Fundamental Principles of Ventricular Assist Devices (VADs)

1. Definition and Concept

• Braunwald's Heart Disease, p. 328

2. Indications and Treatment Strategies

• Cardiac index < 1.8-2.2 L/min/m²
• Systolic BP < 90 mm Hg
• PCWP > 20 mm Hg
• Evidence of end-organ hypoperfusion: oliguria, rising creatinine, elevated lactate, altered mentation, cool extremities

Patients can and often do transition between strategies as their clinical circumstances evolve. Candid discussion of the intended strategy is both legally and morally essential.

• Braunwald's Heart Disease, pp. 328-330

3. Basic Components

LV apex (inflow cannula) → Pump → Ascending aorta (outflow cannula)

• Braunwald's Heart Disease, p. 330

4. Pump Types and Mechanisms

4a. Pulsatile-Flow, Volume-Displacement Pumps (Historical)

• Mimicked the phasic contractions of the native heart
• Provided flexibility for biventricular support
• No longer commercially available for adults; restricted to pediatric temporary use
• Disadvantages: large size, many moving parts, higher energy requirement, limited durability

4b. Continuous-Flow Rotary Pumps (Current Standard)

• Smaller size
• Fewer moving parts - greater durability and reliability
• Limited blood-contacting surfaces
• Reduced energy requirements

Although called "continuous flow," these pumps are not truly non-pulsatile when the native heart is contracting. Flow is greater during systole (lower pressure gradient across the pump) than diastole. This phasic variation imparts a reduced but real pulse pressure to the circulation. Only in ventricular fibrillation or arrest is flow truly non-pulsatile.

• Braunwald's Heart Disease, p. 330

5. Axial vs. Centrifugal Flow Design

• Mechanical bearings: Pivot contact design - potential frictional wear and heat generation over time, may lead to device failure
• Hydrodynamic levitation: Fluid forces alone suspend the impeller; simpler electronics, smaller pump, but impeller may contact housing at very low speeds
• Magnetic levitation (passive or active): Permanent magnets (passive, no power) or electromagnets (active, position sensing); fully contactless design eliminates bearing wear
• Hybrid systems: Combination of hydrodynamic + magnetic levitation (e.g., HM3 uses passive magnetic + hydrodynamic)
• Braunwald's Heart Disease, pp. 330-331

6. Hydrodynamic Properties

• Flow is directly proportional to pump speed (RPM)
• Flow is inversely proportional to the pressure gradient across the pump (aortic pressure minus LV pressure)

• If aortic afterload rises, flow decreases at a fixed RPM
• If the native heart contracts weakly (high LV pressure), less gradient exists and pump can generate more flow
• Clinicians can titrate RPM to balance ventricular unloading and cardiac output

7. Specific Devices

Temporary/Short-term Devices

The IABP-SHOCK II trial demonstrated that IABP does not reduce 30-day, 12-month, or 6-year mortality in cardiogenic shock with LV failure, and it is no longer recommended for this indication. Active percutaneous devices (Impella, TandemHeart) provide better hemodynamic support but have not yet demonstrated a clear mortality benefit in randomized trials. - Harrison's Principles of Internal Medicine 22E

Durable/Long-term Devices

• HeartMate II (HMII): First-generation axial-flow LVAD; most studied with >20,000 implantations worldwide
• HeartMate 3 (HM3): Centrifugal, fully magnetically levitated impeller; superior survival and lower stroke/GI bleeding vs. HMII in the MOMENTUM 3 trial
• HeartWare HVAD: Now discontinued (June 2021) after showing a 3.49x higher hazard ratio for mortality vs. HM3

8. Patient Selection Considerations

• Mild-moderate AS: Not a contraindication
• Severe AS: Must be corrected (bioprosthesis) before LVAD to allow future weaning
• Moderate AI: Causes LV distension with LA-aorta cannulation; with LV apex-aorta devices, AI worsens as LV pressure drops (creates circular flow loop)

• Braunwald's Heart Disease, pp. 329-334

9. Adverse Events and Complications

• Braunwald's Heart Disease; Miller's Anesthesia 10e; Mulholland and Greenfield's Surgery 7e

