High degree atrioventricular block (HAVB) is a frequent complication in ST-segment elevation myocardial infarction (STEMI), which occasionally requires a temporary pacemaker (TP) insertion to maintain cardiac output and to prevent the onset of malignant arrhythmias in the acute phase.1–3 Previous studies have focused on the evolution and prognosis of HAVB following STEMI,1 whereas the role of TP has not been addressed since the early small series,4,5 The purpose of the present study is to characterize the incidence and outcome of patients with STEMI and HAVB who require TP insertion in the current primary percutaneous coronary intervention (PPCI) era. We also aimed to identify potential prognostic factors and differences according to the STEMI location.

We enrolled all consecutive patients with STEMI admitted to a tertiary care referral center for PPCI from 2004 to 2017. The study was approved by the local Ethics Committee of Clinical Research (Hospital Clínico San Carlos). All patients provided informed consent. Our center had an acute cardiac care unit managed by cardiologists since the beginning of the study period. Only patients with STEMI and HAVB who required therapeutic TP insertion were analyzed. During hospitalization, all demographic, clinical, electrocardiographic, echocardiographic and angiographic variables were collected. All patients alive at discharge completed a 1-year follow-up.

STEMI was defined according to the guidelines.6 HAVB was defined as second or third-degree atrioventricular block. The presence of atrioventricular conduction disorders was documented through a standard, 12-lead electrocardiogram in all cases. Electrocardiogram was taken at the time of STEMI-diagnosis, every eight hours after PPCI during the first 24h and daily thereafter.

TP was implanted in case of hemodynamic instability and HAVB with heart rate of ≤ 40bpm refractory to intravenous atropine, isoproterenol and dopamine administration according to our local protocol. The decision and time to start pacing stimulation was left to the treating medical team in each case. In all cases, a fluoroscopy-guided transfemoral approach was used to place the pacemaker electrode into the right ventricle apex. Conduction recovery was assessed daily after revascularization, up to one week before permanent pacemaker implantation.

Unsuccessful PPCI was considered when the PPCI procedure resulted in Thrombolysis in Myocardial Infarction flow grade 0 or I, irrespective of the residual stenosis. Total ischemic time was defined as the time between symptom onset and balloon inflation. Renal insufficiency was defined as a creatinine clearance of less than 60mL/min/1.73m2.

We assessed 30-day and 1-year mortality and in-hospital complications.

Of 3063 patients in the study cohort, 180 (5.9%) had HAVB at the time of cardiac catheterization, and 114 (3.7%) required TP implantation (Fig. 1). Baseline characteristics of the study population are shown in Table 1. There was a high prevalence of cardiovascular risk factors among patients and inferior location of STEMI was the most frequently observed (87%) (Table 1).

Fig. 1.

Flowchart of the study patient population. HAVB, high degree atrioventricular block; STEMI, ST-segment elevation myocardial infarction.

(0.1MB).

Anterior vs inferior STEMI

We aimed to assess potential differences between patients according to the STEMI location (Table 3). As expected, patients with anterior STEMI showed a worse Killip class and lower LVEF compared to those with inferior STEMI. Thirty-day and 1-year mortality of patients with anterior STEMI were almost 4-fold higher than that of patients with inferior STEMI (Table 3, Fig. 2).

Table 3.

Clinical, echocardiographic and angiographic characteristics according to STEMI location.

	Anterior (n=14)	Inferior (n=100)	P
Age (years)	68.6±13.7	67.3±16.2	.743
Male sex	11 (78)	68 (68)	.545
Diabetes mellitus	3 (21)	34 (34)	.544
Hypertension	5 (35)	63 (63)	.046
Smoking habit	8 (57)	43 (43)	.335
Dyslipidemia	6 (43)	49 (49)	.642
Prior AMI	1 (7)	10 (10)	1
Atrial fibrillation	3 (21)	14 (14)	.440
Previous treatment
Acetylsalicylic acid	1 (7)	14 (14)	.690
ACE inhibitor/AR blocker	3 (21)	34 (34)	.544
Beta-blocker	1 (7)	8 (8)	1
Calcium channel blocker	2 (14)	18 (18)	1
Statin	2 (14)	34 (34)	.219
Ischemic time (min)	265±320	211.7±138	.540
Culprit vessel			< .001
Left main	2 (14)	0 (0)
Anterior descending	12 (85)	0 (0)
Circumflex	0 (0)	6 (6)
Right coronary artery	0 (0)	94 (94)
3-vessel disease	7 (50)	23 (23)	.049
Renal insufficiency	6 (46)	30 (31)	.352
Killip class			< .001
I	0 (0)	51 (51)
II	1 (7)	5 (5)
III	1 (7)	4 (4)
IV	12 (85)	40 (40)
LVEF	21±8	49±9	< .001
Failed PCI	6 (42)	27 (27)	.225
30-Day mortality	71.4%	18.9%	<.001
1-Year mortality	71.4%	25.5%	.001

AMI, acute myocardial infarction; ACE inhibitor, angiotensin-converting enzyme inhibitor; AR, angiotensin receptor; LVEF, left ventricle ejection fraction; PCI, percutaneous coronary intervention; STEMI, ST-segment elevation myocardial infarction.

Data are expressed as no. (%) or mean±standard deviation.

Fig. 2.

Kaplan–Meier analysis of mortality among patients with anterior and inferior ST elevation myocardial infarction who required temporary pacing.

