CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 10, November 2012
AFRICA
541
QTc prolongation prior to angiography predicts poor
outcome and associates significantly with lower left
ventricular ejection fractions and higher left ventricular
end-diastolic pressures
PIETER VAN DER BIJL, MARSHALL HERADIEN, ANTON DOUBELL, PAUL BRINK
Abstract
Background:
QT prolongation on the surface ECG is associ-
ated with sudden cardiac death. The cause of QT prolon-
gation in ischaemic heart disease (IHD) patients remains
unknown, but may be due to a complex interplay between
genetic factors and impaired systolic and/or diastolic function
through as yet unexplained mechanisms. It was hypothesised
that QT prolongation before elective coronary angiography is
associated with an increased mortality at six months.
Methods
:
Complete records of 321 patients who under-
went coronary angiography were examined for QT interval
corrected for heart rate (QTc), left ventricular ejection frac-
tion (LVEF), left ventricular end-diastolic pressure (LVEDP)
and known ischaemic heart disease risk factors. Patients
were designated long QTc (LQTc) when they had prolonged
QTc intervals or normal QTc (NQTc) when the QTc interval
was normal. Patients with atrial fibrillation, bundle branch
blocks, no ECG in the 24 hours before angiography, or a
creatinine level
>
200
μ
mol/l were excluded. Survival was
determined telephonically at six months.
Results:
Twenty-eight per cent of the total population had
LQTc. During follow up, 15 patients (4.7%) died suddenly,
73%
of whom had a LQTc. LQTc was significantly associ-
ated with mortality (LQTc 12% vs NQTc 1.7%;
p
<
0.01),
and with lower but normal LVEF (LQTc 52.9
±
15.4%
vs
NQTc 61.6
±
13.6%;
p
<
0.01),
higher LVEDP at LVEF
>
45% (
LQTc 19.2
±
9.0
mmHg vs NQTc 15.95
±
7.5
mmHg;
p
<
0.05),
hypercholesterolaemia and a negative family history
of IHD.
Conclusion
:
In patients with sinus rhythm and normal
QRS width, QTc prolongation before coronary angiography
predicted increased mortality at six months. QTc also asso-
ciated strongly with left ventricular systolic and diastolic
dysfunction, hypercholesterolaemia and a negative family
history of IHD.
Keywords:
QT prolongation, sudden death, coronary artery
disease
Submitted 18/3/12, accepted 30/8/12
Cardiovasc J Afr
2012;
23
: 541–545
DOI: 10.5830/CVJA-2012-060
The QT interval represents ventricular electrical depolarisation
and repolarisation on the surface ECG. It increases with age
and varies with gender, time of day, season of the year and heart
rate.
1-3
Bazett’s formula is frequently used to correct the QT
interval for heart rate, yielding the QTc interval.
4,5
A prolonged QTc interval (LQTc) is a manifestation of a
complex interplay between genetic and environmental factors,
and is a risk factor for life-threatening dysrhythmias and sudden
death. The
forme fruste
of QT prolongation is congenital long
QT syndrome (LQTS), an inherited cardiac ion-channel disease
associatedwithsyncope,malignant ventricular tachydysrhythmias
and sudden cardiac death. LQTS, by exclusion, occurs in
structurally normal hearts.
6
Recently, polymorphisms in the gene for NOS1AP, which
regulates nitric oxide production and thus coronary perfusion,
have been shown to prolong cardiac repolarisation.
7-9
Ethnic
differences in QT interval have also been reported, LQTc
comprising a higher risk among black than white subjects.
10
QT prolongation is an independent prognosticator of cardiac
and all-cause mortality, especially in the context of cardiovascular
disease.
11-13
In addition, it is associated with an increased 10-year
risk of ischaemic heart disease (IHD) and sudden death in the
general population.
14
The fact that interventional cardiologists are more interested
in the ‘ST’ segment than the ‘QTc’ is underscored by the paucity
of QTc studies peri-angiography. In only one study has an LQTc
in the period immediately before coronary angiography been
directly correlated with outcome, but the authors described QT
peak interval instead of QTc.
15
LQTc in the presence of coronary
artery disease increases the risk of sudden cardiac death by a
factor of five.
16
IHD is a cause of systolic and diastolic dysfunction of the
left ventricle, and both of these are independent predictors of
mortality.
17,18
QT prolongation is not only inherited, but also linked
to cardiac hypertrophy, as frequently observed in hypertensive
heart disease.
19
However, no reference to an association between
left ventricular systolic and diastolic dysfunction and QTc could
be identified in the literature. Additionally, the length of the QTc
interval appears to be directly related to the number of large
coronary arteries that are diseased.
20
QT prolongation may also reflect autonomic neuropathy in
patients with diabetes mellitus.
21,22
It does not, however, provide
a reliable measure of the degree of autonomic neuropathy.
23
Although smoking has been associated with a LQTc, it has not
Division of Cardiology, Department of Medicine, Faculty of
Health Sciences, Stellenbosch University and Tygerberg
Academic Hospital, Western Cape, South Africa
PIETER VAN DER BIJL, MB ChB, MMed, DA, FCP (SA), pieter.
MARSHALL HERADIEN, MB ChB, BSc Hons, MMed, Cert Cardiol
(
SA)
ANTON DOUBELL, MB ChB, MMed, HonsBSc, PhD, FCP (SA)
PAUL BRINK, MB ChB, MMed, PhD
