European Journal of Cardiovascular Medicine

Cardiovascular diseases are increasing at the rapid pace and becoming a major cause of morbidity and mortality globally [1]. Among them, ischemic heart disease, specifically ACS, is particularly significant because of its high potential for fatal outcomes. ACS is a composite term applied to a range of conditions that result from acute myocardial ischemia, among which unstable angina, and non-ST-segment elevation myocardial infarction (NSTEMI), along with ST-segment elevation myocardial infarction (STEMI) [2].

Acute myocardial infarction (AMI), a key part of ACS, results from an abrupt diminution of coronary flow to the myocardium with consequent tissue damage owing to decreased oxygen supply. STEMI and NSTEMI affect over 3 million individuals every year and approximately 4 million individuals every year, respectively, globally, with STEMIs being roughly twice as frequent in men compared with women [3].

Because of the great risk of ACS, it is essential to recognize high-risk patients. For the purpose of this, scoring systems such as the Thrombolysis in Myocardial Infarction (TIMI) score and the Global Registry of Acute Cardiac Events (GRACE) model have been developed and are now used in routine risk stratification and clinical decision-making [4].

Within this framework, the electrocardiogram (ECG) continues to be vital in the initial assessment and prognostication of ACS patients It provides useful prognostic information along the spectrum of coronary artery disease, from and after reperfusion therapy, in stable ischemia, and even asymptomatic patients. Consequently, various studies have centered on the prognostic significance of certain ECG elements in ACS [5].

Among these components, QRS morphology as well as its duration and configuration has proved to be an important predictor of poor outcomes. Abnormalities like bundle branch blocks and intraventricular conduction delays can be indicators of underlying electrical malfunction and widespread myocardial damage. Also, atrioventricular (AV) block, a frequent sequel of ACS particularly in inferior or large anterior infarctions presents clinical problems, frequently with bradyarrhythmias, hemodynamic compromise, and a requirement for temporary pacing [6].

Despite extensive research on the individual prognostic value of QRS morphology and AV block, limited data exist on their combined effect in ACS patients. Association of conduction defects with QRS prolongation can be an expression of more extensive myocardial damage, slower electrical restitution, or critical compromise of the conduction apparatus's blood supply issues most germane to the revascularization era. Early identification of this overlap can optimize risk stratification and direct pacing requirements, monitoring, and individualized care. This prospective cohort study at a high-volume TC center in India proposes to assess the prognostic value of QRS morphology in ACS patients with AV block, with emphasis on infarct location, severity of conduction, angiographic appearance, pacing needs, and short-term outcomes.

Study Design and Setting

This was a prospective observational study done at the U.N. Mehta Institute of Cardiology and Research Centre, Ahmedabad, Gujarat. The study was carried out over a defined period from December 1, 2018, to March 30, 2020.

Study Population

The study included ACS patients who developed AV conduction blocks at presentation or during hospitalization before revascularization. Patients were diagnosed with either STEMI or NSTEMI. STEMI was demarcated by new ST-segment elevation right at the J-point in ≥2 contiguous leads: >0.1 mV generally, or >0.2 mV in V2–V3 (men ≥40 years), >0.25 mV (men <40 years), and >0.15 mV (women). New left bundle branch block with increased cardiac biomarkers was also categorized as STEMI. NSTEMI was identified by the elevated troponin above the reference level with ischemic ECG changes. For wide complex rhythms without pre-admission ECG, Sgarbossa criteria were used. The highest AV block grade at admission was recorded for analysis.

Exclusion Criteria

Patients meeting any given criteria were excluded:

1. Documented history of AV conduction abnormalities on available baseline ECGs.
2. Prior use of AV nodal blocking medications before the ACS event.
3. Absence of coronary angiography (CAG) during the hospitalization period.

Sampling and Ethical Approval

A non-probability consecutive sampling method was utilised. A total of 150 patients were screened during the study period. Based on the exclusion criteria, 34 patients were left out, resulting in a final sample size of 116 patients.

The study protocol received ethical clearance from the Institutional Ethics Committee, and written informed consent was obtained from all participants prior to enrollment.

