Sudden Cardiac Death Case File

Sudden Cardiac Death Case File

Eugene C. Toy, Md, Michael d . Faulx, Md

Case 14

A 17-year-old man is brought to the emergency room after collapsing at soccer practice. After training hard for 30 minutes. and just after completing a sprinting exercise, he suddenly fell to the ground. His coach noted that he wasn’t breathing and couldn’t find a pulse and began to administer CPR He regained conscious ness rapidly and is now feeling well. He has no past medical history apart from one prior episode of syncope during athletic training that was attributed to dehydration. He is adopted and is unaware of his family history. His vitals are as follows: BP 118/76, heart rate 58 bpm, and regular, oxygen saturation 99% on room air. Physical examination is remarkable for a late systolic murmur loudest at the left sternal edge that is increased by the ValsaIva maneuver. His ECG is shown in Figure 14-1.

• What is the most likely diagnosis?
• What is the best next diagnostic step?
• What is the best next step in therapy?

Figure 14-1. ECG of the main subject of this case. (Reproduced, with permission, from Michael Faulx, MD.)

Answer to Case 14:

Sudden Cardiac Death

Summary: A 17-year-old man without medical history presents with two episodes of syncope during exercise. The current episode was associated with apnea and pulselessness, suggestive of a serious arrhythmia that spontaneously resolved. His physical examination is suggestive of dynamic outflow tract obstruction, and his ECG reveals significant left ventricular hypertrophy.

• Most likely diagnosis: Sudden cardiac arrest secondary to hypertrophic cardiomyopathy.
• Next diagnostic step: Echocardiogram.
• Next step in therapy: Beta-blocker, cardiac electrophysiology consultation for consideration of implantable cardioverter defibrillator (ICD) implant.

ANALYSIS

Objectives

1. Know the definition and epidemiology of sudden cardiac death (SCD).
2. Describe the conditions that incur an elevated risk of SCD.
3. Summarize risk stratification and prevention of SCD in patients with reduced ejection fraction.

Considerations

Syncope in young patients is usually caused by benign mechanisms; however, certain features of syncope are indicative of serious ventricular arrhythmias. Syncope during exercise may indicate ventricular arrhythmia or left ventricular outflow tract obstruction, both of which are possible in this case. Syncope in a young healthy male, in the absence of obvious vasovagal triggers, is unusual and suggests a cardiac cause. The ECG and physical examination in this case both point to hypertrophic cardiomyopathy, which is associated with syncope and an increased risk of sudden cardiac death.

Approach To:

The Survivor of Sudden Cardiac Arrest

DEFINITIONS

SUDDEN CARDIAC DEATH (SCD): Defined as death following cardiac arrest in a patient with or without known preexisting heart disease in whom the mode and time of death are unexpected. Death generally occurs rapidly after the cardiac arrest with less than one hour between the onset of symptoms and loss of consciousness, although patients who survive for longer after receiving medical interventions and then expire are also considered to have suffered SCD.

SUDDEN CARDIAC ARREST: Sudden and unexpected cessation of cardiac output resulting in loss of consciousness. This is almost invariably due to either tachy- or bradyarrhythmia. Sudden cardiac arrest (SCA) refers to an event that the patient survives, due to spontaneous recovery or defibrillation, and is sometimes called aborted sudden death.

CLINICAL APPROACH

Etiologies

The annual incidence of SCD in the United States is approximately 460,000 cases, accounting for 10–15% of all deaths. SCD is more common in males and rises in incidence after age 30 years, due to the increased incidence of coronary artery disease. While the absolute risk of SCD is greater among high-risk populations, most instances of SCD occur in patients who do not have known risk factors. The terminal rhythm may be ventricular fibrillation (VF), ventricular tachycardia (VT), asystole, or pulseless electrical activity.

