Page 302 - ACCCN's Critical Care Nursing

Cardiac Rhythm Assessment and Management 279

● Patient/device details: patient name, type of device, However, in LBBB septal depolarisation occurs well in
date and time of the printout. advance of the delayed conduction to the lateral left ven-
● Battery information: a bar graph displays the progress tricular wall. The impact on contraction is to create ven-
of the battery towards the Elective Replacement Indi- tricular dyssynchrony, with the septum contracting before
cator (ERI); the Magnet Rate (i.e. the rate that asyn- the lateral wall, rather than synchronously with it.
chronous pacing will occur at if a magnet is placed Similarly, ventricular relaxation becomes dyssynchronous
over the device); the longevity (indicating the which may lessen myocardial perfusion and limit ven-
minimum remaining longevity of the device if the tricular filling, both of which can become contributors to
26
patient was to be paced 100% of the time in the severity of heart failure. Whilst the majority of
the current settings). patients with LBBB have dyssnchrony and systolic dys-
● Current Parameters: basic pacemaker set up including function, the impact may not be of note for those with
base rate, maximum rate at which the atrial rhythm otherwise normal hearts, but becomes much more pro-
will be tracked, AV delay, output settings and pulse nounced when there is existing myocardial disease and/
widths for both chambers. or heart failure. 26,81 With very wide LBBB (e.g. >0.14 sec)
● Episodes: summary of any arrhythmia episodes that the impact is greater, as the dyssynchrony between the
have been recorded since the last interrogation, any septal and free wall contraction is exaggerated. 26,75,81,82
Automatic Mode Switching events that have occurred. In CRT, pacing leads on both the right ventricular (RV)
● Events: an event in pacing terms is a beat, rather than septum and the left ventricular (LV) lateral wall are used
a clinical event; every atrial beat (sensed or paced) and to stimulate both muscle masses at the same time, with
every ventricular beat (sensed or paced) is recorded the aim of improving heart failure in patients with sig-
allowing the calculation of the percentage of atrial and nificant dyssynchrony. LV and RV pacing stimuli may
83
ventricular pacing since the last interrogation; this can be delivered simultaneously, although programming of
be compared to previous reports to assess whether either LV or RV stimulation first by 10–80 msec is seen
pacemaker dependence is increasing or decreasing. more often. The aim is that a reduction in QRS duration
● Test Results: the results of device and lead testing per- can be seen electrocardiographically, preferably with the
formed during the current interrogation as well as QRS returning to normal duration (<0.12 sec). Expected
83
testing from the last session performed, including outcomes of CRT include: 76-83,84
graphic trends of all tests over time shown in a sepa-
rate section of the report. ● improvement in NYHA functional class
● Sense Results: the results of the sensing tests carried ● improvement in quality of life
out in the current interrogation, the last session’s ● improvement in physical function
values are also shown, and graphic trends of sensing ● improvement in ejection fraction and reduction in
over time can be viewed in a separate section of the ventricular size
report. ● reduced hospitalisation for heart failure
● Lead Impedance: the results of impedance measure- ● cardiovascular mortality reduction.
ments from the current interrogation and the last The right ventricular septal lead is implanted in standard
session; this provides information about the integrity fashion, positioned either at the RV apex or outflow tract.
of the pacing leads, connections, and their interface Most commonly the left ventricular lead is also posi-
with the myocardium; impedance is the resistance to tioned transvenously, with the lead advanced through the
current provided by the electrical circuit. Variations in coronary sinus into a coronary vein on the lateral LV wall.
impedance may be seen if the pacing lead is being In a minority of cases a separate mini-thoracotomy may
degraded, the pacing circuit is interrupted or not prop- be necessary for secure positioning of an epicardial
erly connected or the pacing lead becomes dislodged. LV lead. Two types of devices currently exist: CRT-P
Generally, measured impedances do not vary by more (Pacemaker) which is a pacemaker achieving resynchro-
than 100 Ohms between sessions.
nisation, and CRT-D (Defibrillator) which adds resyn-
CARDIAC RESYNCHRONISATION THERAPY chronisation to an implantable cardioverter defibrillator.
These latter devices are implanted more commonly as the
Cardiac resynchronisation therapy (CRT) involves the use combination of severe heart failure and ventricular
of pacing to improve the performance of the left ventricle tachyarrhythmias is frequently present. 85,86
in heart failure patients. Initially CRT was undertaken
only in patients with severe heart failure (NYHA Class Non Responders to CRT
III–IV with ejection fraction <30%) due to dilated cardio-
myopathy with left bundle branch block (LBBB) 74,75 but Disappointingly, up to 25 % of patients who receive CRT
its proven efficacy in all major randomised controlled devices fail to gain the expected benefits of improved
78,80
studies 76-80 has seen the range of indications expand to heart function and are termed non-responders. Failure
include patients with less severe heart failure (NYHA to respond may be due to device- or lead-related factors,
Class I and II). CRT is typically only undertaken after or because of cardiac factors which contribute to worsen-
25
demonstrating failure to respond to optimal pharmaco- ing heart failure, especially myocardial ischaemia, atrial
84
logical therapy. fibrillation , and diminishing responses to adjunctive
pharmacological therapy. It should be noted that the
Optimum systolic performance requires all segments of preference in CRT is to see paced ventricular rhythms
the ventricles to contract more or less synchronously. rather than the patient’s own QRS complexes as pacing