Can a physiologic murmur be caused by ventricular arrhythmia, cardiomyopathy, or atrial dilation?

Can a Physiologic Murmur Be Caused by Ventricular Arrhythmia, Cardiomyopathy, or Atrial Dilation?

No, a physiologic (innocent) murmur cannot be caused by ventricular arrhythmia, cardiomyopathy, or atrial dilation—these conditions produce pathologic murmurs, not physiologic ones.

Understanding Physiologic Murmurs

Physiologic murmurs arise from three specific mechanisms that do not involve structural cardiac abnormalities 1:

• High blood flow rate through normal cardiac structures in conditions like pregnancy, thyrotoxicosis, anemia, or arteriovenous fistula 1, 2
• Increased flow velocity across normal semilunar valves without structural valve disease 1, 2
• Enhanced cardiac output states that create turbulent flow through anatomically normal hearts 3

These murmurs are characterized by grade 1-2/6 intensity, midsystolic timing, normal S2 with physiologic splitting, and absence of other abnormal cardiac findings 2.

Why the Conditions You Asked About Are NOT Physiologic

Cardiomyopathy Produces Pathologic Murmurs

Hypertrophic cardiomyopathy (HCM) creates a pathologic systolic murmur through left ventricular outflow tract obstruction 1, 2. This murmur:

• Is heard maximally at the 4th left intercostal space 4
• Paradoxically increases with Valsalva maneuver (65% sensitivity, 96% specificity), the opposite of physiologic murmurs which decrease 2
• Increases with standing from squatting (95% sensitivity, 84% specificity for HCM) 2
• Represents structural disease requiring echocardiographic evaluation 5

In a study of 15,141 adolescents, HCM was identified in only 0.3% of those with murmurs, and all three cases had abnormal ECGs in addition to their murmurs 5.

Atrial Dilation Is Associated with Pathologic Findings

Atrial dilation does not cause physiologic murmurs but rather indicates underlying structural disease 4:

• Atrioventricular valve regurgitation results from annular dilatation that accompanies ventricular enlargement 4
• During pregnancy, echocardiographic evidence shows that most women demonstrate "physiological" mitral regurgitation, but this occurs alongside mild ventricular chamber enlargement—not isolated atrial dilation 4
• The distinction is critical: the murmur in pregnancy is physiologic because it results from increased cardiac output through normal structures, not from the chamber changes themselves 4

Ventricular Arrhythmias Do Not Cause Murmurs

Arrhythmias themselves do not generate murmurs—they are electrical disturbances, not mechanical flow abnormalities. However:

• Post-ventricular premature beat changes can alter murmur intensity in pre-existing murmurs 4
• Murmurs originating at normal or stenotic semilunar valves increase in intensity during the cardiac cycle after a ventricular premature beat 4
• Systolic murmurs due to atrioventricular valve regurgitation do not change or may diminish with ventricular premature beats 4

Clinical Implications and Red Flags

Any murmur associated with structural heart disease requires echocardiography 2, 6:

• Grade ≥3/6 systolic murmurs mandate echocardiography 1, 2
• Holosystolic or diastolic murmurs virtually always represent pathology 1, 2
• Symptoms including syncope, angina, heart failure, or dyspnea require immediate evaluation 1
• Abnormal S2, harsh quality, or maximal intensity at the upper left sternal border suggest pathology 6

The positive predictive value of any murmur for detecting structural heart disease is only 2.8%, compared to 1.4% in those without murmurs 5. However, when structural disease exists, it is pathologic by definition—not physiologic.

Bottom Line

Physiologic murmurs result exclusively from increased flow through normal cardiac structures in high-output states. Cardiomyopathy represents structural disease, atrial dilation indicates underlying pathology, and arrhythmias are electrical phenomena that don't generate murmurs. If any of these conditions are present, the murmur is pathologic, not physiologic 1, 2.