Evaluation of Unexplained Sudden Cardiac Death

FIGURE 50-1 Twelve-lead electrocardiogram obtained from the patient following resuscitation of aborted sudden cardiac death. Notable findings include down-sloping J-point elevation of 0.1 mV in the inferior and lateral leads. There is also marked associated notching of the QRS in the affected leads. While the QT is prolonged, the QTc corrected for bradycardia is normal at 445 ms.

EXPERT PRESENTATION

• Prior to the evaluation of any episode of sudden cardiac death (SCD), prompt resuscitation and the stabilization of any electrical or hemodynamic instability is imperative. If the patient is unable to follow commands following return of spontaneous circulation, or a substantial period of cerebral hypoxia is suspected, then therapeutic hypothermic cooling should be considered.

• The initial evaluation of SCD should include:

A thorough history collected from the patient, first responders, witnesses, and family members regarding preexisting cardiovascular disease, cardiac symptoms, previous syncopal events, medications (both prescription and over-the-counter), and a family history of SCD. Included in the latter should be a screen for suspicious deaths in the family, that is, epilepsy, drownings, single motor vehicle accidents, and sudden infant death syndrome (SIDS).

A 12-lead ECG and rhythm strip to assess for any evidence of ischemia, ongoing arrhythmia, or suggestive findings of a cardiomyopathy or ion channelopathy.

In adults, coronary angiography to rule out an acute coronary syndrome as the cause of SCD. Computed tomography in younger patients may be considered.

Echocardiography to assess for any structural cardiac abnormalities.

• In the event that a diagnosis is not evident after this preliminary screen, the following potential etiologies for a ventricular tachyarrhythmia must be entertained:

Primary electrical causes/inherited ion channelopathies: Long QT syndrome (LQTS), short QT syndrome (SQTS), Brugada syndrome (BrS), catecholaminergic polymorphic ventricular tachycardia syndrome (CPVT).

Subclinical structural disease: Coronary vasospasm, anomalous coronary arteries and cardiomyopathies including arrhythmogenic right ventricular cardiomyopathy (ARVC), hypertrophic cardiomyopathy (HCM), noncompaction, infiltrative cardiomyopathies.

• Further evaluation may include:

Consultation with a center with expertise in nonischemic sudden death conditions.

Exercise ECG testing to assess for failure of the QT interval to shorten with exercise (LQTS) or initiation of polymorphic or bidirectional ventricular tachycardia (CPVT).

Modified ECG with V₁ and V₂ leads placed 1 or 2 interspaces higher to improve the sensitivity of detecting a Brugada pattern.

Signal-averaged ECG (SAECG), which has utility in diagnosing ARVC.

Cardiac MRI (with contrast) to assess for cardiomyopathies with subtle structural abnormalities.

Pharmacologic challenge: Epinephrine infusion may make latent LQTS and CPVT apparent; procainamide infusion can unmask a Brugada pattern.

Genetic testing: If an inherited ion channelopathy or cardiomyopathy (eg, ARVC) is suspected, then genetic testing may reveal a mutation associated with the condition. A negative result does not exclude any of these conditions; the finding of a gene mutation of uncertain significance is much less helpful both diagnostically and with regards to screening of family members (see Chapter 51, Genetic Testing for Assessment of Inherited Arrhythmias).

DIAGNOSIS AND MANAGEMENT

• The patient demonstrated excellent neurologic recovery once extubated, and a comprehensive history was obtained from him with corroborative details from family members.

He had no previous history of cardiac diagnoses or symptoms.

There is no family history of unexplained syncope or cardiac arrest.

• A comprehensive diagnostic evaluation was performed in order to elucidate the etiology of the patient’s aborted sudden cardiac arrest:

Exercise treadmill test: The patient exercised to 10.4 METS (9 minutes) with no inducible arrhythmias and no abnormal prolongation of the corrected QT interval (QTc) at peak exercise or recovery.