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Surgery for aortic stenosis: with special reference to myocardial metabolism, postoperative heart failure and long-term outcome
Linköping University, Department of Medical and Health Sciences, Thoracic Surgery. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart Centre, Department of Thoracic and Vascular Surgery.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Postoperative heart failure (PHF) remains a major determinant of the outcome after cardiac surgery. However, characteristics of and risk factors for PHF after valve surgery have received little attention.

Post-ischaemic disturbances of myocardial metabolism that may contribute to PHF and are amenable to metabolic treatment have been identified early after coronary surgery (CABG). Knowledge derived from these studies may not be applicable to other patient groups. We therefore studied myocardial energy metabolism in 20 elective patients undergoing aortic valve replacement (AVR) for isolated aortic stenosis (AS). The metabolic studies indicated that myocardial oxidative metabolism had not fully recovered when the procedure was completed. Free fatty acids were the only major substrates taken up by the heart. Signs of preoperative and postoperative metabolic adaptation with substantial uptake of glutamate, previously demonstrated in patients with coronary artery disease, were found. Postoperative infusion of glutamate, (2 mL/kg body weight and hour of 0.125 M solution) based on assessment of myocardial glutamate requirements in CABG patients, resulted in a two-fold increase in myocardial glutamate uptake and a seven-fold increase in AV differences across the leg. This was associated with a significant myocardial uptake of lactate and metabolic changes in the leg suggesting mitigation of net amino acid loss and peripheral tissue lipolysis.

Characteristics of and risk factors for PHF were evaluated in 398 patients undergoing isolated AVR for AS from 1 January 1995 to 31 December 2000. These were compared with 398 patients, matched for age and sex, undergoing on-pump isolated CABG. Forty-five AVR and 47 CABG patients fulfilled criteria for PHF and these were studied in detail. PHF usually presented at weaning from cardiopulmonary bypass. After CABG it was closely associated with preoperative ischaemic events and intraoperatively acquired myocardial infarction. Potential causes and eliciting events of PHF after AVR for AS were obvious only in one-third of the patients. Risk factors for PHF after AVR for AS indicated either pre-existing myocardial dysfunction, increased right or left ventricular after-load, or intraoperatively acquired myocardial injury. PHF was associated with high early mortality after CABG, whereas the consequences of PHF after AVR for AS became evident only with time, resulting in a 42% five-year mortality. Although PHF had a different temporal impact on late mortality after CABG and AVR for AS, it emerged as the statistically most significant risk factor for mortality occurring within 5 years from surgery both after AVR for AS and after CABG. Potential implications of our findings include needs for greater focus on preoperative surveillance of patients with AS for optimal timing of surgery, mitigation of intraoperatively acquired myocardial injury and tailoring of treatment for PHF. Furthermore, the findings have implications for long-term follow up of AS patients after surgery.

Place, publisher, year, edition, pages
Institutionen för medicin och vård , 2006.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 952
Keyword [en]
Aortic stenosis, Surgery, Postoperative heart failure, Long-term outcome, Metabolism
National Category
Clinical Science
Identifiers
URN: urn:nbn:se:liu:diva-7471ISBN: 91-85497-89-4 (print)OAI: oai:DiVA.org:liu-7471DiVA: diva2:22477
Public defence
2006-06-09, Berzeliussalen, Campus US, Linköpings Universitet, Linköping, 13:00 (English)
Opponent
Supervisors
Available from: 2006-09-28 Created: 2006-09-28 Last updated: 2012-01-30
List of papers
1. Different characteristics of postoperative heart failure after surgery for aortic stenosis and coronary disease
Open this publication in new window or tab >>Different characteristics of postoperative heart failure after surgery for aortic stenosis and coronary disease
2004 (English)In: Scandinavian Cardiovascular Journal, ISSN 1401-7431, Vol. 38, no 3, 152-158 p.Article in journal (Refereed) Published
Abstract [en]

Objective: Postoperative heart failure (PHF) remains a major determinant of outcome after cardiac surgery. However, possible differences in characteristics of PHF after valve surgery and coronary surgery (CABG) have received little attention. Therefore, this issue was studied in patients undergoing aortic valve replacement (AVR) and CABG, respectively.

Design: Three hundred and ninety-eight patients undergoing isolated AVR for aortic stenosis were compared with 398 patients, matched for age and sex, undergoing on-pump isolated CABG. Forty-five AVR and 47 CABG patients required treatment for PHF and these were studied in detail.

Results: The AVR group had longer aortic cross-clamp time and higher rate of isolated right ventricular heart failure postoperatively. Myocardial ischemia during induction and perioperative myocardial infarction were more common in the CABG group. One-year mortality was 8.9% in the AVR group vs 25.5% in the CABG group (p = 0.05).

