Cardiac Arrest

Cardiac arrest is the sudden, unexpected cessation of effective heart pumping. It is one of the most time-critical medical emergencies in existence -- irreversible brain damage begins within four to six minutes of cardiac arrest onset, and without treatment, death follows within ten minutes. Yet survival is possible. With immediate bystander CPR and early defibrillation, a significant proportion of cardiac arrest victims can be resuscitated and go on to live full, active lives.

In Singapore, out-of-hospital cardiac arrest (OHCA) affects approximately 1,300-1,500 people each year. Survival rates remain low in part because bystander CPR rates are not yet universal -- research consistently shows that survival is 2-3 times higher when bystanders begin CPR before the ambulance arrives. Every person who knows how to perform CPR and use an AED is a potential link in the Chain of Survival.

What Happens in Cardiac Arrest: The Electrical Failure

The heart beats in a coordinated rhythm because of an electrical conduction system -- a network of specialised cells that generate and transmit electrical impulses in a precise sequence. The sinoatrial (SA) node in the right atrium acts as the heart's natural pacemaker, firing approximately 60-100 times per minute. This impulse travels through the atria, is briefly delayed at the atrioventricular (AV) node, and then spreads through the ventricles, triggering the coordinated muscular contraction that pumps blood to the body and lungs.

Cardiac arrest occurs when this electrical system goes wrong in a way that prevents effective pumping. The four rhythms that cause cardiac arrest are:

Ventricular Fibrillation (VF)

The most common cause of sudden cardiac arrest. The ventricles (lower chambers) fire chaotic, disorganised electrical signals, causing them to quiver rather than contract. No blood is pumped. VF is a shockable rhythm -- a defibrillator can terminate VF and restore organised rhythm. Time-critical: VF degenerates to asystole within minutes.

Ventricular Tachycardia (VT)

A very fast rhythm originating in the ventricles, usually above 150 beats per minute. Sustained VT may cause haemodynamic collapse if the heart cannot maintain adequate output at this rate. Pulseless VT is treated identically to VF -- with CPR and defibrillation. VT can degenerate into VF if untreated.

Pulseless Electrical Activity (PEA)

Organised electrical activity visible on the ECG, but no effective mechanical contraction -- the heart's electrical system fires but the muscle does not respond with a meaningful pump. Caused by reversible factors (the 4 Hs and 4 Ts: hypoxia, hypovolaemia, hypothermia, hyperkalaemia; tension pneumothorax, tamponade, thromboembolism, toxins). Treatment focuses on identifying and reversing the underlying cause.

Asystole

Complete cessation of all electrical and mechanical cardiac activity -- a flat line on the ECG. Indicates terminal cardiac failure or a very prolonged cardiac arrest. Not a shockable rhythm. Managed with CPR and adrenaline while reversible causes are sought. Prognosis is poor without a reversible precipitating cause.

Warning Symptoms Before Cardiac Arrest

Cardiac arrest is often described as occurring 'without warning.' While many cases do occur abruptly and without preceding symptoms, approximately 50% of cardiac arrest victims experience warning symptoms in the hours or days before the event. Recognising these symptoms and seeking immediate medical attention can prevent the arrest from occurring at all.

Symptoms in the minutes to hours before cardiac arrest

Chest pain, pressure, or tightness: May indicate myocardial ischaemia preceding an ischaemia-triggered arrhythmia
Shortness of breath: Sudden or worsening breathlessness at rest or with minimal activity
Palpitations: A racing, irregular, or pounding heartbeat; a sensation that the heart is 'fluttering'
Lightheadedness or near-fainting (pre-syncope) -- the cardiac output is briefly compromised, reducing cerebral perfusion
Unexplained sudden fatigue: Disproportionate exhaustion without obvious cause
Nausea or cold sweats: Particularly in combination with the above symptoms

Symptoms requiring emergency assessment immediately

Chest pain lasting more than a few minutes, or coming and going
Breathlessness that is sudden or severe
Fainting (syncope): Particularly if it occurs during exercise or without obvious precipitant
A racing heart that does not settle within a few minutes
Any of the above in a person with known heart disease, a previous heart attack, or a family history of sudden cardiac death

If you experience symptoms such as chest pain or discomfort, pounding heartbeats, irregular or rapid heartbeats or unexplained wheezing, do seek emergency medical services.

Underlying Conditions That Causes Cardiac Arrest

Cardiac arrest is almost always caused by an underlying cardiac condition -- and identifying that condition after the arrest is one of the most important steps in preventing a second event.

Coronary artery disease

The most common cause of cardiac arrest in adults over 35. Atherosclerotic plaques in the coronary arteries can rupture suddenly, triggering a heart attack and arrhythmia. Scar tissue from a previous heart attack also creates an electrical substrate for ventricular arrhythmias. Comprehensive coronary artery assessment (coronary angiography, CT coronary angiography) is a key part of the post-arrest workup.

