Symptoms of Left Ventricular Outflow Tract (LVOT) Obstruction
LVOT obstruction causes a constellation of symptoms primarily driven by reduced cardiac output, elevated left ventricular pressures, and myocardial ischemia, with the most common presentations being exertional dyspnea, chest pain, syncope or near-syncope, palpitations, and fatigue. 1
Primary Symptom Complex
Exertional dyspnea is the hallmark symptom, resulting from elevated left ventricular diastolic pressures and increased pulmonary venous pressure that worsens with physical activity or catecholamine stimulation. 1 The obstruction prolongs ventricular relaxation and increases chamber stiffness, creating severe abnormalities in diastolic filling that manifest as breathlessness. 1
Chest pain (angina) occurs frequently due to myocardial ischemia from supply-demand mismatch, even in the absence of coronary artery disease. 1 The increased oxygen demand from hypertrophy and adverse loading conditions, combined with compromised coronary blood flow from thickened intramural arterioles, produces ischemia that can be severe enough to cause infarction. 1
Syncope and near-syncope result from the inability to augment cardiac output during exertion, compounded by abnormal blood pressure responses. 1 Approximately 25% of patients demonstrate either failure of systolic blood pressure to rise 20 mmHg or an actual fall in blood pressure during exercise, likely due to autonomic dysregulation and the dynamic obstruction itself. 1
Dynamic Nature of Symptoms
A critical feature is the marked variability of symptoms throughout daily activities. 1 The obstruction is dynamic, worsening with:
- Increased myocardial contractility 1
- Decreased ventricular volume (dehydration, diuretics) 1
- Decreased afterload (vasodilators) 1
- Exercise and Valsalva maneuver 1
- Postprandial periods (after eating) 1
- Alcohol intake 1
Additional Clinical Manifestations
Palpitations occur from atrial fibrillation or other arrhythmias, which are common complications. 1 Atrial fibrillation is associated with various degrees of heart failure and increased risk of systemic thromboembolism and stroke. 1
Fatigue and exercise intolerance result from decreased forward cardiac output and the complex interplay of diastolic dysfunction, mitral regurgitation, and myocardial ischemia. 1
Critical Presentations
In severe cases, patients may present with:
- Cardiogenic shock and hypotension, particularly when LVOT gradients are very high (>100 mmHg) 2, 3, 4
- Acute decompensation mimicking acute coronary syndrome with ST-segment changes on ECG 2, 3
- Refractory shock that paradoxically worsens with conventional treatments (vasopressors, inotropes, diuretics) 4
Physical Examination Findings
On examination, patients typically demonstrate:
- Harsh crescendo-decrescendo systolic murmur best heard at the lower left sternal border, increasing with Valsalva or standing from squatting 1
- Prominent, laterally displaced apical impulse (bifid or trifid) 1
- Pulsus bisferiens (double carotid pulsation) 1
- S4 heart sound from the noncompliant left ventricle 1
- Late systolic murmur of mitral regurgitation at the apex (posteriorly directed) 1
Important Clinical Pitfall
Patients may be asymptomatic at rest but develop severe symptoms with provocation. 1 Up to one-third of patients have labile obstruction with gradients <30 mmHg at rest but ≥30 mmHg with physiologic provocation. 1 This means a normal resting examination does not exclude significant LVOT obstruction as the cause of exertional symptoms. 1
The severity of symptoms generally correlates with the magnitude of obstruction, though the dynamic nature means symptom response to therapy is more clinically relevant than the measured gradient itself. 1