Page 218 - ACCCN's Critical Care Nursing

Cardiovascular Assessment and Monitoring 195

is exaggerated in hypokalaemia. Inverted U waves may
be seen and often associated with coronary heart Practice tip
disease (CHD), and these may appear transiently
during exercise testing. 18 Think of the leads I, II, III, aVR, aVL, aVF, V1-V6 as the ‘eyes’ that
are looking at the heart’s electrical activity from different angles
ECG Interpretation and view the heart’s different areas.
Interpretation of a 12-lead ECG is an experiential skill,
requiring consistent exposure and practice. Some steps to
aid interpretation are noted below. HAEMODYNAMIC MONITORING
● Calculate heart rate: The blood’s dynamic movement in the cardiovascular
● There are many ways to calculate the heart rate. system is referred to as haemodynamics. Haemodynamic
One way is to count the R waves on a 6 sec strip monitoring is performed to provide the clinician with a
and multiply by 10 to calculate the rate (the top greater understanding of the pathophysiology of the
of the ECG paper is usually marked at 3 sec problem being treated than would be possible with clini-
intervals). cal assessment alone. Knowledge of the evidence that
● Use an ECG ruler if one is available. underpins the technology and the processes for interpre-
● Check R-R intervals (rhythm): tation is therefore essential to facilitate optimal usage and
● Are the rhythms regular? evidence-based decisions. 22
● To assess regularity: mark the duration of two
neighbouring R waves (R-R interval) on a plain This section explores the principles related to haemody-
piece of paper, move this paper to check other R-R namic monitoring and the different types of monitoring
intervals on the ECG strip. R-R intervals should be available, and introduces the most recent and appropriate
uniform in a normal ECG which means the patient evidence related to haemodynamic monitoring. The
has a regular ECG rhythm. reasons for haemodynamic monitoring are generally
● Locate P waves (check atrial activity): threefold:
● Observe for the presence or absence of P waves. 1. to establish a precise health-related diagnosis
● Check regularity and shape. 2. to determine appropriate therapy
● Is the P wave positive? 3. to monitor the response to that therapy.
● The relationship between P waves and QRS com-
plexes: is there a P wave preceding every QRS Haemodynamic monitoring can be non-invasive or inva-
complex? sive, and may be required on a continuous or intermittent
23
● What is the duration of the P wave? basis depending on the needs of the patient. In both
● Measure P-R interval (check AV node activity): cases, signals are processed from a variety of physiological
● What is the duration of the P-R interval? variables, and these are then clinically interpreted within
● Measure QRS duration (check ventricular activity): the individual patient’s context.
● Is the ventricular electrical activity normal? Non-invasive monitoring does not require any device to
● Is the QRS complex too wide or narrow? be inserted into the body and therefore does not breach
● Check the presence of Q wave. If present, is it the skin. Directly measured non-invasive variables include
normal or pathological? body temperature, heart rate, blood pressure, respiratory
● Note other clues: rate and urine output, while other processed forms can
● Observe whether the isoelectric line is present be generated by the ECG, arterial and venous Dopplers,
between the S and T waves. transcutaneous pulse oximetry (using an external probe
● Examine the T wave to see whether it is positive, on a digit such as the finger or on the ear), and expired
negative, or flat. Is it less than 0.16 sec? carbon monoxide monitors.
● Examine the duration of the Q-T interval: is it too
long? Invasive monitoring requires the vascular system to be
● Observe for any extra complexes and note their rate cannulated and pressure or flow within the circulation
and shape, and whether they have the same or dif- interpreted. Invasive haemodynamic monitoring tech-
ferent morphology. nology includes:
● systemic arterial pressure monitoring
● central venous pressure
● pulmonary artery pressure
Practice tip ● cardiac output (thermodilution).
The presence of Q waves does not always indicate past myocar- Invasive monitoring has also facilitated greater use of
dial infarct. Other patient clinical information is needed to inter- blood component analyses, such as arterial and venous
pret the significance of Q waves. blood gases.
ECG interpretation should always take a patient’s clinical infor- The invasive nature of this monitoring allows the pres-
mation (patient symptoms, complaints, other haemodynamic sures that are sensed at the distal ends of the catheters to
information) into account. be transduced, and to continuously display and monitor
the corresponding waveforms. The extent of monitoring