Stress Echocardiography

Two Main Categories

• Exercise — preferred in most indications when patient is capable
• Pharmacological — for patients unable to exercise adequately

Exercise is preferred because it is physiological, correlates with symptoms, and provides prognostic factors like exercise capacity and BP response.

Treadmill

• Widely used with more clinical experience than bicycle
• Causes higher heart rate rise, longer exercise duration, and maximum workload compared to bicycle
• Main disadvantage: No imaging during exercise; scanning limited to 1–2 minutes post-exercise
• Protocols: Bruce and modified Bruce
• Patient should perform symptom-limiting exercise
• Standard contraindications and exercise cessation indications should be followed

Bicycle (Supine Semi-recumbent)

• Advantage: Image acquisition during exercise, allowing more scanning time, more images, and hemodynamic data
• Patient pedals at constant cadence ~60 rpm against increasing workload in Watts (W)
• Starting workload: 25 W with 25 W increments every 3 minutes
• Image acquisition begins after second minute has lapsed; stage holding can be performed
• Produces less heart rate rise than treadmill, but due to supine position, preload is higher and BP response is usually higher

Exercise Termination Criteria

Exercise should be terminated when any of the following is present:

• Intolerable symptoms
• Muscular exhaustion
• Severe hypertension: SBP ≥ 220 or DBP ≥ 120 mmHg
• Symptomatic hypotension: > 40 mmHg decrease in SBP
• Significant arrhythmias: SVT, AF, frequent ventricular ectopic beats, 2nd or 3rd degree AV block
• Evidence of ischemia:
  • ≥ 2 mm ST segment depression below baseline
  • New or worsening regional wall motion abnormality

Exercise should also be stopped when a diagnostic end-point is achieved:

• Maximum workload
• Obvious ECG positivity
• Obvious echo positivity
• Severe chest pain

Exercise Adequacy

Dobutamine Protocol

• Starting dose: 5 µg/kg/min
• Increment: 5 µg/kg/min every 5 min (non-ischemia) OR 10 µg/kg/min every 5 min (ischemia detection)
• Maximum dose: 40 µg/kg/min (except severe AS: max 20 µg/kg/min)
• Atropine coadministration: 0.25–0.5 mg boluses at 30–40 µg/kg/min; max total dose 2.0 mg
• Image acquisition begins 2–3 minutes into the stage
• Adequacy: ≥ 85% age-predicted max HR
• Side effects: Palpitations, nausea, headache, anxiety; cardiovascular: arrhythmias, chest pain, hypotension

Vasodilator Protocols

• Atropine 0.25–0.5 mg bolus routinely used with adenosine and dipyridamole (NOT with regadenoson)
• Contraindications: Reactive airway disease, significant A-V conduction disease (adenosine and dipyridamole)
• Significant side effects: Cardiac asystole, hypotension, myocardial infarction, bradycardia
• Reversal: Aminophylline (adenosine and dipyridamole); adenosine has very short half-life
• Mechanism: Hyperemia in normal vessel territory causes steal phenomenon (less perfusion) to areas supplied by stenosed artery

Recommended Views

• Left parasternal long axis
• Left parasternal short axis at papillary muscle level
• Apical 4-chamber (includes RV free wall)
• Apical 2-chamber
• Apical 3-chamber

Image optimization for maximal spatial and temporal resolutions; identical depth for same view across stages.

Stages

• Baseline
• Low dose/load (dobutamine and supine-bicycle)
• Peak dose/load
• Recovery

Ultrasound enhancing agent recommended when 2+ segments not adequately visualized; must be used in all stages.

Interpretation (17-Segment Model)

1. Normal/hyperdynamic
2. Hypokinetic/tardokinetic
3. Akinetic
4. Dyskinetic/aneurysmal

Tardokinesis: Ischemia delays onset of contraction and relaxation.

Images compared side-by-side simultaneously.

Additional Assessments

• RV function: TAPSE or FAC at rest and stress
• EF: Normal contractile reserve = EF increase ≥ 5% with exercise/dobutamine
• Strain: Normal GLS response = increase of ≥ −2%
• ECG: If ECG and echo disagree, echo determines conclusion

Prognosis

• Normal exercise echo: annual event rate < 1%
• Worse prognosis: extensive stress-induced WMA in multivessel distribution, exercise EF < 50%, or exercise wall-motion score index > 1.4

Indication

Assess response of akinetic segments.

Scarred segments: Thinned ≤ 5 mm, akinetic, and bright → not viable.