Coronary artery disease accounts for around 80% of SCD episodes in the United States, and SCD is sometimes the first presentation of CAD. SCD may result from acute ischemia during myocardial infarction, but more commonly is due to ventricular tachycardia or fibrillation caused by myocardial scar from a previous infarct. Other cases may be due to bradyarrhythmias occurring in the setting of severe congestive heart failure in patients with ischemic cardiomyopathy. As such, patients with reduced left ventricular ejection fraction due to prior myocardial infarction have an elevated risk of SCD.

Dilated (nonischemic) cardiomyopathy (DCM) is the underlying cause of approximately 10% of cases of SCD. The mechanisms responsible for SCD in DCM are similar to the mechanisms at play in ischemic cardiomyopathy, namely, scar-related ventricular tachycardia and fibrillation, and bradyarrhythmias due to severe heart failure. Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiovascular disease with a prevalence of 1 in 500. Most but not all patients with HCM have a left ventricular outflow tract gradient, and various phenotypes are recognized. SCD occurs at a rate of about 1% per year, and is predicted by several risk factors: prior SCA, family history of SCD, nonsustained VT, syncope, drop in blood pressure with exercise, and interventricular septal diameter ≥30 mm.

That said, most patients have few or no symptoms and experience no limitation of life expectancy–indeed, many remain undiagnosed. Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C) is a rare genetic cardiomyopathy characterized by heart failure, ventricular tachycardia, and SCD. The causative mutations involve the desmosome. The ECG may show right bundle branch block (RBBB), T wave inversion in V1–V3 and epsilon waves and regional RV motion abnormalities may be seen on echo or MRI.

The channelopathies are genetic disorders of the cardiac ion channels that cause SCD in patients with apparently normal hearts. The most common is the long QT syndrome (LQTS). This has a prevalence of about 1:2,000, and is characterized by an abnormally long QT interval. The main risk is for torsade de pointes causing syncope or SCD. To date, at least 12 different LQTS susceptibility genes have been identified, involving potassium, sodium, and other channels. ECG patterns, arrhythmic triggers (exercise, auditory stimuli, sleep), and effectiveness of therapy vary with the underlying genotype. LQTS is likely a common cause of sudden infant death syndrome (SIDS). Patients are typically treated with beta-blocker therapy. Patients with syncope or SCA despite beta-blocker therapy are treated with ICD implantation and/or left cardiac sympathetic denervation. Patients may also develop acquired long QT due to QT-prolonging drugs or drug-drug interactions involving such drugs, and this may also result in SCA or SCD.

Special care should be exercised when prescribing these agents, especially in elderly females, who are at the highest risk. Brugada syndrome is an autosomaldominant disorder caused by mutations in the SCN5A gene encoding the cardiac sodium channel, which leads to an increased risk of polymorphic VT or VF and SCD. A diagnostic ECG pattern of incomplete RBBB with coved ST segment elevation in leads V1–V3 may be transient or apparent only with drug challenge (Figure 14-2). Arrhythmias commonly occur during sleep, and the risk of SCD is highest in patients with a spontaneous Brugada ECG pattern or prior SCA or syncope. Such patients should undergo ICD implantation; the role of an ICD in asymptomatic patients remains controversial. Pharmacologic therapy is limited to quinidine for selected patients. Catecholaminergic polymorphic ventricular tachycardia (CPVT) is due to mutations in the ryanodine receptor, which controls calcium release from the sarcoplasmic reticulum and results in bidirectional VT during emotional or physical stress. The risk of SCD is high, and treatment is with beta-blockers, flecainide, and an ICD.

Some patients with Wolff-Parkinson-White syndrome also have an increased risk of SCD. This is not related to supraventricular tachycardia but occurs when atrial fibrillation is conducted very rapidly to the ventricles over the accessory pathway and degenerates into VF. The overall incidence of SCD is 0.05–0.1% per year, and exercise testing, Holter monitoring and invasive electrophysiologic studies are used to risk-stratify patients. The main cardiac and noncardiac causes of SCD are presented in Table 14-1.

