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THE IMPACT OF TYPE 2 DIABETES ON CARDIAC ARRHYTHMIAS IN ELDERLY
PATIENTS DURING THE SUBACUTE PHASE OF MYOCARDIAL INFARCTION: A
CLINICAL AND METABOLIC CORRELATION STUDY
Hamroyeva Madinabonu Yo‘ldosh kizi
Bukhara State Medical Institute
Assistant at the Department of Faculty and Hospital Therapy
e-mail: madinabonu_hamroyeva@bsmi.uz
xamrayevamadina96@gmail.com
Abstract:
Type 2 diabetes mellitus (T2DM) is a growing medical-social problem, characterized
by widespread prevalence, increasing incidence, and serious complications. The combination of
micro- and macrovascular complications in T2DM leads to early disability and death. The disease
is often accompanied by atherosclerosis, resulting in lipid and carbohydrate metabolism
disturbances, hypercholesterolemia, hypertriglyceridemia, and low levels of high-density
lipoproteins. T2DM promotes the development of cardiovascular issues, including arrhythmias,
particularly during the acute period of myocardial infarction (MI). The research aims to explore
the prevalence and correlation of arrhythmias in elderly patients with MI and diabetes,
highlighting the role of metabolic factors such as glycemic control and kidney function in
arrhythmia development. The study found that the incidence of arrhythmias was higher in patients
with T2DM, with significant correlations to age, diabetes duration, glycemic control, and the
presence of diabetic nephropathy. Moreover, the study revealed a U-shaped relationship between
the frequency of arrhythmias and HbA1c levels. These findings suggest that optimal management
of diabetes and early detection of arrhythmias can improve outcomes in elderly patients with MI.
Keywords:
Type 2 Diabetes Mellitus, Myocardial Infarction, Arrhythmias, Glycemic Control,
Diabetic Nephropathy, Elderly Patients, Hyperglycemia, HbA1c, Metabolic Factors,
Cardiovascular Disease.
Type 2 diabetes mellitus (T2DM) remains a pressing medical and social challenge due to its
increasing prevalence, rising incidence, and severe clinical outcomes. The combination of
microvascular and macrovascular complications significantly contributes to early disability and
increased mortality among affected individuals.
T2DM and atherosclerosis are integrally linked through shared metabolic disturbances, including
hyperglycemia, hypercholesterolemia, hypertriglyceridemia, and decreased high-density
lipoprotein (HDL) levels. These imbalances foster a cluster of cardiovascular risk factors such as
hyperlipoproteinemia, arterial hypertension, insulin resistance, and hypercoagulability, thereby
exacerbating the progression of cardiovascular diseases.
Myocardial infarction in diabetic patients is of particular clinical concern and is increasingly
drawing attention from researchers. Although T2DM is now more frequently diagnosed in
younger individuals, it predominantly affects middle-aged and elderly populations, where
comorbidities aggravate the course and prognosis of myocardial infarction and complicate its
management.
Cardiac arrhythmias are common and potentially life-threatening cardiac complications in patients
with T2DM. Sudden cardiac death in diabetic individuals has been linked to acute arrhythmias,
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often associated with autonomic nervous system dysfunction and QT interval prolongation.
Notably, elevated glycated hemoglobin levels (>8%) have been correlated with a higher incidence
of ventricular tachycardia, regardless of QT duration. Atrial fibrillation and other
tachyarrhythmias are particularly concerning in diabetic patients with concomitant arterial
hypertension and insulin resistance.
Arrhythmias frequently complicate the clinical course of myocardial infarction. This study aimed
to compare the incidence of arrhythmias in elderly patients during the subacute phase of
myocardial infarction with and without type 2 diabetes mellitus, and to identify potential
arrhythmogenic factors contributing to their development.
Materials and Methods
A total of 194 patients diagnosed with myocardial infarction were enrolled in this study. The
primary group (Group I) consisted of 99 patients with concomitant type 2 diabetes mellitus, while
the control group (Group II) included 95 patients without diabetes. The diagnosis of diabetes was
established according to the criteria set by the WHO Expert Committee (1999).
All participants underwent comprehensive clinical, laboratory, and instrumental evaluations.
