Competence of psychiatric clinicians in interpreting electrocardiograms and QT intervals: can they do this? Does it matter?

AIMS AND METHOD

We assessed the abilities of trainee and consultant psychiatristsin reading and interpreting electrocardiograms (ECGs) and QTintervals using a questionnaire and standardised ECG.

RESULTS

Only 5% of our sample of trainee and consultant psychiatristscould correctly indicate a QTc interval. Performances on othermeasures, such as rate were also poor, with senior house officersperforming better than consultants.

CLINICAL IMPLICATIONS

The increased awareness of problems caused by antipsychoticshas not been reflected in improved knowledge of ECGs amongpsychiatrists. Machines do not reliably calculate QT intervals.We therefore urge better training and understanding of ECGsfor psychiatrists.

Introduction

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Introduction

People with mental illnesses, especially schizophrenia, havea higher mortality rate than the general population, the causesof which are yet poorly understood but could be related toside-effects of antipsychotic medication (Waddington et al, 1998).Psychotropic medication has been shown to increase the risk of serious ventricular arrhythmias and thus, sudden cardiacdeath. Ray et al (2001) and Liperoti et al (2005) showed thatmoderate doses of antipsychotics were associated with largeabsolute and relative increases in the risk of sudden cardiacdeath. Prolonged QT intervals reflect electrical dysfunctionof the myocardium and may indicate predisposition to malignanttachycardias and sudden death. The QT interval is prolongedby a slow pulse and being female, and shortened by anxiety. Importantly, drugs and ischaemia can also prolong it. The correctedQT (QTc) gives a better indication of the risks by allowingfor the pulse rate. There are various methods of calculatingthis, but the most commonly used is the Bazett’s formula(Box 1) because of its relative simplicity, despite inaccuraciesassociated with heart rate. Failure to identify a prolongedQT leaves patients at risk of sudden death.

Recent work by Minerotti et al (2006) has shown increased QTc intervals in healthy men with neurotic personality traits,in alcohol dependence syndrome (Borini et al, 2003), and inincident diabetics (Carnethon et al, 2006). The new consensusstatement on high-dose antipsychotic medication from the RoyalCollege of Psychiatrists (2006) recommends assessing cardiovascularrisk with electrocardiogram (ECG) monitoring prior to use of antipsychotic medication to reduce risk of arrhythmias –we presume this has increased awareness and ordering of ECGs.Proper monitoring of QTc interval may detect prolongation andreduce occurrence of potentially lethal cardiac arrhythmias.

In this context, doctors have come to be more dependent uponcomputer ECG interpretation. The reliability of such programshas not been proven (Willems et al, 1991). Standards regardingthe accuracy of these readings were developed in the 1980s,but they have been largely ignored. Recent work in this area(Krishnan et al, 2006) has highlighted their deficiencies. TheBritish Heart Foundation (2005) advises that computer-assistedECG interpretation can identify important anomalies, but errorsare common and interpretation should not be accepted withoutvisual inspection. Electrocardiogram departments and cardiologistslack the capacity to provide a QTc validation service. We thusfeel that psychiatrists should be competent in this skill –the Royal College of Psychiatrists recommended this in a consensusstatement on high-dose antipsychotic medication (Royal College of Psychiatrists, 2006).

Box 1. QTc calculating formula
Bazett’s formula:
Formula
QTc, QT interval corrected for rate;RR, interval from the onset of one QRS complex to the onsetof the next QRS complex, measured in seconds.
Bazett’sformula over-corrects at high heart rates and under-corrects at low heart rates, but it is widely used in clinical practisebecause of its simplicity.

In a small study, Warner et al (1996) reported that less than 20% of psychiatric trainees were able to identify a prolongedQT interval on an ECG. Moreover, studies in medical and surgicalspecialties have shown lack of elementary knowledge of ECGsamong non-psychiatric doctors (Montgomery et al, 1994). Tenyears on from the publication of Warner et al’s studywe aimed to find out how much psychiatric clinicians knew aboutinterpretation of aspects of an ECG of immediate clinical relevance.

Method

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Method

The study was carried out in London (Oxleas National HealthService (NHS) Foundation Trust) and Manchester (Bolton, Salfordand Trafford Mental Health NHS Trust) hospitals, over a 6-monthperiod. Both consultants and trainees in psychiatry were approachedwith a short questionnaire.

A pilot study produced deceptively good results, as participantstook the questionnaires away and filled in researched, perfectanswers. Therefore, in the proper study, we asked participantsto fill out a semi-structured questionnaire (nine questionsin total; see online data supplement 1) in approximately 10minutes, with the researcher present. Each participant was presentedwith this questionnaire and a copy of an ECG of a healthy person (online data supplement 2) with instructions to calculate therate, mark out the QT interval and calculate the QTc. The questionnaire(one side of an A4 sheet) comprised basic questions about grade,post-graduate training in other specialties, medication onwhich they monitored ECGs and calculation of rate, QT and QTc– all questions considered most relevant in the literature and clinical practice. We did not insist on exact calculationof the QTc, which would have required a calculator, but acceptedthe answer as right if the formula was written down. The normalECG used showed a heart rate of 66 beats per minute with aQT interval of 0.38 seconds. We used the Bazett’s formulato calculate the QTc, which was 0.39 seconds.