Protocol

• Dobutamine viability protocol is the main protocol (other stressors including exercise have been applied)
• Compared to nuclear modalities: more specific but less sensitive (requires > 50% viable myocardium for detectable effect)
• Low dose protocol: Maximum dose usually ≤ 20 µg/kg/min unless evaluating coexisting ischemia
• Termination: No improvement at 20 µg/kg/min OR worsening of segment motion at any dose
• If improvement occurs, dose escalation for ischemia detection is reasonable

Indication

Unexplained exertional dyspnea with normal LA pressure at rest AND resting septal e′ < 7 cm/sec OR lateral e′ < 10 cm/sec.

Modality

• Supine bicycle preferred (more scanning time); treadmill acceptable alternative
• Regional wall motion assessment reasonable (ischemia causes diastolic dysfunction); pure diastolic assessment possible

Parameters to Obtain

• Average septal and lateral E/e′
• Septal E/e′
• Peak TR velocity

Timing of E and e′ recording: When E and A waves are not fused (before fusion at HR ~100–110 bpm or during recovery when distinguishable). Unlike resting assessment, full E/A separation not necessary (E/A ratio not included).

Key Points

• Normal diastolic stress ≠ normal diastolic function; means no evidence of increased LVEDP and LA pressure with exercise
• TR peak velocity alone should not be interpreted (normal individuals can have increase due to increased pulmonary flow)

Alternative Test

Passive leg raising for 3 minutes when patient unable to exercise. Requires baseline septal e′ < 7 cm/sec or lateral e′ < 10 cm/sec. E/e′ > 15 during leg raising is abnormal.

Indications

• Assess LVOT obstruction in symptomatic patients when bedside maneuvers fail to induce peak gradient ≥ 50 mmHg
• Functional capacity assessment
• Risk stratification

Stressor

• Exercise is the only accepted stressor (treadmill or bicycle)
• Dobutamine has no role (not physiological, can induce LVOT obstruction in normal subjects)
• Beta blocker should not be stopped if patient already receiving it

Parameters

• LVOT peak gradient (CW)
• E/e′
• Color Doppler for MR
• TR peak velocity
• EF

Interpretation

• Significant LVOT obstruction: LVOT peak gradient ≥ 50 mmHg, BP drop, or blunted response
• Symptoms may be due to exercise diastolic dysfunction with elevated LA pressure → assess E/e′ and TR peak velocity at baseline and post-exercise
• Dynamic increase in MR related to systolic anterior motion of anterior mitral leaflet and LVOT obstruction
• Marker of poor exercise tolerance: Increase in MR, E/e′, and SPAP
• Markers of worse prognosis:
• LVOT obstruction gradient > 50 mmHg
• Blunted contractile reserve (EF increase < 5%)
• Wall motion abnormalities
• Significant ST depression
• Hypotensive or blunted BP response

Heart Failure

• Contractile reserve: EF increase ≥ 5% AND GLS increase ≥ −2% with stress
• Flow reserve: Stroke volume increase ≥ 20%
• Absent contractile reserve in normal EF = marker of latent systolic dysfunction and subclinical cardiomyopathy
• Dobutamine preserved contractile reserve → better beta blocker response, better EF improvement, better survival, fewer hospitalizations
• Contractile reserve helps distinguish ischemic vs non-ischemic: non-ischemic more likely to have contractile reserve

Mitral Regurgitation

• Indication: Equivocal cases (non-severe MR with symptoms) for dynamic MR assessment, SPAP response, and risk stratification
• Protocol: Treadmill (baseline, peak, recovery) or supine bicycle (baseline, low load, peak, recovery)
• Dobutamine NOT recommended (not physiological) except for ischemia and ischemia-induced MR evaluation

Parameters: MR color Doppler in different views, EF, TR peak velocity, LV views, PISA MR CW and color Doppler (flow convergence), IVC diameter (RA pressure estimation), TAPSE.

Markers of poor prognosis:

• Increase MR severity
• Dynamic pulmonary hypertension with SPAP ≥ 60
• Absence of contractile reserve
• TAPSE < 18 mm

Lack of contractile reserve predicts decrease of LVEF at follow-up (medically treated) and postoperative LV dysfunction.

