Failure to Diagnose Aortic Dissection

Case history

He phoned his GP and was told to go to the practice immediately. Mr Coxell drove himself the short distance to the surgery, where he was seen immediately. After a brief assessment by the GP, he was given some nitrolingual spray and an ambulance was called. The ambulance officers saw Mr Coxell at 1530 and he arrived at hospital at 1603.

On arrival in the Emergency Department (ED), Mr Coxell was assessed by an RMO. The patient gave a history of sudden onset of central chest pain at rest, with the pain then shifting to the right upper chest. His past medical history included longstanding hypertension. He described the pain as severe and continuous from its onset, with only partial relief from the nitrolingual spray. Cardiovascular examination was unremarkable and no cardiac murmur was detected. An ECG, CXR and cardiac enzymes were normal.

The chest pain severity was recorded as follows:

• 1615 – 4/10;
• 1700 – 6/10, Anginine given;
• 1705 – 5/10, morphine 5mg IVI given;
• 1830 – 5/10;
• 1905 – 5/10, panadol and Somac given.

The ED physician reviewed the test results and completed the hospital’s Chest Pain Emergency Management Guide form, which classified the patient as an intermediate likelihood of suffering from ischaemic heart disease (IHD). Part of the pathway on the hospital’s flowchart was for intermediate risk patients to be admitted and, if no recurrent chest pain, then an exercise stress test was  to be undertaken.

The ED physician rang the on-call cardiologist and discussed the findings. A decision was made to admit the patient to the Cardiac Care Unit (CCU), and he was admitted to the unit at 2030 on 31 October 2006.

On arrival in the CCU, the patient experienced further chest pain which was documented as follows on 1 November 2006 by the nursing staff:

• 0030 – 3/10, Anginine given;
• 0050 – no chest pain;
• 0200 – chest pain and unable to sleep;
• 0630 – 4/10, pain radiating to the right arm, 3 Anginine given;
• 0650 – 8 – 9/10, morphine 5mg IVI and Anginine given;
• 0715 – chest pain, Anginine given;
• 0730 – no chest pain.

At approximately 0900 on 1 November 2006, the cardiology RMO examined the patient. She recorded a presenting history of “sharp stabbing central chest pain radiating to the head” and “right sided pain only”. On examination, the RMO also noted an early diastolic cardiac murmur. This was a new sign, which had not been noted in the earlier physical examination of the patient.

The patient was seen by the cardiology registrar at approximately 1100. The registrar was in his first year of training and he was undertaking a second three month term in cardiology. The patient told the registrar that he was pain free. On examination, the registrar also noted the presence of the cardiac murmur. The registrar recorded a management plan, including the performance of an exercise stress test and transthoracic echocardiogram, in accordance with the hospital’s chest pain protocol. The RMO completed the request forms for these diagnostic investigations.

Later that afternoon, the patient underwent an exercise stress test. At 2 minutes into stage 1 of the test, the patient indicated a pain rating of 4/10. As the test continued, the pain escalated to 5 – 6/10. At 7 minutes the patient was becoming fatigued and asked for the test to stop. He was given an Anginine tablet for pain relief but a short time later he lost consciousness and collapsed to the floor.

He was transferred to the CCU where an emergency echocardiogram suggested the possibility of a  pericardial tamponade, but the patient failed to respond to resuscitation and died.

The death was reported to the Coroner. The post-mortem revealed an intimal tear in the aortic arch, immediately proximal to the origin of the brachiocephalic trunk and left common carotid artery. The aortic arch dissection had ruptured into the pericardial sac, resulting in a cardiac tamponade.

Medico-legal issues

A Coronial Inquest was held in April 2010 and the Coroner’s findings were handed down on 2 September 2010.¹ The Coroner found that the patient had died as a result of a cardiac tamponade caused by an aortic dissection after undertaking an exercise stress test.

At the Inquest, evidence was given by the ED physician, cardiologist, cardiology registrar, the RMO and the cardiac technicians who were present during the exercise stress test. An independent expert cardiologist also gave evidence at the Inquest.

Some of the issues considered at the Inquest included:

What was the evidence for and against aortic dissection, following the patient’s presentation at hospital?

Both the treating and independent expert cardiologists agreed Mr Coxell’s aortic dissection commenced on the afternoon of 31 October 2006 with the onset of severe central chest pain while at rest. Evidence was given that aortic dissection can be diagnosed by:

1. the presence of severe chest pain;
2. the pain being intense from onset and described  as sharp in nature;
3. ulse deficit on physical examination;
4. the presence of a cardiac murmur of aortic regurgitation;
5. CXR, although this may be normal;
6. echocardiogram, chest CT, angiogram or MRI may be required to confirm the diagnosis.

The ED physician gave evidence at the Inquest that he did consider the possibility of aortic dissection as part of his differential diagnosis of Mr Coxell’s chest pain. However, he ultimately made a provisional diagnosis of IHD, significantly relying on the fact that in patients presenting with chest pain to hospital it is approximately 1,000 times more likely to be due to IHD than to aortic dissection.

However, it was noted that there were a number of features of the patient’s presentation which were not typical of IHD. These included:

• no ECG changes;
• no increase in cardiac enzymes;
• inadequate response to Anginine;
• no gradual onset of pain or pain subsiding at rest;
• no family history of IHD;
• no diabetes
• no sweating;
• no nausea;
• no shortness of breath.

Was the patient’s aortic dissection diagnosable and treatable?