These included resting electrocardiography (ECG), echocardiography in both M- and B-modes,
and biochemical tests measuring blood glucose, glycated hemoglobin (HbA1c), glucosuria,
microalbuminuria, proteinuria, and full lipid profiles. Sympathetic nervous system activity was
assessed through β-adrenoreceptor binding on erythrocyte membranes (β-ARM) as a functional
biomarker.
In a subgroup of 43 patients from the primary group, serum levels of immunoreactive insulin and
C-peptide were additionally quantified using standard radioimmunoassay kits provided by
Immunotech (Czechia).
The severity of myocardial infarction in all patients was stratified into four subgroups according
to the classification developed by E.S. Niposayeva and D.M. Aronov (1998), which is utilized for
tailored cardiac rehabilitation programs. Stratification criteria included the extent and depth of
myocardial necrosis, degree of heart failure, presence of complications during the acute phase,
and co-existing arterial hypertension.
Statistical analysis was conducted using the Statistica 9.0 software package. Data were presented
as mean ± standard deviation (Mean ± SD) for normally distributed variables, and as medians
with interquartile ranges (Me [Q1–Q3]) for non-normally distributed data. Fisher’s exact test,
Chi-square (χ²), Spearman's rank correlation coefficient, Mann–Whitney U test, and Kruskal–
Wallis test were applied where appropriate. A p-value < 0.05 was considered statistically
significant.
The mean age of the patients was 68.7 ± 7.3 years in Group I and 64.2 ± 8.1 years in Group II.
Women predominated in Group I (92.1%), most of whom had moderately severe diabetes, while
men constituted the overwhelming majority in Group II (99.1%).
Cardiac arrhythmia was a common complication during the subacute period of myocardial
infarction in both groups, occurring more frequently in patients with diabetes — 42.1% versus
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30.4%, respectively (p = 0.0041). The predominant forms of arrhythmia were polymorphic
extrasystole and atrial fibrillation: 51.4% and 37.4% in Group I; 49.1% and 24.9% in Group II.
The frequency of arrhythmias and their associated factors are presented in Table 1. In both groups,
there was a correlation between the presence of arrhythmias and the severity of myocardial
infarction and heart failure, with a stronger association in Group I. In patients with diabetes,
arrhythmias were also correlated with age and early post-infarction angina, which more frequently
complicated the subacute phase of MI in this group — 92.1% vs. 30.9%, p = 0.049 — indicating
reduced coronary reserve and severe atherosclerosis.
Arrhythmias also correlated with echocardiographic indicators of myocardial function (see Table
1). Left ventricular systolic dysfunction was more pronounced in diabetic patients: ejection
fraction was 40.0% (IQR: 39.9–44.0) versus 47.0% (IQR: 40.0–55.0) in controls, p = 0.003; left
atrial size was 42.3 mm versus 39.9 mm, p = 0.03.
Thus, myocardial dysfunction was more severe in diabetic patients with a higher frequency of
arrhythmias. A greater incidence of anginal attacks in this group, suggesting extensive multivessel
coronary artery disease, also correlated with arrhythmias (Table 2).
Patients with arrhythmia were significantly older and had a longer duration of diabetes. A
statistically significant correlation was found between arrhythmias and age (r = 0.4, p = 0.045). All
patients were in a state of chronic diabetes decompensation; however, in Group I, levels of
glycated hemoglobin (HbA1c) and average daily glycemia were significantly lower despite
relatively high levels of immunoreactive insulin and C-peptide.
In 17.2% of patients with arrhythmia, individual glucose measurements did not exceed
3.5 mmol/L during the day, suggesting the likelihood of hypoglycemic episodes, which were
clinically evident in 9.3% of cases. Fasting glycemia variability was significantly higher in
patients with arrhythmia.
The presence of arrhythmias was inversely correlated with HbA1c (r = –0.3, p = 0.02), positively
correlated with serum creatinine levels (r = 0.4, p = 0.03), and inversely correlated with
sympathetic nervous activity as measured by β-ARM (r = –0.5, p = 0.013).
These findings highlight the impact of metabolic factors on arrhythmogenesis in diabetes,
particularly hypoglycemia, which exacerbates tissue hypoxia, stimulates the sympathetic nervous
system, and increases myocardial electrical instability.