Clinical Presentation

Both SCA and SCD present with sudden collapse and loss of circulation. Prodromal symptoms are often present where acute ischemia is the causative event, but are

Figure 14-2. Typical Brugada syndrome ECG. (Reproduced, with permission from, Thomas Callahan, MD.)

generally absent with most other causes. The vast majority of events occur outside of hospitals in everyday settings such as the home, workplace, and public places. The time from onset of SCA to treatment with basic life support (BLS) techniques, such as CPR and defibrillation with an automated external defibrillator (AED), is critically predictive of subsequent survival. People who suffer SCA witnessed by a bystander, who may then initiate CPR and call for help, are more likely to survive than those whose event is unwitnessed. This has led to a movement to educate and train the public in BLS and provide AEDs in public places where SCA is likely to occur and be witnessed, which has been associated with improved survival in airports for instance. Current BLS guidelines emphasize continuous high-quality chest compressions as the most effective way to provide circulatory support and aim to minimize interruptions to this.

Treatment

Treatment of the survivor of SCA is initially focused on hemodynamic support, and the discovery and correction of precipitating causes. Electrogram strips from an AED, if used, are invaluable and should be retrieved and carefully preserved for future review. Therapeutic hypothermia leads to improved neurological outcome and survival after successful revival following cardiac arrest in patients with depressed neurologic function. Amiodarone or lidocaine may be infused in the case of recurrent arrhythmia. Temporary transcutaneous and then transvenous pacing is used when bradyarrhythmias are causative. If acute ischemia is evident by ECG or by patient or witness report of symptoms, immediate coronary angiography is indicated. Electrolyte abnormalities should be sought, although interpretation can be difficult in the setting of prolonged resuscitation. Toxicology and cardiac biomarkers are also routinely ascertained. Radiology studies are guided by specific symptoms, signs, or past medical history.

After acute postarrest management, the survivor of SCA should undergo a detailed assessment under the supervision of a cardiologist or cardiac electrophysiologist experienced in such testing. The 12-lead ECG may reveal acute or prior ischemia, conduction defects, an accessory pathway, HCM, or channelopathy. An echocardiogram is used to assess left ventricular function, valvular abnormalities, and cardiomyopathy. Cardiac MRI is a particularly useful tool and complementary to echo, especially for assessment of HCM and ARVD/C. Drug challenge may be used to assess for Brugada syndrome, LQTS, and CPVT. Genetic testing is useful in specific situations, but given the large number of mutations, including those not yet described, has poor negative predictive value.

The implantable cardioverter defibrillator (ICD) was a major advance in the treatment of survivors of SCA. Similar in design to a pacemaker, it consists of a generator (which contains the battery and circuitry) that is implanted in the upper chest, connected to one or more insulated leads that run via the subclavian vein to the heart. The ICD constantly monitors cardiac rhythm and, on detection of VT or VF, can deliver antitachycardia pacing or a shock to terminate the rhythm. Multiple randomized controlled trials demonstrated superior survival with an ICD compared to antiarrhythmic drugs. Amiodarone and sotalol are still used to reduce arrhythmias in patients with an ICD, but should not be recommended alone for prevention of SCD.

Similar to secondary prevention, antiarrhythmic drugs are not useful for the primary prevention of SCD in patients with ischemic or nonischemic cardiomyopathy. As the left ventricular ejection fraction (LVEF) is the strongest single predictor of future SCD in these patients, it is used as a risk stratification tool. Primary prevention ICD implantation is offered to those patients with ischemic or nonischemic

cardiomyopathy whose ejection fraction, despite guideline-recommended medical therapy, remains less than or equal to 35% (normal, >55%). This led to an approximately 0.25–1 relative third reduction in mortality over medium-term follow-up in several randomized clinical trials. In the current era, about 10% of patients with heart failure and a primary prevention ICD receive appropriate ICD therapy in the first year after implant, with slightly fewer receiving an inappropriate shock (a shock delivered for a rhythm other than VT/VF). Implantation within 40 days of myocardial infarction or 3 months of surgical or percutaneous revascularization is seldom performed, to allow for improvement in LVEF and as clinical trials have failed to show benefit within these timeframes.