Data Collection and Procedures

Data were collected utilizing a structured proforma, including patient demographics, comorbidities (diabetes, hypertension, chronic heart failure), clinical presentation, physical exam, and admission laboratory findings. ECG and echocardiographic data were obtained in all subjects. All received coronary angiography and revascularization according to institutional guideline. PCI was done according to standard protocol. TPI was administered for symptomatic high-grade AV block. AV block resolution was monitored by post-procedure observation.

QRS Morphology Classification

QRS complex morphology was categorized as either narrow complex AV block (QRS duration <120 ms) or broad complex AV block (QRS duration ≥120 ms). This classification was then analyzed in relation to various clinical and procedural factors including:

1. Type of AV block (low-grade vs high-grade)
2. Infract location
3. Culprit vessel on angiography
4. Need for TPI or PPI
5. Recovery of AV conduction after revascularization

In chronic AV block patients, Holter monitoring was done before discharge. Those with no post-procedure conduction abnormalities were usually discharged within 72 hours. Follow-up evaluation was done at 1 month, and 6 months, and then 12 months to monitor AV block recovery and pacing function.

Statistical Analysis

All data entered right into Microsoft Excel 2010 and analyzed with Epi Info Version 7.1. Continuous variables are presented as mean ± SD, and categorical variables counting frequencies and percentages. Comparative tests assessed associations between QRS morphology and infarct type, culprit vessel, TPI/PPI requirements, and AV block recovery during follow-up.

Demographic and Clinical Profile

Out of 150 enrolled patients, 116 met the inclusion criteria and were incorporated in final analysis. Also, cohort mean age was 61.1 ± 10.2 years. Most patients (55.2%) belonged to the 61–80 years age group (Table 1). Males comprised 75.9% of the study population, resulting in a male-to-female ratio of 3.14:1.

Table 1. Distribution of patients according to age group

Comorbidities were prevalent in 92.2% of the patients. Most prevalent was the co-existence of diabetes mellitus and hypertension (47.4%), followed by hypertension (23.3%) and diabetes (17.2%) alone. Only 7.8% of patients had no documented comorbidities (Figure 1).

Figure 1. Distribution of patients according to comorbidities

Distribution of Myocardial Infarction Type and AV Block

The predominant diagnosis among the study population was inferior wall myocardial infarction (IWMI), which was detected in 91 patients (78.5%). Anterior wall myocardial infarction (AWMI) was detected in 14 patients (12.2%), and NSTEMI was detected in 11 patients (9.5%) (Table 2). This distribution aligns with the well-documented higher incidence of conduction system disturbances in inferior MI, because of the high incidence of atrioventricular (AV) node involvement due to supply by the right coronary artery (RCA).

Table 2. Distribution of Myocardial Infarction

Concerning the types of atrioventricular block (AVB), and complete heart block (CHB) was the most common, occurring in 76 patients (65.5%). Second-degree AV block was identified in 23 patients (19.8%), and first-degree AV block was noted in 17 patients (14.7%). All instances of Mobitz type II and 2:1 AV block were categorized as high-grade AV block (HAVB) due to their increased threat of advancement to complete heart block and their strong association with hemodynamic instability (Figure 2).

Figure 2. Distribution of patients according to highest grade of AV block

QRS Morphology and Association with Pacing Requirement

QRS morphology analysis revealed that most patients (78.4%) had narrow complex atrioventricular block (QRS width <120 ms), whereas 21.6% had broad complex AV block (QRS width ≥120 ms) (Table 3).

Table 3. Association between narrow and broad complex AV block and culprit vessels

Temporary pacemaker implantation (TPI) was required in only 3 patients (3.3%) with narrow QRS complexes, all of whom had HAVB (Table 4). Conversely, 84.0% of patients with broad QRS morphology required TPI, a statistically noteworthy variance (p < 0.0001).

Table 4. Association of QRS Morphology with Temporary Pacing

Angiographic Findings and Culprit Vessel Distribution

Triple vessel disease (TVD) was observed in 53 patients (45.7%), double vessel disease in 39 patients (33.6%), and single vessel disease in 24 patients (20.7%) (Table 5, Figure 3). A decline in left ventricular ejection fraction (LVEF) was noted with an increasing number of vessels involved.

Table 5. Angiographic finding of patients

Figure 3. LVEF vs vessel involvement

Right coronary artery (RCA) was most frequently involved (84.5%), followed by the left anterior descending artery (LAD, 80.2%) and the left circumflex artery (LCX, 54.3%) (Table 6). LAD involvement was significantly more common among patients with wide QRS complexes, implying a possible relation with conduction disturbances.