Cardiomyopathies

Dilated cardiomyopathy: The heart muscle becomes weakened and the chambers enlarge, impairing pump function and resulting in arrhythmia.
Hypertrophic cardiomyopathy (HCM): The most common cause of sudden cardiac death in young athletes. Thickening of the heart muscle (particularly the interventricular septum), which obstructs blood flow and causes arrhythmia
Arrhythmogenic right ventricular cardiomyopathy (ARVC): Fat buildup in the right ventricle weakens the heart muscle and commonly causes abnormal heart rhythms during exercise.
Non-ischaemic cardiomyopathy: Any cardiomyopathy with severely reduced heart pumping function increases the risk of cardiac arrest.

Valvular heart disease

Severe aortic stenosis, mitral valve prolapse with significant regurgitation, and other significant valvular lesions increase the risk of arrhythmias and cardiac arrest, particularly when left ventricular function is compromised.

Myocarditis

Inflammatory disease of the heart muscle -- most often viral -- causes acute cardiac dysfunction and arrhythmias. Myocarditis is a recognised cause of cardiac arrest in young people. COVID-19-related myocarditis has been identified as a cause of cardiac events in previously healthy young adults.

Risk Factors for Cardiac Arrest

The majority of cardiac arrest risk factors are shared with general cardiovascular disease risk. Identifying and managing modifiable risk factors significantly reduces the risk of a first cardiac arrest.

Modifiable risk factors

Smoking: It doubles cardiovascular risk including the risk of cardiac arrests.
Hypertension: Chronically elevated blood pressure damages the coronary arteries and increases arrhythmia risk.
Dyslipidaemia: Elevated LDL cholesterol accelerates atherosclerosis and coronary artery disease
Diabetes mellitus: It is associated with accelerated coronary disease and autonomic neuropathy affecting cardiac electrical stability
Obesity: Associated with sleep apnea, atrial fibrillation, and cardiomyopathy, all of which increase cardiac arrest risk
Physical inactivity: A sedentary lifestyle increases your overall cardiovascular risk

Non-modifiable and medical risk factors

Previous cardiac arrest: The most powerful predictor of future cardiac arrest
Family history of sudden cardiac death: First-degree relative with sudden cardiac death under 50
Gender: cardiac arrest is approximately 3-4 times more common in men
Age: Risk of cardiac arrest increases progressively with age as coronary artery disease burden accumulates
Known genetic conditions: Long QT syndrome, Brugada syndrome, hypertrophic cardiomyopathy
Prior arrhythmia: Documented non-sustained ventricular tachycardia, particularly in the context of structural heart disease

Prevention: Who Should Be Assessed?

Cardiac arrest prevention begins with identifying individuals at elevated risk before an event occurs. Preventive cardiology assessment is appropriate for:

Family history of coronary artery disease
First-degree relatives of someone who died suddenly from cardiac causes -- particularly if the death occurred under age 50
Patients with coronary artery disease and poor heart pumping function (less than 35%).
Patients taking certain antibiotics, antifungals, or psychiatric medications that can affect the heart's electrical activity.
History of unexplained syncope (fainting), palpitations, or chest pain particularly during exercise

Cardiac arrest is largely preventable in high-risk individuals who are identified before an event occurs. The preventive cardiology team at Farrer Park Hospital provides comprehensive risk stratification, including ECG, echocardiogram, stress testing, cardiac MRI, and electrophysiology consultation.

How is Cardiac Arrest Assessed?

Echocardiogram: Checks how well the heart pumps, looks for abnormal heart muscle movement, valve disease, fluid around the heart, thickened heart muscle, and other structural problems. Heart pumping function helps determine whether a patient is eligible for an implantable cardioverter-defibrillator (ICD). It is performed once the patient is stable.
Electrocardiogram (ECG): Detects a heart attack, electrical conduction problems, delayed electrical recovery , the Brugada pattern, and extra electrical pathways. If performed during the cardiac arrest, it records the heart rhythm. Repeat ECGs help monitor recovery from heart damage.
Coronary Angiography: A catheter-based X-ray test used to check the coronary arteries for blockages or plaque rupture. It may be performed urgently or as a planned procedure, depending on the ECG findings and the patient's stability. If a blockage is found, a stent can be placed during the same procedure.
Blood Tests: Blood tests check for heart muscle damage, electrolyte imbalances, thyroid, kidney, and liver problems, abnormal blood sugar, drugs or toxins, and blood oxygen and acid–base balance. These tests help identify possible causes of cardiac arrest and abnormal heart rhythms.
Cardiac MRI: It detects heart muscle inflammation, fatty replacement of the right ventricle, heart muscle scarring, blood clots, and other structural abnormalities. It is particularly useful when an echocardiogram is inconclusive or when coronary artery disease does not explain the cardiac arrest.
CT Coronary Angiography: A non-invasive CT scan that looks at the coronary arteries. It is used when catheter angiography is unnecessary or unavailable, and in lower-risk patients after cardiac arrest to assess for coronary artery disease when urgent angiography was not performed.