Abnormal Heart Sounds And Murmurs
Introduction
In the context of MCCQE1 preparation, mastery of cardiac auscultation is paramount. As a core competency under the CanMEDS Medical Expert role, the ability to identify, characterize, and manage abnormal heart sounds and murmurs is frequently tested in both the Multiple Choice Questions (MCQ) and Clinical Decision Making (CDM) components of the exam.
Cardiovascular disease remains a leading cause of morbidity in Canada. Consequently, distinguishing between benign flow murmurs and pathological valvular heart disease is a critical skill for any Canadian physician, from primary care to internal medicine.
Canadian Context: The Canadian Cardiovascular Society (CCS) provides specific guidelines for the management of valvular heart disease. For the MCCQE1, focus on the indications for echocardiography and the timing of surgical referral.
Physiology of Heart Sounds
Understanding the cardiac cycle is the foundation of identifying pathology.
S1 (Lub) = Closure of Mitral and Tricuspid valves (Start of Systole)
S2 (Dub) = Closure of Aortic and Pulmonic valves (Start of Diastole)Extra Heart Sounds
Differentiation between physiological and pathological extra sounds is high-yield for the MCCQE1.
S3 (Ventricular Gallop)
Occurs in early diastole during rapid ventricular filling. Pathophysiology: Caused by blood striking a compliant LV wall. Normal: In children, young adults, and pregnancy (high output states). Pathological: Indicates volume overload (systolic heart failure, severe mitral regurgitation). Sound: “Ken-tuck-y” (S1-S2-S3).Grading of Murmurs
The Levine Scale is the standard used in Canadian clinical practice.
| Grade | Description | Thrill Present? |
|---|---|---|
| I | Faint, requires focused listening | No |
| II | Quiet, but audible immediately | No |
| III | Moderately loud | No |
| IV | Loud | Yes (Palpable) |
| V | Very loud, audible with stethoscope edge touching chest | Yes |
| VI | Audible with stethoscope off the chest | Yes |
Systolic Murmurs
Systolic murmurs occur between S1 and S2. They can be midsystolic (ejection) or holosystolic (regurgitant).
1. Aortic Stenosis (AS)
- Epidemiology: Most common valvular disease in the elderly Canadian population (calcific degeneration).
- Characteristics: Crescendo-decrescendo, harsh, midsystolic ejection murmur best heard at the right upper sternal border (RUSB).
- Radiation: Carotids.
- Associated Findings: Pulsus parvus et tardus (weak and delayed carotid upstroke), soft S2.
- MCCQE1 Key: Symptomatic AS (Angina, Syncope, Dyspnea) requires urgent valve replacement evaluation.
2. Mitral Regurgitation (MR)
- Causes: MVP, Ischemic heart disease, Rheumatic fever (less common in Canada born, relevant for immigrant populations).
- Characteristics: Holosystolic, blowing, high-pitched murmur best heard at the apex.
- Radiation: Axilla.
- Maneuvers: Intensity increases with increased afterload (Handgrip).
3. Mitral Valve Prolapse (MVP)
- Characteristics: Midsystolic click followed by a late systolic murmur.
- Dynamic Auscultation: The click moves earlier with standing (decreased preload).
4. Ventricular Septal Defect (VSD)
- Characteristics: Harsh, holosystolic murmur at the left lower sternal border (LLSB).
- Note: Smaller defects often produce louder murmurs.
🇨🇦 Canadian Clinical Pearl: HOCM
Hypertrophic Obstructive Cardiomyopathy (HOCM) is a leading cause of sudden cardiac death in young athletes. The murmur is a harsh crescendo-decrescendo systolic murmur at the LLSB.
Distinction from AS: HOCM murmur intensity increases with Valsalva (decreased preload) and decreases with squatting (increased preload/afterload). AS acts the opposite.
Diastolic Murmurs
Critical Concept: Diastolic murmurs are always pathological and require investigation (usually Echocardiogram).
1. Aortic Regurgitation (AR)
- Characteristics: Early diastolic, decrescendo, blowing murmur best heard at the left sternal border.
- Maneuvers: Best heard with the patient sitting up, leaning forward, and holding breath in expiration.
- Signs: Wide pulse pressure, water-hammer pulse (Corrigan’s pulse).
2. Mitral Stenosis (MS)
- Epidemiology: History of Rheumatic Fever.
- Characteristics: Opening snap followed by a low-pitched, mid-diastolic rumble best heard at the apex in the left lateral decubitus position.
Dynamic Auscultation (Maneuvers)
This section is extremely high-yield for MCCQE1 MCQs involving similar-sounding murmurs.
| Maneuver | Hemodynamic Effect | Effect on AS | Effect on HOCM | Effect on MVP | Effect on MR/AR/VSD |
|---|---|---|---|---|---|
| Inspiration | ↑ Venous Return (Right heart) | No change | No change | No change | ↑ Right-sided murmurs (TR) |
| Valsalva / Standing | ↓ Preload | ↓ Intensity | ↑ Intensity | Click moves earlier | ↓ Intensity |
| Squatting / Leg Raise | ↑ Preload, ↑ Afterload | ↑ Intensity | ↓ Intensity | Click moves later | ↑ Intensity |
| Handgrip | ↑ Afterload | ↓ Intensity | ↓ Intensity | Click moves later | ↑ Intensity |
Diagnostic Approach
Follow this step-by-step approach for a patient presenting with a new murmur in a Canadian clinical setting.