Conclusions: The incidence of PHF was similar in both groups but different characteristics were found. Isolated right ventricular failure and PHF precipitated by septicemia were more common in AVR patients. PHF was more clearly associated with myocardial ischemia and infarction in CABG patients, which could explain their less favorable survival.

Keyword
aortic valve surgery, complications of surgery, coronary artery bypass surgery, heart failure, prognosis
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-14018 (URN)10.1080/14017430410029734 (DOI)
Available from: 2006-09-28 Created: 2006-09-28 Last updated: 2009-08-21
2. Risk factors for postoperative heart failure in patients operated on for aortic stenosis
Open this publication in new window or tab >>Risk factors for postoperative heart failure in patients operated on for aortic stenosis
2006 (English)In: The Annals of Thoracic Surgery, ISSN 0003-4975, Vol. 81, no 4, 1297-1304 p.Article in journal (Refereed) Published
Abstract [en]

Background

Risk factors for postoperative heart failure (PHF) have not been specifically studied in valve surgery although it has been acknowledged that patient variables may have a more profound influence on postoperative outcome than valve-related factors.

Methods

All patients undergoing isolated aortic valve replacement for aortic stenosis from January 1995 to December 2000 in the southeast region of Sweden were studied (n = 398). Forty-five patients with aortic valve replacement required treatment for PHF. Univariate and multivariate logistic regression analysis was carried out to identify risk factors for PHF.

Results

Thirty-day mortality was 6.7% versus 1.4% for patients with and without PHF, respectively (p = 0.05). With regard to clinical presentation of aortic stenosis, angina was associated with reduced risk, whereas history of congestive heart failure increased the risk for PHF. Five preoperative (hypertension, history of congestive heart failure, severe systolic left ventricular dysfunction, pulmonary hypertension, preoperative hemodynamic instability) and two intraoperative (aortic cross-clamp time, intraoperative myocardial infarction) variables were identified as independent risk factors for PHF. Patient–prosthesis mismatch did not influence the risk of PHF significantly.

Conclusions

Postoperative heart failure was associated with a marked increase in postoperative mortality and morbidity. Risk factors for PHF were variables indicating preexisting myocardial dysfunction, increased right or left ventricular afterload, and intraoperative myocardial injury. Our results highlight issues concerning cross-clamp time and myocardial protection, particularly for patients with preoperatively compromised myocardial function. Asymptomatic patients with significant aortic stenosis should be considered for surgery before substantial echocardiographic evidence of left ventricular dysfunction or increased pulmonary artery pressure develops.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-14019 (URN)10.1016/j.athoracsur.2005.11.036 (DOI)
Available from: 2006-09-28 Created: 2006-09-28 Last updated: 2009-06-08
3. Influence of early postoperative heart failure on five-year survival after surgery for aortic stenosis compared with CABG
Open this publication in new window or tab >>Influence of early postoperative heart failure on five-year survival after surgery for aortic stenosis compared with CABG
Manuscript (Other academic)
Identifiers
urn:nbn:se:liu:diva-14020 (URN)
Available from: 2006-09-28 Created: 2006-09-28 Last updated: 2010-01-13
4. Myocardial metabolism before and after valve replacement for aortic stenosis
Open this publication in new window or tab >>Myocardial metabolism before and after valve replacement for aortic stenosis
Show others...
2006 (English)In: Journal of Cardiovascular Surgery, ISSN 0021-9509, Vol. 47, no 3, 305-313 p.Article in journal (Refereed) Published
Abstract [en]

AIM: Post ischemic disturbances of myocardial metabolism that may contribute to postoperative heart failure and are accessible to metabolic treatment have been identified early after coronary surgery. Knowledge derived from these studies may not be applicable to other patient groups. Therefore we studied myocardial energy metabolism in patients operated for isolated aortic stenosis.

METHODS: Twenty patients undergoing isolated aortic valve replacement (AVR) because of aortic stenosis without significant regurgitation were studied before and immediately after surgery. Myocardial uptake of oxygen and energy substrates was assessed with coronary sinus catheter technique.

RESULTS: Free fatty acids (FFA) were the main source of myocardial energy before and after AVR. A significant uptake of lactate was only recorded preoperatively. A significant uptake of glutamate of the same magnitude as previously described in coronary patients was found pre- and postoperatively. Postoperatively a relative decrease of myocardial oxygen extraction ratio (P<0.001) and oxygen consumption (P=0.14) by approximately 20% was observed.