The prognosis of sudden cardiac arrest remains grim. Of the just over half of events in which resuscitation is attempted, fewer than 10% survive to hospital discharge. There is significant regional variation within the United States, likely due to the efforts of some communities to train the general population in CPR and improve and coordinate emergency medical service (EMS) assets. Prognosis is improved if the initial rhythm is VT or VF (therefore treated with a defibrillation shock and termed “shockable rhythms”), if the SCA is witnessed, and if bystander CPR is administered.

Future directions in the prevention and treatment of SCA lie in “primordial prevention,” which refers to interventions to reduce the prevalence of risk factors for coronary artery disease in the population, and refinement of the current LVEF-centered approach to risk stratification in those with established risk factors for SCA.

CASE CORRELATION

• See also Case 1 (acute coronary syndrome/STEMI), Case 2 (acute coronary syndrome/NSTEMI), and Case 8 (hypertrophic obstructive cardiomyoopathy).

COMPREHENSION QUESTIONS

14.1 A 55-year-old man presents via the emergency department for management following a witnessed cardiac arrest that was preceded by chest pain and successfully aborted by a bystander who used an automated external defibrillator (AED) at the scene. His ECG following his resuscitation revealed 3-mm ST segment elevation in the inferior leads, and he was sent for emergent coronary angiography that revealed acute thrombotic occlusion of the proximal right coronary artery. He was treated with aspiration thrombectomy and PCI with stenting, and his remaining hospital course was unremarkable. His predischarge echocardiogram revealed preserved left ventricular systolic function with mild inferior hypokinesis and an ejection fraction of 55%. He was discharged on metoprolol, lisinopril, atorvastatin, aspirin, and ticagrelor. Which of the following statements is true regarding the secondary prevention of cardiac arrest in this patient?

A. This patient should undergo ICD implantation prior to discharge.

B. This patient should undergo ICD implantation 3 months after his event.

C. This patient should have an electrophysiology study to assess his need for an ICD.

D. This patient should be treated with an antiarrhythmic drug.

E. This patient should require no additional management for arrhythmia.

14.2 Which of the following statements regarding out-of-hospital sudden cardiac arrest (SCA) is true?

A. Bystander CPR is associated with reduced survival in SCA.

B. An initial rhythm of VT/VF is associated with reduced survival in SCA.

C. Interruption of CPR does not impact outcome in SCA.

D. The provision of AEDs in public places is associated with reduced survival in SCA.

E. Therapeutic hypothermia improves neurological outcome after SCA in patients with depressed mental status after resuscitation.

14.3 A 30-year-old woman with a peripartum cardiomyopathy sees you for a scheduled follow-up visit. She was diagnosed with dilated cardiomyopathy 10 months ago when she was hospitalized with decompensated heart failure, and her ejection fraction was found to be approximately 10%. She was treated with medical therapy, which presently includes carvedilol, ramipril, spironolactone, and furosemide, and over time her ejection fraction increased to 25%, but it has remained there in the face of maximal medical therapy. She presently feels well and describes mild dyspnea with moderate physical activity. Her physical examination today is unremarkable. Her ECG reveals sinus rhythm with a heart rate of 60 bpm and a narrow QRS (94 ms). At her last office visit you discussed the possible role of an implantable cardiac defibrillator (ICD) in her care. Her echocardiogram today reveals a dilated left ventricle with an ejection fraction of 23%. Which of the following statements regarding ICD therapy for this patient is true?

A. ICD therapy will improve her exertional symptoms.

B. ICD therapy will reduce her mortality.

C. ICD therapy will allow her to discontinue some of her current medications.

D. ICD therapy would be equivalent to treatment with amiodarone in terms of survival.

E ICD therapy would likely result in at least one shock the 12 months following implantation.