Table 6. Site of occlusion by coronary artery

*Occlusion at multiple sites in one artery was found.

Recovery of AV Block after Revascularization

Recovery patterns of AV block after revascularization also differed in terms of the requirement of temporary pacemaker implantation (TPI). Among 24 patients requiring TPI for high-grade AV block, 11 (45.8%) recovered AV conduction within the first hour, indicating transient ischemia, and 6 (25.0%) recovered within 24 hours. Two patients (8.3%) died within 24 hours due to severe pump failure. Five patients (20.8%) did not recover within a week and required permanent pacemaker implantation (PPI).

Among 92 patients without TPI, 79 (85.7%) regained spontaneous AV conduction at discharge, and 3 (3.2%) remained with permanent abnormalities requiring PPI, suggesting irreversible damage to the conduction system (Table 7).

Table 7. Post revascularization recovery of AV block

One-Year Prognostic Outcome

The patients were followed up at 1 month, and 6 months, and then 12 months. One year later, 103 patients (88.7%) had made a complete recovery from AV block without the need for pacemaker support. Eight patients (6.8%) were still pacemaker-dependent because of ongoing conduction defects, and five patients (4.3%) died during follow-up (Table 8).

Complete recovery was found to be most common in narrow QRS morphology and right coronary artery (RCA) involvement patients. Conversely, long-standing AV block and worse prognosis were more frequent in those with wide QRS complexes, left anterior descending artery (LAD) involvement, and ostial or proximal lesions.

Table 8. Outcome during follow up (n-111)

In this study of 116 ACS patients with AV block, the mean age was 61.1 ± 10.2 years, with a male predominance (75.9%), consistent with global patterns [7]. Comorbidities were present in the majority of patients (92.2%), primarily diabetes and hypertension (47.4%), reflecting the involvement of metabolic syndrome in coronary disease and arrhythmias [7].

IWMI was the most common MI type (78.5%), followed by anterior MI (12.2%) and NSTEMI (9.5%), reflecting the RCA’s involvement in AV nodal ischemia [8,7]. CHB was the most frequent block (65.5%), aligning with earlier studies [8]. Broad QRS complexes were strongly associated with pacing needs 84.0% required temporary pacing versus only 3.3% with narrow QRS (p < 0.0001), suggesting infra nodal block and poor recovery [8,9].

Angiographically, triple vessel disease was most common (45.7%), and LVEF declined with increasing vessel involvement. RCA (84.5%) was the predominant culprit, followed by LAD (80.2%) and LCX (54.3%). Broad QRS blocks were significantly associated with LAD lesions, especially proximal ones, indicating septal ischemia and structural conduction damage [9,7].

Among patients needing TPI, 70.8% recovered within 24 hours post-revascularization, but 20.8% required PPI mostly those with LAD lesions, broad QRS, TVD, and low LVEF supporting the ischemia hypothesis [10,11]. Among those not needing TPI, 85.7% recovered by discharge, though 3.2% later required PPI, pointing to latent conduction injury [13,14].

At one year, 88.7% had AV conduction recovery, 6.8% remained pacemaker-dependent, and 4.3% had died. Favourable outcomes were linked to RCA involvement and narrow QRS; poorer outcomes to LAD lesions, broad QRS, ostial disease, and low LVEF [12,10].

Overall, transient AV block in IWMI often resolves with revascularization, but LAD-related infarcts with broad QRS and multivessel disease predict permanent conduction damage. Judicious use of pacing guided by clinical and angiographic parameters remains essential [15].

RS morphology is a valuable prognostic indicator in acute coronary syndrome (ACS) patients presenting with atrioventricular (AV) block. Broad QRS complexes were significantly related to anterior myocardial infarction, LAD involvement, high-grade AV block, and heightened temporary and permanent pacing requirements. Conversely, Narrow QRS morphology was related to inferior infarction, improved recovery of conduction, and good outcomes after revascularization. Early PCI substantially enhanced AV conduction recovery, especially in patients without extensive myocardial damage. Incorporating QRS morphology into early risk stratification can enhance clinical decision-making, guide pacing therapy, and improve the overall prognosis for ACS patients in the current era of advanced revascularization.

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