Septal flash

Septal flash, also known as septal beaking, is a sign of interventricular dyssynchrony seen on echocardiography or cinematographic cardiac CT/MRI. It represents an abnormal rapid movement pattern of the interventricular septum during pre-ejection systole (i.e. isovolumic contraction):

• septal motion towards the left ventricle ("posteriorly" or "leftward")
• septal motion away from the left ventricle ("anteriorly" or "rightward")

Clinical presentation

The attendant reduction in left ventricular function which often accompanies these entities is that of the heart failure syndrome, including;

• fatigue
• reduced exercise tolerance
• exertional chest pain and/or dyspnea
• anorexia, right upper quadrant pain

ECG

• left bundle branch block
  • widening of the QRS complexes (> 0.12s) with tall, broad monophasic (or notched) R waves in the lateral leads (I, aVL, V4-6, lead II less commonly)
    • associated with discordant ST segment deviation
  • right-sided precordial leads (V1-3) will be predominantly negative (rS or QS complexes, PRWP common) with discordant ST segment deviation
• ventricular paced rhythm
  • sharp pacer "spike" may be present preceding the QRS
  • impulses originate from the right ventricle, with the depolarization vector spreading through myocytes (prolonging the QRS duration) from right to left (thereby producing predominantly negative QS or rS complexes in the right precordium with large positive R waves in the leads I, aVL, V4-5)
  • discordant ST segment deviation is also present 
  • apical location of the pacer lead results in predominantly negative QRS complexes in the inferior leads and resultant left axis deviation (in the frontal plane)

The differentiation of the two rhythms may be difficult, and might be accomplished by looking at lead V6; the polarity of the QRS complex should be positive in a left bundle branch block and is often negative with a prominent S wave in a ventricular paced rhythm. 

Pathology

The finding is seen mainly in left bundle branch block and right ventricular pacing, due to early activation of the interventricular septal myocardium ^1,2,3. The presence of either entity is best ascertained using electrocardiography.

Normally, the interventricular septum moves slightly rightward during early systole, and leftward towards the center of the left ventricle during late systole, together with the other left ventricular walls. In this way, the circular contour of the left ventricle in the short axis is maintained throughout systolic contraction ⁵.

With ventricular dyssynchrony, the septum is activated early in relation to the left ventricle, resulting in myocardial shortening and fast leftward movement. Immediately afterwards, the septum is paradoxically "pushed" rightward towards its presystolic position - this is thought to be due to force from the delayed left ventricular lateral wall activation ¹.

The net effect may be conceptualized as a distorted left ventricular morphology throughout systole (loss of normal circular short-axis contour ¹), signifying inefficient left ventricular function or impaired "squeeze".

Treatment and prognosis

In patients with heart failure with reduced ejection fraction, the presence of septal flash indicates a correctable mechanical abnormality and is a strong favorable predictor of response to cardiac resynchronization therapy (eg, achieving reverse remodeling with improved left ventricular ejection fraction and decreased end-systolic volume) ^4,6.

History and etymology

Abnormal interventricular septal motion has been described since the 1970s by echocardiography. The term "septal beaking" refers to a peaked septal motion tracing on M-mode imaging ¹. This "beak" is observed in the parasternal long-axis view, occurring just prior to the R wave upstroke (if ECG gating is utilized). The term "septal flash" refers to the same finding as assessed by tissue Doppler echocardiography ¹. The terms are used interchangeably ² but the latter has been adopted in cardiac MRI as well ^6,7.

Differential diagnosis

• septal bounce occurs in early diastole as opposed to early systole
  • constrictive pericarditis
  • cardiac tamponade
  • myocardial ischemia
    • associated with regional wall motion abnormalities which demonstrate reduced systolic wall thickening (< 40%)
    • the anterolateral and inferolateral myocardial segments are unaffected in the setting of a left bundle branch block
      • might be involved with ischemia affecting the left circumflex or the left anterior descending artery proximal to the first diagonal branch
    • the apical segments of the left ventricle should also be spared in left bundle branch block