What is the twist score in cardiac function?

Left Ventricular Twist Score in Cardiac Function

LV twist is a quantitative measure of the wringing motion of the left ventricle during systole, calculated as the net difference in rotation between the apex and base, with normal values ranging from approximately 10-16 degrees in healthy adults. 1, 2

Definition and Physiologic Basis

LV twist represents the rotational deformation of the left ventricle resulting from the oblique orientation of myocardial fibers. 2 During systole, the apex rotates counterclockwise (when viewed from the apex) while the base rotates clockwise, creating a wringing motion that augments stroke volume and stores potential energy for early diastolic filling. 2

• Normal twist values: The mean net ventricular twist at end-systole is 12.6 ± 1.5 degrees in healthy subjects 2
• Regional variation: The anterior and lateral walls demonstrate significantly higher twist (20.6 degrees and 17.5 degrees respectively) compared to the inferior wall (8.8 degrees) and septum (3.5 degrees) 2
• Midpoint of rotation: Located at approximately 45% of ventricular length from base to apex 2

Measurement Technique

Twist is measured using speckle-tracking echocardiography (STE) or cardiac MRI with myocardial tagging, analyzing short-axis views at the basal and apical levels. 1, 3

• Peak apical rotation (Par) and peak basal rotation are measured separately 1
• Net twist = apical rotation - basal rotation 2
• Peak untwisting velocity (PUWV) and isovolumic diastole untwisting percentage (Iutw%) quantify diastolic function 1
• Measurements require frame rates >100 frames/second for optimal temporal resolution 3

Clinical Significance in Disease States

Heart Failure with Preserved Ejection Fraction (HFpEF)

Peak LV twist is significantly reduced in HFpEF patients (4.8 ± 2.6 degrees) compared to normal subjects (15.0 ± 3.6 degrees), making it a sensitive marker of myocardial dysfunction despite preserved ejection fraction. 1

• Peak apical rotation, PUWV, and Iutw% are all significantly decreased in HFpEF 1
• PUWV and Iutw% correlate positively with E/A ratio and E/e' ratio 1
• PUWV and Iutw% correlate negatively with left atrial volume index and NT-proBNP levels 1
• These parameters detect myocardial dysfunction earlier than conventional 2D echocardiography measures 1

Hypertrophic Cardiomyopathy (HCM)

HCM patients demonstrate increased basal rotation (-5.5 degrees vs -3.4 degrees in controls) and pattern-dependent apical rotation, with sigmoidal septal curvature showing higher twist (15.3 degrees) than reverse septal curvature (10.6 degrees). 4

• The pattern of LV hypertrophy significantly influences twist mechanics 4
• Untwisting at early diastole (5%, 10%, and 15% of diastole) is consistently decreased in HCM 4
• Twist abnormalities may be detected by MRI before structural changes become apparent on conventional imaging 5

Heart Failure with Reduced Ejection Fraction

Cardiac resynchronization therapy (CRT) response can be predicted by immediate improvement in LV twist, with responders showing increase from 4.3 ± 2.4 degrees to 8.5 ± 3.2 degrees at 6 months. 6

• Immediate post-CRT twist improvement is the strongest predictor of reverse remodeling (odds ratio: 1.899) 6
• LV lead position matters: apical and midventricular positions improve twist, while basal positions do not 6
• Twist remains severely reduced in heart failure (approximately 5 degrees) compared to normal (15 degrees) 6

Congenital Heart Disease Applications

MRI studies of systemic right ventricles and single ventricles may show abnormalities of myocardial twist, torsion, radial motion, shortening, and strain relations, providing critical functional assessment when conventional measures are inadequate. 5

• Twist assessment is particularly valuable in complex anatomy where standard ejection fraction calculations are unreliable 5
• Serial twist measurements may guide intervention timing in single-ventricle patients at risk for heart failure 5

Timing Considerations

LV twist increases steadily throughout systole after isovolumic contraction, with peak twist occurring at approximately 80% of systole, while the unwinding motion contributes critically to early diastolic filling. 5, 2

• During isovolumic contraction, all ventricular segments initially rotate counterclockwise 2
• Basal segments reverse direction mid-systole while apical segments continue counterclockwise 2
• Delayed peak untwisting rate indicates diastolic dysfunction even when other parameters appear normal 5

Clinical Pitfalls

• Twist measurements vary among ultrasound vendors and software versions, limiting direct comparison across platforms 5
• Technical challenges include requirement for high frame rates and optimal image quality at both basal and apical levels 3
• Loading conditions, heart rate, and age affect twist values and must be considered in interpretation 2
• Twist can be passive (tethering) rather than active contraction, particularly in regional dysfunction 5