Chapter 31-8: Cardiac Syncope

TEXTBOOK PRESENTATION

Cardiac syncope refers to syncope secondary to disorders arising within the heart. Arrhythmias (either tachyarrhythmias or bradyarrhythmias) are the most common. Less common disorders include acute coronary syndromes, obstructive syndromes (aortic stenosis, HCM and pulmonary embolism), and rare causes (aortic dissection and atrial myxoma). Classically, patients with cardiac syncope are elderly patients with known heart disease (ie, HF or CAD) who experience sudden syncope, which may occur without warning. Patients may have palpitations.

DISEASE HIGHLIGHTS

1. Cardiac syncope is associated with markedly increased mortality compared with reflex syncope, orthostatic syncope, or syncope of unknown cause.

2. Among patients with dilated cardiomyopathy, sudden cardiac death (presumably arrhythmogenic) accounts for 30% of the mortality.

3. Patients in whom cardiac syncope is suspected should be admitted for evaluation.

4. Although there are a large number of cardiac dysrhythmias, only a relative few produce syncope. Most supraventricular tachyarrhythmias will not cause syncope because the AV node limits the ventricular response rate. The most common arrhythmias associated with syncope include

   1. Tachycardias

      1. VT

      2. Supraventricular tachycardias associated with an accessory pathway (ie, WPW syndrome) or those associated with a very rapid ventricular responses.

   2. Bradycardias

      1. Sinus node dysfunction

         1. Sinus bradycardia (< 35 bpm)

         2. Sinus pauses (defined as > 3 seconds or > 2 seconds with symptoms)

      2. AV heart block (second- or third-degree)

      3. Atrial fibrillation with a slow ventricular response

EVIDENCE-BASED DIAGNOSIS

1. History

   1. Certain clinical findings substantially increase the likelihood of cardiac syncope when present, including

      1. Preexistent heart disease

      2. An abnormal ECG

      3. Syncope associated with chest pain

      4. Syncope during exertion (LR+, 6.5–14)

      5. Syncope when supine (LR+, 2.5 –∞) or sitting

   Syncope during exertion is unusual but worrisome and suggests cardiac syncope.

   2. Other symptoms may suggest cardiac syncope but are less specific (palpitations, syncope of sudden onset, dyspnea associated with syncope).

   3. A careful consideration of a patient’s associated symptoms, physical exam findings, or ECG abnormalities may suggest a particular cause of cardiac syncope (see Table 31-1).

   4. Cardiac syncope is unlikely in patients without known or suspected cardiac disease on the basis of the initial history, physical exam, and ECG (LR–, 0.09–0.12).

   5. Table 31-3 summarizes the sensitivity, specificity, and LR for symptoms in predicting cardiac syncope.

2. ECG

   1. An abnormal ECG increases the OR of cardiac arrhythmias in patients without vasovagal syncope (OR, 23.5 [CI, 7 – 87]).

   2. Certain ECG findings in patients with syncope may suggest particular cardiac etiologies (Table 31-1).

      1. ECG evidence of prior MI or a long QT interval increases the likelihood of VT.

      2. ECG findings of significant bradycardia, second- or third-degree AV block increase the likelihood of syncope due to sick sinus syndrome (SSS) or AV block.

      3. Bundle branch block (BBB) on ECG increases the likelihood of both AV block and VT.

         1. Mortality in patients with syncope and BBB is 28% at 40 months. 32% of the deaths were sudden death.

         2. The increased mortality is attributed to a combination of VT or electromechanical dissociation in ...