Imaging assessment of left ventricular function

Global function and calculated parameters

Hemodynamic assessment is based on the ratio of ejected blood volume to ventricular dimensions. To standardize parameters across different patients, normalization to body surface area (body surface area) is used.

Key volumetric parameters:

• End-diastolic volume (EDV) — maximum chamber filling at the end of diastole (end-diastolic volume).
• End-systolic volume (ESV) — residual volume after maximum emptying (end-systolic volume).
• Stroke volume (SV) — difference between EDV and ESV (stroke volume).
• Ejection fraction (EF) — ratio of stroke volume to end-diastolic volume (ejection fraction).
• Cardiac output (CO) — product of stroke volume and heart rate (cardiac output).

Volumes can be calculated in two ways. The geometric model (geometric assumption) works quickly but depends on the ventricular shape being ideal; it is extremely inaccurate in deformations (e.g., post-infarction aneurysm) and the complex anatomy of the right ventricle. The volumetric method (slice summation) sums the volumes of multiple adjacent slices. It requires more analysis time but yields the most accurate figures.

Myocardial strain and wall motion abnormalities

In systole, the ventricle ejects approximately 2/3 of its volume. The complex architecture of muscle fibers provides not just compression, but complex deformation (myocardial strain): shortening along axes, wall thickening, and characteristic twisting (torsion).

Visual analysis of regional wall motion (wall motion) distinguishes:

1. Normokinesia — adequate wall motion.
2. Hypokinesia — reduced contraction amplitude.
3. Akinesia — complete absence of motion in the affected area.
4. Dyskinesia — paradoxical outward bulging of the wall during systole.
5. Hyperkinesia — enhanced motion (often as a compensatory reaction of adjacent healthy zones).

Systolic wall thickness is also evaluated: from normal thickening to its absence or thinning (wall thinning).

American Heart Association 17-segment model

To standardize the description of the LV regardless of modality (whether ultrasound or MRI), the AHA model is used, often presented as a polar 'Bull's eye plot' (Bull's eye plot). The ventricle is conventionally sliced along the short axis into four levels:

• Basal level (6 segments: anterior, inferior, septal, and lateral).
• Mid-ventricular level (6 segments with analogous names).
• Apical level (4 segments: anterior, septal, inferior, lateral).
• Apex (1 segment, evaluated on the long axis).

Segments correspond to the blood supply territories of the major coronary arteries: the left anterior descending (LAD), right coronary (RCA), and circumflex (LCx) arteries. However, in myocardial infarction, this model has limitations: the actual necrosis zone may occupy only part of a segment, intermingling with viable tissue. In such situations, compartmental models more accurately reflect the extent of damage.

Main imaging modalities

• Echocardiography (Echocardiography). First-line, bedside method. Allows visualization of infarction complications (thrombi, aneurysms), but suffers from a suboptimal acoustic window in some patients and is forced to rely on geometric assumptions.
• Cardiovascular MRI (CMR). The gold standard for volumetry. 'Bright-blood' scanning with a balanced SSFP sequence provides excellent myocardial-blood contrast without iodinated agents. Slice series are aligned along the long axes (horizontal and vertical) and the short axis.
• Cardiac CT (CCT). An alternative to MRI for volume assessment, but entails radiation exposure throughout the cardiac cycle and requires intravenous contrast.
• Radionuclide methods. Planar ventriculography and ECG-gated SPECT (gated blood pool SPECT) allow assessment of wall motion and regional ejection fraction.

Functional significance of stenoses and stress imaging

The anatomical severity of a vascular stenosis (even on CT coronary angiography) correlates poorly with actual physiological blood flow. This is why revascularization without proven ischemia often fails to reduce mortality compared to optimal medical therapy.

The functional severity of a stenosis can be assessed invasively during catheterization by measuring the fractional flow reserve (Fractional Flow Reserve, FFR). A drop in the index to 0.75 and below is a reliable sign of inducible ischemia. To select patients for revascularization non-invasively, stress testing is used. It aims to detect reversible ischemia, which manifests as angina symptoms, ECG changes, perfusion defects, or the appearance of regional wall motion abnormality zones. Intervention is indicated for a significant ischemic burden (>5–10%).

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Phases of the cardiac cycle: valvular events and isovolemic periods.
• Quantitative assessment of myocardial deformation: speckle-tracking and MRI tagging.
• Prognostic significance of right ventricular assessment in myocardial infarction.
• Compartmental models of infarction distribution versus the 17-segment model.
• High-resolution imaging features of coronary stents (photon-counting).

Other topics in the «Chest Radiology» section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.