Residency · Residency · Cardiothoracic Surgery

Minimally Invasive Cardiac Surgery: Mini-Sternotomy and Mini-Thoracotomy

Introduction

Minimally invasive cardiac surgery (MICS) encompasses a range of techniques that reduce surgical trauma compared to conventional full median sternotomy. Approaches include upper or lower mini-sternotomy, right mini-thoracotomy, and thoracoscopic-assisted procedures. When properly applied, MICS offers reduced blood loss, shorter hospital stays, faster recovery, improved cosmesis, and preserved sternal integrity, all while maintaining surgical quality and outcomes equivalent to conventional approaches.

Mini-Sternotomy Approaches

Upper Mini-Sternotomy (Ministernotomy)

The upper mini-sternotomy is a partial sternotomy from the sternal notch extending to the 3rd or 4th intercostal space with a "J" or "T" extension to the right. Its primary indications are isolated aortic valve replacement or repair, ascending aortic surgery, and select combined procedures. It provides excellent exposure to the aortic valve, ascending aorta, and proximal arch. Central cannulation of the ascending aorta and right atrial appendage is typically feasible, and standard aortic cross-clamping and cardioplegia delivery are performed.

Lower Mini-Sternotomy

The lower mini-sternotomy is a partial sternotomy from the xiphoid extending superiorly to the 3rd intercostal space. It is less commonly used but provides access to the mitral and tricuspid valves via the right atrium, with limited exposure to the ascending aorta.

Advantages of Mini-Sternotomy

Preserving the lower sternal integrity reduces the risk of deep sternal wound infection. Patients experience reduced blood loss and transfusion compared to full sternotomy, along with earlier mobilization and shorter ICU and hospital stays. Respiratory mechanics are improved because of the intact lower sternum. Additionally, reduced adhesion formation facilitates future redo sternotomy.

Limitations

The restricted operative field creates a longer learning curve. Conversion to full sternotomy may be necessary if exposure is inadequate or complications arise. The approach is not suitable for all patients, particularly those with severe adhesions from prior surgery or extreme body habitus.

Right Mini-Thoracotomy

Approach

The right mini-thoracotomy uses a 5-8 cm incision in the right 3rd or 4th intercostal space, with or without rib spreading. Video-assisted thoracoscopy provides enhanced visualization. Peripheral cannulation is achieved through the femoral artery and femoral vein (percutaneously or via open access). Endoaortic balloon occlusion (Intraclude catheter) replaces direct aortic cross-clamping and is positioned in the ascending aorta under TEE guidance for cardioplegia delivery and aortic occlusion. Alternatively, a transthoracic Chitwood clamp can be applied directly to the ascending aorta through the incision or a separate port.

Indications

The most established indication for right mini-thoracotomy is mitral valve repair or replacement. Tricuspid valve surgery is frequently combined with mitral procedures. Other indications include atrial septal defect closure, redo mitral or tricuspid surgery (avoiding hazardous redo sternotomy), and concomitant maze procedure for atrial fibrillation.

Surgical Technique for Mitral Valve Surgery

Femoral arterial and venous cannulation is established, with an additional SVC cannula via the right internal jugular vein for bicaval occlusion. CPB is initiated with vacuum-assisted venous drainage. Aortic occlusion is achieved by endoaortic balloon inflation or Chitwood clamp. Cardioplegia is delivered through the endoaortic balloon or directly via the aortic root. The left atriotomy is performed through the interatrial groove (Sondergaard groove) or using a transseptal approach. Mitral valve repair or replacement is carried out with long-shafted instruments and video assistance. De-airing uses the endoaortic balloon vent and CO2 flooding of the operative field.

Advantages

Avoiding sternotomy preserves sternal integrity, which is critical for patients who may require future cardiac surgery. Patients experience significantly reduced pain and faster return to activity, along with superior cosmetic results. The risk of mediastinitis and sternal dehiscence is eliminated, and hospitalization is shorter (4-5 days versus 6-8 days).

Cannulation and Perfusion Strategies for MICS

Peripheral Cannulation

Femoral artery cannulation provides retrograde arterial flow but carries risk of retrograde aortic dissection and atheroembolism; preoperative CT angiography is recommended to assess aortic and iliofemoral atherosclerosis. The femoral vein accommodates a long multistage venous cannula advanced to the SVC under TEE guidance. The axillary artery provides antegrade flow and avoids retrograde atheroembolism, making it useful in patients with peripheral vascular disease.

Endoaortic Balloon

The endoaortic balloon is positioned in the ascending aorta via the femoral artery alongside the arterial return cannula or through a separate side-arm. It functions as an internal aortic cross-clamp, cardioplegia port, and aortic root vent. Continuous TEE monitoring is required to confirm position and detect migration. It is contraindicated in significant aortic regurgitation, ascending aortic dilatation, or severe peripheral vascular disease.

CO2 Field Flooding

CO2 insufflation into the operative field displaces air, reducing the risk of air embolism. CO2 is more soluble than nitrogen and is rapidly absorbed. This is standard practice for all MICS procedures.

Patient Selection

Ideal Candidates

Ideal candidates include patients undergoing first-time cardiac surgery with isolated valve pathology, those with normal peripheral vasculature, adequate ventricular function, and BMI below 40 (relative, with body habitus considerations).

Relative Contraindications

Relative contraindications include significant peripheral vascular disease (precluding safe femoral cannulation), severe aortic regurgitation (precluding endoaortic balloon use), ascending aortic dilatation above 4 cm, prior right thoracotomy with dense pleural adhesions, and need for concomitant CABG with limited coronary access.

Outcomes

Operative mortality is equivalent to conventional surgery in experienced centers. MICS consistently demonstrates reduced blood transfusion, ventilator time, ICU stay, and hospital length of stay. Deep sternal wound infection rates are lower in the thoracotomy approach (which avoids sternotomy entirely). Long-term valve durability and freedom from reoperation are equivalent. The learning curve typically requires 50-75 cases to achieve proficiency.

Key Clinical Pearls

Preoperative CT angiography of the entire aorta and iliofemoral system is mandatory before peripheral cannulation to assess for atherosclerosis and anatomic suitability. TEE is indispensable during MICS for monitoring endoaortic balloon position, guiding de-airing, and assessing valve repair quality. CO2 field flooding significantly reduces air embolism risk and should be used in all MICS cases. Conversion to full sternotomy should be performed without hesitation if exposure is inadequate or a complication arises -- surgical safety always takes priority over minimally invasive goals. MICS is particularly valuable in patients who may need future cardiac surgery, as it preserves the virgin sternum.

References

1. Glauber M, Miceli A, Gilmanov D, et al. Right anterior minithoracotomy versus conventional aortic valve replacement: a propensity score matched study. J Thorac Cardiovasc Surg. 2013;145(5):1222-1226.
2. Goldstone AB, Atluri P, Szeto WY, et al. Minimally invasive approach provides at least equivalent results for surgical correction of mitral regurgitation: a propensity-matched comparison. J Thorac Cardiovasc Surg. 2013;145(3):748-756.
3. Svensson LG. Minimally invasive surgery with a partial sternotomy "J" approach. Semin Thorac Cardiovasc Surg. 2007;19(4):104-112.
4. Modi P, Hassan A, Chitwood WR. Minimally invasive mitral valve surgery: a systematic review and meta-analysis. Eur J Cardiothorac Surg. 2008;34(5):943-952.

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