Extracardiac Thoracoabdominal Atherosclerosis in Heart Transplant Candidates is not Associated with Standard Modifiable Cardiovascular Risk Factors

This study demonstrates that among heart transplant candidates, the burden of extracardiac thoracoabdominal atherosclerotic plaque is higher in those with ischemic cardiomyopathy but is not associated with the presence of standard modifiable cardiovascular risk factors, suggesting that these risk factors are ineffective markers for determining the need for atherosclerosis screening in this population.

The Gist

The Big Picture: Checking the "Pipes" Before the "Engine" Swap

Imagine your heart is the engine of a car. When an engine breaks down completely (heart failure), doctors sometimes need to swap it out for a new one (a heart transplant).

Before they install the new engine, they have to make sure the rest of the car—the fuel lines, the wiring, and the chassis—is in good shape. If the fuel lines are clogged with rust (atherosclerosis), a new engine might not last long because the "pipes" feeding it are damaged.

This study looked at a group of people waiting for a heart transplant. The doctors wanted to answer two big questions:

1. Does the type of heart failure matter? (Did the heart fail because of a clogged artery, or for some other reason?)
2. Can we predict how clogged the "pipes" are just by looking at the patient's "risk checklist" (smoking, diabetes, high blood pressure)?

The Surprise Discovery: The Checklist Was Wrong

Usually, doctors use a "Risk Checklist" (called SMuRFs) to guess how bad a patient's arteries are. This checklist includes:

• Smoking
• Diabetes
• High Blood Pressure
• High Cholesterol

The old thinking was: "If you have these risk factors, your pipes are probably rusty. If you don't have them, your pipes are probably clean."

This study found that this logic doesn't work for heart transplant candidates.

The researchers used a special 3D X-ray (CT scan) to look at the entire "plumbing system" from the neck down to the groin. They found that:

• The "Clean" Pipes Were Actually Dirty: Many patients who had zero items on the Risk Checklist (the "SMuRF-less" group) still had significant rust and clogs in their arteries.
• The "Dirty" Pipes Were Everywhere: Even patients who did have the risk factors didn't necessarily have more clogs than the "clean" group. The amount of rust was surprisingly similar between the two groups.

The Analogy: It's like checking a car's oil change history. You might think, "If this car never had an oil change (the risk factor), the engine must be ruined." But in this study, they found that some cars with perfect oil records had terrible engines, and some cars with messy records had surprisingly clean ones. The "history book" didn't tell the whole story; you actually had to look under the hood.

The Real Difference: Why the Heart Failed

While the "Risk Checklist" failed to predict the clogs, the reason the heart failed in the first place did matter.

• Group A (Ischemic): These patients had heart failure because their heart's own blood supply was blocked (like a clogged fuel line).
• Group B (Non-Ischemic): These patients had heart failure for other reasons (like a weak battery or a structural issue), not because of clogged arteries.

The Finding: The "Ischemic" group had significantly more rust and clogs in their body's arteries than the "Non-Ischemic" group. This makes sense: if your heart failed because of clogged arteries, it's likely your whole body's plumbing is clogged too.

Why This Matters for Patients

1. Don't rely on the "Low Risk" label.
If a patient waiting for a transplant says, "I don't smoke, I don't have diabetes, and my blood pressure is fine," doctors used to think, "Great, their arteries are probably fine."
This study says: "Wait, don't assume that." Even "perfect" patients can have dangerous clogs.

2. The scan is already happening, so let's use it.
Patients waiting for a heart transplant already get a full-body CT scan. Doctors usually do this just to make sure the patient doesn't have cancer before giving them a new heart.
This study suggests we should also use that same scan to look for clogged arteries. It's like getting a free bonus inspection. If the scan shows heavy rust, the doctors can treat the patient more aggressively (with better medicines) before and after the transplant to protect the new heart.

The Bottom Line

• The "Risk Checklist" is a bad map: Having no risk factors (no smoking, no diabetes) does not guarantee that your arteries are clean.
• The "Heart History" is a better map: If your heart failed because of clogged arteries, your whole body likely has clogged arteries.
• The Solution: We need to stop guessing based on the checklist and start looking at the actual "pipes" using the scans we are already taking.

In short: You can't judge a book by its cover, and you can't judge a patient's artery health just by their risk factors. You have to look at the picture.

Technical Summary

1. Problem Statement

Atherosclerotic cardiovascular disease (ASCVD) is the leading cause of global morbidity and mortality. Current risk stratification relies heavily on Standard Modifiable Risk Factors (SMuRFs): diabetes, hypertension, hyperlipidemia, and smoking. However, a growing phenotype of "SMuRF-less" patients experiences major adverse cardiac and cerebrovascular events (MACCE) despite lacking these traditional risk factors, highlighting a disconnect between conventional risk models and actual disease progression.

In patients with end-stage heart failure (ischemic or non-ischemic cardiomyopathy) awaiting heart transplantation, thoracoabdominal computed tomography angiography (CTA) is routinely performed to screen for malignancy. The authors posit that this existing imaging modality offers a unique, non-invasive opportunity to assess extracardiac atherosclerotic plaque burden across the entire aorta and its branches. The study aims to determine if this plaque burden correlates with SMuRFs or if it exists independently, particularly in "SMuRF-less" candidates, thereby challenging current risk assessment paradigms.