We aimed to approach 100 doctors and to get roughly equal numbersof senior house officers v. specialty registrars and consultants.As senior house officers congregated at the Member of the RoyalCollege of Psychiatrists (MRCPsych) course teaching it waseasy to get them to fill out the forms and return them betweenlectures. Things were more difficult with consultants and anumber of questionnaires were left uncompleted as we were askedto return later to collect them. Our responses from consultantsfor non-participation varied: some did not have the time, somefelt it was not relevant to them, and some gave no explanationat all. A total of 49 senior house officers in psychiatry,out of 64 approached (77%, pre-membership), 8 out of 10 specialist registrars (80%) and 5 out of 26 general adult, old age, forensicand learning disability consultants (19%) agreed to completethe semi-structured questionnaire (total response rate 62%).As copies of the same ECG of a healthy person verified by acardiologist was used, there were no uncertainties about therate, QT interval and QTc.

Results

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Results

No statistically significant differences were noted in responsesbetween hospitals in the two cities and the data was pooled.

Using Fisher’s exact test, subgroup analysis showed thatclinicians with previous experience in other medical specialtieswere significantly more likely to calculate the heart ratecorrectly (P=0.0193, Fisher’s exact test). However, theywere no more likely to read ECGs themselves or able to performQT interval indication/calculation (P=1) than those with nomedical experience.

Specialty registrars and consultants were significantly lesslikely to read ECGs and calculate the heart rate correctlythemselves (P=0.0245, Fisher’s exact test) than seniorhouse officers (the small number of participating consultantsseverely limits the validity of these conclusions). QT intervalindication/calculation was equally poor for both groups.

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Fig. 1. Heart rate calculation (%).

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Fig. 2. QT interval calculation.

General questions
About three-quarters of respondents felt the questionnaire hadhighlighted deficiencies in their knowledge (Table 1).

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Table 1. Overview of ECG interpretation by psychiatric clinicians

Calculations
The respondents’ ability to calculate heart rate and QTinterval on the ECG is shown in Table 2 and Figs. 1 and 2.Only 62% of respondents calculated the heart rate correctlyand 5% correctly indicated/calculated QTc using Bazett’sformula.

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Table 2. Calculation of heart rate and QTc

Presentation of the findings and discussion with colleaguesat an Oxleas NHS Trust audit meeting brought forward suggestionsthat psychiatrists could not be expected to read ECGs and thatthey should depend on automated readings and on general practitionersto provide physical healthcare (including interpreting ECGs).

Krishnan et al (2006) suggest overreading of 12 lead ECGs is required to circumvent errors of computerised ECG interpretation.In light of this, we undertook a further audit of ECG tracingsof machines used by the Oxleas NHS Foundation Trust, lookingat the accuracy of the measurement of QT intervals. Fifty-threeconsecutive ECGs performed on three of the Trust’s fiveMortara Eli 250 electrograph machines (which use Mortara’sVeritas analysis algorithm for interpretation) were reviewed. We found that on a sample of 53 consecutive ECGs, seven QTintervals were incorrectly measured. Thus, 13% of the sampleof Trust ECG machine QT reports were inaccurate and 6% hadunderestimated QT interval.

Discussion

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Discussion

This study suggests that knowledge of role of ECGs and the interpretation of heart rate, QT interval measurement and QTc calculationis unsatisfactory among psychiatrists. The study was carriedout across teaching and non-teaching settings in a sample weexpect is representative of UK psychiatrists generally, thoughseveral consultants did not participate for various reasons,which may limit the generalisation of findings. Our sample sizeof 64 respondents was more than twice the size of the earlierstudy of psychiatric trainees by Warner et al (1996). Ourresponse rate was 62% compared with 97% in the earlier study.We endeavoured to cover all trainees and consultants in theparticipating hospitals, but were limited by the nature ofour criteria, namely that the specified questionnaires be completedand returned immediately to the researchers. There were statisticallysignificant differences between the trainee and consultant groups,but the small number of consultants could affect validity.

Most respondents were aware of the need to monitor ECGs, buta significant proportion was unable to calculate heart rateand measure QT intervals. These findings replicate those ofprevious studies (Montgomery et al, 1994) of doctors workingin acute medicine, in which 24% of doctors correctly identifiedthe QT interval, as well as a study of psychiatrists in training(Warner et al, 1996) in which 20% of the sample identifiedprolonged QT intervals correctly. We expected that the increasedawareness of the cardiotoxicity of psychotropics and interactionbetween medications would have made psychiatrists more adeptat QT interval and ECG abnormality interpretation, but thisstudy indicates that the problem remains.

As reviewed in the introduction, evidence suggests that it isimportant to monitor QT intervals and ECGs in high-risk patientgroups. The British Heart Foundation has presented good evidence,in line with the Oxleas Trust audit, that computerised readingsof ECGs are not completely reliable. Data suggest that thetype of error made by computerised ECG recording includes dangerous underestimation of the QT interval. Requesting other cliniciansto check all ECGs will have huge resource and time implications.We therefore think it essential that psychiatrists improvetheir skills in this important area. The view that psychiatristsmonitor mental health and do not have time to provide holisticcare is potentially dangerous. O’Brien & Oyebode (2003),acknowledging that widespread monitoring of the psychiatricpopulation is difficult, suggested that some interested psychiatristsmay do more of this work than others. We argue that ECG interpretationis a basic medical skill and calculation of rate, rhythm andQTc measurement are relatively straightforward and deserve to be carried out within existing services (for a short instructionon how to interpret ECGs see online data supplement 3).

The statement on high-dose antipsychotic medication publishedby the Royal College of Psychiatrists (2006) calls for trainingin ECG interpretation for clinicians, and also for ready accessto a cardiologist for interpretation. This need is being addressedin some ways by the introduction of an ECG interpretation ObservedStandardised Clinical Examination (OSCE) station in the MRCPsychexam and could be one reason for improved knowledge of ECGsamong senior house officers compared with consultants. Introductionof mandatory ECG teaching for psychiatrists in training andrefresher courses for consultants is one way forward and will help improve the care of our patients.

References

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