There are several distinct ECG patterns that deserve special mention because they can represent potentially lethal underlying pathology. Each of the ECG patterns discussed below, when recognized in the appropriate clinical situation, should prompt further investigation. Though not an exhaustive list, Table 17.1 summarizes the patterns discussed in this chapter.

Wellens’ Syndrome

Wellens’ syndrome is a pre‐infarct pattern seen on the 12‐lead electrocardiogram (ECG). It occurs in the patient with acute coronary syndrome (ACS), who may or may not be experiencing chest discomfort but in whom there is no other evidence of acute myocardial infarction. The natural history of the associated lesion is catastrophic anterior wall myocardial infarction or death within 60–90 days in up to 75% of such patients (Box 17.1).

Brugada Syndrome

In 1992, Pedro and Joseph Brugada described a syndrome that is associated with sudden cardiac death in patients with no atherosclerosis and a structurally normal heart. The abnormality found in these patients involves a mutation of the ion channels in the cardiac cell membrane. The mutation leads to a predisposition toward malignant dysrhythmias (Figure 17.2) that terminate in ventricular fibrillation. Patients with this syndrome were noted to have characteristic changes on their ECGs that can lead the informed clinician to diagnose a potentially fatal condition.

Electrocardiographic Manifestations

Characteristic electrocardiographic changes of Brugada syndrome include a complete or incomplete right bundle branch block and ST segment elevation in the right precordial leads (leads V1–V3; Figure 17.3). There are two types of ST segment morphologies that have been described:

ECG pattern	Etiology	Clinical manifestations
Wellens’ syndrome	High‐grade stenosis of the proximal LAD artery	Anterior wall STEMI Malignant ventricular dysrhythmia Death
Brugada syndrome	Genetic mutation of cardiac sodium channels	Syncope/“seizure”a Malignant ventricular dysrhythmia Sudden death
Hypertrophic cardiomyopathy (HCM)	Genetic mutation of cardiac sarcomere	Syncope (exertional) Malignant ventricular dysrhythmia Sudden death
Long QT syndrome (LQTS) – congenital	Genetic mutations of transmembrane ion channels	Syncope/“seizure”a Torsades de pointes Sudden death
Long QT syndrome – acquired	Medications/toxins, Electrolyte abnormality, CNS event	Syncope/“seizure”a Torsades de pointes Sudden death

^a Primary seizure disorder is not infrequently misdiagnosed when, in fact, the patient has experienced convulsive syncope as a result of a malignant ventricular dysrhythmia.

Convex upward “coved” elevation

• It has a positive terminal R wave and characteristic slurring of the S wave that may be either straight or convex (Figure 17.3a). It has an appropriately discordant (negative) T wave.

Concave upward “saddle‐type” elevation

• It is more easily identified by the “horse’s saddle” appearance of the ST segment elevation (Figure 17.3b). The terminal R wave is positive but the S wave forms a concave appearance with a positive T wave.

Clinicians should be aware that the characteristic patterns are not fixed but may change with influences such as fever, medications, and age.

Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is primarily a disorder of the myocardium (Box 17.2). At rest, most patients with HCM are asymptomatic. Symptoms usually manifest as patients are subjected to conditions producing decreased preload, afterload, or contractility – physical exertion, significant emotional distress, and so on. The most feared complication of HCM involves the development of malignant ventricular dysrhythmias, such as polymorphic ventricular tachycardia (Figure 17.2) or ventricular fibrillation. Such events occur most frequently in the setting of exertion – thus, exertional syncope is a typical presentation.