10. Monitoring and Management

• INTERMACS (Interagency Registry for Mechanically Assisted Circulatory Support): The primary registry tracking outcomes of all durable MCS devices in the United States. Provides risk stratification profiles (INTERMACS profiles 1-7, with 1 = critical cardiogenic shock, 7 = advanced NYHA III).
• Pump speed is titrated to optimize cardiac output while preventing ventricular suction (over-decompression of the LV)
• Echocardiography guides cannula position, RV function assessment, aortic valve opening frequency, and detection of complications
• Mean arterial pressure (not standard cuff systolic/diastolic) is the relevant blood pressure measurement in continuous-flow VAD patients

Summary

VADs work by mechanically unloading a failing ventricle and generating forward flow. The field has shifted from bulky pulsatile pumps to compact continuous-flow rotary pumps, with the centrifugal magnetically levitated design (HM3) now representing the gold standard for durable support. The three strategic goals - bridge to recovery, bridge to transplant, and destination therapy - frame all clinical decision-making. Complication management, particularly GI bleeding, stroke, driveline infection, and right heart failure, remains the central challenge of long-term VAD support.

• Durable Mechanical Circulatory Support: JACC Scientific Statement (2023) - PMID 37758441: Comprehensive 2023 JACC statement covering current evidence and management
• Right Heart Failure with LVAD - ESC HFA Consensus Statement (2024) - PMID 38853659: Pre/peri/post-operative strategies for RV failure management

Mitral Valve Stenosis

1. Definition and Overview

• Braunwald's Heart Disease, p. 761; Grainger & Allison's Diagnostic Radiology, p. 334

2. Etiology and Epidemiology

Rheumatic Mitral Stenosis (RMS) - Most Common Cause

• Results from repeated group A Streptococcus (GAS) pharyngeal infections triggering an autoimmune response that mimics valve antigens (both humoral and cellular immune mechanisms)
• Acute rheumatic fever (ARF) typically occurs in the second decade; MS manifests 2-3 decades later
• The mitral valve is the most commonly involved valve in rheumatic heart disease (RHD)
• MS accounts for 40% of all rheumatic heart disease; ~60% of pure MS patients have a recalled history of rheumatic fever
• More common in women (2:1 for isolated MS) - even though ARF affects both sexes equally
• Global prevalence of RHD: ~33.4 million cases (concentrated in low-middle income countries - South/East Asia, sub-Saharan Africa, Oceania)
• In endemic regions: aggressive course, symptomatic in 2nd-4th decade
• In non-endemic regions: indolent course, present in 5th-7th decade

Degenerative (Non-Rheumatic) Mitral Stenosis (DMS)

• Primarily due to mitral annular calcification (MAC) - accounts for ~41% of severe MS on echo in western series
• Increasingly recognized in patients with aortic stenosis undergoing TAVR (11-18%)
• More common in older women, associated with atherosclerotic risk factors and severe CKD

Rare Causes

• Congenital mitral stenosis
• Prior chest radiation
• Mucopolysaccharidosis
• Ball valve thrombus
• Left atrial myxoma (obstructive)
• Cor triatriatum (membrane divides LA, mimicking MS)
• Post-surgical/transcatheter mitral valve procedures
• Braunwald's Heart Disease, pp. 759-761; Grainger & Allison's, p. 334

3. Pathology and Morphology

• Leaflet thickening and nodularity
• Commissural fusion (primary mechanism in RMS)
• Leaflet calcification
• Chordal fusion and shortening (subvalvular apparatus)
• Valve narrows to a "fish-mouth" or "hockey stick" appearance (diastolic anterior leaflet bowing)

4. Pathophysiology

MVA narrows → Pressure gradient across mitral valve →
↑ Left atrial pressure → LA dilation + pulmonary venous hypertension →
Dyspnea, pulmonary edema → Secondary pulmonary arterial hypertension →
RV pressure overload → RV dilation/failure + tricuspid regurgitation

1. Cardiac output decreases as MVA decreases, especially on exertion
2. Heart rate matters critically - tachycardia shortens diastole, reducing filling time across the stenotic valve, dramatically worsening the gradient. This is why AF with fast ventricular response is so hemodynamically dangerous in MS.
3. Left ventricular function is generally preserved in pure MS (the LV is actually "protected" from volume overload), though reduced preload from the obstruction can reduce LV stroke volume
4. Pulmonary hypertension (PAH): Chronic LA hypertension → pulmonary venous congestion → reactive pulmonary arterial hypertension. Severe PAH can become irreversible.
5. Atrial fibrillation: LA dilation promotes AF. AF removes the atrial "kick" that contributes 20-30% of LV filling, further worsening hemodynamics

• Braunwald's Heart Disease; Grainger & Allison's, p. 334; Textbook of Clinical Echocardiography

