Cardiology

Background

Cardiac arrest is the sudden cessation of effective cardiac mechanical activity, resulting in loss of systemic circulation and immediate hemodynamic collapse. It manifests clinically as unresponsiveness, absence of a palpable pulse, and apnea or abnormal breathing. Cardiac arrest is a medical emergency that, if untreated, rapidly leads to death. It is caused by electrical or mechanical failure of the heart and is distinct from myocardial infarction, though MI can precipitate arrest. 

II) Classification/Types

By Rhythm Type: 

• Shockable rhythms: 

• Ventricular fibrillation (VF) 

• Pulseless ventricular tachycardia (VT) 

• Non-shockable rhythms: 

• Asystole 

• Pulseless electrical activity (PEA) 

By Setting: 

• Out-of-hospital cardiac arrest (OHCA) 

• In-hospital cardiac arrest (IHCA) 

By Cause: 

• Cardiac causes (e.g., ischemic heart disease, cardiomyopathy) 

• Non-cardiac causes (e.g., hypoxia, electrolyte abnormalities, trauma) 

Pathophysiology 

Cardiac arrest occurs due to a failure of the heart to generate adequate mechanical contraction despite electrical activity (PEA), or due to a lethal arrhythmia such as ventricular fibrillation or pulseless ventricular tachycardia, or complete electrical silence (asystole). The underlying mechanism often involves electrical instability secondary to myocardial ischemia, scar tissue, electrolyte imbalances, or structural heart disease. This results in cessation of cardiac output, leading to global tissue hypoxia and rapid organ failure. Without prompt restoration of circulation, irreversible brain injury and death ensue within minutes. 

Epidemiology 

• Annual incidence of out-of-hospital cardiac arrest is approximately 50–100 per 100,000 population. 

• In-hospital cardiac arrest occurs in 1 to 5 per 1,000 hospital admissions. 

• Higher incidence in older adults and males. 

• Coronary artery disease is the leading underlying cause, accounting for about 70% of adult cases. 

• Survival rates vary widely: 10–20% for out-of-hospital arrests with wide variability depending on time to intervention and etiology. 

• Improved survival linked to bystander CPR and early defibrillation. 

Etiology 

I) Causes

Cardiac Causes: 

• Acute myocardial infarction/ischemia 

• Cardiomyopathies (hypertrophic, dilated, arrhythmogenic) 

• Structural heart disease (valvular disease, congenital anomalies) 

• Primary arrhythmias (long QT syndrome, Brugada syndrome) 

• Myocarditis 

Non-Cardiac Causes: 

• Hypoxia (e.g., respiratory failure, drowning) 

• Electrolyte disturbances (hyper/hypokalemia, hypocalcemia) 

• Severe acidosis 

• Drug toxicity/overdose (e.g., digoxin, tricyclic antidepressants) 

• Trauma 

• Pulmonary embolism 

• Hypovolemia 

• Cardiac tamponade 

• Tension pneumothorax 

II) Risk Factors

• Known coronary artery disease or prior myocardial infarction 

• Reduced left ventricular ejection fraction (<35%) 

• Heart failure 

• Advanced age 

• Male sex 

• Family history of sudden cardiac death 

• Smoking, hypertension, diabetes mellitus 

• History of syncope or documented ventricular arrhythmias 

Clinical Presentation 

I) History (Symptoms)

• Sudden collapse or loss of consciousness, often witnessed 

• May have preceding symptoms such as chest pain, palpitations, dyspnea, or syncope 

• Family history of sudden unexplained death or inherited arrhythmias may be present 

II) Physical Exam (Signs)

• Unresponsive and pulseless on arrival 

• Apnea or agonal respirations 

• Absent peripheral pulses 

• Signs of underlying heart disease may be noted (e.g., murmurs, jugular venous distension) 

• Post-resuscitation neurological status varies depending on downtime and quality of CPR 

Differential Diagnosis (DDx) 

• Pulseless electrical activity (PEA) 

• Asystole 

• Severe bradycardia or pulselessness due to non-cardiac causes 

• Seizure or syncope mimicking arrest 

• Artifact on ECG or pulse checks 

Diagnostic Tests 

Initial Work-Up (During Resuscitation) 

• ECG: Identify rhythm (VF, VT, asystole, PEA) and ischemic changes 

• Point-of-care ultrasound (POCUS): Evaluate cardiac contractility, tamponade, pneumothorax 

• Capnography: End-tidal CO₂ monitoring to assess CPR quality (<10 mmHg suggests poor perfusion) 

• Blood tests: Electrolytes, arterial blood gas, cardiac enzymes, toxicology screen 

Advanced Testing (Post-Resuscitation) 

• Echocardiogram: Assess cardiac function and structural abnormalities 

• Coronary angiography: For suspected acute coronary syndrome 

• Cardiac MRI: Evaluate for cardiomyopathies and fibrosis 

• Electrophysiology studies: For arrhythmia evaluation 

• Genetic testing: In suspected inherited arrhythmia syndromes 

Treatment 

I) Acute Management

• Immediate initiation of high-quality cardiopulmonary resuscitation (CPR) 

• Early defibrillation for shockable rhythms (VF/VT) 

• Advanced Cardiac Life Support (ACLS) protocols: airway management, IV/IO access, administration of epinephrine and antiarrhythmics (e.g., amiodarone) 

• Identification and treatment of reversible causes (Hs & Ts) including hypoxia, hypovolemia, tamponade, tension pneumothorax, thrombosis, toxins 

• Early coronary reperfusion therapy if acute coronary syndrome is suspected 

II) Chronic/Post-Resuscitation Management

• Hemodynamic stabilization and intensive care monitoring 

• Targeted treatment of underlying cardiac conditions (revascularization, heart failure management) 

• Implantable cardioverter-defibrillator (ICD) placement for secondary prevention in survivors 

• Beta blockers and antiarrhythmics as indicated 

• Cardiac rehabilitation and lifestyle modification 

Medications 

Device Therapy 

• Implantable cardioverter-defibrillator (ICD): For secondary prevention in cardiac arrest survivors and primary prevention in high-risk patients 

• Pacemakers: For bradyarrhythmias or conduction abnormalities 

• Mechanical circulatory support: ECMO or ventricular assist devices in refractory cardiogenic shock 

Patient Education, Screening, Vaccines 

• Educate patients and families on early recognition and emergency response to cardiac arrest 

• Screen first-degree relatives in cases of inherited arrhythmia syndromes 

• Promote lifestyle changes: smoking cessation, diet, exercise 

• Ensure vaccination against influenza and pneumococcus to prevent cardiac complications from infections 

Consults/Referrals 

• Cardiology: For comprehensive cardiac evaluation and management 

• Electrophysiology: For arrhythmia assessment and ICD implantation 

• Genetics: In suspected inherited cardiac conditions 

• Critical Care: For post-arrest intensive care management 

• Psychology/Psychiatry: For psychological support and counseling post-event 

Follow-Up 

Short-Term 

• Monitor for recurrent arrhythmias 

• Neurological assessment and rehabilitation as needed 

• Optimize medical therapy and hemodynamic status 

Long-Term 

• Regular cardiology follow-up for device checks and medication adjustments 

• Cardiac rehabilitation programs 

• Family screening for inherited conditions 

• Psychological support for patients and families 

Prognosis 

• Dependent on etiology, speed and quality of resuscitation, and neurological outcome 

• Out-of-hospital cardiac arrest survival to hospital discharge is approximately 10–20% 

• Better outcomes seen with rapid CPR, early defibrillation, and reversible causes 

• ICD therapy significantly reduces mortality in high-risk patients