Minimally Invasive Cardiac Surgery

Off-Pump Coronary Artery Bypass (OPCAB) / Minimally Invasive Direct Coronary Artery Bypass

Overview

• OPCAB is a coronary artery revascularization technique that avoids the use of the CPB circuit.
  • OPCAB may be performed with an invasive approach (full median sternotomy) or a minimally invasive approach (small thoracotomy or partial median sternotomy).
• Minimally invasive direct coronary artery bypass (MIDCAB) is a subtype of OPCAB.
  • It is less invasive compared to full median sternotomy coronary artery bypass surgery.
  • It can be performed without CPB, i.e., “off pump MIDCAB.”
  • It may also be performed with CPB via peripheral femoral vessel cannulation (either as a primary plan, or as a bail-out in the event of refractory hemodynamic instability).
  • Perceived benefits of off-pump MIDCAB include:
    • Avoidance of a full median sternotomy allows for faster recovery (although not necessarily lower pain scores).^1,2
    • Avoidance of CPB, which may reduce the stroke risk, inflammatory responses, and impairment of coagulation that come with the use of the bypass circuit and aortic manipulation.^1,2
• Some patients may undergo a “hybrid” approach in which the most accessible coronary arteries are revascularized surgically, followed by percutaneous coronary intervention (PCI) on additional vessels.²
• Figure 1 compares two OPCAB approaches: coronary revascularization via traditional median sternotomy versus a mini-thoracotomy (MIDCAB).

Indications and Contraindications^3,4

Off-Pump MIDCAB Procedure^4-7

• Transverse incision in the left anterior 4th-5th rib space
• The left lung is deflated to facilitate harvesting of the left internal mammary artery (LIMA) via direct visualization, endoscope, or robot.
• The radial artery may also be harvested at the same time.
• Surgeon opens the pericardium and places a mechanical traction device to partially immobilize the portion of the heart to be grafted (can reduce cardiac output).
• Intravenous (IV) heparin is given when the distal portion of the LIMA is ready to be separated and when the other conduits are ready; the typical activated clotting time (ACT) goal is greater than 300-350 seconds (150-250 IU/kg of IV Heparin).
  • If CPB is needed, cannulae can be placed peripherally in the femoral artery and vein (necessitating 300-400 IU / kg doses of IV Heparin and an ACT goal greater than 480 seconds). Two additional incisions in the left thorax would be made to place an aortic cross-clamp and a cardioplegia delivery line; alternatively, an endovascular aortic occlusion balloon can be placed via the femoral artery under TEE guidance.
• Anastomosis between LIMA and left anterior descending (LAD) is created, blood flow is restored, and pericardial fat is used to pad the distal portion of the graft
• Protamine reversal is given once graft patency is established
• The pericardium is partially closed, and the LIMA-LAD is directly visualized during lung reinflation
• A left chest tube is placed.
• Thoracotomy is closed with care taken to avoid graft contact with the chest wall.
• Patients selected for a “hybrid” approach may then be transferred to the cardiac catheterization lab for PCI of arteries not managed surgically.²

Anesthetic Management

• Preoperative evaluation:⁷
  • Focus on cardiac, respiratory, and vascular comorbidities.
  • Transthoracic echocardiogram (TTE):
    • Note baseline wall-motion abnormalities and valvular issues.
    • Significant aortic insufficiency may preclude the use of emergent CPB due to unstable cardioplegia and LV distention.
  • 12-lead ECG:
    • Note pre-existing conduction abnormalities.
    • Have intra-operative pacing techniques available (will have further arrhythmias during manipulation of the beating heart).
  • Computed tomography chest:
    • Often obtained for surgical planning.
    • Useful for an anesthesiologist to delineate the anatomy for double-lumen tube placement.
  • Risk factors for hypoxemia and hemodynamic instability on OLV:
    • Obesity
    • Older age
    • Chronic lung disease
    • Reduced exercise capacity
    • Pulmonary function testing and baseline arterial blood gas are not required but can be predictive of post-operative pulmonary complications.
    • RV dysfunction and pulmonary hypertension (assess right ventricular systolic pressure, right ventricular size/function): OLV can increase afterload on the right ventricle and precipitate right heart failure with hemodynamic collapse.
  • Screen patients for contraindications to TEE probe placement.
• Intraoperative considerations:
  • Monitoring and equipment:

• • Induction:
    • Tailor induction to the patient’s specific situation
    • General goals for patients at risk of myocardial ischemia include avoidance of:
• Tachycardia
• Ventricular overdistention
• Hypoxemia
• Non-sinus rhythm
• Excessive decreases in systemic vascular resistance
  • Intubation:
    • A left-sided double-lumen tube is preferred. A single-lumen tube with a bronchial blocker can be considered for difficult airways, where a tube exchange at the end of the case may pose excessive risk.
    • Always recheck the endotracheal tube position with bronchoscopy after the surgical team repositions the patient into the semi-lateral position.
  • Maintenance:
    • Tranexamic acid is not routinely given as there is no clear benefit in reduction of blood loss or need for transfusions in off-pump cases.²
    • The biggest concerns are myocardial ischemia, hypoxemia from OLV, hypotension from surgical retraction and manipulation of the beating heart, and hemodynamic instability from coronary vessel manipulation.^1,2
    • One-lung ventilation and hypoxemia:
• Utilizing continuous positive airway pressure and oxygen insufflation to improve hypoxemia can significantly obstruct the surgeon’s view.
• Often, desaturation is improved after addressing low cardiac output with fluids, vasopressors, and inotropic support.
• In some cases, the surgeon may need to pack the lung to maintain exposure while returning to two-lung ventilation.
  • Distal grafting and management of hemodynamic instability:
• The highest risk of instability occurs during distal grafting: if a shunt is not used, ischemia is required to achieve a bloodless field.
• Expect greater instability for multivessel grafting compared to single-vessel LIMA-LAD grafting; anterior sites require less twisting of the heart.
• Vasoactive infusions and dilute bolus syringes should be readily available (such as phenylephrine, norepinephrine, and epinephrine).
• Note that due to the placement of retractors and stabilizers, the LV will appear hypokinetic or akinetic on TEE. Note any changes in regional wall motion, especially during distal grafting.
• A generalized approach to maintaining hemodynamic stability during heart stabilization and grafting is summarized in Figure 2.

• Postoperative care:²
  • Full use of multimodal analgesia, with a goal of early extubation (in the operating room versus in the intensive care unit [ICU]).
  • Regional anesthesia can be utilized (thoracic epidural, spinal anesthesia, paravertebral block, erector spinae plane block, serratus anterior plane block, pectoral 2 plane block, and intercostal nerve block, single-shot vs. catheter). However, the use of neuraxial anesthesia in procedures that require high-dose heparin is controversial.
  • Note that for patients receiving a hybrid approach (partial surgical revascularization followed by PCI), anesthesia and ICU teams must be cognizant of post-operative ischemia.

Complications

• Need for repeat target vessel revascularization (lower rates of repeat revascularization for MIDCAB compared to PCI).⁶
• OPCAB may be associated with higher mortality and less favorable graft patency than on-pump CABG when performed in low-volume centers, due to a learning curve between on- and off-pump revascularization.⁵
• Myocardial infarction (myocardial infarction rates and overall mortality are similar between MIDCAB and PCI).^4,6
• Atrial fibrillation (MIDCAB may show similar or slightly reduced risk of atrial fibrillation compared to traditional CABG).¹
• Need for blood transfusions (mixed data as to whether MIDCAB procedures are associated with similar or slightly reduced transfusion rates compared to on/off-pump full median sternotomy approaches).1,5
• Wound infection (rates may be lower in MIDCAB compared to full-sternotomy OPCAB).⁵
• Pleural effusion (higher rates in MIDCAB compared to full-sternotomy OPCAB).⁵
• Conversion to CPB (higher conversion rate in patients receiving MIDCAB compared to full-sternotomy OPCAB, although 30-day mortality and 6-month graft patency are similar).⁵

Limited Thoracotomy and Port Access Valvular Surgery

Overview

• Limited thoracotomy and port-access valvular surgery is a minimally invasive alternative for mitral valve replacement/repair (MVR), tricuspid valve replacement/repair (TVR), and aortic valve replacement/repair (AVR).
• Their level of invasiveness lies between a full median sternotomy and a percutaneous valve replacement approach.
• One-lung ventilation (OLV) is often utilized to facilitate surgical exposure.
• Peripheral (femoral-femoral) CPB is required, which is performed under transesophageal echocardiography (TEE) guidance.
• Central CPB cannulation may be utilized in partial median sternotomy approaches.

Indications and Contraindications

• Minimally invasive valve surgery can be performed on patients with a history of prior median sternotomy, as pleural adhesions typically do not form as a result of this type of incision.^8,9
• Therefore, MICS may be an appropriate alternative to re-sternotomy to avoid the risk of damaging prior coronary grafts.^8,9
• Patients should have anatomy suitable for a minimally invasive approach.
• Absolute and relative contraindications to minimally invasive valve surgery are outlined in Table 3.