(0.09MB).

The present study explores the incidence and outcomes of patients with HAVB who required TP insertion in a large cohort of STEMI patients. The main findings of our study were as follows: (a) patients with STEMI who require TP implantation corresponds to a high-risk population with poor outcomes; (b) LVEF≤40% and acute renal failure are independent mortality risk factors in this patient population; (c) patients with anterior STEMI who required TP had a ∼4-fold increased mortality risk compared to those with inferior STEMI; and (d) TP could be safely removed within the first 24h in most patients.

While the improvement of antithrombotic therapy and early reperfusion have led to a significant decrease in the incidence of HAVB in STEMI patients,7 the rate of TP insertion among this patient population have remained steady between 2.6% and 10.9% in the current PPCI era.8,9 A possible explanation for these wide variations might be the lack of standardization of the optimum time and indication to start temporary pacing between different centers. According to current clinical guidelines, TP should be inserted in patients with STEMI and HAVB with hemodynamic instability not responding to atropine, or with low unstable scape rhythm.10 In our study, this proportion was 3.7%, similar to that reported by Gang et al. in a contemporary cohort.9

Patients in our cohort were highly unstable as shown by the high incidence of cardiogenic shock, ventricular arrhythmias and mortality. They also had extensive coronary artery disease and experienced a high rate of complications during angioplasty such as non-reflow phenomenon or failed-PCI. There was a high 30-day mortality (24.5%) in our study population. This poor outcome is probably not entirely related to the HAVB and temporary pacing itself but also to the relatively larger infarct size, higher reperfusion times and lower rates of reperfusion success. TP insertion in STEMI patients has been previously associated with large infarct size, low LVEF and mortality.7,11,12 Infarct size has been also correlated with development of HAVB and the need for temporary and definitive pacemakers after STEMI.7 Moreover, in a study by Singh et al.,12 TP insertion was associated with an almost 3-fold increase in mortality rate, and proved to be an independent mortality risk factor among patients with HAVB. As in our study, those results suggest that patients with STEMI and HAVB who require TP deserve special consideration and a high degree of skills in the acute phase. Anticipation to the onset of potential complications and a rapid therapeutic response could make a difference on prognosis.

Low LVEF and impaired renal function resulted independently associated with a higher 30-day mortality after multivariate adjustment, both in the entire cohort and in patients with inferior STEMI, where infarct size is usually smaller. When considering only inferior STEMI, where infarct size is usually much lower than in those with anterior STEMI, low LVEF and impaired renal function still remained independently associated with 30-day mortality in the multivariate analysis. Contrarily, right ventricle infarction, a well-known mortality predictor among patients with inferior STEMI,13 did not result an independent mortality risk factor in this model. A potential explanation for this finding is that patients with inferior STEMI and HAVB requiring TP present larger infarct sizes and lower left ventricle function. Thus, the LVEF importance seems to exceed that of the right ventricle infarction in this setting of patients with HAVB who need TP insertion.

Considering STEMI location, although the proportion of patients with anterior STEMI in our study cohort was relatively small, we found that patients with anterior STEMI had almost 4-fold increased mortality risk compared to those with inferior STEMI. Previous studies have reported a dreadful prognosis of heart block in patients with anterior STEMI.14,15 This poorer clinical outcome of HAVB in anterior STEMI compared to inferior MI is due to the different underlying mechanism leading to heart block in each case. While HAVB in inferior STEMI is usually a ‘benign’ process due to increased vagal tone and ischemia of the nodal arteries with rapid recovery after reperfusion, the onset of HAVB in anterior STEMI reflects a vast necrosis that is difficult to recover, even after reperfusion.

Finally, TP could be safely removed within the first 48h in most patients in our cohort. Only 8 of them (7%) required a definitive pacemaker. Patients who needed a permanent pacemaker showed higher rates of left bundle branch block and longer ischemic times compared to those who did not. Current guidelines recommend long waiting times after revascularization before implantation of a definitive pacemaker.10,16 However, the lack of specific recommendation about waiting times has led to open interpretations of the guidelines.3,11,17 Some authors suggest that early permanent pacemaker insertion should be considered in patients with poor or failed revascularization, heart failure, arrhythmias and important comorbidities. However, our results support that a case by case approach should be taken before implantation of a definitive pacemaker.

Patients with STEMI and HAVB who require TP insertion are at great risk of short-term adverse outcomes, especially those with anterior STEMI. Low LVEF and impaired renal function at admission are independently associated with mortality in this patient population. TP could be safely removed in most patients, and only a small proportion of them will require a definitive pacemaker implant.

There is no funding source to declare related to this study.

C. Ferrera, L. E. Enríquez, FJ. Noriega, L. Borrego, V. Cañadas, P. Jiménez Quevedo, N. Pérez Castellano, A. Fernández Ortiz, J. Pérez Villacastín, C. Macaya, and A. Viana Tejedor have substantially contributed to the conception of the work. All authors participated in the acquisition, analysis, and interpretation of the data for the work. C. Ferrera and L. E. Enríquez drafted the work. F. J. Noriega, L. Borrego, V. Cañadas, P. Jiménez Quevedo, N. Pérez Castellano, A. Fernández Ortiz, J. Pérez Villacastín, C. Macaya, and A. Viana Tejedor revised it critically for important intellectual content. All authors have given final approval of the version to be published. All authors agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

There are no potential conflicts of interest to declare.