ИНДЕКС ПРОИЗВОДИТЕЛЬНОСТИ МИАКАРДА

Айрапетян Г.Г.

Доцент, кандидат медицинских наук, зав. отделениен неотложной кардиологии, Ереванский государственный медицинский университет им. М. Гераци, МЦ  “Эребуни” г. Еревана

ИНДЕКС ПРОИЗВОДИТЕЛЬНОСТИ МИАКАРДА

                                                                                                        Аннотация

В исследовании изучена роль суммарного индекса производительности миокарда обоих желудочков в сравнении с индексами левого или правого желудочков для прогнозирования ранних и поздних сердечных случаев при первичном инфаркте миокарда левого желудочка нижней локализации с элевацией сегмента ST. Показано, что суммарный индекс более надежный предиктор, чем традиционные  и отдельные и может служить критерием для выявления больных с высоким риском ближайшего и отдаленного исхода заболевания.

Ключевые слова:индекс миокарда, нижний инфаркт, прогноз

Hayrapetyan H.G.

Associate Professor, MD, Head of Urgent Cardiology Department, Yerevan State Medical University n.a. M.Heratsi, “Erebouni” MC, Yerevan, Republic of Armenia

MYOCARDIAL PERFORMANCE INDEX:  IS IT  WORTH SUMMING UP LEFT AND RIGHT INDICES IN LEFT INFERIOR STEMI?

Abstract

The study aimed to evaluate the prognostic role of combined myocardial performance index of both ventricles against left or right ventricular indeces of myocardial performance for early and late cardiac events in left ventricualar inferior primary ST-segment elevated myocardial infarction. Aggregated parameter is shown to be the stronger prognostic factor than traditional ones alone and would help identifying high-risk patients for both early and late clinical outcomes.

Keywords: myocardial performance index, left inferior STEMI, prognosos.

The Doppler-derived myocardial performance index (MPI), also known as Tei index, is a simple, noninvasive, easy to estimate and reproducible measure of combined systolic and diastolic ventricular function [1].

Left ventricular (LV) MPI has previously been shown to be a useful indicator for myocardial dysfunction in distinguishing patients with a poor in-hospital outcome, and its value is an independent predictor of cardiac events during hospitalization [2-3]. In post-infarction phase, LV MPI has shown prognostic value regarding death, heart failure, and new cardiac events [4-5]. Still, a little known about right ventriclural (RV) MPI, especially, for ischaemic heart diseases. However, a few studies reported that RV MPI can predict post-infarction heart failure [6-7].

As LV inferior ST-segment elevated myocardial infarction (SETMI) is a unique pathology when involvement of RV in acute myocardial infarction (AMI) could lead to RV dysfunction and worsen clinical outcomes  [8], it would be reasonable to assess function of not only LV, but also RV in such patients. 

The aim of this study was to test prognostic importance of a combination of LV MPI (as a measurement of LV dysfunction) and RV MPI (as that of RV dysfunction) against single LV MPI or RV MPI in patients with primary LV inferior STEMI. As specific objectives, the study evaluated abilities of LV MPI, RV MPI and the sum of LIMP and RIMP for independently predicting early (in-hospital) cardiac mortality  and cargiogenic shoks (CSh) and late (1-year) cardiac mortality and rehospitalization in population of the same patients.

Materials and Methods

Study population: We prospectively considered 273 consecutive patients (age range: 38-42; age mean 58,2±4,5 years; males: 85,5%) with newly diagnosed LV inferior STEMI who underwent Doppler myocardial imaging (DMI) at the Department of Intensive Cardiology of Erebouni Medical Centre, Yerevan in 1999-2011.

All patients were informed completely about the study.

All DMI examinations and calculations of LV and RV MPIs were performed based on Doppler time intervals with an ultrasound machine “Siemens G65” (Germany) within 24 hours of LV inferior STEMI onset. Methodology of standard 2D echocardiographic and DMI examinations was based on the American Society of Echocardiography's Guidelines [9]. The combined MPI of both ventricles (“total” MPI or tMPI) was calculated as a simple sum-up of LV and RV MPIs.

With regard to the diagnosis of LV inferior STEMI and treatment strategy, patients were treated according to the institutional AMI protocol driven by the current guidelines [10]. Based on LV MPI, RV MPI and tMPI values, all 273 patients were categorized into below presented groups:

LV MPI≥0,55 (n=145) vs. LV MPI<0,55 (n=128);

RV MPI≥0,45 (n=120) vs. RV MPI<0,45 (n=153); and

tMPI≥1,00 (n=107) vs. tMPI<1,00 (n=166).

