MITRAL STENOSIS

Nick Tehrani, MD

Epidemiology of MS

Hx of Rheumatic fever is elicited in only 50% of path proven cases

Other causes

Severe MAC

Congenital MS

Clinical Diagnosis of Rheumatic Fever

Diagnosis of acute rheumatic feverTwo major Jones criteria, OROne major criterion, and two minor criteria

Major MinorCarditis FeverErythema marginatum PR prolongationChorea ESR elevationSubcutaneous nodules Hx of Rheumatic fever

Clinical Diagnosis of Acute Rheumatic Fever

Additionally, serologic evidence of recent streptococcal infection is needed:

Positive bacteriologic culture

Increase in ASO titers

Increase in anti-DNAse B titers

Histopathology

The acute valvular pathology caused by Rheumatic fever is:

Mitral Regurgitation

Over the next several decades stenosis accrues by:Thickening of the leafletsFusion of the commisuresFusion or shortening of the chordae

Definitions of severity of Mitral Stenosis

Valve Area:<1.0 cm2 Severe1.0-1.5 cm2 Moderate>1.5-2.5 cm2 Mild

Mean gradient: >10 mmHg Severe5-10 mmHg Moderate<5 mmHg Mild

Flow Across a Normal Mitral Valve in Diastole

Flow Across the Stenotic Valve

Persistent LA-LV gradient in diastole sustained flow throughout diastole

The slope of the envelope is proportional to the severity of stenosis

Flow Across the Stenotic Valve

Note the “A” in patient who is in sinus

Diastolic Transmitral Pressure Gradient due to Limited LV Filling

Pathophysiology

Limited flow into the LV has 3 major sequale:Elevation of Lt. Atrial pressureSecondary RV pressure overloadReduced LV ejection performance

Due to diminished preloadTachycardic response to compensate to decreased SV worsens the transmitral gradient

Determinants of Transmitral Pressure Gradient

Increased Flow, OR

Decreased orifice size

Incr. Gradient.

Elevated LA

pressure

HR=72

HR=100

Variability

The three inter-related parameters are:

HR

CO

Trans-mitral gradient

Mitral valve area

Heart rate variability

CO measurement and reproducibility

Problems are

Introduced by:

Different ways of Measuring Mitral Valve Area

Echocardiographic:

PISA

2-D

Pressure half-time

Cath:

Gorlin’s Equation

Pressure half time

The Gorlin Equation

Torricelli’s Law:

gh2Cv V

Cc x V

Flow Area

Cc =Coefficient ofOrifice contraction

Cv=Coefficient of

Velocity

The Second Equation:

The Gorlin Equation

Substituting for V, in Torricelli’s Eq.

h x 980 x 2 x Cc x Cv

Flow Area

h 44.3 x C

Flow Area

Simplification of the above:

C 44.3?

The Numerator of the Equation

Flow Across any Valve:

For Mitral (and Tricuspid) valve:

(HR) DFP)or (SEP

CO Flow

HR x DFP

CO Flow

h 44.3 x C

Flow Area

The Gorlin Equation

Substituting for “Flow” and “h” in the first Eq.:

h C x 44.3

Flow Area

HR x DFP

CO Flow

Ph

Gorlin’s Formula for Mitral Area

The Gorlin Formula for Mitral Valve area:

P C x 44.3

HR x DFP

CO

Area Valve

Gorlin’s Formula for Mitral Area

CO Cardiac outputDFP Diastolic Filling PeriodHR Heart Rate44.3 Derived ConstantC Correction factor for valve type

C=1.0 for all valves except MitralC=0.85 for Mitral valve

P Mean pressure gradient

How Do you use this Eqn.?