5. Severity Classification

AHA/ACC Disease Stages (2020 Guideline)

• Braunwald's Heart Disease, Table 75.1, p. 762

6. Clinical Features

Symptoms

• Dyspnea - the cardinal symptom; initially on exertion, progressing to rest dyspnea, orthopnea, and paroxysmal nocturnal dyspnea
• Fatigue - especially with onset of PAH or over-diuresis
• Palpitations - often a consequence of AF, increase with age
• Hemoptysis - from pulmonary venous congestion or rupture of pulmonary-bronchial anastomoses
• Peripheral edema, ascites - when RV failure develops
• Systemic thromboembolism / stroke - due to LA stasis, especially with AF and LA appendage thrombus
• Pulmonary edema - precipitated by AF, pregnancy, infection, exercise

Physical Examination Signs

In older adults, the loud S1 and opening snap may be absent due to calcified, fibrotic leaflets with reduced mobility.

• Braunwald's Heart Disease, pp. 762-764; Grainger & Allison's, p. 334

7. Investigations

Electrocardiogram

• P-mitrale: Broad, bifid P wave in lead II (> 0.12 sec) - LA enlargement
• Atrial fibrillation - common
• Right axis deviation, RV hypertrophy - with severe PAH
• Left atrial abnormality (negative terminal component of P wave in V1)

Chest X-Ray

• LA enlargement: double shadow at right cardiac border, elevation of left main bronchus, straightening of left heart border
• Pulmonary venous hypertension: upper lobe blood diversion, Kerley B lines, pulmonary edema
• Mitral valve calcification
• RV enlargement (late)

Echocardiography (Gold Standard)

• Leaflet thickening, doming (hockey-stick deformity), calcification
• Commissural fusion
• LA enlargement; LA appendage thrombus (TEE superior)
• Subvalvular apparatus involvement

• Pressure half-time (PHT) method: MVA = 220/PHT (most widely used); PHT is the time for peak mitral gradient to fall by half
• Planimetry (direct measurement): most reliable; from parasternal short-axis at leaflet tips; 3D echo even more accurate
• Continuity equation: MVA = (LVOT TVI × LVOT area) / MV TVI
• Mean transmitral gradient: calculated from CW Doppler

Cardiac MRI

• Useful when echo is suboptimal
• Cine-MRI shows restricted leaflets and anterograde flow void
• Direct MVA planimetry with good correlation to echo

Cardiac Catheterization

• Indicated when non-invasive findings are inconclusive or discordant with symptoms
• Simultaneous measurement of LA and LV diastolic pressures (or PCWP as LA surrogate)
• Gorlin formula: MVA = CO / (DFP × HR × 44.3 × √mean gradient)
• Braunwald's Heart Disease; Grainger & Allison's Diagnostic Radiology, pp. 334-337; Textbook of Clinical Echocardiography

8. Complications

9. Management

Medical Therapy

• Diuretics: Reduce pulmonary venous congestion and symptoms
• Beta-blockers / rate-limiting calcium channel blockers (diltiazem, verapamil): Control heart rate, prolong diastolic filling time - especially important in AF or with exertion
• Anticoagulation (warfarin, target INR 2-3): Indicated for MS with AF, prior embolism, or LA thrombus. Benefit in sinus rhythm with LA thrombus or severe MS is also recognized.
• Penicillin prophylaxis: Secondary prophylaxis against GAS infection to prevent recurrent ARF (essential in endemic regions in young patients)
• Digoxin: Rate control in AF
• Avoid aggressive reduction of preload with nitrates (can precipitate hypotension)

Indications for Intervention (AHA/ACC 2020 Guidelines)

• Stage D (symptomatic severe MS, MVA ≤ 1.5 cm²) - Class I
• Asymptomatic severe MS (Stage C) with PASP > 50 mmHg - Class IIa
• Symptomatic moderate MS (MVA 1.5-2.0 cm²) with elevated gradient on exercise - selectively considered

Percutaneous Balloon Mitral Valvuloplasty / Commissurotomy (BMV/PTMC)

• Pliable, non-heavily calcified leaflets
• No more than mild-moderate MR
• No LA thrombus (TEE essential prior to procedure)
• No significant subvalvular fusion

• MVA typically doubles (from ~1.0 to ~2.0 cm²) with immediate symptomatic relief
• Success rates: >90% in LMICs/younger patients; <50% in older patients with calcified valves
• ~80% of patients remain free of death, mitral surgery, or repeat BMV over 15 years; ~66% at 20 years