There were no statistically significant differences between the groups regarding age and frequencies of arterial hypertension (AH), diabetes mellitus (DM), chronic obstructive pulmonal disease (COPD), RV myocardial infarction (RVMI) and primary PCI (pPCI) besides last two ones between tMPI≥1,00 vs. tMPI<1,00 which was further neutralized by logistic regression model. 

Table 1 summarizes the baseline clinical characteristics of the study population by defined groups.

For the hospital treatment period all cases of cardiac deaths and CSh and for the post-treatment one year - all cases of cardiac deaths and rehospitalization were carefully registered. No patient data was lost to 12-month follow-up.

Statistical methods: Statistical analyses were performed with a commercially available software program SPSS 17.0 (SPSS, Inc., Chicago, IL, USA). Comparisons between groups for categorical variables were performed using the χ2 (chi-square) followed by calculation of relative risks (RR). Adjusted Odds Ratios (OR_adj) were worked out to evaluate the individual prognostic importance of research parameters – LV MPI, RV MPI and tMPI via logistic regression model involving all known co-variables (age, gender, AH, DM, COPD, RVMI and pPCI).

Table 1 - Baseline characteristics of groups

Baseline characteristics	The whole population (n=273)	LV MPI		RV MPI		tMPI
		≥0,55 (n=145)	<0,55 (n=128)	≥0,45 (n=120)	<0,45 (n=153)	≥1,0 (n=107)	<1,0 (n=166)
Males, n (%)	240 (87,9)	127 (87,6)	113 (88,3)	108 (90,0)	132 (86,3)	97 (90,7)	143 (86,1)
Age, mean (SD)	57,3 (5,9)	57,1 (5,9)	57,7 (6,0)	57,1 (6,1)	57,6 (5,8)	57,4 (5,0)	57,4 (5,7)
DM, n (%)	71 (26,0)	39 (26,9)	32 (26,0)	34 (28,3)	37 (24,2)	27 (25,2)	44 (26,50)
AH, n (%)	103 (37,7)	52 (35,9)	51 (39,8)	39 (32,5)	64 (41,8)	35 (32,7)	68 (41,0)
COPD, n (%)	91 (33.3)	55 (37,9)	36 (28,1)	41 (34,2)	41 (32,7)	50 (38,3)	103 (30,1)
RVMI, n (%)	131 (48,0)	74 (51,0)	57 (44,5)	66 (54,2)	65 (43,1)	61 (57,0)	70 (42,2)*
pPCI, n (%)	72 (24,0)	36 (24,8)	36 (28,1)	27 (22,5)	45 (29,7)	17 (15,9)	55 (33,1)**
Killip III-IV, n (%)	41 (15.0)	22 (15,2)	19 (14,8)	18 (15,0)	23 (15,0)	17 (15,9)	24 (14,4)
LV EF, mean	45,3	45,1	45,4	45,0	45,5	44,9	45,6

Notes: * p<0,05 **p<0,01

All statistical tests were two-sided, and p-values less than 0,05 were considered statistically significant. In the multivariate models, a variable was considered a significant predictor of end-points of the p-value was less than 0,05.

Results and Discussions

We made both unadjusted (table 2) and adjusted (table 3) risk analysis separately for LV MPI, RV MPI and tMPI.

Unadjusted risk analyses indicated that patients with LV MPI ≥0,55 were about 3,5 times greater in risk on CSh, 3,0 times – in risk on one-year cardiac death and 2,0 times - in risk on re-hospitalization. However, LV MPI ≥0.55 did not add a risk to in-hospital cardiac mortality. Further, RV MPI ≥0,55 added only risks of in-hospital deaths and CSh, about 2,4 and 3,8 times respectively. Contrary to above two traditional criteria, the suggested tMPI≥1,00 beared excess risks for all 4 parameters – about 2,4 times for in-hospital caridiac mortality, 4,7 times for CSh, 2,4 times for post-infarction one-year cardiac mortality and 2,3 times for rehospitalization.

Table 2 summarizes between-group comparitive analysis of frequencies of cases of in-hospital cardiac deaths, CSh, post-infarction one year cardiac deaths and re-hospitalization.

