Internal Medicine/Heart Murmur

Introduction to Cardiac Murmurs

Cardiac murmurs are common findings in clinical practice and can result from various cardiac and vascular abnormalities. These murmurs are often detected during auscultation, the process of listening to the heart sounds using a stethoscope. Heart murmurs can be indicative of underlying structural or functional issues within the heart, making their evaluation a crucial aspect of diagnosing and managing cardiovascular conditions.

Systolic Heart Murmurs

Systolic heart murmurs occur during ventricular systole, the phase of the cardiac cycle when the ventricles contract and pump blood into the aorta and pulmonary artery. These murmurs are characterized by their timing, location, radiation, intensity, and pitch. Common causes of systolic murmurs include:

• Aortic Stenosis: This condition involves the narrowing of the aortic valve opening, causing turbulence as blood is forced through the constricted valve.
• Hypertrophic Cardiomyopathy: In hypertrophic cardiomyopathy, the heart muscle becomes abnormally thick, leading to turbulent blood flow and a characteristic systolic murmur.
• Mitral Regurgitation: This condition occurs when the mitral valve does not close properly during systole, allowing blood to flow backward into the left atrium.
• Ventricular Septal Defects (VSD): VSDs are congenital heart defects where there is an abnormal communication between the right and left ventricles, resulting in a murmur due to the shunting of blood.

Diastolic Heart Murmurs

Diastolic heart murmurs occur during ventricular diastole, the phase when the ventricles relax and fill with blood. These murmurs are also characterized by timing, location, intensity, and pitch. Common causes of diastolic murmurs include:

• Aortic Regurgitation: In aortic regurgitation, the aortic valve does not close properly during diastole, allowing blood to leak back into the left ventricle.
• Mitral Stenosis: This condition involves the narrowing of the mitral valve, obstructing the flow of blood from the left atrium to the left ventricle.
• Pulmonic Regurgitation: Pulmonic regurgitation occurs when the pulmonic valve does not close tightly during diastole, causing blood to flow back into the right ventricle.

Continuous Murmurs

Continuous murmurs are unique in that they span both systole and diastole, starting in systole and extending into part or all of diastole. These murmurs are characterized by their persistence and can be associated with specific conditions, including:

• Patent Ductus Arteriosus: This congenital heart defect involves a persistent connection between the aorta and the pulmonary artery, creating a continuous pressure gradient throughout the cardiac cycle, resulting in a continuous murmur.
• Ruptured Sinus of Valsalva Aneurysm: In this condition, there is a rupture in one of the sinuses of Valsalva, leading to turbulent blood flow and a continuous murmur.
• Coronary Arteriovenous Fistula: This anomaly involves an abnormal connection between a coronary artery and a cardiac chamber or blood vessel, resulting in continuous blood flow and a continuous murmur.

Dynamic Auscultation

Dynamic auscultation involves observing changes in the intensity and characteristics of heart murmurs during specific maneuvers. These maneuvers include:

• Respiration: Changes in intrathoracic pressure during breathing can affect venous return and may impact the intensity of certain murmurs.
• Isometric Exercise (Handgrip): Sustained handgrip can alter left ventricular afterload and affect the loudness of murmurs, particularly those associated with mitral regurgitation and ventricular septal defects.
• Transient Arterial Occlusion: Inflating blood pressure cuffs on both upper extremities can temporarily alter systemic blood pressure and influence murmur intensity.
• Pharmacologic Manipulation: The administration of vasopressor agents or inhaled amyl nitrite can modulate systemic vascular resistance and affect the loudness of certain murmurs.