• Worsening MR: mild MR in ~20%; acute severe MR (anterior leaflet tear) < 1-2%
• Interatrial shunt (60-70% initially; persists <10%)
• Cardiac tamponade ~5%, stroke ~3%, mortality ~3% (higher in older patients)

Surgical Intervention

Degenerative/MAC-related MS

• More complex; BMV generally less effective (calcific rather than commissural mechanism)
• Transcatheter mitral valve replacement (TMVR) is an emerging option for MAC-related severe MS
• High procedural risk; results still limited
• Braunwald's Heart Disease, pp. 764-870; Grainger & Allison's, pp. 336-337

10. Special Situations

MS in Pregnancy

• Significant hemodynamic risk - increased plasma volume and heart rate of pregnancy worsens gradient
• May precipitate pulmonary edema, particularly in previously asymptomatic patients
• Management: beta-blockers for rate control, diuretics cautiously
• BMV can be performed safely during pregnancy (with lead shielding to minimize fetal radiation)
• Delivery should be planned in a high-risk obstetric center

MS in the Elderly

• Often MAC-related rather than rheumatic
• Loud S1 and OS may be absent (calcified leaflets)
• BMV success rate < 50%; higher complication rates
• MVR carries ≥ 10% perioperative mortality

Concurrent Aortic Valve Disease

• Present in ~1/3 of rheumatic MS patients
• AS severity can be overestimated in the presence of MS (reduced flow)
• BMV can be performed first if MS is predominant; caution - sudden LV preload increase post-BMV can precipitate pulmonary edema in undetected severe AS

Summary Table: Severity and Management

• Valvular Heart Disease review 2024 (PMID 38278576) - Current primary care management overview
• Management of acute decompensated valvular heart disease 2025 (PMID 39663714) - European Heart Failure 2025 review covering acute MS management

Valvotomy (Mitral Commissurotomy / Balloon Mitral Valvuloplasty)

1. Rationale and Principle

This is why valvotomy is only effective in rheumatic MS (commissural fusion mechanism). It is not indicated in degenerative/MAC-related MS, where there is no commissural fusion and the calcification is annular.

• Washington Manual of Medical Therapeutics; Fuster and Hurst's The Heart, 15th Edition, p. 1012

2. Types of Valvotomy

3. Percutaneous Balloon Mitral Commissurotomy (PBMC / BMV)

History

Mechanism

Indications (AHA/ACC 2020 Guidelines)

• Very high thromboembolic risk
• Planning for pregnancy
• Scheduled for major non-cardiac surgery
• Fuster and Hurst's The Heart, 15th Ed; Braunwald's Heart Disease; Washington Manual

Absolute Contraindications

• LA/LAA thrombus (TEE must be performed before procedure)
• Moderate or severe MR (grade ≥ 3/4)
• Severe or bicommissural calcification
• Absence of commissural fusion (i.e., degenerative/MAC-related stenosis)

Patient Selection: The Wilkins Echo Score

• ≤ 8 = Favorable for PBMC - likely to be successful
• > 8 = Surgery recommended (PBMC less likely to succeed)
• Sabiston Textbook of Surgery, Table 112.7; Harrison's Principles of Internal Medicine 22E

Equipment / Balloon Systems

1. Inoue balloon (hourglass/double lumen; triple lumen) - most widely used and preferred
2. Accura balloon (double lumen; similar to Inoue)
3. Single or double peripheral angioplasty balloon (Lock technique)
4. Reusable metallic valvulotome (used in some LMICs)

Step-by-Step Procedure

1. Venous access - typically via right femoral vein
2. Transseptal puncture - needle punctures the interatrial septum under fluoroscopic/echocardiographic guidance, entering the LA from the RA (Fig. 274-3A)
3. Septal dilation - the interatrial septum is dilated with a dilator to allow passage of the balloon catheter
4. Balloon advancement - the balloon catheter (Inoue type) is advanced from the LA across the mitral valve and into the LV in its deflated state
5. Stepwise balloon inflation (Fig. 274-3B-D):
   • Distal portion inflated first (anchors in LV)
   • Proximal portion inflated (anchors in LA)
   • Middle portion then inflated - this splits the fused commissures
6. Immediate assessment - Doppler echocardiography and pressure measurements confirm increased MVA and reduced gradient

Pre-procedure TEE is mandatory to exclude LA appendage thrombus and assess degree of MR. The procedure has a steep learning curve and should be performed only at high-volume centers.

