Contrast Echocardiography

Contrast echocardiography covers two genuinely distinct techniques that are easy to conflate under one name: right heart contrast using agitated saline, a simple bedside technique for detecting intracardiac shunts, and left heart contrast using a commercial ultrasound-enhancing agent (UEA) injected intravenously, used for LV opacification and myocardial perfusion imaging. This page covers both, along with the agents, imaging technique, and safety considerations behind left heart contrast specifically.

Right Heart Contrast (Agitated Saline)

Right heart contrast uses agitated saline — saline mechanically mixed with a small amount of air to create microbubbles too large to pass through the pulmonary capillary bed. Injected peripherally, it opacifies the right heart; if bubbles appear in the left heart within one to two cardiac cycles, this indicates a right-to-left intracardiac shunt.

• Patent foramen ovale (PFO) — right-to-left shunting may be present only after a Valsalva maneuver, because of the transient rise in right atrial pressure relative to left atrial pressure that the maneuver produces.
• Atrial septal defect (ASD) — even a predominantly left-to-right shunt usually shows some right-to-left component when pressures on both sides of the defect briefly equalize, which is what allows detection with right heart contrast despite the shunt’s net direction.
• Other uses — identifying a persistent left superior vena cava, and delineating the systemic venous inflow pathway in complex congenital heart disease.
• Pulmonary arteriovenous fistula (PAVF) — the timing of left heart opacification is what distinguishes an intrapulmonary shunt from an intracardiac one. An intracardiac shunt (PFO/ASD) opacifies the left heart within one to two cardiac cycles, as above; a PAVF instead shows delayed opacification, typically three to five cycles or more, since blood must still traverse the pulmonary vasculature through an abnormal direct arteriovenous connection rather than an intracardiac defect. Sensitivity is imperfect, and CT remains the definitive diagnostic study when PAVF is suspected.
• A real limitation — a small ventricular septal defect usually will not be detected by right heart contrast, since little right-to-left shunting occurs across a small VSD. Right heart contrast is also needed less frequently now than in the past, given the sensitivity of color Doppler and TEE for shunt detection directly; its primary remaining niche is PFO detection.

Left Heart Contrast: Agents and Composition

Left heart (UEA) contrast agents are microbubbles encapsulating a high-molecular-weight, biologically inert gas (sulfur hexafluoride or a perfluorocarbon) within a thin outer shell (phospholipid or human albumin). Their size — typically 1–8 μm, well under the pulmonary capillary diameter — allows them to survive transpulmonary passage and reach the left heart after a peripheral venous injection, unlike right-heart agitated saline bubbles. Because they act as pure intravascular tracers, the degree of signal enhancement in any tissue is directly proportional to the relative blood volume within that tissue — which is the physical basis for both LV opacification and, at the microcirculatory level, myocardial perfusion imaging.

The three currently available agents differ meaningfully in composition, dosing, and side-effect profile:

Agent	Gas	Shell	Bubble size	Typical dosing	Common side effects
SonoVue / Lumason	Sulfur hexafluoride	Phospholipid	2–8 μm	Bolus 0.3–0.5 mL; infusion 0.5–1.5 mL/min	Headache (~2%), nausea, dysgeusia
Optison	Perfluoropropane	Human albumin	3.0–4.5 μm	Bolus 0.1–0.3 mL	Headache (~5%), flushing, back pain
Definity / Luminity	Perfluoropropane (octafluoropropane)	Phospholipid	1.1–2.5 μm	Bolus 1 mL; infusion 1–2 mL/min	Headache (~2%), flushing, dizziness

Lumason/SonoVue, Optison, and Definity are approved for LV opacification; Lumason additionally carries approval for liver and vesicular imaging, and SonoVue is approved in Europe for coronary artery disease detection and Doppler signal enhancement. All three have been used off-label or under evolving approval for myocardial perfusion imaging on commercially available systems for nearly two decades.

Imaging Technique

Contrast imaging depends on a very different instrument setup than standard 2D imaging, and getting it wrong is a common source of a poor-quality study:

• Very low mechanical index (MI < 0.2) with fundamental nonlinear imaging is the current standard for optimal LV opacification and endocardial resolution. This is deliberately below the MI that would be needed to generate adequate contrast signal with conventional harmonic imaging — the advantage being that essentially no nonlinear signal comes from tissue at this power level, giving inherent background subtraction, and minimal far-field attenuation since the received signal is at the fundamental frequency.
• Pulse sequence scheme matters — amplitude modulation and combined amplitude/phase modulation techniques offer high contrast sensitivity and minimal far-field attenuation at the cost of some resolution; phase inversion and tissue harmonic imaging offer higher resolution but more far-field attenuation, and typically run at a slightly higher MI (0.2–0.4).
• Getting the dose and rate right takes real experience — too much microbubble density causes shadowing (excess attenuation at the near field, obscuring the apex); too little, or bubble destruction from too high an MI, produces a swirling appearance with inadequate opacification rather than uniform enhancement.
• Gain, time-gain compensation, and focal depth all need adjustment specifically for contrast imaging rather than left at standard 2D settings — the goal is myocardial contrast enhancement without near-field shadowing in the LV cavity.

Myocardial Perfusion Imaging (MCE)

Myocardial contrast echocardiography (MCE) extends UEA use beyond simple cavity opacification to actual perfusion assessment. Because microbubbles are pure intravascular tracers, signal enhancement in the myocardium is dominated by the capillary compartment. The technique works by deliberately destroying microbubbles within the microcirculation with a high-MI pulse, then tracking how fast and how completely the signal replenishes — the microvascular flux rate and microvascular blood volume, whose product gives an index of perfusion.

