Sudden Cardiac Arrest from Ischemic Causes

Introduction

Sudden cardiac arrest (SCA) is a dramatic event characterized by the sudden cessation of mechanical cardiac activity, resulting in the absence of perfusion to vital organs. When the cardiac arrest is caused by an acute ischemic event, it is referred to as sudden cardiac arrest from ischemic causes, which is the most common cause of sudden cardiac death.

Most cases are due to ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT), events that occur in the context of acute coronary syndrome (ACS) or advanced chronic ischemic heart disease.

Pathophysiology

In patients with ischemic heart disease, acute myocardial ischemia can generate electrical and structural changes that facilitate the initiation of malignant ventricular arrhythmias:

• Ischemia and myocardial hypoxia: alterations in depolarization and repolarization.
• Increased sympathetic activity: facilitation of arrhythmic triggers.
• Electrical re-entry phenomena: substrate for ventricular fibrillation.
• Ion metabolism disturbances: potassium and calcium imbalances that increase electrical instability.

If the cardiac rhythm is not restored promptly with defibrillation, cardiac arrest rapidly evolves into asystole, leading to patient death.

Ischemic Causes of Sudden Cardiac Arrest

The main ischemic causes of sudden cardiac arrest include:

• Acute myocardial infarction (STEMI and NSTEMI) with critical myocardial ischemia.
• Wellens' Syndrome: severe ischemia with high risk of VF.
• Chronic ischemic heart disease: ventricular remodeling with risk of fatal arrhythmias.
• Coronary microcirculation dysfunction: ischemia without epicardial obstruction (INOCA).
• Coronary spasm (vasospastic angina) with transient occlusion.

Clinical Presentation

Ischemic sudden cardiac arrest is typically preceded by prodromal symptoms but may present unpredictably. The warning signs include:

• Sudden chest pain, often oppressive and retrosternal.
• Dyspnea, more common in patients with left ventricular dysfunction.
• Palpitations and the sensation of impending fainting.
• Sudden loss of consciousness, followed by absence of carotid pulse and respiration.

If not treated immediately, the patient progresses to cardiac death.

Diagnosis

Ischemic cardiac arrest is a clinical diagnosis based on:

1. ECG monitoring

   Reveals ventricular fibrillation, pulseless ventricular tachycardia, or in advanced cases, asystole.

2. Cardiac biomarkers

   High-sensitivity troponins confirm myocardial necrosis in the case of infarction.

3. Emergency coronary angiography

   Indispensable for survivors of cardiac arrest to identify and treat critical coronary occlusions.

Treatment

The treatment for ischemic cardiac arrest follows the **ALS (Advanced Life Support)** protocol:

1. Early defibrillation

Immediate defibrillation is the only effective treatment for ventricular fibrillation and pulseless ventricular tachycardia.

2. High-quality CPR

Cardiopulmonary resuscitation (CPR) with effective chest compressions and adequate ventilation improves survival.

3. Post-arrest therapy

After restoring circulation, it is essential to:

• Hemodynamic stabilization: fluid therapy and inotropic support.
• Immediate coronary angiography: for revascularization in patients with suspected infarction.
• Temperature management: therapeutic hypothermia for patients in coma.

Prevention

The prevention of ischemic cardiac arrest is based on:

• Control of cardiovascular risk factors: hypertension, diabetes, smoking, and dyslipidemia.
• Myocardial revascularization: angioplasty or bypass in high-risk patients.
• Implantation of defibrillator (ICD): in patients with advanced ischemic heart disease.

Prognosis

The prognosis depends on the speed of intervention:

• Defibrillation within 3-5 minutes: survival up to 70%.
• Absence of CPR for more than 10 minutes: survival < 10%.

Timely treatment and secondary prevention are essential to reduce mortality.

Bibliography
1. Boriani G, Mei DA, Vitolo M, Imberti JF. European Guidelines 2022 on Ventricular Arrhythmias and Sudden Cardiac Death: An Important Push for a Multidisciplinary Effort in Diagnostic and Therapeutic Approaches for Accurate Personalization. G Ital Cardiol. 2022;23(12):901-906.
2. Zeppenfeld K, et al. ESC Guidelines 2022 for the Management of Patients with Ventricular Arrhythmias and Prevention of Sudden Cardiac Death. G Ital Cardiol. 2023;24(3 Suppl. 1):e1-e132.
3. Priori SG, et al. 2015 ESC Guidelines for the Management of Patients with Ventricular Arrhythmias and Prevention of Sudden Cardiac Death. Eur Heart J. 2015;36(41):2793-2867.
4. Olasveengen TM, et al. European Resuscitation Council Guidelines 2021: Basic Life Support. Resuscitation. 2021;161:98-114.
5. McDonagh TA, Metra M, Adamo M, et al. 2021 ESC Guidelines for the Diagnosis and Treatment of Acute and Chronic Heart Failure. Eur Heart J. 2021;42:3599-3726.
6. Soar J, et al. European Resuscitation Council Guidelines 2021: Advanced Life Support. Resuscitation. 2021;161:115-151.
7. Adabag AS, et al. Sudden Cardiac Death in Ischemic Heart Disease. J Am Coll Cardiol. 2017;69(12):1577-1593.
8. O'Gara PT, et al. 2013 ACCF/AHA Guidelines for STEMI. Circulation. 2013;127(4):529-555.
9. Redberg RF, et al. Sudden Cardiac Arrest: Early Defibrillation Saves Lives. Circ Cardiovasc Qual Outcomes. 2015;8(6):517-524.
10. Herlitz J, et al. Out-of-Hospital Cardiac Arrest in Sweden: Time Trends and Outcomes During the Period 2000–2008. Resuscitation. 2012;83(4):428-435.