Considering the frequent presence of diabetic nephropathy, mostly at the proteinuric stage, and
the higher creatinine levels in patients with arrhythmia, it is logical to assume nephropathy as an
aggravating factor for hypoglycemia. Diabetic nephropathy worsens the course of myocardial
infarction, correlating with its severity (r = 0.3, p = 0.004).
To further assess the association between arrhythmia and HbA1c levels, Group I patients were
divided into three subgroups:
A
: HbA1c ≤ 7.0%,
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B
: HbA1c 7.0–8.5%,
C
: HbA1c > 8.5% (see Table 3).
The highest frequency of arrhythmias (82.3%) was found in subgroup A. It correlated
significantly with the severity of heart failure (r = 0.89, p = 0.00019), HbA1c level (r = –0.72,
p = 0.0053), and sympathetic activity (r = 0.79, p = 0.0008). The maximum β-adrenoreceptor
response in this subgroup supports the hypothesis of increased adrenergic activity, possibly driven
by hypoglycemia.
In subgroup C, arrhythmias correlated with the end-diastolic dimension of the left ventricle
(r = 0.59, p = 0.029) and hypercholesterolemia (r = 0.91, p = 0.029). The lowest frequency of
arrhythmias was observed in patients with HbA1c levels between 7.0% and 8.5%.
The highest rate of arrhythmias in diabetic patients during the subacute phase of myocardial
infarction was observed in those with relatively low HbA1c values. This may be attributed to both
more severe myocardial dysfunction and metabolic disturbances, particularly hypoglycemia
(including latent forms), as well as sympathetic overactivation.
Hypoglycemia risk is exacerbated by diabetic nephropathy, especially in the presence of chronic
renal failure, which impairs the inactivation of both exogenous and endogenous insulin. We
observed chronic renal failure in 13.1% of patients with arrhythmia.
Increased fasting glycemic variability in patients with arrhythmia is currently considered a
potential predictor of cardiovascular mortality in elderly diabetic patients.
Therefore, arrhythmia, along with reduced ejection fraction and diabetic nephropathy, represents a
frequent and prognostically unfavorable complication of myocardial infarction in elderly patients
with diabetes mellitus. The main arrhythmogenic factors include hemodynamic disturbances
(heart failure, myocardial dysfunction), severity of coronary insufficiency with recurrent angina,
and metabolic abnormalities.
Relatively low HbA1c levels in elderly patients with severe cardiovascular disease are considered
an adverse factor associated with a higher frequency of arrhythmias due to hypoglycemia risk,
particularly against the background of diabetic nephropathy. Hyperactivity of the sympathetic
nervous system in these patients contributes to myocardial electrical instability, increasing
arrhythmia risk. At the same time, decompensated diabetes with HbA1c > 8.5% is also frequently
associated with arrhythmias, linked to the severity of myocardial dysfunction and metabolic
abnormalities, including hyperlipidemia.
When HbA1c is maintained within 7.0–8.5%, both the frequency of arrhythmias and sympathetic
activity appear to be at their lowest. Deviation from this range leads to either increased risk of
hypoglycemia or severe metabolic disturbances, including damaging effects of hyperglycemia and
pronounced hyperlipidemia.
Conclusions
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In elderly patients with type 2 diabetes mellitus, cardiac arrhythmias, as recorded by ECG
monitoring, significantly more frequently complicate the subacute period of myocardial infarction
(42.1% vs. 30.4%;
p
= 0.0041), correlating with the severity of myocardial and coronary
insufficiency, as well as with the patients’ age.
Arrhythmias in the setting of myocardial infarction and diabetes mellitus are more commonly
observed in patients over the age of 95, with a longer duration of diabetes, relatively lower levels
of glycated hemoglobin (HbA1c ≥ 7%), elevated levels of immunoreactive insulin and C-peptide,
and the presence of diabetic nephropathy. All these factors suggest an increased risk of
hypoglycemic episodes, which may act as one of the triggering mechanisms for arrhythmogenesis.
A U-shaped relationship was identified between the frequency of cardiac arrhythmias and HbA1c
levels: the lowest incidence of arrhythmias was observed in patients with HbA1c levels within the
range of 7.0–8.5%.
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