Aortic Regurgitation

• Main use: Reveal symptoms in severe asymptomatic AR
• NOT for re-grading AR severity (exercise-induced HR increase shortens diastole and limits AR quantification)
• Contractile reserve can be assessed
• Lack of contractile reserve predicts LV systolic dysfunction at follow-up and post-operatively

Mitral Stenosis Indications

• Assessing symptoms in severe asymptomatic MS with MVA < 1 cm²
• Assessing symptoms/hemodynamic consequence in pliable valve for balloon valvuloplasty with MVA > 1 and < 1.5 cm²
• Planning for pregnancy or major surgery with MVA > 1 and < 1.5 cm²
• Re-assess severity in symptomatic nonsevere MS with MVA > 1.5 cm²

MS Parameters

• MV inflow CW Doppler
• TR CW Doppler
• IVC diameter (RA pressure estimation)

MS Interpretation

• Re-graded as severe: MV mean gradient > 15 mmHg with exercise OR > 18 mmHg with dobutamine
• Exercise SPAP > 60 mmHg = marker of hemodynamically significant MS

Aortic Stenosis Indications

1. Asymptomatic severe AS: Exercise testing to reveal symptoms or abnormal BP response
2. Low flow low gradient AS

• Stress testing contraindicated in severe AS with probable symptoms
• Dobutamine NOT recommended for asymptomatic severe AS evaluation

AS Parameters

• Apical 4-chamber and 2-chamber views optimized for EF assessment
• CW Doppler across aortic valve
• TR CW Doppler
• IVC diameter (RA pressure estimation)

AS Markers of Poor Prognosis

• Increase in mean aortic pressure gradient ≥ 18–20 mmHg during exercise
• Absence of contractile reserve
• SPAP > 60 mmHg during exercise

Lack of LV contractile reserve due to LV afterload mismatch or lack of coronary flow reserve during exercise.

Prosthetic Valves – Abnormal vs. Normal

• Normal prosthetic valves inherently stenotic with overlapping values; stress echo useful for differentiation
• Both exercise and dobutamine can be used

Parameters: CW Doppler across prosthetic valve, TR CW Doppler, IVC diameter (RA pressure estimation).

Low Flow Low Gradient Prosthesis

Definitions:

• Low flow: SVi < 35 ml/m²
• Small prosthetic valve: EOA < 1.0 cm²; EOA < normal reference; Indexed EOA < 0.85 cm² (aortic) or < 1.2 cm² (mitral)
• Abnormal DVI: < 0.35 (aortic) or > 2.2 (mitral)
• Preserved flow reserve: SV increase ≥ 20%

Indication: Low dose dobutamine in symptomatic patients with low flow low gradient prosthesis and small area or abnormal DVI.

Parameters: LVOT area (baseline), LVOT PW Doppler, CW Doppler across prosthetic valve.

Interpretation Algorithm:

1. First step: Determine flow reserve. If absent → indeterminate
2. Second step: Assess mean gradient increment and EOA change:
   • Significant Δ mean gradient (> 20 mmHg aortic, > 10 mmHg mitral) with EOA reduction < 0.3 cm² → dysfunctional or PPM
   • Isolated PPM: stress EOA close to or within normal reference; stenotic valve: stress EOA way below reference
   • Non-significant Δ gradient with EOA increase by 0.3 cm² → pseudo-dysfunction or PPM
   • Stress indexed EOA within normal (> 0.85 cm²/m² aortic, > 1.2 cm²/m² mitral) → purely pseudo-dysfunctional; otherwise → PPM

Mitral Valve Annuloplasty

• Some degree of MS common, particularly with complete annuloplasty ring
• Resting Doppler underestimates functional MS severity
• Indication: Symptomatic patient with annuloplasty and MV mean gradient > 3 mmHg
• Parameters: CW of mitral inflow, CW of TR, IVC diameter
• Interpretation: Functional MS significant when exercise/dobutamine MV mean gradient ≥ 7 mmHg AND SPAP ≥ 50 mmHg

Other Indications: Pulmonary hypertension, congenital heart disease (see ASE guidelines).

Stress Reporting (IAC 2018)

Components: Demographics, Quantitative data, Report text, Summary.

Demographics (minimum): Date, facility name, patient name, DOB/age, indication, sonographer name/initials, ordering physician, height/weight, gender, BP at procedure, rhythm.

Report Text (must include):

• Exercise time/load
• Maximum heart rate achieved
• Whether stress adequate or not
• Resting BP and BP response to stress
• Reason for termination
• Cardiac symptoms during examination
• Summary of stress ECG findings
• Pre-exercise segmental wall motion and global systolic function (if for ischemia)
• Post-exercise segmental wall motion and global systolic function (if for ischemia)

Report Summary: Pertinent positive findings (ischemia, viability, coronary distribution, LV cavity size, EF response) and negative findings.