Atrioventricular synchronous pacing in hypertrophic
obstructivecardiomyopathy
Fredrik Gadler
Department of Cardiology, Karolinska hospital, Stockholm, Sweden
The study addresses major issues of cardiac pacing in hypertrophic
obstructivecardiomyopathy (HOCM). The influence of ventricular pacing
site and atrioventncular(AV)-delay on left ventricular outflow tract
(LVOT) gradient. The long-term effectsof pacing in HOCM patients with
provocable LVOT obstruction only and radiofrequencymodification of
AV-conduction as adjunct therapy to optimise pacing. Furthermorethe
influence of pacing on septal structure and any lasting effects of pacing
followingcessation of pacing and the impact of long-term pacing on
quality of life in HOCMpatients.
Measurements were made in 15 patients of LVOT gradient and cardiac output
at anumber of AV-delays during septal and apical right ventricular
stimulation and sinusrhythm. Apical stimulation reduced the LVOT > 30% in
all subjects whereas septalstimulation reduced LVOT gradient in only
three subjects. Cardiac output did notdiffer between conditions. These
data support that an apical stimulation site isof crucial importance for
successful pacing in HOCM.
A comparison between 19 patients with provocable LVOT gradient only and
22 subjectswith resting LVOT gradients was made after a pacing duration
of at least six months.Symptomatology improved to a comparable extent in
both groups in parallel with increasedexercise capacity in the majority
of subjects. Thus, patients who only exhibit significantLVOT obstruction
during provocation benefit as much from pacemaker treat ment aspatients
who already have significant obstruction at rest, both acutely and
long-term.
Six patients with rapid native AV-conduction and refractory to pacing,
due tolack of full apical preexcitation underwent radiofrequency
modification of the AV-node.Significant lasting prolongation of
AV-conduction and full apical preexcitation wasachieved in five subjects,
one subject developed complete AV-block after one month.During one year
of follow up a significant decrease in LVOT obstruction and
symptomatologywas observed. Thus, radiofrequency modification of
AV-conduction enhances effectsof pacing in HOCM patients in whom it is
difficult to achieve full apical preexcitation.
Ten patients successfully paced for a mean of 19 months were randomised
to eitherthree months of continued or discontinued pacing. No patient
completed the full threemonths of inactive pacing due to retum of
intolerable symptoms in parallel with increasedLVOT obstruction. Pacing
does not seem to induce lasting effects after cessation,at least not to a
degree positively influencing hemodynamics and symptomatology.
Quality of life was studied in 82 patients randomised to each three
months ofactive or inactive pacing. After the crossover study, a six
month period of preferredpacing mode followed. Seventy-six patients
preferred active pacing at the end ofthe crossover period. Active pacing
induced profound positive changes in almost allareas of quality of life.
Pacing has beneficial effects on hemodynamics as well as quality of life
in patientswith hypertrophic obstructive cardiomyopathy also in patients
with LVOT gradientduring provocation only. To achieve these effects an
apical pacing site with an individualoptimised atrioventricular delay is
of crucial importance. Radiofrequency modificationof atrioventricular
conduction can be used to enhance effects of pacing. Pacing doesnot seem
to induce lasting effects of a magnitude to influence hemodynamics or
symptomsafter cessation of pacing.
Key words: HOCM, pacing, LVOTobstruction, quality of life
ISBN 91-628-2748-