Oberhoffer 2006.

Study characteristics
Methods	Study period May 2003 to November 2004. Parallel RCT of two high risk groups undergoing CABG (preoperative IABP versus no preoperative IABP). Measurements included preoperative left‐ventricular ejection fraction and post operative cardiac index.
Participants	Group A (27 patients) IABP inserted 1 hour preoperatively and Group B (35 patients) no preoperative IABP. All were high risk patients as defined by having two of the following criteria: ejection fraction less than 35%, unstable angina, left main stem stenosis (>70%) or reoperation.
Interventions	Primary treatment: Coronary artery bypass grafting on cardiopulmonary bypass. Primary additional randomised intervention: IABP.
Outcomes	Mortality: Cardiac index, Pharmacological support and Intensive Care stay were all measured however a lack of sufficient original unprocessed data excluded a meta‐analysis.
Notes	PROSPECTIVE RANDOMIZED STUDY OF PREOPERATIVE INTRAAORTIC BALLOON COUNTERPULSATION IN HIGHRISK CORONARY ARTERY BYPASS GRAFTING PATIENTS Martin Oberhoffer, Marion Weis, Sandra Eifert, Darius Rassoulian, Bruno Meiser, Michael Schmoeckel, Bruno Reichart, Calin Vicol. 16th World Congress of World Society of Cardio‐Thoracic Surgeons, Ottawa, Canada August 2006
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Abstract only
Allocation concealment (selection bias)	Unclear risk	Abstract only
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Abstract only
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Abstract only
Selective reporting (reporting bias)	Unclear risk	Abstract only
Other bias	Unclear risk	Abstract only

Most of the included trials above have the same Principal Investigator, however correspondence with the authors confirms all studies are entirely independent.
All studies examine the role of the preoperative IABP in patients undergoing CABG, however each study looks at slightly different patient characteristics and outcomes.

Christenson 1997a: Main patient study group: hypertensive patients with ischaemic heart disease and poor left ventricular function.
Christenson 1997b: Main patient study group: high risk redo CABG surgery.
Christenson 1997c: Main patient study group: heterogeneous group of "high risk"patients with patient examining timing of preoperative IABP and cost effectiveness.
Christenson 1999: Main patient study group: heterogeneous group of "high risk"patients with patient examining timing of preoperative IABP.
Christenson 2003: Main patient study group: off‐pump patients.
Correspondence with the Principal Investigator (Dr Christenson) has confirmed adequate allocation concealment. "For each trial, sealed envelopes containing group identity was prepared prior to the start of the trial, mixed and kept in a box. Once a patient fulfilled the study entry criteria set forth, a secretary drew one envelope, the envelope was opened and the patient was assigned to the group mentioned".

All studies demonstrate very high rates of post operative conversion to IABP in the control groups.
There was a rate of conversion to cardiopulmonary bypass in the control group of the off‐pump study.

Oberhoffer 2006: This independent study was accepted in abstract form for the 16th World Congress of the World Society of Cardio‐Thoracic Surgeons, Ottawa, Canada, August 2006. The work was not presented at the meeting. Telephone and e‐mail contact has been made with Dr Oberhoffer who assures us of his intention to publish this work in a pier review journal however to date it has not been published in full form.