Step 1: Figure out the Numerator First:

Dimensional analysis:

HR x DFP

CO Flow

)(beats/min x (sec/beat)

cc/min cc/sec

P C x 44.3

HR x DFP

CO

Area Valve

Figure out the DFP

DFP in Sec/beat

Measure the Distance in mm from MV opening to MV closing in one beat

Convert distance to time

100 speed= 100 mm/sec, makes life easy

50 speed= 50 mm/sec, tough life

mm/Secin speedPaper

1beat / mmin DFP

P C x 44.3

HR x DFP

CO

Area Valve

Figure out the Heart Rate

Assuming Patient is in SinusMeasure the RR interval in mmConvert to Beats/min by…

In 100 speed just divide 6,000 by the RR in mm

Beats/minin HR

mm/beat RR

mm/Secin SpeedPaper Sec/min 60

P C x 44.3

HR x DFP

CO

Area Valve

Let’s Figure out the Denominator

P C x 44.3

HR x DFP

CO

Area Valve

No Mitral Stenosis

Diastolic Transmitral Pressure Gradient due to Limited LV Filling

Left Atrial

Tracing

Need to Left Shift the PCWP Tracing

V A

C

DFP

Planimeter

Shifted Over

Instrumentation

The trickiest part is to set up the instrument correctly:

The reading must be adjusted to

0.0000

From Planimetered Area to Mean Pressure Gradient

Area as provided by the instrument is in (in)x(in)

Must convert to (cm)x(cm)

Multiply by 6.45 cm2/In2

To obtain mean Area under the curve

Divide the Area by the DFP in cm

To convert cm of pressure to mm of Hg

Multiply the above # in cm, by the “scale factor”

Get “Scale factor” from the tracing: mm Hg/cm

How many tracings to Planimeter

If patient is in sinus => 5 tracings

If patient is in A-Fib.=> 10 tracings

Putting things in Perspective

P C x 44.3

HR x DFP

CO

Area Valve

CC/Sec

mm Hg

cm2

CC/sec.cm2.(mm Hg)P0.5

Potential Pitfalls

Wedge vs. LA PressureStiff End-hole catheter: CournandVerify true wedge by checking O2 SatMean Wedge should be less than Mean PA

Cardiac OutputTrue Fick vs. Thermodilution vs. Green dye

Concurrent MR with MS:Gradient across the valve reflects forward and regurgitant flowCO reflects the net forward flow only

Likely underestimation of the true valve area

Mitral Stenosis and the LA

Even in sinus rhythm, the low velocity flow predisposes to formation of atrial thrombi.

Low flow pattern is seen as spontaneous contrast on echocardiography

17% of patients undergoing surgery for MS have LA thrombus

In one third of cases thrombus restricted to the LAA

Pulmonary Hypertension

Normal pressure drop across pulmonary bed:

10-15 mm Hg

Expected mean PA in Mitral Stenosis: Mean LA (elevated of course) + (10-15 mm Hg)

In MS, Mean PA pressure often exceed the expected.

Pulmonary Hypertension

This pulmonary hypertension has two components:

Reactive pulmonary arterial vasoconstriction,

Potentially Fixed resistance, secondary to morphologic changes in the pulmonary vasculature

How Do you use this Eqn.?

Step 1: Figure out the Numerator First:

Dimensional analysis:

HR x DFP

CO Flow

)(beats/min x (sec/beat)

cc/min cc/sec

P C x 44.3

HR x DFP

CO

Area Valve

Figure out the DFP

DFP in Sec/beat

Measure the Distance in mm from MV opening to MV closing in one beat

Convert distance to time

100 speed= 100 mm/sec, makes life easy

50 speed= 50 mm/sec, tough life

mm/Secin speedPaper

1beat / mmin DFP

P C x 44.3

HR x DFP

CO

Area Valve

Figure out the Heart Rate

Assuming Patient is in SinusMeasure the RR interval in mmConvert to Beats/min by…

In 100 speed just divide 60,000 by the RR in mm

Beats/minin HR

mm/beat RR

mm/Secin SpeedPaper Sec/min 60

P C x 44.3

HR x DFP

CO

Area Valve

V A

C

DFP

Planimeter

From Planimetered Area to Mean Pressure Gradient

Area as provided by the instrument is in (in)x(in)

Must convert to (cm)x(cm)

Multiply by 6.45 cm2/In2

To obtain mean Area under the curve

Divide the Area by the DFP in cm

To convert cm of pressure to mm of Hg

Multiply the above # in cm, by the “scale factor”

Get “Scale factor” from the tracing: mm Hg/cm