Minimally Invasive Valve Replacement/Repair Procedure

• Patient positioning: supine with right side slightly elevated⁸
• General surgical approaches: ^8,9,10
  • Location and types of incisions:
    • Partial sternotomy approach:
      • Used for AVR, MVR, or TVR.
      • 7cm partial sternotomy, allowing room for central cannulae.
    • Limited thoracotomy approach:
      • Used for AVR: right anterior thoracotomy.
      • Used for MVR or TVR: right mid-axillary thoracotomy.
    • Port-access approach:
      • Used for AVR, MVR, or TVR.
      • Limited right-thoracotomy and additional smaller incisions for ports utilized for the thoracoscope and atrial retractor.
• Requirement for one-lung ventilation (OLV)
  • Often required in port-access and limited thoracotomy approaches
  • May not be needed in the partial sternotomy approach.⁸
• Cannulation for CPB
  • A partial sternotomy approach allows for central CPB cannulation.
  • Limited thoracotomy and port-access approaches often utilize peripheral (femoral-femoral) CPB cannulation.
  • Peripheral cannulation should be guided by TEE (bi-caval view).⁹
• Aortic cross-clamping and cardioplegia
  • Aortic cross-clamping may be performed by a transthoracic aortic clamp or an endoballoon9 (Figure 3).
  • Retrograde cardioplegia may be instituted via the right internal jugular vein or the right atrium and requires TEE guidance.
  • For isolated tricuspid valve repairs, arrest of the heart may not be needed.⁸
• Valve repair or replacement is performed, the patient weaned from CPB, and valvular function is assessed with TEE.

Anesthetic Management

• Preoperative evaluation:¹⁰
  • Determine the etiology of valvular pathology: myxomatous valve, rheumatic disease, endocarditis, papillary muscle dysfunction from ischemia, or valvular calcification.
  • TTE: screen for signs of pulmonary hypertension, additional valvular dysfunction and their severity.
  • Left heart catheterization: coronary artery disease is a common comorbidity and ischemic changes can cause valvular dysfunction via papillary muscle damage.
  • Pulmonary function testing can be used to identify patients who are at the highest risk of post-op pulmonary complications and hypoxia from OLV.
  • CT Angiogram of chest/abdomen/pelvis: might be obtained by surgery to assess vascular anatomy and suitability for cannulation for CPB; can also be evaluated for tracheobronchial anatomy prior to double-lumen tube (DLT) placement.
• Intraoperative management:
  • Monitors:
    • Standard American Society of Anesthesiologists monitors (will need modification of standard ECG electrodes due to interference with the location of surgical incisions).
    • Arterial line (bilateral radial arterial lines if using an endoballoon rather than a transthoracic aortic cross clamp, to detect balloon migration).⁹
    • Cerebral oximetry (detection of differential hypoxemia on peripherally cannulated CPB).⁹
  • Induction: should be tailored to the patient’s valvular pathology
  • Intubation: often a DLT or bronchial blocker with a single-lumen tube is needed to facilitate surgical exposure by deflating the right lung; may not need OLV if the approach is via partial median sternotomy.⁸
  • Maintenance: volatile or intravenous anesthesia is feasible, although the depth of anesthesia may be unpredictable due to changes in volume of distribution and circuit-binding while on CPB.
  • Presurgical TEE exam to confirm diagnosis, exclude other valvular pathologies such as aortic regurgitation, confirm the integrity of interatrial septum, and assess the size of the aortic root and ascending aorta.⁹
  • Transition to OLV to facilitate surgical dissection and exposure
  • Full CPB-dose of Heparin (300 IU/kg) with ACT goal greater than 480 seconds if utilizing CPB.
  • Pain control: utilization of opioids; consider non-opioid adjuncts such as ketamine, dexmedetomidine, or clonidine, and regional anesthesia (thoracic wall blocks such as paravertebral, serratus anterior plane block, erector spinae plane, and pectoralis I and II blocks). Neuraxial techniques are often not utilized due to the need for anticoagulation on CPB.⁹
• Postoperative care:
  • Extubate in the operating room versus in the ICU, depending on patient factors and institutional protocols.
  • Note that bleeding may be more difficult to detect than in patients who received full median sternotomies due to smaller incisions; therefore, have a high index of suspicion for tamponade, hemorrhage at peripheral cannulation sites, or other closed hemorrhages if post-op hemodynamic instability is present.⁹
  • Monitor for peripheral limb ischemia if femoral cannulation sites were utilized.⁹

Complications^9,10

• Chest-wall hemorrhage (2-9%)
• Atrial fibrillation (10-40%)
• Stroke (1-3%)
• Conversion to sternotomy (2%)
• Vascular injury (rare)
• Pneumonia
• Acute kidney injury
• Minimally invasive valve surgery may have reduced pain scores and faster recovery compared to traditional median sternotomy, despite an association between MICS and longer CPB and cross-clamp times.⁹