Sudden cardiac death
Formal Definition
Unexpected natural death from cardiac causes within 1 hour of symptom onset (or unwitnessed within 24h of last being seen in normal health), most commonly due to ventricular arrhythmias (VF, VT) in the setting of underlying structural heart disease (ischemic cardiomyopathy, heart failure) or inherited channelopathies (long QT syndrome, Brugada syndrome, hypertrophic cardiomyopathy); the majority occur out-of-hospital with extremely low survival rates without immediate bystander CPR and defibrillation; primary prevention (ICD for EF <35%) and community AED programs are key public health interventions.
How It's Used on the Ward
"SCD" or "cardiac arrest" — the patient s heart suddenly goes into a fatal rhythm (usually VF) and they collapse; survival depends on immediate CPR and defibrillation; the underlying cause is usually coronary disease or a scarred heart from prior MI; survivors need to be worked up for the cause and often need an ICD.
Example
""62-year-old male watching television, suddenly collapsed. Wife called 911. EMS arrived 9 minutes later — CPR in progress, AED attached: shockable rhythm (VF). First shock delivered (200J biphasic), CPR resumed. Second shock after 2 min of CPR: still VF. Amiodarone 300mg IV after second shock. Third shock: organized rhythm achieved. ROSC achieved after 18 minutes. Transported to ED: BP 92/60, intubated, therapeutic hypothermia protocol initiated (target 33°C for 24h). Cardiology admits: EF 30% on echo (newly reduced), LAD disease on cath. ICD placed before discharge. Diagnosis: sudden cardiac death from VF in setting of ischemic cardiomyopathy with reduced EF.""
Clinical Context
Most common mechanism: VF or pulseless VT (~80%). Risk factors: coronary artery disease (80% of SCD in adults), reduced EF (strongest predictor — EF <35% = ICD indication for primary prevention), prior MI, heart failure, inherited channelopathies. Evaluation after ROSC: cardiac catheterization (rule out acute coronary syndrome), echocardiogram (EF assessment), cardiac MRI (scar quantification), genetic testing if channelopathy suspected (LQTS, Brugada, HCM). Therapeutic hypothermia (targeted temperature management 32-36°C for 24h): standard of care post-ROSC for comatose patients. ICD implantation: secondary prevention (survived VF/VT arrest → ICD regardless), primary prevention (EF <35%, NYHA II-III, 40 days post-MI). Community response: AED placement, CPR training, public access defibrillation programs. Survival from out-of-hospital VF: ~10% overall, ~30-40% with immediate bystander CPR.