• Valsalva Maneuver: The Valsalva maneuver involves increasing intrathoracic pressure followed by a decrease in venous return, ventricular filling, and cardiac output. Most murmurs decrease in intensity during the strain phase of the Valsalva maneuver, except for those associated with Mitral Valve Prolapse (MVP) and Hypertrophic Obstructive Cardiomyopathy (HOCM), which become louder.
• Rapid Standing/Squatting: Abrupt changes in posture from squatting to standing can affect venous return and left ventricular afterload, impacting the intensity and timing of murmurs.
• Passive Leg Raising: This maneuver can be used to increase venous return in patients who cannot perform squatting and standing. It may affect the intensity of certain murmurs, particularly those associated with HOCM.
• Post-Premature Ventricular Contraction: A change in the intensity of a systolic murmur in the beat following a premature ventricular contraction (PVC) can help distinguish Aortic Stenosis (AS) from Mitral Regurgitation (MR). Systolic murmurs due to left ventricular outflow obstruction, such as AS, increase in intensity in the beat after a PVC, while the intensity of the murmur of MR remains relatively stable.

The Clinical Context

In addition to auscultation and dynamic maneuvers, an accurate assessment of heart murmurs involves considering the clinical context and other physical examination findings. Key factors to consider include:

• Symptoms: Symptoms suggestive of cardiovascular, neurologic, or pulmonary disease can provide important clues to the etiology and significance of a heart murmur.
• Associated Findings: Findings relevant to the jugular venous pressure, arterial pulses, other heart sounds (e.g., S1, S2, S3, S4), lung sounds, abdominal findings, skin findings, and extremity findings can aid in the differential diagnosis.
• Laboratory Studies: Results from laboratory studies, electrocardiograms (ECGs), and chest X-rays obtained earlier in the evaluation may contain valuable information to help assess the cause of a heart murmur.
• Clinical Syndromes: Recognizing clinical syndromes, such as infective endocarditis or myocardial rupture following a myocardial infarction, can provide important diagnostic insights.

Echocardiography

Echocardiography is a valuable diagnostic tool for the assessment of cardiac murmurs. This non-invasive imaging technique provides detailed information about cardiac structure and function, including:

• Valve Structure and Function: Echocardiography can assess the condition and function of heart valves, identifying issues such as stenosis or regurgitation.
• Chamber Size and Wall Thickness: The size and thickness of cardiac chambers can be measured, aiding in the diagnosis of conditions like hypertrophic cardiomyopathy.
• Ventricular Function: Echocardiography allows for the evaluation of left and right ventricular function.
• Pulmonary Artery Pressures: Estimated pulmonary artery pressures can be determined.
• Intracardiac Shunt Flow: Echocardiography can detect intracardiac shunts, such as atrial septal defects (ASD) or ventricular septal defects (VSD).
• Aortic and Pulmonary Flow: The flow of blood through the aorta and pulmonary artery can be assessed.

Other Cardiac Testing

In some cases, additional cardiac testing may be necessary to fully evaluate heart murmurs. This includes:

• Transesophageal Echocardiography (TEE): TEE can provide enhanced sensitivity in cases where transthoracic echocardiography (TTE) is limited by patient factors or anatomy.
• Cardiac Magnetic Resonance (CMR) Imaging: CMR provides quantitative information about valvular function, ventricular size, and myocardial perfusion. It is particularly useful when there is a discrepancy between clinical and echocardiographic findings.
• Cardiac CT: Cardiac CT can help assess aortic valve anatomy and exclude coronary artery disease in certain patients before valve surgery.
• Invasive Angiography and Hemodynamic Assessment: In some cases, invasive angiography and hemodynamic assessment may be required for a comprehensive preoperative evaluation.

Integrated Approach

The accurate identification and evaluation of heart murmurs involve a systematic approach that integrates findings from cardiac auscultation, clinical history, physical examination, and various diagnostic tests. The need for further testing should be determined based on the specific characteristics of the murmur and the clinical context. Cost-effectiveness and the potential impact on patient outcomes should guide decisions regarding non-invasive imaging.

In summary, heart murmurs are important clinical signs that can indicate underlying cardiac conditions. A comprehensive evaluation, including dynamic auscultation, echocardiography, and additional testing when needed, allows healthcare providers to diagnose and manage these conditions effectively.