Table 2 – Compartivie between-group analyses of unadjusted risks

Morbidity and mortality variables	LV MPI			RV MPI			tMPI
	≥0,55	<0,55	RR	≥0,45	<0,45	RR	≥1,00	<1,00	RR
In-hospital mortality, %	10,3	6,3	ns	12,5	5,2	2,4*	13,1	5,4	2,4*
Cardiogenic shock, %	11,0	3,1	3,5*	12,5	3,3	3,8**	14,0	3,0	4,7**
Post-infarction one-year, % mortality	13,3	4,5	3,0*	11,6	7,3	ns	14,5	6,0	2,4*
Post-infarction one-year rehospitalization, %	23,3	11,6	2,0*	23,2	13,9	ns	27,7	12,1	2,3**

Notes: * p<0,05 ** p<0,01, ns=not significant difference

Adjusted risk analysis further indicated an advantage of tMPI over both LV MPI and RV MPI as inheriting much greater risk of stidied mortality and morbidity variables with lower p values. Particularly, logistic model approved that patients with tMPI≥1,00 were about 2,4 times in greater probability on hospital cardiac death and 4,7 times - on CSh in hospital treatment period and  2,4 times - on cardiac death and 2,3 times - on rehospitalization in post-infarction one year period. As with traditional EchoCG criteria, LV MPI failed to predict in-hospital mortality and RV MPI – post-infarction one-year mortality and rehospitalization.  

Table 3 summarizes main findings of analyses of prognostic significance of three EchoCG criteria – LV MPI, RV MPI and tMPI in terms of OR_adj.

Table 3 – Comparitive analysis of prognostic significance of different EchoCG criteria.

Morbidity and mortality variables	LV MPI≥0,55	RV MPI ≥0,45	tMPI≥1,00
	ORadj	ORadj	ORadj
In-hospital mortality	NS	2,5*	2,2*
Cardiogenic shock	3,9*	4,5**	4,8**
Post-infarction one-year mortality	5,0**	NS	2,2*
Post-infarction one-year rehospitalization	2,8**	NS	3,0**

Notes: * p<0,05 ** p<0,01, NS=not significant difference

So far, findings on prognostic usefulness of MPI remains somehow controversial. While there are some studies underlining the role of LV MPI in distinguishing patients with higher cardiac mortality risk [11], other researchers suggested that in the acute phase of myocardial infarction, LV MPI measured in admission cannot be a useful to predict which patients are at high risk for in-hospital cardiac events [12].

To date, some research was done to define reference ranges of LV MPI for practical use. One study revealed that LV MPI≥0,47 is useful to predict which patients with first AMI are at high risk for hospital cardiac events (death, heart failure, arrhythmias, or post-AMI angina) [2]. Another study showed that the LV MPI>0,45 with AMI patients was the strongest independent predictor of the development of congestive heart failure [13]. One-year survival in first AMI patients with LV MPI<0,63 was 89%, and 37% in patients with LV MPI≥0,63 [14].

Studies have demonstrated the clinical utility and value of RV MPI in line with other EchoCG parameters. RV MPI was extensively researched for diseases and conditions accompanied with the pulmonal hypertension, however, to date, a little is known on the usefulness of RV MPI in patients with AMI [15, 16]. A review revealed that RV MPI>0,40 by pulsed Doppler indicates RV dysfunction [17].

In this prospective study, we found Doppler measurements of both LV and RV functions to be risk factors for early hospital and late 1-year cardiac mortality and morbidity. MPIs provided prognostic information beyond that of other measurements of cardiac function and traditional risk factors. Especially, RV MPI at arrival to the hospital in the acute phase of LV inferior STEMI allows noninvasive prediction of subsequent CSh and early cardiac mortality.

In addition, study results indicated that predictive capacity of MPIs in this study could be explained by the fact that LV MPI reflects global LV function, RV MPI – global RV function, and tMPI as the sum of LIMP and RIMP - combined global functions of both ventricles. In addition, the study outlines the usefulness of tMPI as a “universal risk factor” for both early and rate cardiac mortality and morbidity.

We explored the relevant literature and found no data that would compare predictive patterns of LV MPI and RV MPI, especially in patients with LV inferior STEMI. Moreover, there was no paper that could examine the MPI indicator combining both LIMP and RIMP.

In conclusion, the sum of LIMP and RIMP seems to be a clinically relevant measurement of both ventricles’ global function and may prove to be a valuable tool in assessing the risk of both early and late cardiac mortality and morbidity.