2. Methodology

• Study Design: Single-center, retrospective observational cohort study conducted at a tertiary referral hospital in Sydney, Australia.
• Population:
  • Inclusion: 167 heart transplant candidates (82 Ischemic Cardiomyopathy [ICM], 85 Non-Ischemic Cardiomyopathy [NICM]) who underwent thoracoabdominal CTA between 2012 and 2025.
  • Matching: NICM patients were matched to ICM patients by age and sex.
  • Exclusion: Patients with peripartum cardiomyopathy, prior heart transplants, or incomplete CTA imaging.
• Data Collection:
  • Clinical data (SMuRFs, comorbidities, medications) were extracted from medical records.
  • Patients were classified as SMuRF-less (absence of diabetes, hypertension, hyperlipidemia, and smoking) or having SMuRFs.
• Image Acquisition:
  • Thoracoabdominal CTA performed using contrast-enhanced protocols (75–100 mL Ultravist 300).
  • Scans covered the neck to the aortoiliac bifurcation.
• Image Analysis (Plaque Quantification):
  • Software: Osirix MD V14.1.2.
  • Segmentation: A semi-quantitative approach evaluated 78 arterial segments per patient based on the Ishimaru classification (zones of the aorta) and major branch vessels (carotids, renal, mesenteric, etc.).
  • Plaque Characterization: Segments were classified as having no plaque, non-calcified/high-risk plaque (soft, mixed, or ruptured), or calcified plaque.
  • Burden Metric: Total plaque burden was defined as the count of arterial segments affected by atherosclerosis.
• Statistical Analysis:
  • Comparison of plaque burden between ICM and NICM groups.
  • Comparison between SMuRF-less and SMuRF-positive groups.
  • Multivariate linear regression to identify independent predictors of plaque burden (adjusting for age, sex, renal function, lipids, inflammation, and pharmacotherapy).

3. Key Contributions

• First-of-its-kind Analysis: This is the first study to investigate differences in high-risk extracardiac plaque burden specifically between ICM and NICM patients in the advanced heart failure population.
• Re-evaluation of SMuRFs: It challenges the efficacy of SMuRFs as the sole predictor for systemic atherosclerosis in transplant candidates, demonstrating that "SMuRF-less" status does not equate to a lack of extracardiac disease.
• Repurposing Routine Imaging: It establishes thoracoabdominal CTA (routinely done for malignancy screening) as a viable, high-yield tool for assessing systemic atherosclerotic burden without additional radiation or cost.
• Identification of Alternative Drivers: The study highlights that systemic inflammation (hsCRP) and age are stronger predictors of calcified plaque burden than traditional lipid profiles or SMuRF status in this specific cohort.

4. Key Results

• Patient Demographics:
  • Median age: 58 years; 16% female.
  • SMuRF-less prevalence: 24% of the total cohort (20% of ICM, 28% of NICM).
• Plaque Burden by Cardiomyopathy Type:
  • ICM vs. NICM: Patients with ICM had a significantly higher total plaque burden than NICM patients (11 segments vs. 6 segments per patient; p < 0.001).
  • ICM patients also had higher burdens of soft, mixed, and calcified plaque types.
• Plaque Burden by Risk Factor Status (SMuRFs):
  • No Association: There was no significant difference in total, non-calcified, or calcified plaque burden between patients with SMuRFs and those who were SMuRF-less (p > 0.17 overall; p > 0.30 within ICM and NICM subgroups).
  • This indicates that the absence of traditional risk factors does not predict the absence of extracardiac atherosclerosis.
• Multivariate Regression Findings:
  • Total/Non-calcified Plaque: Neither ICM history nor SMuRF history remained significant predictors after adjusting for covariates.
  • Calcified Plaque: Significantly associated with Age (p=0.038), History of SMuRFs (p=0.017), and hsCRP (p=0.002).
  • Inverse Associations: LDL levels were inversely related to calcified plaque burden (p=0.002), and ARNI use (Angiotensin Receptor-Neprilysin Inhibitor) was inversely related to non-calcified plaque burden (p=0.044).
• High-Risk Plaque in NICM: Notably, 89% of NICM patients (76/85) had high-risk (soft/mixed/ruptured) plaque in at least one extracardiac segment, despite often lacking traditional risk factors.

5. Significance and Clinical Implications

• Limitations of Current Screening: Relying solely on SMuRFs to determine the need for atherosclerosis screening in heart transplant candidates is ineffective. A significant portion of "low-risk" (SMuRF-less) candidates harbor extensive extracardiac disease.
• Systemic Nature of Disease: The findings confirm that atherosclerosis is a systemic process that extends beyond the coronary arteries. In advanced heart failure, the burden of extracardiac disease varies by etiology (ICM > NICM) but is not strictly dictated by traditional risk factors.
• Clinical Optimization: The presence of extracardiac plaque on routine pre-transplant CTA should serve as a biomarker for intensified medical optimization (e.g., lipid management, anti-inflammatory strategies) prior to and following transplantation to reduce the risk of MACCE and cardiac allograft vasculopathy.
• Future Directions: The study suggests that future risk stratification models for heart failure patients must incorporate imaging markers of systemic disease (like extracardiac plaque) and non-traditional risk factors (like hsCRP) rather than relying exclusively on conventional risk factor checklists.

Limitations Noted: The study used a semi-quantitative approach due to heterogeneity in CT scanners over a 13-year period. Image quality was occasionally degraded by metallic artifacts from implanted devices (LVADs, pacemakers), and the study lacked concurrent coronary CTA data for all patients.