CONCLUSION: Preoperative and postoperative metabolic adaptation with substantial uptake of glutamate, previously claimed to be due to chronic or repetitive ischemia, was demonstrated. The results indicate that oxidative metabolism had not fully recovered when the procedure was completed. However, the potentially unfavorable postoperative metabolic state with predominant reliance on FFA as energy source was out-balanced by the unloading effect of AVR with a reduction in myocardial oxygen extraction.

Keyword
Aged, Amino Acids, Aortic Valve Stenosis, Biological Markers, Blood Glucose, Energy Metabolism, Fatty Acids, Female, Glycerol, Heart Valve Prosthesis Implantation, Hemodynamics, Humans, Lactic Acid, Male, Middle Aged, Myocardium, Oxygen, Oxygen Consumption, Postoperative Care, Preoperative Care, Treatment Outcome
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-14021 (URN)
Available from: 2006-09-28 Created: 2006-09-28 Last updated: 2009-06-08
5. Does glutamate influence myocardial and peripheral tissue metabolism after aortic valve replacement for aortic stenosis?
Open this publication in new window or tab >>Does glutamate influence myocardial and peripheral tissue metabolism after aortic valve replacement for aortic stenosis?
2006 (English)In: Clinical Nutrition, ISSN 0261-5614, Vol. 25, no 6, 913-922 p.Article in journal (Refereed) Published
Abstract [en]

Background & aims

Glutamate plays an important role for myocardial metabolism in association with ischaemia. Patients with coronary artery disease characteristically demonstrate increased uptake of glutamate. Improved recovery of myocardial metabolism and haemodynamic state after coronary surgery has been reported in patients treated with glutamate infusion. However, the effect of glutamate has not been studied after other cardiac surgical procedures. In addition, the effects of glutamate on peripheral tissue metabolism remain to be described.

Methods

Twenty patients undergoing surgery for aortic stenosis were studied after randomisation to blinded infusion of glutamate or saline during 1 h immediately after skin closure. Myocardial and leg tissue metabolism were assessed with organ balance techniques.

Results

Postoperative glutamate infusion induced a marked increase in myocardial and leg tissue uptake of glutamate. This was associated with a significant uptake of lactate in the heart. The negative arterial–venous differences of amino acids and free fatty acids across the leg were significantly smaller in the glutamate group. Haemodynamic state remained stable and did not differ between groups.

Conclusion

The heart and peripheral tissues consumed the exogenously administered glutamate after surgery for aortic stenosis. Potentially favourable effects of glutamate on myocardial and peripheral tissue metabolism are suggested.

Keyword
Glutamate; Myocardial metabolism; Humans; Aortic stenosis; Surgery
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-14022 (URN)10.1016/j.clnu.2006.04.002 (DOI)
Available from: 2006-09-28 Created: 2006-09-28 Last updated: 2009-06-08
6. Assessment of myocardial glutamate requirements early after coronary artery bypass surgery
Open this publication in new window or tab >>Assessment of myocardial glutamate requirements early after coronary artery bypass surgery
Show others...
1998 (English)In: Scandinavian Cardiovascular Journal, ISSN 1401-7431, Vol. 32, no 3, 145-152 p.Article in journal (Refereed) Published
Abstract [en]

Glutamate is an important substrate for the intermediary metabolism of the heart, particularly in association with ischemia. Early after coronary artery bypass surgery (CABG) myocardial uptake of glutamate seems to be limited by substrate availability (arterial levels). However, glutamate is not an innocuous substrate. As arterial levels of glutamate are important both for myocardial uptake and adverse effects, an attempt was made to determine a minimum dose of glutamate sufficient to supply the needs of the heart after CABG. Ten patients received and infusion of 220-240 ml of 0.1 M L-glutamic acid solution at varying rates during two 30-min periods, starting 2 h after uncomplicated elective CABG. Intravenous glutamate infusion caused a dose-dependent linear increase in arterial glutamate and an increased myocardial uptake of glutamate. However, myocardial uptake of glutamate correlated with arterial levels only at lower infusion rates. Although maximal peak uptake in individual patients (6.6 ± 1.1 μmol/min) occurred at an average increase of arterial whole blood glutamate of 172 ± 34 μmol/L, the greatest impact on myocardial glutamate uptake was achieved by increasing arterial whole blood glutamate by less than 100 μmol/L. This implies that an infusion rate of 30-40 mg glutamate/kg BW/h could suffice to achieve a maximal or near maximal myocardial glutamate uptake in most patients after CABG. The adequacy of this dosage remains to be confirmed in high-risk patients.

Keyword
adverse effects, biological transport, cardiac surgery, coronary artery disease, dose-response, human glutamate, metabolism, myocardium
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-14023 (URN)10.1080/14017439850140102 (DOI)
Available from: 2006-09-28 Created: 2006-09-28 Last updated: 2012-08-08Bibliographically approved

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