Atrioventricular synchronous pacing in hypertrophic obstructive cardiomyopathy

The study addresses major issues of cardiac pacing in hypertrophic obstructive cardiomyopathy (HOCM). The influence of ventricular pacing site and atrioventricular (AV)-delay on left ventricular outflow tract (LVOT) gradient. The long-term effects of pacing in HOCM patients with provocable LVOT obstruction only and radiofrequency modification of AV-conduction as adjunct therapy to optimise pacing. Furthermore the influence of pacing on septal structure and any lasting effects of pacing following cessation of pacing and the impact of long-term pacing on quality of life in HOCM patients.

Measurements were made in 15 patients of LVOT gradient and cardiac output at a number of AV-delays during septal and apical right ventricular stimulation and sinus rhythm. Apical stimulation reduced the LVOT > 30% in all subjects whereas septal stimulation reduced LVOT gradient in only three subjects. Cardiac output did not differ between conditions. These data support that an apical stimulation site is of crucial importance for successful pacing in HOCM.

A comparison between 19 patients with provocable LVOT gradient only and 22 subjects with 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 increased exercise capacity in the majority of subjects. Thus, patients who only exhibit significant LVOT obstruction during provocation benefit as much from pacemaker treatment as patients who already have significant obstruction at rest, both acutely and long-term.

Six patients with rapid native AV-conduction and refractory to pacing, due to lack of full apical preexcitation underwent radiofrequency modification of the AV-node. Significant lasting prolongation of AV-conduction and full apical preexcitation was achieved 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 symptomatology was observed. Thus, radiofrequency modification of AV-conduction enhances effects of 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 either three months of continued or discontinued pacing. No patient completed the full three months of inactive pacing due to return of intolerable symptoms in parallel with increased LVOT 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 of active or inactive pacing. After the crossover study, a six month period of preferred pacing mode followed. Seventy-six patients preferred active pacing at the end of the crossover period. Active pacing induced profound positive changes in almost all areas of quality of life.

Pacing has beneficial effects on hemodynamics as well as quality of life in patients with hypertrophic obstructive cardiomyopathy also in patients with LVOT gradient during provocation only. To achieve these effects an apical pacing site with an individual optimised atrioventricular delay is of crucial importance. Radiofrequency modification of atrioventricular conduction can be used to enhance effects of pacing. Pacing does not seem to induce lasting effects of a magnitude to influence hemodynamics or symptoms after cessation of pacing.