The independent expert cardiologist gave evidence that the patient’s aortic dissection could probably have been detected by an echocardiogram on 1 November 2006. The treating cardiologist stated that if either the RMO or registrar had consulted him on 1 November 2006, he would have directed that an echocardiogram be performed as soon as possible. Had the aortic dissection been diagnosed, urgent surgical intervention was required to repair the dissection. The cardiologists gave evidence that there was a 74% chance of a successful surgical outcome for a type A dissection. If left untreated, the mortality rate of aortic dissection is generally high in the first 48 hours. It progresses at a morality rate of about 1% per hour from the commencement of the dissection. The Coroner concluded:

“Mr Coxell’s death could have been avoided if he had undertaken a diagnostic test such as an echocardiogram or CT aortogram” and “death was also likely to have been avoided by not doing the exercise stress test”.

The expert cardiologist stated that the exercise stress test was the “precipitating factor that altered a contained aortic dissection into a lethal cardiac tamponade”.

Should the registrar have contacted the on-call cardiologist?

The registrar did not contact the consultant following his examination of Mr Coxell on the morning of 1 November 2006 and he made a clinical decision to proceed with further investigations, of which the exercise stress test was one. He did not require approval for carrying out the investigations and he was aware he could access the on-call consultant, if needed. The Coroner commented that the “circumstances as to when he should be contacting the consultant had not been made clear to him in his training”.

The registrar gave evidence that his decision as to whether to call the consultant was based on his own assessment of the patient’s stability. He acknowledged that he may not have reviewed the nursing notes before or after seeing the patient. In hindsight, he accepted that he should have contacted the consultant, particularly because of the patient’s changed clinical status. This included the ongoing chest pain following his admission to the CCU. He also accepted that the identification of the cardiac murmur was a significant new clinical finding that should have been recorded and discussed with the on-call cardiologist.

Discussion

It has been estimated that 6.4% of all adverse events in hospital are related to diagnostic errors and 83.3% of these errors are preventable.²  In diagnostic errors, more human and organisational causes related to lack of knowledge or problems with transfer of knowledge are identified compared with other adverse events. Lack of knowledge, inappropriate application of knowledge, inadequate information transfer, urgency of decision making and lack of supervision all contribute to diagnostic errors.

Identifying and implementing strategies to minimise diagnostic errors is complex and difficult. Cognitive factors are thought to contribute to about three quarters of diagnostic errors in medical practice.³

Cognitive factors include:

• Availability – tendency to judge diagnoses as more likely if they are more easily retrievable from memory;
• Base rate neglect – tendency to ignore the true rate of disease, and pursue rare but more exotic diagnoses;
• Representativeness – tendency to be guided by prototypical features of disease without appropriate consideration of base rates of disease and the tendency to miss atypical variants;
• Confirmation bias – tendency to seek data to confirm, not refute the hypothesis;
• Premature closure – tendency to stop too soon without an appropriate consideration of alternative possibilities.⁴

A taxonomy for the cognitive component of diagnostic error has been proposed:

• Faulty knowledge;
• Faulty data gathering;
• Faulty information processing;
• Faulty verification.

In this taxonomy, the majority of errors are the result of reasoning deficits, and most of these involve ‘premature closure’ – closing the interview or diagnostic process before the correct diagnosis had emerged. Studies of the diagnostic process have revealed that, within a few seconds to minutes of first seeing a patient, the clinician advances one or more diagnostic hypotheses. The single best predictor of diagnostic success is the occurrence of the correct diagnosis as a hypothesis early in the consultation. For medical practitioners this occurred approximately six minutes into the clinical encounter, and for medical students it was closer to 10 minutes. Thus, the critical aspect of the diagnostic thinking occurred with minimal information early in the clinical encounter.

A study of 464 patients who presented to hospital with a type A aortic dissection revealed that while the sudden onset of severe sharp pain was the single most common presenting complaint, the clinical presentation was diverse.⁵

Classical physical findings such as aortic regurgitation and pulse deficit were noted in only 31.6% and 15.1% patients respectively. The initial CXR and ECG were frequently not helpful (no abnormalities were noted in 12.4% and 31.3% of patients, respectively). CXRs showed an absence of mediastinal widening in 37.4% of patients with type A dissection and abnormal aortic contour was noted in the minority of those patients. Of note, severe pain was the most common presenting symptom and 84.8% recorded abrupt onset of pain. The pain was described as sharp more often than tearing or ripping. Indeed, it has been suggested that medical practitioners can improve their diagnostic accuracy of aortic dissection by specifically asking about the quality of the patient’s pain, the radiation of the pain and the intensity of its onset. The authors of the study concluded:

“Acute aortic dissection is uncommon, but complications develop rapidly and the outcome is often fatal. The typical presentation is characterised by acute onset of severe pain.  However, clinical manifestations are diverse, and what were previously considered to be classic symptoms and signs are often absent. Therefore, a high clinical index of suspicion is necessary”.

References

1. Inquest into the death of Harry Coxell, File Number 312/08; State Coroner’s Court, Glebe.
2. Zwaan L, de Bruijne M, Wagner C et al. Patient Record Review of the Incidence, Consequences, and Causes of Diagnostic Adverse Events. Arch Intern Med 2010; 170(12):1015-1020.
3. Graber ML, Franklin N, Gordon R. Diagnostic Error in Internal Medicine. Arch Intern Med 2005;165:1493-1499.
4. Norman GR, Eva KW. Diagnostic error and clinical reasoning. Medical Education 2010;44:94-100.
5. Hagan PG, Nienaber CA, Isselbacher EM et al. The International Registry of Acute Aortic Dissection (IRAD): New Insights Into an Old Disease. JAMA 2000; 283(7):897-903.