• Fuster and Hurst's The Heart, p. 1013; Harrison's, p. 1548

Hemodynamic Results

• MVA doubles (e.g., 1.0 → 2.0 cm²)
• Mean transmitral gradient falls dramatically
• LA pressure decreases
• Symptoms resolve rapidly

Definition of Procedural Success

Post-dilation MVA > 1.5 cm² with MR grade < 2/4 - achieved in over 80% of appropriately selected patients

• Sabiston Textbook of Surgery

Complications

• Braunwald's Heart Disease; Sabiston Textbook of Surgery; Fuster and Hurst's The Heart

Special Situation: BMV in Pregnancy

• Treatment of choice for severe symptomatic MS in pregnancy
• High success rates, minimal radiation (< 10 min fluoroscopy with lead shielding)
• Fetal development unaffected when performed correctly
• Best performed after 24 weeks (before 20 weeks: poorer fetal outcomes)
• Far superior to surgical intervention in pregnancy (surgery carries ~9% maternal mortality and ~30% fetal loss)
• Braunwald's Heart Disease, p. 765

4. Long-Term Outcomes After BMV

• Older age
• Higher NYHA class at baseline
• Suboptimal initial result (insufficient MVA increase)
• Higher Wilkins score

• Occurs over years; if mechanism is re-fusion of commissures, repeat BMV can be performed with reasonable success
• If restenosis is due to leaflet rigidity/degeneration, results are less favorable
• Braunwald's Heart Disease; Fuster and Hurst's The Heart

5. Open Mitral Commissurotomy (OMC)

Indications

• PBMC not feasible or contraindicated
• Failed previous PBMC
• Restenosis after prior surgery
• Concurrent cardiac surgery needed (CAD, aortic valve disease, tricuspid repair)

Technique

• Performed under cardiopulmonary bypass (CPB)
• Mitral valve exposed through a left lateral atriotomy (anterior to pulmonary veins) or right atriotomy + incision through the atrial septum
• Under direct vision:
  • Division of fused commissures with a knife or scissors
  • Mobilization of scarred chordae and papillary muscles (subvalvular apparatus)
  • Debridement of calcium deposits
  • Removal of LA thrombus
  • Ligation of LA appendage (reduces future embolic risk; a major advantage over BMV)
  • Maze procedure can be added concurrently to reduce AF burden

Results

• Operative mortality: < 2%
• 10-year survival: ~96%
• 10-year freedom from reoperation: ~90% (Sabiston) / ~98% at 9 years (Braunwald's)
• Results comparable to MVR but avoids long-term prosthetic valve complications
• More favorable than PBMC in older patients with subvalvular fusion, leaflet calcification, and reduced valve flexibility
• Mulholland and Greenfield's Surgery 7e; Harrison's Principles; Sabiston Textbook of Surgery

6. Closed Mitral Commissurotomy (CMC)

• Performed without cardiopulmonary bypass
• Surgeon inserts a finger (transatrial) and a transventricular dilator (Tubbs dilator) to split the valve
• Lower resource requirements - used predominantly in LMICs where CPB is unavailable
• Results: inferior to OMC and BMV (less increase in MVA, higher restenosis)
• When BMV is available, BMV should be preferred over CMC
• Braunwald's Heart Disease; Fuster and Hurst's The Heart

7. Mitral Valve Replacement (MVR)

• Significant calcification or subvalvular fusion making repair unlikely to succeed
• Concomitant moderate-severe MR
• Failed PBMC or OMC
• Severe symptomatic MS in patients not candidates for repair

• Mechanical: Durable; requires lifelong anticoagulation
• Bioprosthetic: No long-term anticoagulation; but high failure rate in young patients

• Operative mortality: 5-6% (higher than OMC)
• Freedom from reoperation at 15 years: 50-75%
• Sabiston Textbook of Surgery; Mulholland and Greenfield's Surgery

8. Comparison Summary

9. Approach to Patient Selection (Algorithm)

Severe MS confirmed (MVA ≤ 1.5 cm², symptomatic OR PASP > 50 mmHg)
         ↓
Assess anatomy: Echo (Wilkins score), TEE (LA thrombus, MR degree)
         ↓
Wilkins score ≤ 8, no LA thrombus, MR < Grade 3?
    YES → BMV/PBMC (procedure of choice)
    NO  → Surgical options
              ↓
       Repair feasible? → Open Commissurotomy (preferred in young)
       Repair not feasible, significant MR/calcification → MVR