Step 1: History and Physical
Assess for symptoms (chest pain, dyspnea, syncope, palpitations). Determine functional status (NYHA class). Perform a focused physical exam including dynamic auscultation.
Step 2: Initial Investigations
Order a 12-lead ECG to look for hypertrophy (LVH/RVH), ischemia, or conduction abnormalities. Order a Chest X-ray (CXR) to assess cardiac silhouette and pulmonary vasculature.
Step 3: Definitive Diagnosis
Transthoracic Echocardiogram (TTE) is the gold standard for diagnosing valvular pathology, assessing severity, and measuring ejection fraction.
Step 4: Specialist Referral
Refer to a cardiologist if:
- Murmur is diastolic.
- Murmur is grade >3/6 systolic.
- Patient is symptomatic.
- Echocardiogram shows moderate-severe valve disease.
Canadian Guidelines (CCS)
The Canadian Cardiovascular Society guidelines emphasize the following for valve disease:
- Aortic Stenosis: Intervention (TAVI or SAVR) is indicated for severe AS when symptoms appear or if EF <50%.
- Antibiotic Prophylaxis: In Canada, prophylaxis for infective endocarditis is NOT recommended for routine dental procedures in patients with native valve disease (including MVP, AS, MR). It is reserved for high-risk patients (prosthetic valves, previous endocarditis, unrepaired cyanotic congenital heart disease).
Mnemonics for MCCQE1
- MRS. ASS: Mitral Regurgitation = Systolic; Aortic Stenosis = Systolic.
- MS. ARD: Mitral Stenosis = Diastolic; Aortic Regurgitation = Diastolic.
- Right-sided murmurs increase with Respiration (Inspiration).
- Left-sided murmurs increase with exhaLation.
Key Points to Remember for MCCQE1
- Symptomatic Aortic Stenosis has a poor prognosis without intervention; recognize the triad of Angina, Syncope, and Heart Failure.
- Differentiation between AS and HOCM using the Valsalva maneuver is a classic exam question.
- Diastolic murmurs always warrant an echocardiogram.
- S3 is normal in pregnancy and youth but pathological in older adults (Heart Failure).
- S4 indicates a stiff ventricle (Hypertension/LVH).
Sample Question
Stem: A 72-year-old man presents to the emergency department after an episode of syncope while shoveling snow. He reports increasing shortness of breath on exertion over the past 6 months. He has no chest pain currently. His past medical history is significant for hypertension and dyslipidemia. Physical examination reveals a blood pressure of 110/85 mmHg and a heart rate of 78 bpm. On auscultation, a harsh, grade III/VI crescendo-decrescendo systolic murmur is heard best at the right second intercostal space, radiating to the neck. The second heart sound (S2) is soft.
Lead-in: Which of the following physical examination findings is most likely associated with this patient’s condition?
Options:
- A. Widened pulse pressure
- B. Pulsus parvus et tardus
- C. Midsystolic click
- D. Holosystolic murmur radiating to the axilla
- E. Opening snap
Explanation
The correct answer is:
- B. Pulsus parvus et tardus
Detailed Explanation:
The patient presents with the classic triad symptoms of severe Aortic Stenosis (AS): exertional dyspnea and syncope (angina is the third). The physical exam description (harsh, crescendo-decrescendo systolic murmur at the right upper sternal border radiating to carotids) is diagnostic for AS.
- Option B (Pulsus parvus et tardus): This refers to a carotid pulse that is weak (“parvus”) and delayed (“tardus”) due to the obstruction of blood flow from the left ventricle into the aorta. This is a hallmark physical finding in significant aortic stenosis.
- Option A (Widened pulse pressure): This is characteristic of Aortic Regurgitation, not stenosis. AS typically presents with narrow pulse pressure.
- Option C (Midsystolic click): This is the hallmark of Mitral Valve Prolapse.
- Option D (Holosystolic murmur radiating to the axilla): This describes Mitral Regurgitation.
- Option E (Opening snap): This is associated with Mitral Stenosis.
MCCQE1 Takeaway: Recognize the clinical presentation of AS (Old age + Syncope/Angina/Dyspnea + Systolic ejection murmur) and associate it with the delayed carotid upstroke.
References
- Canadian Cardiovascular Society. (2021). 2021 CCS Guidelines on the Management of Valvular Heart Disease.
- Toronto Notes. (2023). Cardiology: Valvular Heart Disease. Toronto Notes for Medical Students, Inc.
- Medical Council of Canada. (2023). MCCQE Part I Objectives: Cardiovascular System.
- UpToDate. (2024). Auscultation of cardiac murmurs in adults.