ANSWERS

14.1 E. This patient should not require additional management for arrhythmia. Although he presented with a shockable (VT/VF) cardiac arrhythmia, this occurred in the context of an acute inferior myocardial infarction that was promptly and successfully revascularized. In the absence of recurrent ventricular arrhythmias and in the presence of normal systolic function, this patient would be considered to be at acceptably low risk for recurrent arrhythmia and would not require additional assessment with an EP study or consideration for ICD implantation. Antiarrhythmic therapy has not conclusively reduced mortality in patients who survival cardiac arrest.

14.2 E. Therapeutic hypothermia for 24–36 hours following revival after cardiac arrest in patients with altered mental status. Survival following out-of-hospital cardiac arrest has improved in recent years in part because of better awareness of heart disease in the general population and the availability of AED therapy in public places. Immediate, uninterrupted bystander CPR also improves outcome, as does presenting initially with a “shockable” rhythm such as VT or VF.

14.3 B. This patient would be expected to derive a survival benefit from ICD implantation. ICD implantation does not improve heart failure symptoms unless the patient undergoes implantation of a cardiac resynchronization therapy (CRT) device; our patient has mild symptoms and a normal QRS duration, which would likely preclude CRT therapy. In the first year after implantation approximately 10% of heart failure patients receiving an ICD for primary prevention will receive an appropriate shock from their devices.

CLINICAL PEARLS

• The term sudden cardiac death (SCd) applies if the patient has died otherwise, sudden cardiac arrest (SCA) is used.
• Most episodes of SCd occur in patients with coronary artery disease; such patients should undergo risk assessment with echocardiography to determine 1 VEF.
• Continuous high-quality CPR followed by advanced cardiac life support (AC1 S) algorithms and further diagnostic and therapeutic procedures as dictated by the individual circumstances, are the priorities in the management of SCA.
• An lCd should be offered to survivors of cardiac arrest in whom a clear transient and reversible cause cannot be proven.
• Primary prevention lCd s are offered to patients with heart failure and 1VEF<35% on optimal medical therapy.
• Primary prevention lCd s lead to a 0.25—0.33 reduction in mortality in selected patients.

References

Buxton AE. Risk stratification for sudden death in patients with coronary artery disease. Heart Rhythm. 2009;6:836–847. 

Connolly SJ, Hallstrom AP, Cappato R, et al. Meta-analysis of the implantable cardioverter defibrillator secondary prevention trials. Eur Heart J. 2000;21(24):2071–2078. 

Epstein AE, DiMarco JP, Ellenbogen KA, et al. American College of Cardiology Foundation; American Heart Association Task Force on Practice Guidelines; Heart Rhythm Society. 2012 ACCF/AHA/ HRS focused update incorporated into the ACCF/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities: a report of the American College of Cardiology Foundation/ American Heart Association Task Force on Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2013;61:e6–e75. 

Hazinski MF, Nolan JP, Billi JE, et al. Part 1: Executive summary: 2010 international consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations. Circulation. 2010;122(16 Suppl 2):S250–S2575. 

The Hypothermia After Cardiac Arrest Study Group. Mild therapeutic hypothermia to improve the neurologic outcome after cardiac arrest. N Engl J Med. 2002;346:549–556. 

Myerburg RJ, Castellanos A. Cardiac arrest and sudden cardiac death. In: Libby P, Bonow RO, Mann DL, Zipes DP, eds. Braunwald’s Heart Disease: A Textbook of Cardiovascular Medicine. 9th ed. Elsevier, Sauders, Philadelphia, PA; 2011:chap 41. 

The Public Access Defibrillation Trial Investigators. Public-access defibrillation and survival after out-ofhospital cardiac arrest. N Engl J Med. 2004;351:637–646.

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