patients with both arrythmia and cardiogenic shock but the difference in the presentation between proximal and non-proximal groups is not statistically significant. A prospective cohort study may be needed to validate the findings.

The right ventricle ischemia and infarction is due to decreased right ventricle contractile power. This decreases the blood flow to the lungs. The symptoms are peripheral edema, elevated jugular venous pressure, hypotension and hypoxia. The triad of hypotension, elevated JVP and clear lung fields is pathognomonic of right ventricular dysfunction. Right ventricle myocardial dysfunction or infarction in clinical practice is detected by ECHO. (15)

In-hospital mortality is noted in RVMI. It is associated with infarction in the inferior wall in 25 – 50% of the cases. Hemodynamic compromise is noted in more proximal lesions in RCA as it results in decreased RV filling and RV function (16). We reported 85% of those patients with RVMI RCA proximal lesion had cardiogenic shock indicating poor prognosis (17).

In our study, the smokers had more proximal occlusion and the difference is statistically significant. A higher sample size would have given a better association.  The risk of other behavioural patterns was not included in the study. This could bias the results.

We reported higher Troponin T value (3.91±1.71) in proximal RCA stenosis as compared to (2.85±1.4) non-proximal RCA stenosis. This could be because of the involvement of a bigger muscle mass. However, the difference is not statistically significant. The arrythmia in proximal RCA stenosis 24 (58.5%) is comparatively higher in this group. These findings are consistent with the reports in other similar studies (10,11)

ajesh et al  reported that TAPSE, Sm were less in the proximal stenosis group and MPI was more in the same group. The RV functional parameters can be used to predict RV infarction and predict RCA lesion with a good sensitivity and specificity. We could have got better results if our sample size had been more and we limited the time interval between the ECG and echocardiography. This time difference might have caused difference in TAPSE values (11).

The systolic phase is followed by immediate filling and the value is not measurable in right ventricle contraction in normal conditions (IVRT). A measurable IVRT is caused by increased end systolic right ventricle pressure. We found that the IVRT was prolonged and ET was small in patients with proximal RCA stenosis. This difference is statistically significant. This projects that higher number of patients with RVMI were present in proximal RCA stenosis as indicated by other similar studies (10).

We found that MPI was significantly higher in patients with proximal stenosis as compared to those with non-proximal stenosis. The myocardial performance index (MPI) is inclusive of the physiological function in both systolic and diastolic phase. MPI of both ventricles are higher in patients with myocardial infarction is reported in many studies (18).

Limitations:

The sample size of the study is small and if age-sex matching of the respondents in both arms could have contributed more towards association. Equal numbers in both groups should have been maintained.

The echocardiographic assessment parameters Sm, ET, IVRT, IVCT and MPI are diagnostic parameters which aid in predicting proximal right coronary artery lesion.

Recommendations:

This echocardiographic assessment can be extended to primary health care level for early diagnosis of the right coronary artery lesion and initiating prompt and early referral to save lives of many patients.

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