This can meaningfully add information beyond a simple wall motion assessment: a segment with a wall motion abnormality can be distinguished as having (1) no perfusion, (2) hypoperfusion with some antegrade or collateral flow, or (3) normalized perfusion despite persistent dysfunction — i.e., stunning rather than infarction. Additional described uses include improving the diagnostic accuracy of point-of-care evaluation in acute chest pain beyond clinical data, ECG, and early enzymes; enhancing stress echocardiography sensitivity (particularly for moderate rather than severe stenosis, or multivessel disease); assessing myocardial viability; and differentiating an intracardiac mass as thrombus versus tumor by its perfusion pattern.

A genuine point of disagreement worth knowing about: sources differ on how established MCE perfusion imaging actually is in everyday practice. It has been described with real enthusiasm as comparable to, or possibly exceeding, radionuclide SPECT imaging for ischemia detection in some studies — but is also fairly described as technically demanding in practice, since only a small fraction of cardiac output perfuses the myocardium itself, leaving a relatively small microbubble signal to work with, further limited by mechanical and ultrasound-related bubble destruction. Outside dedicated centers, other perfusion modalities — nuclear imaging, cardiac MRI, and PET — remain the more widely used clinical standard for myocardial perfusion assessment. This is worth knowing as a calibration point rather than treating MCE perfusion imaging as a routine, universally adopted technique.

Safety: A History Worth Understanding, Not Just a Warning Label

UEA safety has an unusually instructive regulatory history, and the full arc matters more than a flat “rare reactions can occur” statement:

In 2007, the FDA issued a Black Box warning contraindicating UEA use in most critically ill patients — including those with acute MI or acute coronary syndromes, worsening or decompensated heart failure, serious ventricular arrhythmias or QT prolongation, respiratory failure, severe emphysema, pulmonary embolism, or pulmonary hypertension. This followed spontaneous reports of four patient deaths in close temporal relationship to UEA administration — reports that established a temporal association but not a proven causal one, and critics at the time noted the agents’ previously excellent safety record and the real risks of the alternative procedures (TEE, nuclear scintigraphy) patients would otherwise need.

In 2008, a large cohort study of 18,671 hospitalized patients undergoing echocardiography (12,475 unenhanced, 6,196 with the UEA Definity) found no significant difference in 24-hour mortality between groups (0.37% unenhanced vs. 0.42% with UEA) — and notably, zero deaths occurred within 1 hour of UEA administration in the contrast arm. Multiple further studies over the following years, several FDA-mandated, continued to support this safety profile. Based on this accumulated evidence, the FDA modified the Black Box warning, and current consensus holds that UEAs are not only safe but genuinely useful in the ICU setting — including in patients with the very diagnoses originally on the contraindication list.

The one clearly established risk is a serious allergic (anaphylactoid) reaction, occurring in roughly 1 in 10,000 patients. These are categorized as CARPA reactions (complement activation-related pseudoallergy) — a distinct mechanism from classic IgE-mediated type 1 hypersensitivity. Practically, this means CARPA reactions don’t require prior exposure to occur, tend to be milder or absent on repeat exposure (the opposite pattern from a typical drug allergy), and resolve spontaneously more often than not — though they can occasionally be life-threatening and should be managed like any other anaphylactic reaction, with rapid access to intramuscular epinephrine. Reaction rates run somewhat higher in women and in individuals with pre-existing atopic (food or drug allergy) history.

Clinical Impact: The Evidence for Routine Use

The case for UEA use in technically difficult studies is not marginal. In one pivotal outcomes study of 632 consecutive patients with technically difficult or uninterpretable baseline studies, UEA administration reduced the uninterpretable-study rate from 11.7% to 0.3%, and the technically-difficult rate from 86.7% to 9.8%. This translated into a downstream management change — an avoided procedure, a medication change, or both — in 35.6% of patients overall, and in roughly two-thirds of patients in a surgical ICU subgroup specifically. In ICU patients with very difficult baseline studies (over half of myocardial segments not visualized from any view), UEA use improved the ability to estimate ejection fraction from 31% of studies to 97%, and improved agreement with TEE for regional wall motion assessment from 48% to 70% — while remaining more cost-effective than TEE as the alternative. See Left Ventricular Ejection Fraction and LV Systolic Function for where contrast fits into the broader EF workflow, and Mitral Stenosis for left atrial thrombus assessment, where contrast can play a complementary role alongside TEE.

Practical Considerations

• A standard operating procedure matters — the interpreting physician is responsible for overall quality control, and staff (sonographers, nurses, fellows) need specific training in bolus and infusion technique for optimal LV opacification, separate from general 2D imaging competency.
• Vendor-specific settings — accessing fundamental nonlinear imaging, and optimizing time-gain compensation, focus, MI, and flash-impulse settings, differs by ultrasound platform and requires familiarity with the specific system in use.
• Right heart and left heart contrast are not interchangeable — agitated saline is prepared at the bedside from saline and air and is used specifically for shunt detection; UEAs are purpose-manufactured, pharmaceutical-grade microbubble agents administered under a physician’s order for opacification or perfusion imaging. Using the wrong technique for the clinical question (e.g., expecting agitated saline to opacify the LV) will not work, since its bubbles are specifically too large to survive pulmonary transit.